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Flow Meas. I nst rum. Vo l 2 Ju ly 1991

eviewT u r b i n e a n d r e la t e d f lo w m e t e r s : . In d u s t r ia lp r a c t i c e *R . C . B A K E RT h is f ir s t p a p e r r e v i e w s t h e c o n s i d e r a b l e r a n g e o f d e si g n s o f m e t e r t h a t f a l l i n t ot h e f a m i l y o f t u rb i n e , p r o p e l l e r o r p a d d l e f lo w m e t e r s a n d w h i c h h a v e b e e np r o d u c e d c o m m e r c i a l l y . T h e p a p e r a tt e m p t s to b r i n g t o g e th e r s o m e o f t h e k e yf e a tu r e s o f e a c h d e s i g n . T h e p a p e r d o e s n o t p r o v i d e a c o m p l e t e l is t o f a l lf l o w m e t e r d e s i g n s i n th i s fa m i l y o r o f a l l m a n u f a c t u r e r s . I n c l u s i o n i n th e p a p e rd o e s n o t c a r r y a n y r e c o m m e n d a t i o n o r o th e r w i se , a n d l i m i t s o f p e r f o r m a n c e a r et h e a u t h o r ' s a s s e s s m e n t a n d w i l l b e d i f fe r e n t f o r d i f f e r e n t m a n u f a c t u r e r s . W h e r es u c h l i m i ts a p p l y t o a p a r t i c u l a r d e v i c e f r o m a n i d e n t if i a b le m a n u f a c t u r e r t h e ys h o u l d b e c h e c k e d w i t h t h e m a n u f a c t u r e r , w h o m a y h a v e e x te n d e d o r o th e r w i s ec h a n g e d t h e m . A f t e r a n i n t r o d u c t i o n o f th e h i s t o ry a n d g e n e r a l p r in c i p l e s , t h ep a p e r r e v i e w s i n t u r n t h e s p e c i a l f e a tu r e s o f p r e c i s i o n l i q u i d m e t e rs , ga s m e t e r sa n d w a t e r m e t e rs . I t t h e n b r i e f l y r e v i e w s v a r i o u s s p e c i a l d e v i c e s. I n a s u b s e q u e n tp a p e r i t is i n t e n d e d t o b r in g t o g e th e r t h e m o s t i m p o r t a n t r e fe r e nc e s a n d t h e m o s tu s e f u l d a t a a n d t o p r o v i d e a n i n t r o d u c t i o n t o th e m a t h e m a t ic s o f th e sef l o w m e t e r s .K e y w o r d s : t u r b in e f l o w m e t e r s , p r o p e l le r f lo w m e t e r s , p a d d l e f lo w m e t e r s

1 4 7

I n t r o d u c t i o nBackgroundI n t h i s fi rs t p a p e r t h e p r e s e n t s ta t e o f d e v e l o p m e n t o ft h i s m e t e r i s r e v i e w e d f r o m t h e i n d u s t r i a l v i e w p o i n t . As u b s e q u e n t p a p e r w i l l r e v i e w p u b l i s h e d w o r k o n th es u b j e c t. T h e p a p e r is a im e d a t a w i d e r e a d e r s h ip .P r e c i s i o n t u r b i n e l i q u i d m e t e r s , g a s m e t e r s a n d w a t e rm e t e r s a r e c o n s i d e r e d a s s e p a r a t e f a m i l i e s . T h e p a p e rc o n s i d e r s e a c h f a m i l y o f m e t e r s i n t u r n a n d s t a r t s b yr e v i e w i n g s o m e o f t h e m a n y a n d v a r i e d d e s i g n s t h a tl o o s e l y fa l l w i t h i n e a c h f a m i l y . T h i s is f o l l o w e d b y t h ee f f e c t s o f i n s t a l l a t i o n o n t h e m e t e r s a n d l i k e l y a c h i e v -a b l e i n s t a l l e d p r e c i s i o n . S o m e s p e c i a l d e v i c e s a r e t h e nc o n s i d e r e d . T h e p a p e r e n d s w i t h a r e v i e w o f a d v a n -t ag e s , d is a d v a n t a g e s a n d a p p l i c a t i o n s o f th e s e m e t e r s .F ir st , h o w e v e r , a b r i e f h i s t o r ic a l r e v i e w i s i n o r d e r .S p i ra ls , s c r e w s a n d w i n d m i l l s h a v e a l o n g h i s t o ryo f u s e f o r s p e e d m e a s u r e m e n t . R o b e r t H o o k p r o p o s e da s m a l l w i n d m i l l i n 1 6 8 1 f o r m e a s u r i n g a i r v e l o c i t ya n d l a t e r o n e f o r u s e a s a s h i p s l o g ( d i s t a n c e m e t e r ) .A C a p t a i n P h i p p s i n 1 7 7 3 e m p l o y e d t h e p r i n c i p l e t h a ta s p i r a l in t u r n i n g m o v e s t h r o u g h t h e l e n g t h o f o n et u r n o f t h e s p i r a l . T h i s p r i n c i p l e h e u s e d a s a s h i p s

*Neither the autho r nor the publishers shall be liab le in any w ay forloss or dam age resulting from information contained n this paper.Most of the information has been obtained from manufacturersliterature and wh ile the author believes t to be correct at the tim e ofwriting users shou ld always refer to the mo st current specificationsfrom the manu facturer*The Sainsbury Fam ily Charitable Trusts, 9 Red Lio n Co urt, London.Visiting Professor, Cranfield nstitute of Technology

l o g . I t a p p e a r s t h a t V i t r u v i u s , a R o m a n a r c h i t e c t ,s u g g e s t e d a m o r e b a s i c f o r m o f t h i s m e t h o d .R e i n h a r d W o l t m a n n i n 1 8 7 0 d e v e l o p e d a m u l t i -b l a d e d f a n t o m e a s u r e r i v e r f l o w s 1 , a d e v i c e t h a t w a sa f o r e r u n n e r o f t h e l o n g h e l i c a l s c r e w t y p e m e t e r s t il lc a l l e d a f t er h i m a n d u s e d w i d e l y f o r p ip e f l o w s i n th ew a t e r i n d u s t r y . T h e f ir s t m o d e r n m e t e r s , o f t h e ty p ew i t h w h i c h w e a r e m a i n l y c o n c e r n e d , w e r e d e v e l o p e di n t h e U S A i n 1 9 3 8 2 . T h e s e w e r e a t t r a c t iv e f o r f u e lf l o w m e a s u r e m e n t i n a ir b o r n e a p p l i c a ti o n s . T h e y c o n -s i s te d o f a h e l i c a l l y b l a d e d r o t o r a n d s i m p l e b e a r i n g s .I m p r o v e d s le e v e b e a r in g s w e r e d e v e l o p e d f o r l o n g e rl if e w i t h h a r d e n e d t h r u s t b a l l s o r e n d s t o n e s tow i t h s t a n d t h e a x i a l l o a d . A n a l t e r n a t i v e d e v e l o p e do v e r s e v e r a l y e a r s a n d p a t e n t e d b y P o t t e r ( 1 9 6 1 ) w a st o p r o f i l e t h e h u b o f t h e r o t o r s o t h a t t h e p r e s s u r e

b a l a n c e a c r o s s t h e r o t o r h e l d i t a g a i n s t t h e a x i a l d r a gf o r c e s r a t h e r t h a n t h e t h r u s t b e a r i n g s . T h i s a l l o w e d t h er o t o r t o r u n o n a s i n g l e j o u r n a l b e a r i n g .Qu al i tat ive d escript ion of ope rat ionT h e t u r b i n e c o n s i s t s o f a b la d e d r o t o r w h i c h t u r n s d u et o t h e f l o w i n th e p i p e . I n m o s t o f t h e d e s i g n s to b ed i s c u s s e d , t h i s r o t o r i s d e s i g n e d t o c r e a t e t h e m i n i -m u m d i s t u r b a n c e a s t h e o n c o m i n g f l o w p a ss e s r o u n di t. I d e a l l y i t c u t s p e r f e c t l y t h r o u g h t h e f l u i d i n a h e l i xs o t h a t e v e r y r e v o l u t i o n o f th e h e l i x r e p r e s e n t s o n ec o m p l e t e a x i a l l e n g th o f t h e s c r e w a n d h e n c e a le n g t ho r v o l u m e o f t h e f l u i d . I n p r a c t i c e t h e r e a r e d r a gf o r c e s w h i c h s l i g h t l y r e t a r d t h e r o t a t i o n . T h e s e r e s u l tf r o m : f r i c t io n a l d r a g o n t h e b la d e s , t h e h u b , t h e f a c e so f t h e r o t o r a n d t h e t i p o f t h e b l a d e s ; b e a r i n g d r a g ,

