reciprocating compressors for industrial refrigeration series … documents/grasso... ·...

- 1-Reciprocating Compressors for industrial refrigeration / Series Grasso 8SPI2010/v008

Reciprocating Compressors for industrial refrigerationSeries Grasso 8S

Product Information (PI)pador9070

- 2- Reciprocating Compressors for industrial refrigeration / Series Grasso 8S PI2010/v008

Copyright

All Rights reserved. No part of this publication may be copied or published by means of printing, photocopying, microfilm or otherwise without prior written consent of Grasso.This restriction also applies to the corresponding drawings and diagrams.

Legal Notice

This publication has been written in good faith. However, Grasso cannot be held responsible, neither for any errors occurring in this publication nor for their consequences.


Table of Contents

Section Title Page

1 DESCRIPTION AND SELECTION OF COMPRESSOR 7

1.1 INTRODUCTION AND SCOPE 7

1.1.1 OUTLINE 7

1.1.2 TYPE DESIGNATION 7

1.1.3 APPLICATION 7

1.1.4 SELECTION COMPRESSOR AND ACCESSORIES 7

1.1.5 PRESSURE TESTS 7

1.1.6 ACCEPTANCE TEST 7

1.1.7 STANDARD SCOPE OF SUPPLY 7

1.2 GENERAL DATA 9

1.2.1 TECHNICAL DATA 9

1.2.2 MAIN DIMENSIONS AND SPACE REQUIREMENTS 10

1.2.2.1 Grasso 58S and Grasso 68S 11

1.2.2.2 Grasso 58SW and Grasso 68SW 12

1.2.3 ELECTRICAL DATA 13

1.2.4 SOUND RATING GENERAL 13

1.2.4.1 SOUND DATA 8S 13

1.2.5 FREE FORCES AND MOMENTS 14

1.2.5.1 SURVEY 14

1.2.6 POSITION OF CENTRE OF GRAVITY 14

1.3 LIMITS OF OPERATION AND FIELDS OF APPLICATION 17

1.3.1 GENERAL LIMITS AND FIELDS OF OPERATION GRASSO 8S 17

1.3.2 PRECISE FIELD OF APPLICATION 17

1.3.3 LIMITATIONS OF PART-LOAD OPERATION 17

1.3.4 FIELD OF APPLICATION 18

1.4 LUBRICATING OILS (choice and recommendations) 21

1.5 DESIGN DETAILS OF COMPRESSOR 23

1.5.1 COMPRESSOR HOUSING 23

1.5.1.1 DIAGRAMS Grasso 68SW 24

1.5.2 CYLINDERS AND MOVING PARTS 25

1.5.3 SUCTION AND DISCHARGE VALVES 25

1.5.4 STARTING TORQUE / BY-PASS VALVE SELECTION GRASSO 8S 25

1.5.5 CAPACITY CONTROL SYSTEMS 25

1.5.5.1 GENERAL 25

1.5.5.2 PRINCIPLE OF CAPACITY CONTROL 27

1.5.5.3 DESCRIPTION OF CAPACITY CONTROL 27

1.5.5.4 OPERATION OF CAPACITY CONTROL 27

1.5.5.5 PARTIALLY UNLOADED STARTING 28

1.5.6 CYLINDER HEAD COVERS 28

1.5.7 RELIEF VALVES 28

1.5.8 DIRECT DRIVE OIL PUMP 28


1.5.8.1 OIL CHANNEL AND OIL PRESSURE REGULATOR 29

1.5.8.2 OIL LUBRICATION SYSTEM 30

1.5.9 MAIN CONNECTIONS AND SUCTION GAS STRAINER 30

1.5.9.1 SUCTION GAS STRAINER 30

2 DESCRIPTION AND SELECTION OF ACCESSORIES 31

2.1 PART-LOAD POWER CONSUMPTION AND ALLOWED PART LOAD STEPS COMSEL 31

2.2 CYLINDER NUMBERING 31

2.3 CAPACITY CONTROL 31

2.4 CONTROLS SINGLE STAGE 31

2.5 CRANKCASE OIL LEVEL SWITCH 31

2.5.1 DETAILS CRANKCASE OIL LEVEL FLOAT SWITCH 32

2.6 WATER COOLED CYLINDER HEADS AND COOLING WATER REQUIREMENTS 33

2.6.1 Water treatment 33

2.6.2 COOLING WATER REQUIREMENTS 35

2.7 CRANKCASE HEATER 35

2.7.1 HEATER FITTING DETAIL 35

2.8 STOP VALVES, CHECK VALVES AND FLANGES SUCTION AND DISCHARGE CONNECTIONS 35

Section Title Page


Preface documentations

Typographic signs:

Indicates a WARNING. READ IT CAREFULLY!