0955-5986/91/030147-15 (~) 1991 But terwor th-Heinemann Ltd

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1 4 8 R . C . B a k e r T u r b i n e a n d re l a t e d f l o w m e t e r s : I. I n d u s t r ia l p r a c t i c ea l s o a f r i c t i o n a l e f f e c t ; a n d d r a g d u e t o t h e m e a n s b yw h i c h t h e r o t a t i o n is m e a s u r e d , w h i c h is u s u a l l y am a g n e t i c d r a g . T h e s e d r a g f o r c e s a f f e c t t h e o t h e r w i s ei d e a l r e l a t io n s h i p o f c o n s t a n t f l u i d v o l u m e f o r e a c hr o t o r r e v o l u t i o n a n d l e a d t o n o n - l i n e a r i t y .T h e r o t o r h a s t o b e h e l d i n t h e s t r e a m a n d s os u p p o r t s a r e i n v a r i a b l y n e c e s s a r y to h o u s e th e b e a r -i n g s . V i r t u e i s m a d e o f n e c e s s i t y a n d t h e s e s u p p o r t sa r e u s e d t o p r o v i d e f l o w s t r a i g h t e n i n g , s i n c e th et u r b i n e m e t e r i s o n e t y p e o f m e t e r p a r t i c u l a r l y s u s c e p -t i b le t o s w i rl . T h e o n c o m i n g f l o w w i l l t h e r e fo r e n e e dt o f l o w o v e r t h e u p s t r e a m s u p p o r t a n d t h e n a t u r a l l yo c c u r r i n g p r o f i l e w h e r e t h e v e l o c i t y o f t h e fl u i d iss l o w e r a t t h e p i p e w a l l t h a n a t th e c e n t r e o f t h e p i p ew i l l b e r e d i s t r i b u t e d i n t o t h e a n n u l a r p a s s a ge p a s t t h eb l a d e s a n d , p e r h a p s m o s t i m p o r t a n t , t h e r e w i l l b e ar e d u c t i o n i n a n y s w i r l c o m p o n e n t d u e t o c o n s e r v a ti o no f a n g u l a r m o m e n t u m d u r i n g t h e r e d i s tr i b u ti o n a s w e l la s t h e e f f e c t o f th e s u p p o r t s . T h e v e l o c i t y i n t h i sp a s sa g e w i l l v a r y a s m a l l a m o u n t w i t h r a d i a l p o s i t i o n ,a n d a w e l l d e s i g n e d t u r b in e r o t o r w i l l g e n e r a l l y h a v eh e l i c a l b l a d e s t o m a t c h t h e a x i a l a n d t a n g e n t i a l v e l o -c i t y o f t h e r o t o r a t e a c h r a d i a l p o s i t io n .T h e m a i n v a r i a n t s f ro m t h i s d e s c r i p t i o n a r e th ep e l t o n a n d p a d d l e w h e e l d e s i g n . In th e f o r m e r at a n g e n t i a l j e t o f f l u i d h i t s t h e b u c k e t s o r b l a d e s o f t h ew h e e l a n d c a u s e s th e m t o r o t a te . T h i s d e s ig n h a s t w oa l t e r n a t iv e v i r tu e s : i t c a n b e m a d e a s a s i m p l e i n s e r -t i o n p r o b e t o o b t a i n a n e s t i m a t e o f t h e f lo w r a t e ; a n d i tc a n b e u s e d i n v e r y s m a l l f l o w s t o r e g i s t e r w h e r e o t h e rd e s i g n s f a i l. O t h e r d e s i g n s u s i n g l a r g e r p a d d l e w h e e l sa n d a n g l e d p r o p e l l e r s a r e a l s o a v a i l a b l e .T h e d e s i g n s a n d th e i r l i m i t a t io n s s e t o u t b e l o w d on o t p r e t e n d t o p r o v i d e a c o m p l e t e l is t o f a l l fl o w m e t e rd e s i g n s i n t h is f a m i l y , t o b e r e p r e s e n t a t i v e o f e v e r ym e m b e r o f th e f a m i l y o r t o b e e xh a u s t iv e . T h e a u t h o rh a s b a s e d h i s v a l u e s o n m a n u f a c t u r e r s ' c l a i m s a n d n o to n i n d e p e n d e n t t e s ts , a n d h a s s o u g h t t o i n d i c a t e t h i si n t h e t e x t . M o s t p r e c i s i o n s p e c i f i c a t i o n s a r e b a s e d o nr a t e , b u t a n i n d i c a t i o n i s u s u a l l y g i v e n i n t h e p a p e rw h e r e t h e y r e l a t e to f u l l s c a l e d e f l e c t i o n ( fs d ). W h i l et h e a u t h o r h a s a t t e m p t e d t o p r o v i d e a s f a i r a n da c c u r a t e a d e s c r i p t i o n a s p o s s i b l e , a s s t a t e d i n t h ef o o t n o t e t o t h e f i r s t p a g e , n e i t h e r h e n o r t h e p u b l i s h e r ss h a l l b e l ia b l e i n a n y w a y f o r l os s o r d a m a g e r e s u l t i n gf r o m i n f o r m a t i o n c o n t a i n e d i n t h i s p a p e r , a n d a l lp e r f o r m a n c e l im i t s g i v e n o r i m p l i e d i n t h e p a p e rs h o u l d b e c h e c k e d w i t h t h e m a n u f a c t u r e r.P r e c is i o n l iq u i d m e t e r sP r i n c ip a l d e s i g n c o m p o n e n t sF i g u re 1 g iv e s f iv e e x a m p l e s o f c o m m e r c i a l d e s i g nsw h i c h i n t r o d u c e m o s t o f t h e e s s e n t i a l f e a t u r e s o f t h e s em e t e r s . C o n s i d e r i n g F i g u r e l a , a f i r s t e s s e n t i a l c o m -p o n e n t i s t h e r o t o r i ts e lf , w h i c h is li k e a s m a l l p r o p e l -l e r o r t u r b i n e . T h i s i s f o r m e d e i t h e r f r o m s t r a ig h t o rt w i s t e d ( h e l i c a l) b l a d e s . I t is s u g g e s te d t h a t f o r g o o dd e s i g n : t h e h u b r a d i u s s h o u l d b e a p p r o x i m a t e l y h a l ft h e ti p r a d i u s; t h e b la d e s w h e n v i e w e d a x i a l ly s h o u l dj u s t b l o c k t h e c r o s s s e c t i o n o f t h e p i p e ; a n d t h e a x i a ll e n g t h o f t h e b l a d e s s h o u l d b e a p p r o x i m a t e l y e q u a l t ot h e b l a d e s p a n , w h i c h i s t h e l e n g t h o f th e b l a d e f r o mh u b t o t i p .I t i s i m p o r t a n t t o r e m e m b e r t h a t , u n l i k e t h e p o w e r

t u r b i n e , t h e m e t e r a i m s t o c u t t h r o u g h t h e f l u i dw i t h o u t d i s t u r b i n g t h e fl o w . T h i s c le a r l y is a n i m p o s -s i b l e i d e a l , b u t n e v e r t h e l e s s t h e p o w e r e x t r a c t e d f r o mt h e f lu i d i s v e r y s m a l l a n d th e i n c i d e n c e o f t h e f l o wo n t o t h e b l a d e s i s c o n s e q u e n t l y a l s o v e r y s m a l l . T h er e a s o n f o r th e p o p u l a r i t y o f h e l i c a l l y t w i s t e d b l a d e s i st h a t th e r e l a t i v e a n g l e o f a p p r o a c h o f t h e f l u i d o n t ot h e b l a d e s v a r i e s w i t h r a d i u s a n d s o fl a t p l a t e b l a d e sw i l l n o t a l l o w a c o n s t a n t a n g l e o f a t ta c k a n d w i l l l e a dt o u n n e c e s s a r i l y l a r g e i n c i d e n c e a n g l e s , b o t h p o s i t i v ea n d n e g a t iv e , a n d t h u s w i l l i m p a r t u n n e c e s s a r y f l o wd i s t u rb a n c e a n d d r a g .T h e r o t o r i s u s u a l l y m a c h i n e d f ro m s o l id a n d t h ef l a t p la t e b l a d e s o f te n h a v e l e a d i n g a n d t r a i l in g e d g e sw h i c h a r e m i ll e d i n a c o n s t a n t e n d p l a n e . T h e c ro s ss e c t i o n o f t h e b l a d e a t a c o n s t a n t r a d i u s w i l l t h e r e f o r eb e e s s e n t i a l l y a p a r a l l e l o g r a m . S h a r p e d g e s s h o u l d b ea v o i d e d s i n c e t h e y m a y c a u s e c a v i t a t i o n . G r i f f it h sS i l v e r w o o d 3 d e s c r i b e h o w s m a l l c h a n g e s i n th e s h a p eo f t h e t r a i l i n g e d g e s c a n c a u s e a c h a n g e o f t h e b l a d e s 'a e r o d y n a m i c d r a g a n d c o n s e q u e n t l y o f t h e m e t e rc a l i b r a t i o n ( F i g u re 2 ) .T h e r o t o r s p i n d l e m u s t b e h e l d c e n t r a l l y i n t h ep i p e i n b e a r i n g s . T h e s e a r e s u p p o r t e d b y h a n g e r s a n dp o s i t i o n t h e b e a r i n g s c e n t r a l l y i n t h e p i p e . T h e y a r ec o m m o n l y u s e d a s f l o w s t ra i g h te n e r s to r e d u c e s w i r l.T h e s h a p e v a r ie s c o n s i d e r a b l y : i n F i g u r e l a , b , e t h eh a n g e r s a r e f l a t p l a t e s ; i n F i g u r e l c t h e r e a r e t h r e es tagge r ed se t s o f h ange r s ; a nd i n F igu r e l d t hey a r epa r a l l e l t ubes .T h e r o t a t i o n o f t h e r o t o r i s s e n s e d b y a p i c k u pw h i c h m o s t c o m m o n l y s e ns e s a c h a n g e i n th e m a g -n e t i c m a t e r i a l p e r m e a b i l i ty i n it s v i c i n i t y a s a b l a d ep a s se s ( m a g n e t i c r e l u c t a n c e c h a n g e ) . A l t e r n a t iv e s t ot h i s a r e t o u s e t h e e d d y c u r r e n t e f f e c t o r d y n a m o e f f e c ta s a b l a d e p a s s e s t h r o u g h t h e m a g n e t i c f i e l d o f t h es e n s o r ( m a g n e t i c i n d u c t i v e ) , o r to u s e a m o d u l a t e dh i g h - f r e q u e n c y s i g n a l ( m o d u l a t e d c a r r i e r o r ra d i o -f r e q u e n c y ) . T h e c a p a c i t a n c e e f f e c t c a n a l s o b e u s e d tos e n s e t h e p r o x i m i t y o f a p a s s i n g b l a d e t o t h e s e n s o rh e a d . O p t i c a l f i b re s h a v e b e e n t r ie d , b u t i f t h e o p t i c a lp a t h p a s s e s t h r o u g h t h e f l u i d t h e r e i s a d a n g e r o f t h ew i n d o w s b e c o m i n g f o u l e d . F o r i n c re a s e d i n te g r it ys o m e m e t e r s h a v e t w o s e n s o rs s p a c e d a t a b o u t 1 2 0 ( F i g u re l d ) a n d t h e p u l s e t r a i n s f r o m b o t h a r e s e n s e da n d t h e p h a s e a n g l e c o n s t a n t l y c h e c k e d .A n a d d i t io n a l p o i n t t o b e n o te d is t h e m e t h o d o fr e m o v a l o f i n t e r n a l s . I n s m a l l s i z e s o f m e t e r t h ei n t e r n a l s a r e h e l d i n p o s i t i o n b y c i r c l i p s , t h e r e m o v a lo f w h i c h a l l o w s t h e in t e r n a ls t o b e w i t h d r a w n . I no t h e r d e s i g n s a n d l a r g e r s i z e s t h e b e a r i n g a s s e m b l ie sm a y b e r e m o v e d f ro m t h e b o d y b y r e l e a s in g a t a p e rl o c k i n g n u t .

e a r in g d e s i g n m a t e r i a lsC l e a n l i q u i d sO p e n b a l l b e a r i n g s o f s t a i n l e s s s t e e l o r o t h e r c o m p a t -i b l e m a t e r i a l a r e s u i t a b l e f o r l i q u i d s w i t h l u b r i c a t i n gp r o p e r ti e s i n th e t e m p e r a t u r e r a n g e - 5 0 t o 2 5 0 C b u ta f i l t e r s h o u l d b e u s e d o f a m e s h s i z e s m a l l e n o u g h t op r e v e n t s o l i d p a r t i c l e i n g r e s s i n t o t h e b e a r i n g s .

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F igu re 1 E x am p les o f p r ec is i on c om m er c ia l t u r b inef lowm eter des igns fo r l iqu ids : (a) Endress Hausercorrosion-resistant me ter design for up to 50 m m dia-me ter show ing materia ls ; (b ) KD G Mo brey L td me terdes ign fo r g reater t han 75 m m d iame ter show ing co m-ponents ; ( c ) cu tawa y and d isassembled v iew o f aFoxboro m eter w i th ov erhung be ar ing ; (d ) ITT Bartonmeter with paral le l ax is st raightening tubes; (e) Hydr i lA O T m e t e r des ign f o r 100 m m t o 500 m m d iam e t e r (Ibody, 2 rotor , 3 sup por t nut , 4 suppo r t p late, 5suppor t t ube, 6 suppor t vane, 7 lock tab , 8 endsup por t assembly, 9 f lange, 10 pic ku p assem bly, 11p icku p s tub) (a l l diagrams reprodu ced w i th permission)

b e a r i n g s , p o s s i b l y w i t h c a r b i d e p i n i o n s a n d a s t e l l it es le e v e , a r e s u i t a b le i n t h e r a n ge - 5 0 t o 4 0 0 Cu n l u b r i c a t e d . T u n g s t e n c a r b i d e w i t h c o b a l t b o n d i n g i sm o s t c o m m o n , b u t th e c o b a l t i s l e a c h e d o u t b y a c i d i cs o l u t i o n s u s e d f o r c l e a n i n g . S t e l l i t e m a y t h e n b e u s e da s a l e s s d u r a b l e a l t e r n a t i v e f o r m o r e c o r r o s i v e f l u i d s .A m o r e r e c e n t a l t e r n a t i v e i s n i c k e l - b o n d e d c a r b i d eb u s h e s w i t h t i t a n i u m c a r b i d e s h a ft s. A n a l t e r n a t i v ed e s i g n u s e s r o t o r p i n s o f h a r d m e t a l i n s a p p h i r e

b e a r in g s w i t h t h r u s t p l a t e a n d r i n g s m a d e w i t h c u r v e dc o n t a c t s u r f a c e s fo r l i n e c o n t a c t . P T F E is u s e d i n s o m ea p p l i c a t io n s . C e r a m i c b e a r in g s a r e i n c r e a s i n g l y c o m -m o n , s u c h a s A I 2 0 ~ ( F i g u re l a ). O n e m a n u f a c t u r e ru s es a b a l l a n d s l e e v e d e s ig n . T h e s h a f t is t i p p e d w i t ha n e l l i p s o i d a n d r u n s i n a c e r a m i c s l e e v e so th a t l i n ec o n t a c t i s a c h i e v e d .T y p i c a l b e a r i n g l i f e is c l a i m e d t o b e 1 2 t o 2 4m o n t h s w h e n u s e d w i t h 5 0 t o 7 5 d u t y c y c l e i n

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1 5 0 R . C . Baker - Tu rb ine and re la ted f l owm ete rs : I . I ndus t r i a l p rac t i ceC a l i b r Q t i o n c o n s ta n t s h i f t T u r b i n e b l o d e p r o f i l e

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F igu re 2 E f fec t o f t r a i l i ng edge on ca l i b ra t i on 3 rep ro -d u c e d w i t h p e r m i s s i o n )

c l e a n p a r t i c u l a t e - fr e e g a s o l i n e . F o r b a l l r a c e b e a r i n g sc o r r e c t l y l u b r i c a t e d a l if e o f 4 to 6 0 0 0 h i s c l a i m e da n d f o r j o u r n a l b e a r in g s 2 0 0 0 0 h o r m o r e , d e p e n d i n gu p o n t h e p r o p e r t i e s o f th e m e a s u r e d f l u i d a n d r a t e o ff l o w . F o r s o m e l a rg e r s iz e s (a b o v e a b o u t 8 0 m m ) o n l ya n u p s t r e a m b e a r i n g i s u s e d c o n s i s t i n g o f a t u n g s t e nc a r b i d e b u s h a n d s h a f t o r o t h e r s u i t a b l e m a t e r i a l s .S p e c i a l b e a r i n g s a r e a v a i l a b l e f o r c r y o g e n i c a p p l i c a -t io n s . S o m e m a n u f a c t u re r s p r o v i d e a p p l i c a t i o n c h a r ts .Stra inersT y p i c a l v a l u e s f o r s t r a i n e r s a r e g i v e n b y m a n u f a c t u r e r sw i t h m a x i m u m a l l o w a b l e p a r t i c u la t e s iz e s ( T a b le 1 ).H o w e v e r , o t h e r m a n u f a c t u r e r s m a y b e le s s s t r i n g e n t int h e i r s p e c i f i c a t i o n s .M a t e r i a l sB e c a u s e th e s i g n a l is u s u a l l y o b t a i n e d f r o m m a g n e t i cs e n s i ng i t is c o m m o n t o m a k e t h e t u b e f ro m a u s t e n i ti cs t a i n l e s s s t e e l t o a l l o w t h e m a g n e t i c f i e l d t o p e n e t r a t e .H o w e v e r , c a r b o n s t e el i s u s e d fo r fl a n g e s a n d s o m e -t i m e s a l s o f o r t h e b o d i e s . I n t h i s i n s t a n c e p r o v i s i o n i sm a d e f o r t h e p i c k u p a s s e m b l y t o f u n c t i o n d e s p i t e t h em a g n e t i c b o d y .Size rangesM e t e r s iz e s a r e t y p i c a l l y : 6 to 5 0 0 m m f o r fl a n g e d a n d6 t o 5 0 m m f o r th r e a d e d . I n s o m e d e s i g n s t h e b o r e

Table I Specifications or strainersMeter Par t icu la te s izes ( /~m ) Mesh Hole s ized iame te r B ea r ings ( mm)(mm) Ball Journal13 60 100 150 0 .10020 90 142 100 0 .1502 5 - 8 0 1 0 0 1 8 5 8 0 0 .1 7 51 0 0 - 1 5 0 1 4 2 2 51 6 0 0 . 2 0 02 0 0 - 3 0 0 2 5 1 4 0 1 4 0 0 . 3 0 0B ased on da ta f rom Foxbo r o and K D G Mob r ey

r e d u c e s s o t h a t a t t h e p r o p e l l e r t h e b o r e r a d i u s i s am i n i m u m . F l o w r a ng e s t y p i c a l l y a re 1 0 :1 t u r n d o w n( b u t m a y b e u p to 3 0 : 1 ) f o r f l o w r a t e s o f 0 . 0 3 t o7 0 0 0 m 3 h - I . O v e r s p e e d u p t o 1 . 5 t i m e s t h e m a x -i m u m f l o w r a t e m a y b e p e r m i t t e d f o r s h o rt p e r io d s , b u ti f i t t a k e s p l a c e f o r p r o l o n g e d p e r i o d s t h e b e a r i n g l i fei s r e d u c e d .P r es s u re lo s s es a t m a x i m u m f l o w r a t e w i t h w a t e ra s t h e f l o w i n g m e d i u m i n 1 2 m m s iz e s ra n g e u p t o0 . 2 b a r ( 2 x 1 04 N m - 2 ) a n d i n 2 0 0 r a m s iz e s u p t o0 . 2 5 b a r ( 2 .5 x 1 0 4 N m - 2 ) .M a x i m u m p r e ss u re s ra n g e u p t o 2 5 b a r f o r h y -g i e n i c d e s ig n s , u p t o 2 4 0 t o 4 0 0 b a r f o r t h re a d e dd e s i g n s a n d a c c o r d i n g t o t h e f l a n g e r a t i n g f o r f l a n g e ddes igns .T e m p e r a t u r e r a n g e s a r e t y p i c a l l y - 5 0 t o 1 5 0 Cb u t m a y b e a s w i d e a s - 2 6 5 t o + 3 1 0 C.S o m e m a n u f a c t u r e r s g i v e p l o t s o f t h e e f f e c t o fc h a n g e o f v i s c o s it y o n t h e p e r f o r m a n c e o f th e i rm e t e r s . T h e b e a r i n g , a s w e l l a s t h e b l a d e d e s i g n , w i l lh a v e a n i n f l u e n c e o n t h i s ( F i g u r e 3 ). A c c e p t a b l e v i s -