Indicates an IMPORTANT note or procedure to which you should pay special attention.

Indicates a HINT.

General

1 All documentation can be downloaded via grasso-global.com.

2 Grasso’s technical manuals includes “generic paragraphs”; this means that it can occur that not all data as described is relevant for the current compressor series as mentioned in this manual. (For instance, not all compressor series are suitable for all mentioned refrigerants or not all compressor series includes two-stage compressors)

1) Product Information (PI)

Contents

All product information (engineering data) for this series compressor and the corresponding accessories. It is meant to be a guide to the selection of these components.

User group

Project engineers, application engineers, sales managers, product managers for both sales representatives, contractors and end-users.

2) Installation and maintenance manual (IMM)(Supplied together with the compressor)

Contents

This manual will provide information on how to transport, install, start-up and maintain the compressor (package). It also contains a number of "Product Information Sheets" and the current "Parts List"

User group

To be used in the field by qualified personnel for both sales representatives, contractors and end-users.

3) Service Instruction Manual (SIM)

Contents

Description of (re)assembling, inspection, repair and part or total overhaul of the bare shaft compressor. This manual should be used together with the 'Installation and Maintenance Manual'.

User group

To be used in the field by qualified personnel of contractors.

4) Parts list (PL)

Contents

All current parts of the compressor and accessories together with the design changes (if applicable) to previous supplied components ("History").

User group

Service and parts departments for both sales representatives, contractors and end-users.

5) Service & Maintenance Schedules

Contents

Service and maintenance schedules up to the date of required overhaul of the bare compressor.

User group

Service and parts departments and in the field by qualified personnel for both sales representatives, contractors and end-users.

6) Instructions for accessories(Supplied together with the compressor)

Contents

All the relevant mounting and installation instructions and spare parts information for those accessories supplied with the compressor.

User group

To be used in the field by qualified personnel for both sales representatives, contractors and end-users.

Grasso’s technical manuals includes “generic paragraphs”; this means that it can occur that not all data as described is relevant for the current compressor series. For instance, not all compressor series are suitable for all mentioned refrigerants or not all compressor series includes two-stage compressors.

7) DirectivesEquipment supplied according to PED regulations and Machine Directives EN60204, EN292, EN294, EN378

- 7-Reciprocating Compressors for industrial refrigeration / Series Grasso 8S

1. DESCRIPTION AND SELECTION OFCOMPRESSOR

PI2010/v008

1. DESCRIPTION AND SELECTION OF COMPRESSOR

1.1 INTRODUCTION AND SCOPE

1.1.1 OUTLINE

Grasso 8S is the designation of a series of semi hermetic, single- acting, reciprocating refrigeration compressors with trunk-type pistons and with 5 and 6 cylinders in W-arrangement.

1.1.2 TYPE DESIGNATION

The following examples will explain the type designation:

6 cylinder single-stage compressor type

Grasso 68S-W:6 Number of cylinders8S Series indicationW Water cooled

1.1.3 APPLICATION

• Industrial (light duty) operation.• Evaporating temp. between -21 C and + 15.0 C.• Refrigerants: NH3 only.• For particular applications (cascade systems, chemical

processes, etc.) consult Grasso.

1.1.4 SELECTION COMPRESSOR AND ACCESSORIES

Consult Grasso's software program COMSEL (COMpressor SELection) which can be downloaded from Grasso’s internet site.

1.1.5 PRESSURE TESTS

• Test pressure 38.0 bar(e).• Design pressure 26.0 bar(a).• Test run with air.

1.1.6 ACCEPTANCE TEST

• Acceptance test under design conditions, acc. to ISO 917, witnessed by the customer possible on request.

1.1.7 STANDARD SCOPE OF SUPPLY

• Standard bare compressor:� painting pigeon blue� oil and suction filters� Filled with nitrogen� Mating flanges suction and discharge connections� Purge valve on discharge line

Supplied loose:

• Installation and Maintenance Manual(IMM).

Not included:

• oil charge.