c o s i t y l i m i t s f o r s m a l l e r s i z e s ( le s s t h a n 8 0 m m ) m a yb e u p t o 1 5 m P a s (I 5 cP ) a n d f o r s i z e s a b o v e I 0 0 m mu p t o 5 0 m P a s ( 5 0 c P ). T h e s e v i s c o s i t y l i m i t s p r e v a i la s a r e s u l t o f i n c r e a s i n g n o n - l i n e a r i t y w i t h r e d u c i n gR e y n o l d s n u m b e r .O t h e r m e c h a n i c a l d e s i g n f e a tu r e sI n t e r n a l s m a y b e m a d e f r o m s t a i n l e s s s t e e l , b u t o t h e rm a t e r ia l s s u c h a s T e f l o n a n d p o l y t h e n e a r e a l s o u s e d .I n o r d e r t o i n c r e a s e t h e p u l s e r a t e f r o m i m p e l l e r sw i t h t y p i c a l l y 6 to 8 b l a d e s , a s h ro u d r in g w i t h h o l e si s u s e d ( F i g u r e 4 ) . T h i s i n c r e a s e s t h e n u m b e r o f p u l s e sd u e t o t h e h o le s c h a n g i n g t h e m a g n e t ic r e l u c ta n c ea n d a l s o a l l o w s v i s c o s i t y c o m p e n s a t i o n t o i m p r o v el o w - s p e e d p e r f o r m a n c e . T h e s h r o u d c a n a l s o g i v eg r e a t e r s t r e n g t h a n d r e d u c e d b l a d e v i b r a t i o n .I n s o m e s m a l l d e s i g n s o f t u r b i n e m e t e r t h e b l a d e sh a v e a T - s h a p e s o t h a t a t t h e t i p t h e y a r e l o n g e r( l o n g e r c h o r d ) t h a t a t t h e h u b . O n e r e a s o n g i v e n f o rt h i s is t o i m p r o v e i n s e n s i t i v i ty t o v i s c o s i t y c h a n g e ,w h i c h m a y r e s u lt f r o m a g r e a te r d r iv i n g t o r q u ea c h i e v e d b y i n c r e a s in g t h e b l a d e l i ft a t t h e m a x i m u mr a d i u s . I t m a y a l s o f la t t e n t h e c h a r a c t e r i s t i c h u m p a tl o w s p e e d .S o m e d e s i g n s c a n b e u s e d b i d i r e c t io n a l l y , b u t o fc o u r s e r e q u i r e c a l i b r a t i o n i n e a c h d i r e c t i o n .S o m e d e s i g n s a r e i n t r i n s i c a l l y s a f e , f l a m e p r o o f o rh y g i e n i c .R e s p o n s e t i m e c o n s t a n t s m e a s u r e d w i t h w a t e r o rw i t h a li q u i d o f s im i l a r d e n s i t y r a n g e f r o m 0 . 0 0 5 t o0 . 0 5 s f o r a 5 0 f l o w r a t e c h a n g e .A f t e r u s e w i t h c o r r o s i v e f l u i d s , t h e m e t e r s h o u l db e c l e a n e d w i t h s o lv e n ts . H o w e v e r , m a x i m u m r o ta -t i o n a l s p e e d s s h o u l d b e c a r e f u l l y o b s e r v e d .

a v i ta t ionC a v i t a t io n i s c a u s e d w h e n t h e l o c a l p r e s s u r e d r o p sb e l o w t h e v a p o u r p r e s s ur e o f th e l i q u i d a n d r e s u l ts i na t w o - p h a s e f l o w o f i n c r e a s e d v o l u m e , w h i c h t h e r e -f o r e c a u s e s o v e r r e a d i n g . I t m a y a l s o c a u s e d a m a g e t ot h e i n t e r n a l s . A s i m p l e r u l e i s t h a t th e p r e s s u r e d o w n -s t re a m o f t h e m e t e r s h o u l d b e a t l e a s t o n e b a r a b o v ea t m o s p h e r i c p r e s s u r e . M o r e g e n e r a l l y t h e r u l e g i v e n i s

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Figure 3 V iscosity curves af ter Fox boro repro duc ed with permission) : a) me ter with tungsten carbide bal l andceram ic s leeve su itab le fo r p rocess f lu ids the drag is more s ign i f icant an d reduces the tu rndown ) ; b ) me ter w i thba l l bear ings , w h ich is on ly su i tab le fo r l iqu ids w i th reasonab le lubr ica t ing proper t ies and no d i r t t he v iscos it ycurves an d tu rnd own are superio r)

F igu re 4 K D G M o br ey t u r b ine w hee l w i t h s h r oud r i ngreproduce d w i th permiss ion)

that the back pressure should be at least twice thepressure drop ac ros s the m eter plus the absolutevap our pressure times 1.25.le c t ro m a g n e t ic d e s ig n a n d p e r f o r m a n c eMo st comm only to obta in rotor speed b lade passingis sensed by the change in the magnetic f ield aroundthe sensor.

Reluc tance p icku psThese consist of a coil with a magnet and soft- ironpole piece such that as the blades p ass the flux isaltered and a pulse is created in the coil. To use sucha pickup rotor blade material must be magnetic.Altern atively magnets may be embedded in the rotor.I nduc t ive p ickupsThese consist of a coil in a high-frequency bridgecirc uit. A s the blades of magnetic material p ass there

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1 5 2 R . C . B ak er - Tu rb ine and re la ted flowmete rs : I . Indust r ia l p rac t i cei s a c h a n g e i n t h e m a g n e t i c r e a c t a n c e o f t h e c i r c u i tc a u s i n g a n a m p l i t u d e o r fr e q u e n c y m o d u l a t i o n o f t h eh i g h - f r e q u e n c y c a r r i e r .T h e r e s u l t i n g s ig n a l m u s t b e a m p l i f i e d w i t h c a r ea n d s h i e l d e d f r o m e x t r a n e o u s n o i s e d u e t o v o lt a g es o u r c e s o r m a g n e t i c f i e ld s a s s p u r i o u s p u l s e s c a ni n t r o d u c e s i g n i f i c a n t e r r o r s .

V i b r a t i o n m a y a l s o c a u s e m i c r o p h o n i c e ff ec ts .S c r e e n e d c a b l e s h o u l d b e u s e d a n d t h e d i s t a n c e f r o mt h e f lo w m e t e r t o t h e p r e - a m p l i f ie r s h o u l d b e a s s h o r ta s p o s s i b l e ; t y p i c a l l y n o t g r e a t e r t h a n t w o m e t r e s .T y p i c a l l y t h e p u ls e i s a m p l if i e d f ro m a b o u t 1 5 m VR M S t o 8 V a m p l i t u d e a n d i s o f 0 . 5 t o 2 0 m s d u r a t i o n .P u ls e r a te r a n g e s f r o m 5 0 H z t o 3 k H z a n d i m p e d a n c ef ro m 0 . 3 t o 1 . 5 k Q . A m a x i m u m t ra n s m i s s i o n c a b l el e n g t h i s g i v e n a s 1 0 0 0 m e t r e s b y o n e m a n u f a c t u r e r .T h e s i g n a l i s t h e n a p p l i e d t o a s i g n a l c o n v e r t e r , a ne l e c t r o n i c g e a r b o x , t o c o n v e r t p u l s e r a t e i n t o c u b i cm e t r e s p e r h o u r a n d t o t a l i n t o c u b i c m e t r e s . A h i g hp u l s e d e n s i t y is d e s i r a b l e w h e r e a m e t e r i s t o b ec a l i b r a t e d a g a i n s t a v o l u m e t r i c s t a n d a r d s u c h a s ap r o v e r l o o p w h e r e g e n e r a l l y i t is r e c o m m e n d e d t h a t1 0 0 0 0 p u l s e s o r m o r e s h o u l d b e c o l le c t e d p e r u n i tr e f e r e n c e v o l u m e .Radio-f requency p ickupsA t v e r y h i g h f r e q u e n c i e s o f s i g n a l t r a n s m i s s i o n t h e s k i ne f f e c t i s s u c h t h a t t h e e l e c t r o m a g n e t i c f i e ld is e s s e n -t i a l ly r e f le c t e d b y th e p a s s i n g b la d e s w i t h n e g l i g i b l ed r a g e f f e c t o n t h e w h e e l .harac te r i s t i cs

T h e t y p i c a l c h a r a c t e r i s t i c o f t h e p r e c i s i o n t u r b i n em e t e r i s s h o w n i n F i g u r e 5 . T h e r e a r e f o u r r e g i o n s t on o t e :( i) t h e h i g h e s t p r e c i s i o n r e g i o n ;( ii ) a n e x t e n d e d r a n g e , w h i c h s h o u l d b e u s e d o n l yb r i e f l y a n d w i t h c a r e t o a v o i d e x c e s s b e a r i n gw e a r ;( ii i) t h e n o r m a l r a n g e o f o p e r a t i o n , w h i c h i n c l u d e sb o t h t h e h i g h p r e c i s i o n r e g i o n a n d a l s o a l o w e rf l o w r e g io n w h i c h is o f te n s h o w n a s h a v i n g a' h u m p ' ;( iv ) a l o w f l o w r e g i o n w h e r e d r a g f o r c e s a r e d o m i -n a n t a n d w h e r e t h e p e r f o r m a n c e o f t h e m e t e r i sl ess r e l i ab le .M o s t o f t h e s e r e g i o n s a n d t h e i r c a u s e s a r e o b v i o u s .T h e o n e t h a t i s o f te n p u z z l i n g is t h e h u m p r e g io n i n

T y p i c a lP e r f o r m a n c eC u r v e s

.

) r e s t r i c t e d f l o w r a n g ( 0 . 2 5 o f r e a d i n g o v e ro p e r a t i n g f l o w r a n g e

f l o w r a t eo

1 0 0 1 2 0

F igu re 5 Charac te r is t ic fo r a p rec is ion l iqu id me te ra f te r KD G Mob rey rep roduced w i th pe rmission )

( ii i) . T s u k a m o t o & H u t t o n 4 h a v e c o n f i r m e d t h e o r e t i c -a l l y t h a t a h u m p i n t h e c h a r a c t e r i s t i c c a n b e c a u s e db y m o v e m e n t o f th e p o i n t o f tr a n s i ti o n o f t h e b l a d eb o u n d a r y l a ye r n e a r th e l e a d i n g e d g e o f th e b l a d e sf r o m t u r b u l e n t i n t h e h i g h p r e c i s i o n r e g i o n t o l a m i n a r .G r i f fi t h s a n d S i l v e r w o o d 3 h a v e s u g g e s t e d t h a t c h a n -g i n g t h e p r o f i l e o f t h e b l a d e t r a i l i n g e d g e b y f i l i n g o f ft h e c o r n e r l e a d s t o a re m o v a l o f th e h u m p a n d a ni n c r e a s e o f s p e e d o f r o t a t i o n o f o v e r 1 d u e , p r e s u m -a b l y , t o c h a n g e s i n t h e p o i n t o f s e p a r a t i o n a n d r e d u c -t i on o f d r ag ( F igu r e 2 ) .P r essu r e l oss a r i ses l a r ge l y f r om the p r essu r e r e -d u c t i o n a t t h e r o t o r a n d b e a r i n g s u p p o r t s a n d t h ef a i l u r e f u l ly t o r e c o v e r t h e p r e s s u r e d o w n s t r e a m f o r a na r e a r a ti o m = A l i A 2 , w h i c h w i l l b e a m a x i m u mpr essu r e l oss o f :

2Aploss T p V 1 KF o r p r e s s u r e c h a n g e d u e t o a r e a c h a n g e o n l y ( n e g l e c t -i n g f r ic t i o n ) K = ( m 2 - 1 ), a n d f o r v a l u e s o f m = ~ -,p = 1 0 3 k g m - 3 a n d V l = 1 0 m s - 1 . T h is g iv e s a p re s -s u re c h a n g e o f 0 . 3 9 b a r ( 3 . 9 x 1 0 4 N m - 2 ) , a v a lu ea b o u t 5 0 g r e a t e r t h a n t h o s e m e n t i o n e d i n t h e e a r l i e rs e c t i o n o n s i z e r a n g e s . E x p e r i m e n t a l v a l u e s o f K r a n g ef r o m 0 . 4 t o 0 . 9 , d e p e n d i n g o n t h e g e o m e t r i c d e t a i l s o ft h e m e t e r . F o r K = 0 . 5 , p = 1 0 3 k g m - 3 a n dV l = 10 m s - T t he p r es su r e l oss is 0 .25 ba r .Precis ionT y p i c a l v a l u e s o f t h e p r e c i s i o n g i v e n b y m a n u f a c t u r e r sa r e + 0 . 1 2 t o + 0 . 2 5 f o r t h e h i g h - p r e c i s io n r a n g e a n d_ + 0 .2 5 t o + 0 . 5 f o r t h e l o w e r p a r t o f t h e n o r m a lr a n g e . T h i s i s u s u a l l y g i v e n a s a l i n e a r i ty . T h e m e t e r sa r e c a p a b l e o f c a l i b r a t i o n t o a c h i e v e t h e s e v a l u e s a n dp o s s i b l y s l i g h t l y b e t t e r t h a n -+ 0 .1 to + 0 . 5 o v e r at u r n d o w n r a t i o o f 6 :1 a t l ea s t. R e p e a t a b i l i t y i s t y p i c a l l yg i v e n a s - + 0 . 0 5 f o r m e t e r s o f le s s t h a n o r e q u a l t o5 0 m m a n d + 0 . 0 2 f o r m e t e r s o f g r e a te r t h a n o re q u a l t o 7 5 m m . S u c h p r e c i s io n v a l u e s d o n o t t a k ei n t o a c c o u n t b i a s e r r o r s o f t e n p r e s e n t i n c a l i b r a t i o ne q u i p m e n t .I ns ta l l a t ionB e c a u s e o f th e s u s c e p t i b i l i t y o f t u r b i n e m e t e r s t oa s y m m e t r y a n d s w i r l g e n e r a t e d b y u p s t r e a m f i t t i n g s i tis c o m m o n f o r m a n u f a c t u r e r s to p r o v id e r e c o m m e n d a -t io n s f o r u p s tr e a m p i p e c o n f i g u r a ti o n s i n c l u d i n g t h eu s e o f f lo w c o n d i t i o n e r s . T h e s e a re s o m e t i m e s a c c o m -p a n i e d b y a d ia g r a m . A t y p i c a l e x a m p l e is s h o w n i nF i g u r e 6 . T h i s s u g g e s t s t h a t a n u p s t r e a m s t r a i g h t l e n g t ho f 1 0 d i a m e t e rs is re q u i r e d w i t h t h e d o w n s t r e a m e n do f a f l o w s t r a i g h t e n e r t h r e e d i a m e t e r s l o n g p o s i t i o n e da t leas t f i ve d iam e te r s ups t r ea m o f the m e te r . I t i sa l w a y s s l i g h t l y s u r p r i s i n g t h a t s o m e o t h e r m a n u -f a c t u r e r s w h o p r o v i d e a u s e f u l d i a g r a m l i k e t h i s o n es u g g e s t t h a t w i t h o u t a f l o w s t r a i g h t e n e r t h e u s e rs h o u l d a l l o w , s a y , 1 0 d i a m e t e r s o f s tr a i g h t p i p e u p -s t re a m o f th e f l o w m e t e r . I n t h e f ir s t p l a c e i t s e e m s t on e g a t e th e u s e o f t h e s t r a ig h t e n e r , w h i l e o n o t h e rg r o u n d s o f p u b l i s h e d i n f o rm a t i o n a n d t h e li k e l y d e c a yo f f l o w d i s t u r b a n c e s , i t s e e m s to b e f a r to o s h o r t ad i s t a n c e . A P I 2 5 3 4 ~ s u g ge s ts f r o m e x p e r i e n c e t h a t a nu p s t re a m l e n g th o f 2 0 d i a m e t e r s a n d a d o w n s t r e a ml e n g t h o f f i v e d i a m e t e r s p r o v i d e e f f e c t i v e s t r a i g h t e n i n g

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Flow Meas. Ins trum. Vo l 2 Ju ly 1991 153

To achieve he maxim um performance rom a turbine f low m eter it is essential h at straight pipe sectionsaref itted im m ediatelyupstreamand downstreamof the flow m eter position. For liqu id flow s the dimensionsindicated below should be considereda minimum and for gas f low they should be m ult iplied by 4.d ] i_ ~ ftow stroighteneri ~

l L I m o o o olOd m inim um ~ el m inimuml - - 1 mFigure 6 Instal lat ion for a prec is ion l iq uid m eter as suggested by Q uad rina reproduced wi th permission)i n m a n y i n s t a ll a ti o n s . In a d d i t io n , m a x i m u m a l l o w a b l em isa l i gnmen t o f t he me te r bo re and the p reced ingp ipe wo rk i s 5 . One m anu fac tu re r g i ves the ups treamd is tances quo ted i n Tab le2 fo r pa r t i cu la r f it t ings ,wh ich a re a l so g i ven i n re fe rence 5 . Ano the r manu fac -tu re r o f fe rs a wa fe r cons t ruc t i on a l l ow ing i ns ta l l a t ionbetw een f langes. P resum ably great care is neede d inthe pos i t i on ing o f t h i s me te r t o ob ta in sa t i s fac to ryresults.MaintenanceProb lems can a r i se f rom: de fec t i ve bea r ings ; j ammedbear ing o r ro to r ; damaged b lades ; de fec t i ve p i ckup ;b reak i n t he t ransmiss ion pa th o r amp l i f i e r f a i l u re ;ext ran eou s s ignal in ter ference .Serv i c ing shou ld take p lace a t l eas t annua l l y . I fposs ib le l i nes shou ld be d ra ined and the f l owmete rremoved fo r i nspec t i on fo r f o re ign ma t te r and to checkfo r f r ee ro ta t i on o f bea r ing and p rope r t i p c lea rance . I fnecessa ry the me te r shou ld be washe d w i th c lean f l u ido r an app rop r ia te c leaner . I f t he im pe l l e r t ouches thecas ing i t may i nd i ca te a damaged o r worn bea r ing . I tw i l l t hen p robab ly be necessary to re tu rn i t t o themanu fac tu re r f o r rep lacemen t . E lec t r i ca l con t i nu i t ys h o u l d b e c h e c k e d a n d t h e c o r re c t b e h a v i o u r o f t h esenso r shou ld be con f i rmed .T h e n a t u r e o f t h e o u t p u t p i c k u p s i g n a l w a v e f o r mwi l l o f t en revea l t he ex i s tence o f v i b ra t i on and non -un i fo rm ro ta t i on (worn bea r ings ) when examined w i than osc i l l oscope .