- 8- Reciprocating Compressors for industrial refrigeration / Series Grasso 8S


PI2010/v008



PI2010/v008

1.2 GENERAL DATA

1.2.1 TECHNICAL DATA

Table 1.2-1 Technical Data Grasso 8S

COMPRESSOR TYPE Grasso 58 68

Number of cylinders z 5 6

Cylinder arrangement 2 x W

Cylinder bore D mm 110

Piston stroke S mm 85

Swept volume at full-load, n=1500 min-1 Vs m3/h 362.5 435

Standard steps of capacity control

(expressed in percentage of full load swept

volume)

% 100 -80 -40 100- 67- 33

Mass of bare compressor (excl. motor, without

accessories)(For motor weights Table 1.2-7)

without water

coolingkg

642 650

incl. water

cooling674 682

Oil charge in crankcase and oil circuit (centre line

of sight glass)dm3 17.7



PI2010/v008

1.2.2 MAIN DIMENSIONS AND SPACE REQUIREMENTS

Table 1.2-2 Legend for all sketches main dimensions and space requirements

Legend

Number of cylinders 5 6

1 Suction line DN mm 80(88.9 x 3.2)

2 Discharge line DN mm 65(76.1 x 2.9)

3 Suction pressure and temperature G1/4”

4 Discharge pressure (and temperaturea)

a. In case water cooling is NOT applied

G1/4”

5 Oil pressure G1/4”

6 Crankcase pressure G1/4”

7 Return oil from oil separator or rectifier G1/4”

8 Oil charge and drain valve G1/4”

9 Oil temperature G1/4”

10 Crankcase heater G1/2”

11 Purging and evacuation stop valve G1/4”

12 Sight glass diameter 29 mm

13 Water inlet/outlet (hose) DN25

14 Discharge temperature protectionb

b. In case water cooling is applied

G1/4”

MINIMUM REQUIRED FREE SPACE

Refer to drawings below

A

Minimum required free space for removal of suction filter, piston and cylinder liner

470

B 1360

C 690

D 1000



PI2010/v008

1.2.2.1 GRASSO 58S AND GRASSO 68S

Fig. 1.2-1 Grasso 58S and Grasso 68S



PI2010/v008

1.2.2.2 GRASSO 58SW AND GRASSO 68SW

Fig. 1.2-2 Grasso 58SW and Grasso 68SW



PI2010/v008

1.2.3 ELECTRICAL DATA

General

Mimimum insulation resistance is 50 MOhm.

Technical motor data

Table 1.2-3 Motor data

1.2.4 SOUND RATING GENERAL

GeneralThe sound characteristics of the compressor series are stated in Lw. Lw is the average measured "sound power level" of the bare shaft compressor block without electrical motor. These values are applicable for the following conditions of operation:• All cylinders in operation (full-load)• All refrigerants• All suction pressures

Sound power-frequency characteristics (Lw)The sound level table shows the sound power level (Lw, expressed in dB, re 10-12 W) as a function of the octave band centre frequency for all compressor types at different speeds. The data represent the sound power emitted by the compressor (body) only so excluding the influence of the electric motor and V-belt drive. Each dB-value is the direct or derived result of laboratory measurements according to ISO 9614-1 (Measurement accuracy +/- 3 dB) and carried out by means of latest sound intensity analyzing system Model: Difa, type DSA 220C, software version D-TAC200 3.30 with a Microtech intensity probe SIS90 and Microtech microphones MK290.

Sound pressure level (Lp)

The sound pressure level, at a certain required distance (> 3 mtr.) from the center of the package, can in theory be calculated with the formula: Lp= Lw - 8 -20log R.

Refer to following paragraph.(R = distance form the centre of the package to the required distance in m. (minimum value > 3 m.)

Measured sound pressure level (Lp)

The real measured sound pressure level lies between Lw and calculated Lp level due to the following influence factors: 1) Additional components like oil separators, pipe lines,

type of drive motor etc. can increase the calculated sound pressure level Lp.

2) The acoustic data of the engine room. (These must be known before any calculation can be performed).