Precision gas m etersPrincipal designcomponentsF igu re7 sh ows a t yp i ca l gas tu rb ine m e ter . Wh i l em a n y o f t h e p r e v i o u s c o m m e n t s c o n c e r n i n g l i q u i dTable2 Upstreamdistances or particular ittingsFit t ing Upstream distance(diameters)Reducer 15Swept e lbow 20Two swept bends in the same plane 25Two swept bends in perpendicular 40planesValve 50

j/ ~ / / / / / / / / / ' / / ' / / , / , / / /

Figure 7 Diagram of an Instromet gas turbine m t rreproduced with permission)

meters are re levant , i t i s c lear tha t there are s ign i f ican tdes ign d i f fe rences . The mos t obv iou s i s t he l a rge hu band com para t i ve l y sma ll f l o w passage . The reason fo rth is is to impar t as large a torque as poss ib le on ther o t o r b y m o v i n g t h e f l o w t o t h e m a x i m u m r a d i u s a n dinc reas ing the f l ow ve loc i t y . The second d i f f e rence i sthe f requen t use o f a worm and gea r ou tpu t d r i ve ,resu l t i ng f rom the demand by mos t na t i ona l au tho r i t i esfo r a me chan ica l d i sp lay . I t i s com mo n, how ever , t oinc lude an e lec t r ica l ou tp u t as we l l as the mech an ica lregister.I n a recen t des ign 6 the m a in ro to r i s f o l low ed bya second ro to r t o se nse the con d i t i on o f t he i ns ta l ledf l owmete r . The speed o f t he second whee l as a ra t i oo f t he f ir s t w i l l change i f t he f l ow leav ing the f ir s twhe e l i s de f l ec ted mo re by ro ta t i ona l cons t ra in t s onthe f i r s t whee l . I t i s poss ib le f o r changes i n t heupst ream f low a lso to a f fec t the ra t io . Se l f cor rect ion isc la imed fo r t h i s dev i ce .Bearing designShie lded ba l l bear ings are somet imes used. Externa ll ub r i ca t i on i s necessa ry i n some des igns by us ingins t rumen t o i l . Spec ia l l ub r i can ts a re ava i l ab le fo r usew i t h o x y g e n . U n d e r n o r m a l u s e l u b r i c a t i o n s h o u l d b e

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1 5 4 R . C . B a k e r - T u r b i n e a n d r e l a t e d f l o w m e t e r s : I . I n d u s t r i a l p r a c t i c esu f f i c i en t two o r t h ree t imes pe r yea r . Some des igns ,such as sealed ba l l bear ings, do not need externa llubr icat ion. Sealed ba l l bear ings are su i tab le for gasescon tam ina ted w i th so l i d pa r t i c l es .Mater ia lsRoto r ma te ri a l i s t yp i ca l l y D e l r i n o r a lum in ium ,usual ly the la t ter for s izes greater than 150 mm. Some-t imes stainless steel is used.Size rangeFor 25 mm d iame te r t he range i s f r om abou t 0 .8 to10 m ~ h - l ; f o r 50 mm d iamete r t he range i s f romabou t 5 to 100 m ~ h -1 (w i th a m in imu m f l ow responseo f 1 .2 m 3 h -1 ) and fo r 600 mm d iamete r t he range i sf rom abou t 1000 to 25 000 m 3 h -~ . On e t ype o f fe rs a30 :1 tu rnd ow n ra t io . Num bers o f b lades a re t yp i ca l l y12 to 24 and max imum pu lse f requenc ies can be3 kHz . M ax im um p ressu re ra t i ng i s up to 100 ba r .These f i gu res can va ry s ign i f i can t l y be tween manu-facturers.

haracter ist icsF igu re 8 shows one man u fac tu re r 's t yp i ca l ca l i b ra t i oncu rve . The f l owra te Q in ac tua l un i t s (m 3 h -1 ) i sre la ted to t he base fl owra te Qb (m 3h -1 ) b y thee q u a t i o n :

(273.15 + T) PbQ = Q b X x2 7 3 . 1 5 + Tb pwhe re pb = 1 .01325 ba r and Tb = 6 0 C . The p ressu reloss i n t he me te r a t ma x imu m f l owra te i s 5 .5 mbar f o rthe 5 0 mm d iamete r me te r and 14 mba r fo r t he600 mm d iamete r me te r. P ressu re l oss i s o f cou rsed i rec t l y re la ted to t he dens i t y , and the re fo re to t hep ressu re , o f t he f l ow ing ga s . Re ference shou ld bemade to manu fac tu re rs ' da ta fo r g i ven cond i t i ons .Precis ionA t yp i ca l spec i f ica t i on fo r unce r ta in t y i s + 2 f rom them i n i m u m f l o w r a t e , min t o 2 0 o f t h e m a x i m u mf lo w r a t e , Q m a x , a n d + 1 f ro m 2 0 Qmax to Qmax .Some l i nea r i t y c la ims o f +0 .5 a re made .The l i nea r pe r fo rmance may be as good as+ 0 . 5 o n a b o u t 2 0 :1 tu r n d o w n w i t h r e p e a t a b i l it y+ 0 . 0 2 . M a x i m u m f l o w v e l o c i t i e s c a n b e u p t o3 0 m s - 1 . O t h e r d a t a a v a i l a b l e t o t h e a u t h o r s h o wremarkab le ca l i b ra t i on s tab i l i t y w i th sh i f t s o f o rde r

Atmosphericair2 ~ High pressure

2 I I I I I I I I I I II 0 20 50 I00Flow rote n % of OmoxF i g u r e 8 C h a r a c t e r i s t i c o f a n I n s t r o m e t g a s m e t e r r ,:p r o d u c e d w i t h p e rm i s s io n )

+0 .2 i n n ine yea rs w i th abo u t 108 m 3 o f natu ra l gashav ing been t ranspor ted th rough the tu rb ine me te rs a te ight bar l ine pressure.Insta l la t ionGases shou ld be c lean and f ree f rom l i qu ids and dus t ,o r a f i lt e r w i th 5 p ,m f i l t r a t i on qua l i t y o r be t te r shou ldbe used . The ups t ream p ipework shou ld be c leanedbefore ins ta l l ing the meter .O w i n g t o t h e la rg e h u b , w h i c h is a c o m m o nfea tu re o f gas me te r des ign , t he f l ow i s red i s t r i bu tedand the me te r appears no t t o be pa r t i cu la r l y sens i t i veto ups t ream f l ow d i s to r t i on . However , sw i r l and pu l sa -t i on can cause s ign i f i can t e r ro rs . Me te rs have a bu i l t - i nf l ow s t ra igh tene r wh ich removes some o f t he sw i r l .S t ra igh ten ing vanes may be necessa ry i f p ipe f i t t i ngsare a t f ive d iam eters or le ss upst ream. The m etershou ld be ca re fu l l y cen t red and p ro tube rances shou ldbe avo ided fo r a t l eas t f i ve d iamete rs ups tream. Do wn -s t ream the p ipework shou ld be fu l l bo re , bu t no o the rrest r ic t ions are p laced on i t .Excess ive speeds can damage the meter , but 20excess may be a l l owab le fo r sho r t pe r i ods .Temp era tu re shou ld be measured dow ns t reamw i t h i n t w o d i a m e t e r s .I f , as a resu l t o f changes in the process condi -t i ons , l iqu id cond ensa te i s p roduce d i n t he p ipew orkthen means o f d ra inage shou ld be p rov ided .

SensingFor a h igh - f requency s igna l , a p rox im i t y sw i t ch ope ra t -i ng o f f t he a lum in iu m b lades , me ta l s t r ips con ta ine d i nthe hub o r a f o l l ower d i sc on the ma in sha f t w i thm a g n e t i c p r o b e o r p r o x i m i t y s w i t c h a l l o w u p t o3 kHz . Fo r l ow f requenc ies o f 1 to 10 pu lses pe rrevo lu t ion a reed swi tch or s lo t sensor are used.In t r i ns i ca l l y sa fe sys tems a re ava i l ab le .

W a t e r m e t e r sPr inc ipa l des ign com ponentsF igu re9a ,b shows d iag rams o f wa te r me te rs . A com-mon des ign o f t h is me te r (b ) is f o r a comp le te me-chan ica l i nse r t t o be des igned to f i t i n to a f l anged i ronsec t i on o f p ipe w i th a spec ia l l y made cen t ra l con ta in -ment sect ion. The inser t cons is ts o f : f low s t ra ighteners ,wh ich a l so i nco rpo ra te the ups t ream bear ing ; t hero to r , wh ich i s usua l l y o f he l ica l des ign and m ay havea subs tan t i a l c l ea rance be tween the b lade t i ps and thecas ing ; t he ro to r sha ft , t he m o t ion o f wh ich i s t rans -m i t t ed v ia a r i gh t -ang le worm gear assemb ly i n to awa te r t i gh t gea r box ; and a rudder (o r t r imming vane)ups tream o f t he ro to r , wh ich p rov ides a mechan ica lca l i b ra t i on ad jus tmen t by a l t e r ing the ang le a t wh ichthe in le t f lo w s t ream h i ts the ro tor b lades. Wa ter isa l l owed to en te r t he gea r box v ia a f i l t e r , and theca l i b ra t i on rudder ad jus te r w i th in t he gea r box i saccessed th rough the ca l i b ra t i on po r t p rov ided i n t hetop cove r . When the cove r i s f i t t ed ove r t he gea r boxto fo rm a wa te r t i gh t j o in t , t he ou tpu t f r om the gea rbox i s t r ansmi t t ed v ia a magne t i c co up l i ng to thetota l iz ing reg is ter o f the meter .