3) The stated Lw levels are average levels. It could be that at a certain position (motor, oil separator etc.) higher values can be can be measured

1.2.4.1 SOUND DATA 8S

Fig. 1.2-3 Fictional frame

Table 1.2-4 Sound power levels for 5 and 6 cylinder compressors at 50

Hz (1500 min-1)

Mo

tor

po

wer

UN fN IN nN

Pa max

a. Maximum power consumption

I max

I A/I

N

MA

/MN

MS/

MN

MK/M

N

Star

tkW Vb

b. Euro voltage UN +/- 10%

Hz A

min

-1

kW A c

c. With Star-Delta the value will be reduced with 30%

c c c

55

400 star

50

107

1500

73

129

4.9 1.5 1.25 1.8 star

-del

ta

690

del

ta

62 75

dir

ect

75

400 star 146

100

176

5.4 1.7 1.45 2.0 star

-del

ta

690

del

ta

84 102

dir

ect

TcoC

Lw, (sound power level )in dB

Octave bands OverallPower32 63 125 250 500 1000 2000 4000 8000

- dB dB(A)

60 70 84 101 91 99 99 92 85 78 101

50 69 84 98 91 96 96 89 81 78 98

40 69 83 95 90 93 93 86 80 78 96

30 68 83 92 89 90 90 83 78 78 93

20 68 83 90 89 87 87 80 77 78 90



PI2010/v008

1.2.5 FREE FORCES AND MOMENTS

Free forces and moments are inertia forces and their resulting moments, generated by not fully balanced masses of the compressor main moving parts (crankshaft, connecting rods, pistons).As indicated in the adjacent figure there can be distinguished horizontal and vertical free forces, called H and V respectively, both acting in a vertical plane I, which is perpendicular to the crankshaft centre line at a distance L from the vertical centre plane of the compressor foot on drive end.Likewise, there are horizontal and vertical free moments, called Mh and Mv and respectively acting in a horizontal plane II and a vertical plane III, which both pass through the crankshaft centre line.Each free force and moment consists of a "primary" component (see table below for the different compressor types) with a frequency equal to the compressor speed and a "secondary" component with a frequency of double the compressor speed.

Fig. 1.2-4 Planes

1.2.5.1 SURVEY

1.2.6 POSITION OF CENTRE OF GRAVITY

General

For the proper design of a concrete compressor foundation or of the vibration-free mounting of a complete compressor-unit on a steel base frame, the following data, among other things, are required:

• Exact position of the centre of gravity of the compressor.

• Free forces and moments, generated by the compressor.

Position of centre of gravity

In figure Fig. 1.2-5 point Zc and Zm represents the centre of gravity of the compressor resp. electric motor. Its spatial position within the vertical plane through the crankshaft centre line is determined by the two indicated distances Xc/Xm and Yc/Ym, the magnitude of which, in dependance of the compressor type (number of cylinders) and motor type, can be taken from Table 1.2-6 resp Table 1.2-7. The resulting centre of gravity Z of the compressor and motor assembly lies on the line that connects Zc and Zm, whereby its position is determined by the distances x and y, as indicated in the figure, which can be calculated as follows:

x = (Xc.Mc - Xm.Mm) / (Mc + Mm)y = (Yc.Mc + Ym.Mm) / (Mc + Mm)

where: Mc (kg) = mass (weight) of bare compressor and Mm (kg) = mass (weight) of electric motor.

Legend

VPI vertical plane I

VPIII vertical plane III

HPII horizontal plane II

F flywheel end of compressor

CF centre line of compressor foot

CL centre line crankshaft

L distance VPI and centre line compressor foot

Qty

cyl

ind

ers

Free force and moments

Distance plain I and centre line compr.

foot L (mm)

Forces H (horizontal) and V (vertical) in (N); Moments Mh

(horizontal) and Mv (vertical) in (N.m)a

a. 1 N = 0.102 kgf = 0.225 lbf; 1 N.m = 0.102 kgf.m = 0.738 lbf.ft.

Primary Sec.

1475 rpmb

b. For different speed n (min-1), all forces and moments have to be multiplied by (n/1500)2

5

ForcesH 897 738

215V 897 426

MomentsMh 113 31

Mv 113 11

6

ForcesH 0 966

215V 0 322

MomentsMh 0 20

Mv 0 20



PI2010/v008

Fig. 1.2-5 Position of centre of gravity

Table 1.2-5

Table 1.2-6 Coordinates compressor

Table 1.2-7 Coordinates motor

Example:Grasso 68S, without water cooling, with 75 kW motor;x = (273 x 650 - 278 x 345)/(650 + 345) = 81.9 mmy = (117 x 650 + 22 x 345)/(650 + 345) = 71.9 mm

Legend Fig. 1.2-5

CL Centre line compressor and motor

CF Compressor foot (reference x)

Z Centre of gravity motor and compressor (reference y)

Zc Centre of gravity compressor

Zm Centre of gravity motor

Number of cylinders

Mc (Mass in kg) Xc Yc

5Standard

642 271 117

6 650 273 117

5Water cooled

674 272 123

6 682 270 124

Motor power (kW) Mm (Mass in kg) Xm Ym

55345 278 22

75



PI2010/v008



PI2010/v008

1.3 LIMITS OF OPERATION AND FIELDS OF APPLICATION

1.3.1 GENERAL LIMITS AND FIELDS OF OPERATION GRASSO 8S

When operating the compressor, none of the limits of operation as stated in the table below must be exceeded.1

The diagrams overleaf represent the overall fields of application in which the individual operation limits are taken into account.