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rT n FTT

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F i gu re 9 D i ag r am s o f w a t e r m e t er s: a ) G as and W a t e r M e t e r M an u f ac t u r e r s L t d m e t e r ; b ) Ken t H e l i x m e t e r ; c )G as an d W a t e r M e t e r M anu f ac t u r e r s m e t e r w i t h s ha f t pe r p end i c u l a r t o the p i pe a l l d i ag r am s r ep r od uc ed w i t hpe r m i s s i on )

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157

Size (mm) 50 65 80 100 150Qm~x (m3 h- ' ) 30 50 80 120 300Qn (m ~ h -1) 15 25 40 60 150t (m ~ h -1 ) 4.5 7.5 8 12 30Q r n i n (m 3h - l ) ] .2 2 1.2 1.8 4.5Start ing f low (approx.) 0.34 0.68 0.68 0.91 1.59Head loss at qmax bar) 0.20 0.04 0.09 0.08 0.09

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Fluid dynornic Indicat ing turbine Slave turbinecontrol devicesFigure 12 Qu antum Techno logy me ter reproducedwith permission

t u rb ine reduces sw i r l and hence the e f fec t o f ups t reamf low d i s to r t i on . W i th a spec ia l des ign o f RF p i ckupc la ims o f _+0 .01 l i nea r i t y f o r a t u rnd ow n o f be twee n350 and 500 :1 a re c la imed . I n gaseous f l ow theserangeab i l i t i es a re c la imed to co r respond to a masstu rndown in excess o f 1000 :1 . The p ressu re d rop i sl ow . I f t h i s dev i ce can ach ieve the pe r fo rmance c la imsmade fo r i t t hen i t w i l l be a use fu l t oo l f o r cus tod yt rans fe r and l eak -de tec t i on app l i ca t i ons .P e l t o n w h e e lTh is ope ra tes l i ke a hyd rau l i c pe l t on whee l by us ingt h e i m p u l s e d u e t o t h e f l u i d j e t m o m e n t u m . T oach ieve th i s t he f l ow i s cons t r i c ted to a sma l l ou t l e tand hence fo rms a h igh -speed j e t . Typ i ca l des igns a reshow n in F igu re 13 . I t i s des igned fo r use w i th l i qu idsand may be su i t ab le fo r use up to a bou t 100 ba r .I n t r i ns i ca l l y sa fe ve rs ions a re ava i l ab le . An ups treamf i l te r w i th 60 mesh i nse r t i s recomm ended . W i tho u t abypass the me te r can ope ra te down to abou t

I m i n - 1 . L i n e a r it y is c l a i m e d t o b e + 1 o f re a d i n ga n d r e p e a t a b i l it y t o b e + 0 . 1 o f r e a d in g . M a x i m u mf requency ou tpu t p roduced by fe r r i t es i n t he t i ps o f t hev a ne s a t m a x i m u m f l o w is a b o u t 1 5 0 H z . W i t h P V Cbod y, PTF E rotor an d s ta in less s tee l shaft the tem-p e r a t u r e l i m i t s m a y b e - 4 0 a n d 1 1 0 C . T h e m a x -imum a l l owa b le v i scos i t y is c la imed to be 20 cP . Themete r may be su i t ab le fo r wa te r , so l ven ts , chemica l sand c lean l i qu ids .The pe l ton w hee l p r i nc ip le i s used i n F igu re 13ca lso to p roduce a me te r capab le o f ve ry l ow f l owra tes .This meter may be const ructed f rom sta in less s tee lw i th t he ro to r f r om PTFE and con ta ins magne ts i n thero to r vanes . The bea r ing may cons i s t o f a ro to rmounted on a s ta in less s tee l shaf t w i th tungsten ba l lsand sapph i re caps . The range o f t he me te r may bead jus ted by chang ing the j e t s i ze . The me te r shou ld be

moun ted i n a ho r i zon ta l p ipe w i th t he j e t ho r i zon ta l ,p r e s u m a b l y t o m i n i m i z e p r o b le m s o f g a s w h i c h m a ycome ou t o f so lu t i on and co l l ec t . The me te r shou ld bema in ta ined fu l l a t a l l times . The d ev i ce i s f o r sma ll( a b o u t 6 m m ) p i p e w o r k w i t h r an g es f ro m 0 . 0 0 3 t o0 . 2 5 m 3 h -1 a n d m a x i m u m t u r n d o w n o f b e t w e e n 3 0 :1and 50 :1 . L inea r i t y i s c la imed to be + 1 o f f sd w i thr e p e a t a b i li t y o f + 0 . 3 o f f sd . M a x i m u m p r e ss u re m a ybe as much as 69 ba r o r i n some cases as much as2 0 0 b a r . M a x i m u m o p e r a t i n g t e m p e r a tu r e m a y b e110 C and v i scos i t y up to 70 cP .F i g u r e 1 3 d s h o w s a v e r y s i m i l a r p e l t o n w h e e ldes ign used as a bypass fl owm ete r , wh ich ope ra tesacross an or i f ice to a l low h igher ranges, and becausethe f l ow th roug h m a in and bypass a re p ropo r t i ona l ,t he me te r i s app rox im a te l y l i nea r w i th ranges up to1 2 0 0 m 3 h - ~ , w i t h l i n e a r it y c l a im e d t o b e + 1 o f fs dand abo u t 50 :1 tu rnd ow n a t 1 cP . V i sco s i t y may a f fec tthe pe r fo rmance o f t he fl owm ete r .B e a r i n g l e s s m e t e rTh is me te r i s shown in F igu re 14 . A f te r t he i n le t t hel i q u i d d i v i d e s a n d f l o w s u p w a r d s a n d d o w n w a r d s p a s tthe ro tor . The f low l i f ts the ro tor o f f i ts seat ing due tothe l ower s ta t i c p ressu re i n t he f l ow than under t hero to r . The f l ow a t bo th ends o f t he ro to r passes tu rb inew h e e l s b e f o re l e a v i n g t h ro u g h t w o c h a n n e l s w h i c hjo in a t the ex i t . Sens ing magnets are sealed in to ther im o f t he l ower ro to r and the i r passage i s sensed byan i ndu c t i ve co i l . We t ted su r faces may be e i t he r PVCo r P V D F .I t i s recommended tha t a t l eas t 10 d iamete rsups t ream and f i ve d iamete rs downs t ream a re a l l owedand tha t the me te r i s mou n ted ho r i zo n ta l l y f o r bestpe r fo rmance a t l ow f l ow . Reverse f l ow mus t no t bea l l owed , p resu mab ly because i t w i l l cause i nco r rec tfo rces and wear and may damage the ro to r . A spec ia lve rs ion i s made fo r use w i th ac ids and d ry chem ica l stha t a re compa t ib le w i th PVC. The bas i c i ns t rumen tcan a l so cope w i th pa r t i cu la te m a t te r (f o r 80 mm s i zeup to 3 mm par t ic l es ) . The bas i c i ns t rume n t has a s izerange o f abou t 15 to 80 mm d iamete r w i th f l o w rangef rom abou t 0 .2 to 5 .2 m 3 h -1 w i th 10 :1 tu rnd ow n fo reach i ns t rumen t and 5 :1 l i nea r range w i th c la ims fo rl i n e a r it y o f + 0 . 5 o f r e a d i n g a n d r e p e a t a b i l it y a b o u t+0 .13 o f read ing . P ressure d rop i s abo u t 0 .85 ba r a tm a x i m u m f l o w w i t h a m a x i m u m w o r k i n g p r es s ur e o f16 ba r a t 20 C (PVDF) and a tempera tu re range o f- 4 0 C t o 1 1 0 C ( PV D F ).P a d d l e w h e e l f l o w m e t e r sThe members o f t h i s f am i l y a re no t h igh -p rec i s ionins t rumen ts and the desc r ip t i on i n fe ren t i a l somet imes

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1 5 8 R . C . B a k e r - T u r b i n e a n d r e la t e d f lo w m e t e r s : I . I n d u s t r i a l p r a c t i c e

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F i g u r e 1 3 P e l t o n w h e e l m e t e r s : a ) D a t a I n d u s t r ia l C o r p o r a t i o n ; b ) N i x o n I n s t ru m e n t s ; c ) R h o d e s ; d ) L i t re m e t e ra l l d i a g r a m s r e p r o d u c e d w i t h p e r m i s s i o n )

a p p l i e d t o t u r b in e f lo w m e t e r s is p r o b a b l y a p p r o p r i a t ef o r t h e s e b e c a u s e th e f l o w o f f lu i d t h r o u g h t h e m e t e r i si n f e r r e d f r o m t h e e f f e c t o n t h e r o t o r o f i t s i n t e r a c t i o nw i t h a p r o p o r t io n o f th e f lu i d f l o w . T h r e e e x a m p l e sa r e g i v e n .

F i g u r e 1 4 R h o d e s b e a ri n g le s s m e t e r r e p r o d u c e d w i t hp e r m i s s i o n )

V a n e f l o w m e t e rF i g u re 1 5 a s h o w s a d i a g ra m o f t h e p r i n c i p l e o f o p e r at io n . T h e l i q u i d h i ts th e v a n e s a n d i m p a r ts m o m e n t u mt o t h e m . T h e c l e a r a n c e b e t w e e n t h e v a n e s a n d t h e

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I F l o w . _ . . . 4 . ~ ~ . . .

v a n ea

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Figure 15 Paddle wh eel meters : a ) Rosemount vane f lowme ter ; b ) Rhod es PT f lowme ter ; c ) Rhode s RT f lowm eteral l d iagrams reproduced wi th permission)

cas ing d i s t i ngu i shes th i s me te r f r om the pos i t i ve d i s -p lacem en t me te r and a l l ow s the f l u id to s l i p pas t t hevanes on the re tu rn .The f l ow ranges fo r t h i s me te r cove r 0 .45 to abou t12 m 3 h -~ w i th a ma x im um p ressu re d rop o f abou t1 . 4 b a r a n d a m a x i m u m a l l o w a b l e k i n e m a t i c v i s c o s i t yo f abou t 48 cS t .A n g l e d p a d d l eF igu re 15b shows an examp le o f t h i s me te r w i th th reeto fou r b lades on a sha f t ang led a t 45 . I t i s des ignedw i t h a r e m o v a b l e b o d y a n d s h o u l d h a v e 1 0 d i a m e t e r sups t ream s t ra igh t p ipe and f i ve d iamete rs downs t ream.Mater ia ls may be p last ic , gunmeta l or s ta in less s tee l .Ba l l bear ings are used. I t is cap able o f ope rat ing f roma b o u t 0 . 6 to 1 4 0 m 3 h -~ w i t h a 1 5 :1 t o 2 0: 1 t u r n -d o w n r a t io i n t e m p e r a tu r e s u p t o a b o u t 2 0 0 C a n d u pto ab ou t 6 9 ba r. I t i s i n t r i ns i ca l l y sa fe and su i tab le fo ruse w i th fue l o i l , an ima l f a ts and wa te r f l ow .The f l owm ete r i n F igu re 15c ope rates on the samep r i n c i p l e , b u t i n t h e c o n v e r s e w a y t o a p a d d l e w h e e l .The f l u id pass ing pu l l s t he r idged w hee l w i th i t . Thef l owm ete r i nc lud ing ro to r i s made f rom s ta in less s tee land runs i n ba l l bea r ings l ub r i ca ted by the f l u id . Amagne t i n the ro to r ac t i va tes a reed sw i t ch . The me te ri s c la imed to have the fo l l ow ing pe r fo rmance . L inea r -i t y i s o f o rde r +2 o f f sd and repea tab i l i t y i s + 1 o ffsd. Range is f rom abo ut 0 .15 to 3 m 3 h -1 w i th a 10:1t u r n d o w n r a t io i n f l u id s u p t o a b o u t 2 0 0 C a n d u p t oabou t 35 ba r . Ten d iamete rs sho u ld be a l l ow ed up -s t ream. I t is su i tab le for heated fue l o i ls , fa ts andlow-v i scos i t y c lean f l u ids .Ins e r t ion m e te rsFor f l ow measu remen t i n l a rge -d iamete r p ipes inse r -t i on p robes (F igu re16a) w i th a p rope l l e r o f 15 to3 0 m m d i a m e t e r a n d a b o u t + 1 r e p e a t a b i l it y a re