Table 1.3-1 General limits and fields of operation

1.3.2 PRECISE FIELD OF APPLICATION

The field of application diagrams as shown in this manual can vary slightly from the actual field of application for each particular selection.

The actual field of application is dependent on refrigerant, type of compressor, speed, suction superheat and partload steps.

Always consult Grasso's software program, COMSEL, to determine the precise field of application for an actual compressor selection.

1.3.3 LIMITATIONS OF PART-LOAD OPERATION

General

If a compressor operates continuously at the minimum part-load, the manufacturer should be consulted first to check whether this is allowed under the expected design conditions.

In case of operating continuously at part-load, the general field of application is reduced in the sense that for each step of capacity reduction the limit line for Tdis,max moves to the right.

1. In practice, it is not so much the individual operation limits as combinations of them that are decisive for the conditions under which a compressor may operate. To check the various possibilities in this respect, use should be made of the "fields of application" ).

REFRIGERANT NH3

Compressor speed min-1 1500

Line frequency - Hz - 50

Suction pressure = evaporating pressure =crankcase pressure

a po bar(a)min. 1.5

max. 8.5

Evaporating temperature = saturation temperature at suction pressure to °C

min. -21.0

max. +19.0

Suction superheat t K min. > 0

Discharge pressure = condensing pressure b pc bar(a) max. 26.0

Condensing temperature = saturation temperature at discharge pressure tc °C max. +59.8

Discharge temperature te °C max. +155

Pressure ratio per stage (pc/po) c j -min. 1.0

max. 10

Pressure difference (pc-po) d p bar max. 25

Oil temperature in crankcase e toil °Cmin. +20

max. depending on type of oil, refer Section 1.4

a. 1 bar = 105 N/m2 = 100 kPa = 1.02 kgf/cm2 = 14.5 psi.b. This pressure is also the maximum allowable pre-set value of the HP safety switch.c. Pressure ratio limits are not absolute but arbitrary values based on practical considerations.d. The standard built-in overflow safety valve(s) between suction and discharge side has been factory-set to 24.5 (+ 10%) bar to prevent advanced opening during normal

operation at p = (pc - po) 24.0 bar.e. Indicated minimum value is the lowest oil temperature at which compressors are allowed to be started.The maximum oil temperature depends on the operating

conditions of the compressor, the oil type used and (for halocarbon refrigerants only) the solvability of the refrigerant in the oil. A minimum actual oil viscosity of 15 cSt is always required. When using ammonia as refrigerant, the maximum oil temperature will be exceeded only when a combination occurs of high ambient temperature, high suction superheat and part-load operation. In that case an oil cooler is required. A water-cooled oil cooler always form part of the standard delivery of a Grasso7W-compressor.



PI2010/v008

1.3.4 FIELD OF APPLICATION

Suction superheat (dT0) between 0 and 10 K.

Table 1.3-2 Explanation field of appication water cooling, area 1A, 1B, 2 and 3 (Refer Fig. 1.3-1), WATER COOLED

Areaa

a. Additional limitations superheat; 0 < Superheat suction <=10 K

Compressor type

Minimum allowed part load step (%)

Area 1ATcb-Toc < 49 oC + (10 - dTo)/3d

b. -20<=To<=+19 oCc. Tc >= +20 oCd. Superheat < 10K increases the field of application

Grasso 68S 100

Area 1BTc-To < 49.0 oC + (10 - dTo)/3d Grasso 58S 100

Area 2Tc-To < 46.5oC + (10 - dTo)/3d

Grasso 68S 67

Grasso 58S 60

Area 3Tc-To < 44.0oC + (10 - dTo)/3d

Grasso 68S 33

Grasso 58S 40



PI2010/v008

Fig. 1.3-1 Field of application, with and without water cooling, based on a superheat of 10K



PI2010/v008



PI2010/v008

1.4 LUBRICATING OILS (CHOICE AND RECOMMENDATIONS)

For lubrication of refrigeration compressors, several brands and types of specially developed lubricating oils are on the market. The choice of oil depends not only on its good lubrication properties (viscosity) and chemical stability at the operating conditions of the compressor, but also on the operating conditions of the refrigerating plant (solidifying and floc point, solubility).

Grasso has tested and approved for use in its reciprocating-compressors the brands and types of oil as listed in table below.The choice of the lubricating oil depends on the operating conditions of the compressor and refrigerant.The oil viscosity should always be more than 10 cSt.

Some of the oil types listed in this table may be marketed under other names and/or designations; these oils can also be used, provided their identity can be proved beyond any doubt. Application of other oils is not permitted without the written consent of Grasso.

Table 1.4-1 Accepted oil types, NH3

Brand Type designation Remarks

CPI Recommended! CPI-412/100PAG oil

For direct expansion systems chillers only

For all other oils consult Grasso



PI2010/v008



PI2010/v008

1.5 DESIGN DETAILS OF COMPRESSOR

1.5.1 COMPRESSOR HOUSING

Figure below shows the basic construction of the compressors.

The cylinder head covers are provided (optional) with water in- and outlet connections linked up with each other in series by means of rubber hoses.

The compressor housing of all compressor types are made of cast iron and comprise the crankcase and the bearing cover with built-on oil discharge filter housing on oil pump side. Where the cylinders are located the crankcase has a double wall; the intermediate space is a suction chamber which communicate with the suction connection, situated on the motor side.



PI2010/v008

1.5.1.1 DIAGRAMS GRASSO 68SW

Fig. 1.5-1 Cross section Grasso 68SW (refer Table 1.5-1)



PI2010/v008

Table 1.5-1 Legend Fig. 1.5-1

1.5.2 CYLINDERS AND MOVING PARTSThe cylinders are formed by interchangeable, centrifugally cast iron cylinder liners pressed into the crankcase. The collar on top of the cylinder liner is provided with openings and acts as a seat for the suction valve ring.In the cylinder liners aluminium alloy pistons are located, on which compression rings and oil scraper ring are fitted.

The connecting rods have a split-type big end, in which precision bearing shells are positioned.The gudgeon pin is mounted in the small end of the connecting rod on a bronze bush.

The nodular cast iron crankshaft is mounted in sleeve bearings consisting of interchangeable, one-piece bushes pressed into the bearing covers.

The axial force of the crankshaft is taken up by a thrust bearing on the oil pump end.

The crankshaft is dynamically balanced.

1.5.3 SUCTION AND DISCHARGE VALVESThe suction and discharge valves of the compressor contain valve rings, kept in closed position under spring tension. The lift of the valve rings is limited by the stroke limitor.

The suction valve consists of one valve ring and one or

more sinusoidal springs, mounted between the collar of the cylinder liner and the outer discharge valve seat. The collar integrates the suction seats and the valve guide. The discharge valve seat is used as stroke limiter of the suction valve.

The discharge valve consists of one ore more valve seats, valve rings and sinusoidal springs, and a stroke limiter. The valve seats are bolted to the stroke limiter with the central bolt. The whole discharge valve (the so called “discharge valve assembly“) is pressed down by one or more buffer springs, which prevents for serious damage in the case of the presence of liquid in the suction gas.

1.5.4 STARTING TORQUE / BY-PASS VALVE SELECTION GRASSO 8S

General

The electric motor has to be checked for proper starting, because 2 cylinders are loaded during starting. Starting torque is dependant on starting conditions.

Selection by-pass valve Grasso 8S, NH3, when using star-delta starting

Tc= saturated condensing temperature, To = saturated evaporating temperature during starting the compressor:

Table 1.5-2 Grasso 8S, Tc >= 35 oC

Table 1.5-3 Grasso 8S, Tc <35 oC

1.5.5 CAPACITY CONTROL SYSTEMS

1.5.5.1 GENERAL

The capacity control, i.e. the decrease in capacity at constant speed and under constant operating conditions, takes place stepwise by successively cutting out cylinders.This is effected by isolating the discharge space direct above the valves for each individual cylinder head from the common discharge chamber and by putting it into communication with the common suction chamber, located in the compressor housing.