used . These can be i nse r ted th rough a va l ved T -p ieceon the p ipe . A se ries o f measuremen ts can be mad e tofo rm the bas i s fo r an i n teg ra t i on o f t he p ro f i l e . The re i su s u a l l y a l i m i t t o t h e p r o x i m i t y t o t h e p i p e w a l l a twh ich measuremen ts can be made . The p ro f il e shapet h u s d e t e r m i n e d a l l o w s t h e c o m p u t a t i o n o f v o l u m e t r i cf l ow . In th i s mode they a re a l so used fo r i n s i t uca l i b ra t i on , a l t houg h the ove ra l l unce r ta in t y i s un l i ke l yto be be t te r t han + 2 . A l te rn a t i ve l y they can be usedt o o b t a i n a s in g l e m e a s u r e m e n t f ro m w h i c h a f l o w r a t ei s deduce d based on p rev ious p ro f i l e measuremen ts o ron ca l cu la t i on o f t he p ro f i l e shape from Reyno ldsnumber da ta , assuming no sw i r l o r asymmet ry .A n o t h e r d e v i c e h a s b e e n d e v e l o p e d f o r c r u d e o i lf l o w m e a s u r e m e n t ( F i g u r e 1 6 b ) , w h i c h c o n s is t s o f aro to r o f up to 140 mm d iame te r t ha t i s capab le o fc o p i n g w i t h w a x a n d f i b r o u s m a t e r i a l s i n t h e f l o w . F o ra f l ow range o f 0 .15 to 12 ms -1 the p rec i s ion i sc l a im e d t o b e a b o u t + 0 . 3 a t t h e t o p o f t h e r an g ea n d + 5 a t t h e b o t t o m , w i t h a r e p e a t a b i l it y o f+0 .15 . Con s t ruc t i on i s f r om s ta in less s tee l w i thtungs ten ca rb ide o r ce ram ic j ou rna l bea r ings o r ca r -bon fo r h igh -p ressu re gas . Va r ious p i ckups a re ava i l -ab le .Va r ious o the r des igns o f wa l l -moun t ing p robe a reava i l ab le fo r ho t t app ing o r f i t t i ng i n to a T -p iece i n thewa l l . An exa mp le i s show n in F igu re 16c .F o r a i r f l o w h a n d - h e l d d e v i c e s a r e c o m m o n(F igu re 16d ) , pa r t i cu la r l y i n the a i r - cond i t i on ing i ndus -t r y , g i v i ng a range o f abo u t 0 .25 to 3 0 ms -~ w i thp rec i s ion c la ims as h igh as +1 .D i s c u s s i o nThe cons ide rab le range and d i v e rs i t y o f des igns can bes e e n f r o m t h is p a p e r . T h e o n e d r a w b a c k o f t h e f a m i l yo f des igns i s t ha t w i th ro ta t i on the re i s o f ten thepo ten t i a l p rob lem o f wear to cons ide r , espec ia l l y f o r

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16 R. C. Baker - Turb ine and re la ted flowme ters : I . Indus tr ia l prac t icePressure chamber

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F igu re 16 Inse rt ion p robes : a ) Qua dr ina p robe rep roduced w i th pe rmiss ion ) ; b ) M au f lo c rude o i l inse r tionf lowm ete r rep roduced w i th pe rmiss ion f rom F . M. A . L td ) ; c ) F low Research Corpo ra t ion p rob e ins ta lla t iond iag ram rep roduced w i th pe rmission ); d ) A i r f low anem om ete r rep roduced w i th pe rmission )

n o n - l u b r i c a t i n g l iq u i d s a n d d r y c o n t a m i n a t e d g a se s .H o w e v e r , a g a i n s t t h i s m u s t b e s e t t h e e x t r a o r d i n a r yv e r s a t i l it y o f t h e f a m i l y o f d e s i g n s . V e r y h i g h p r e c i s i o ni s a c h i e v e d i n s o m e ; v e r y l a rg e t u r n d o w n r a t i o isa c h i e v e d i n o th e r s ; s u i t a b i l i t y f o r a w i d e r a n g e o ff l u i d s a n d a v e r y w i d e p r i c e r a n g e a r e a l s o f e a t u r e s o ft h e f a m i l y . N e w d e s i g n s w i t h e x t r a o r d i n a r i ly l a rg et u r n d o w n a n d o t h e rs w i t h s e l f- c h e c k i n g a b i l i ty i n d i c -a t e t h a t t h e f a m i l y i s f a r fr o m d y i n g o u t .

C o n c l u s i o n sT h e advantages a v a i la b l e a m o n g s t t h i s fa m i l y o f f l o w -m e t e r s ( b u t n o t n e c e s s a r i l y i n o n e d e s i g n ) a r e : h i g hp r e c i s i o n ; g o o d t u r n d o w n r a t io ; v e r s a t i l it y ; s u i t a b i l i t yf o r w i d e t e m p e r a t u r e r a n g e a n d h i g h p r e s s u re ; p r o d u c -t i o n i n a w i d e r a n g e o f s iz e s , f l o w r a n g e s a n d c o n -f i g u r a t i o n s ; e s s e n t i a l l y d i g i t a l ; f a s t r e s p o n s e i n t h el i q u i d m e t e r s ; e a s y t o i n s t a ll ; c a n b e h y g i e n i c a n din t r i ns i ca l l y sa fe .

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Flow Meas. Instrum. Vol 2 Ju ly 1991The disadvantages are tha t t hey a re v i scos i t y -dependen t and no t su i t ab le fo r h igh v i scos i t i es ; ca l i -b ra t i on i s necessa ry and th i s somet imes changes w i thbear ing wear ; t hey can be damaged f rom ove r speed-ing due to c lean ing and gass ing ; cav i t a t i on i s poss ib leunder some o pera t i ng c ond i t i ons ; f o r gases they pe r -form bet ter a t h igh pressure; there is a ro ta t ing com-

p o n e n t w h i c h w e a r s ; t h e y a re s o m e w h a t s e n s i t iv e t oins ta l l a t ion con d i t i ons ; f i l tr a t i on i s needed i f t he f lu idis not c lean.They can be app l i ed to : cus tody t rans fe r andf isca l measuremen ts ; c r yoge n ic l i qu ids ; f ood m e te r i ng ;o i l s and fa t s ; wa te r ; c rude o i l ; gas ; and many o the rf lu ids .A c k n o w l e d g e m e n t sThe au tho r i s g ra te fu l f o r t he c r i t i ca l and cons t ruc t i vecomments o f Char les Gr i f f i t hs , who read the paper i nde ta i l and made many sugges t i ons fo r improv ing theaccu racy and c la r i t y o f t he tex t and a l so fo r t hose o fChr i s Kok , whos e exp er ience o f gas tu rb ine me te rswas pa r t i cu la r l y va luab le . I am g ra te fu l t o t he manu-fac tu re rs fo r pe rm iss ion to use i l l us t ra t i ons o f t he i rp roduc ts i n t h i s paper and fo r mak ing cons t ruc t i vec o m m e n t s w h e r e a p p r o p r ia t e . I a ls o a c k n o w l e d g e w i t hg ra t i t ude the many va luab le d i scuss ions w i th co l -l eagues f rom indus t r y and w i th pa r t i c i pan ts on Cran -f i e ld sho r t cou rses , and the i n te res t i ng oppor tun i t i es to

161observe f l owm ete r p e r fo rmance i n va r i ous app l i ca t i onso f fe red by consu l ta t i on fo r i ndus t r y .

R e f e r e n c e s1 Medlock, R. S. The histor ical development of f low meter-ing. Measurement Control Special Issue on Flo w, Ed.R. C. Baker). 19 5) June 1986) 11-222 Watson, G. A . and Furness R A. Dev elopm ent andappl icat ion of the turbine me ter. Pro c. Transducer 77Conf. Flow Measu rement Session, We mbley, London June1977)3 Gri f f i ths , G. and Si lverwood, P. A. S elect ion and appl ica-t ion o f f low measurement ins t rume ntat ion. Bul le t in5126-A HYD RIL Product ion Technology Div is ion 1986)4 Tsukamoto, H. a n d H u t t o n S. P. Theoretical prediction ofmeter factor for a hel ical turbine f lowmeter. Conf. FluidControl and M easurement, Tokyo, Japan September 1985)5 AN SI /API 2534-1971 Measurement o f l iqu id hydrocarbonsby turbine me ter systems. Am erica n Petroleum Inst i tute,Am erican N ational Standards Inst itute catalogue 1990)6 L e e W . F . Z . B la k e s le e D . C . a n d W h i t e R . V . Aself-correcting and self-checking gas turbine meter. J.Fluids Engng 104 June 1982) 143 -1487 ISO 4064 M easurement o f water in c lose d condui ts -Meters for cold po tab le water. In terna t iona l StandardsOrganisat ion8 BS 5728 M easurem ent of the f low of cold p otable water inclosed conduits. Bri t ish Standards Inst itute