Legend Fig. 1.5-1

1 Terminal box motor 21 Main bearing drive end

2 Water cooling hose 22 Suction and discharge valve assembly

4 Cooling water inlet/outlet connection 24 Cylinder liner

5 Discharge line connection 25 Cylinder cover, water cooled, with capacity control

7Meassure point crankcase

pressure / oil return from oil separator or rectifier

26 Connecting rod

9 Crankcase heater 28 Sight glass

10 Oil charge and drain valve 29 Compressor foot

11 Measure point oil temperature 30 Cylinder cover, watercooled,

without capacity control

12 Discharge manifold 31 Crankcase

13 Lifting eye motor 32 Tube for pressure equalizing

14 Terminal box 33 Bearing cover

15 Motor housing 34 Main bearing pump end

16 Stator 35 Oil filter housing

17 Suction cover 36 Oil discharge filter

18 Suction line connection 37 Oil pump

19 Crankshaft 38 Oil suction filter

20 Rotor

A Cross section A-A; refer to Fig. 1.5-3

Tc > 35 oCNominal motor power (kW)

55 75

7.5 < To < 15 Select 75 kW motorEVRAT20

0 < To < 7.5EVRAT20

To < 0 By-pass not required

Tc =< 35 oCNominal motor power (kW)

55 75

7.5 < To < 15EVRAT20

By-pass not required0 < To < 7.5

To < 0 EVRAT15



PI2010/v008

This socalled “internal recirculation control” is, (apart from the flow resistance in valves and channels,) free from losses because the cut out cylinders do not compress gas but just circulate it under suction pressure.



PI2010/v008

1.5.5.2 PRINCIPLE OF CAPACITY CONTROL

Fig. 1.5-2 Capacity control system

1.5.5.3 DESCRIPTION OF CAPACITY CONTROL

Each controllable cylinder head cover is provided with a by-pass slide valve, which can move horizontally forward and backward in a guide bush and is connected via a push rod to a hot gas operated control piston in a horizontal control cylinder. Slide valve, push rod and control piston form one integral steel part.

Via a three-way solenoid valve , which is mounted outside on top of the cylinder head cover against the sealing cover of the control cylinder, the control piston can be communicated either to suction pressure (via lines c and b, the former connected to the control cylinder and the latter to the by-pass chamber) or to discharge pressure (via lines a and c, the former connected to the permanent discharge chamber in the cylinder head cover).

Actually, only line a, coming from the solenoid valve, is an external one; the two others b and c are internal bores provided in the sealing cover of the control cylinder and in the walls of the cylinder head cover.

1.5.5.4 OPERATION OF CAPACITY CONTROL

If the solenoid valve is not energized, line a is connected via line c to the control cylinder, so that hot gas from the permanent discharge chamber enters this cylinder and, as the diameter of the control piston is substantially larger than that of the slide valve, the combination

Legend

1 Cylinderhead cover, incl. capacity control, without water cooling

2 Three-way solenoid valve

3 By-pass slide valve annex hot gas operated control piston

3a Hot gas operated control valve

3b By-pass slide valve

3c Push rod

4 Spring, to ensure partially unloaded starting

5 Guide bush

6 Control discharge pressure line

7 Permanent discharge chamber, connected to common discharge manifold

8 Space direct above discharge valves

9 Flow suction gasses (From suction chamber to cylinder)

10 Valve seat / stroke limitor

11 Chamber connected to common suction chamber

12 Piston

13 Cylinder liner

14 Sealing cover

15 Flow discharge gasses

U Cylinders are unloaded, solenoid valve (2) is not energized

L Cylinders are loaded, solenoid valve (2) is energized

S Suction pressure

D Discharge pressure



PI2010/v008

piston-rod-valve will move to the leftmost position, causing the slide valve to shut off entirely the permanent discharge chamber from the space direct above the discharge valves and the latter to be communicated via a ring of circular openings in the guide bush with the space between control piston and slide valve (by-pass chamber), which is in permanent communication with the common suction chamber in the compressor housing. The cylinder(s) then operate unloaded as a result of the by-pass thus effected.

When the solenoid valve is energised, line b is connected via line c to the control cylinder, so that there is no pressure difference across the control piston and the combination piston-rod-valve is kept in its loaded position by the pressure prevailing in the permanent discharge chamber and exerted onto the righthand face of the slide valve. The space direct above the discharge valves then communicates, via the afore mentioned circular openings in the guide bush of the slide valve, with the permanent discharge chamber, so that the cylinder(s) operate normally.

For the standard capacity control part-load steps of the various compressor types and the corresponding energising sequence of the solenoid valves.

1.5.5.5 PARTIALLY UNLOADED STARTING

In order to be sure that all controllable cylinder always start fully unloaded when there is no pressure difference between discharge and suction, a spring is mounted between each sealing cover and control piston to ensure that all control pistons and slide valves are kept in their unloaded position, regardless of whether the corresponding solenoid valves are energised or not.

On the other hand, to create sufficient discharge pressure to operate all available capacity control slide valves when starting the compressor at zero pressure difference between discharge and suction, at least one cylinder of each compressor type is non-controllable. Consequently, when the discharge pressure is higher than the suction pressure, only partially unloaded starting is possible.Therefore, it is recommended to always check the electric drive motor in this respect, depending on compressor design speed and starting conditions.

1.5.6 CYLINDER HEAD COVERSFor each pair of cylinders viewed lengthwise to the compressor, a cylinder head cover is provided, which feeds the discharge gases to the discharge manifold.

Moreover, and only if the compressor is equipped with standard capacity control, all cylinder head covers except one contain an internal bypass valve, controlled by discharge pressure via an electrically operated three-way solenoid valve.

In case of a water cooled compressor each cylinder head is additionally provided with a cast-in cooling water channel, located inside the lower part of the cylinder head over its entire length and consisting of two equal parallel branches, which are connected to each other in series.

1.5.7 RELIEF VALVES

In order to prevent excessive pressure difference in the compressor, one pressure independent relief valves is provided.

This counter pressure independent type of relief valve act on the difference between discharge and ambient pressure.

The valves are fitted externally against the crankcase housing. The relief valves are spring-loaded valves adjusted at the works.

1.5.8 DIRECT DRIVE OIL PUMP

Table 1.5-4

The direct-driven oil pump, suitable for both directions of rotation, is fitted in the bearing cover, which also comprises the oil suction and discharge chamber.

The oil suction strainer of metal wire mesh (max. opening 315 microns) is immersed in the crankcase oil sump and is only accessible after having removed the inspection side cover.

The oil discharge filter consists of a ring-shaped paper filter element with a filtration rating of 25 microns, retaining the fine (metal) particles suspended in the oil. The direction of the oil flow is from the inside to the outside through the filter element. The filter is fitted with a central stud to the oil pump housing and can be easily replaced from outside by only removing the oil filter housing.

The lubricating oil circuit, accommodated mainly inside the compressor housing. From the oil filter housing the

Legend

1 Oil discharge filter 4 Crankshaft

2 Oil pump element 5 Oil suction filter

3 Oil suction line

��



PI2010/v008

oil flow is forced via a bore in the bearing cover direct into the crankshaft channel for lubricating the main bearings, connecting rods and pistons. Sufficient lubrication of the cylinder walls is ensured by the oil which is being splashed around in the crankcase. The connecting rods have an internal oil channel through which the oil is supplied to the small end bearings.

1.5.8.1 OIL CHANNEL AND OIL PRESSURE REGULATOR

The oil channel in the crankshaft ends in the main bearing drive side from where excess of oil is fed back to the crankcase via an internal oil return. In this oil return line an adjustable lubricating oil pressure regulator is fitted. This spring-loaded ball valve allows the return oil to pass at a certain pre-set pressure only, thus determining the pressure in the lubricating system. Besides the oil return connection also a connection for the lubricating oil pressure safety switch is provided.

Location oil pressure regulator

Fig. 1.5-3 Oil pressure regulator, cross section of Fig. 1.5-1

Table 1.5-5

Legend Fig. 1.5-3

1 Oil pressure regulator

2 Measure point of oil pressure at the end of the lubrication system



PI2010/v008

1.5.8.2 OIL LUBRICATION SYSTEM

Fig. 1.5-4

1.5.9 MAIN CONNECTIONS AND SUCTION GAS STRAINER

The suction connection communicates with the electric motor (= suction) chamber via a built-in single, cylindrical suction gas strainer of woven mesh with a filtration rating of 140 microns.

This filter is accessible only after having removed the suction welding neck flange and thus the entire suction stop valve, if any.

1.5.9.1 SUCTION GAS STRAINER

Fig. 1.5-5

Table 1.5-6

Legend

1 Oil suction filter

7 Oil lubrication pressure regulator2 Oil pump

3 Oil discharge filter

4 Thrust bearing 8 Oil sump

5 Crankshaft A Oil lubrication pressure

6 Oil return line B Crankcase pressure

Legend Fig. 1.5-5

1 Gauze filter

2 Ring flange

3 Gasket


2. DESCRIPTION AND SELECTION OFACCESSORIES

PI2010/v008

2. DESCRIPTION AND SELECTION OF ACCESSORIES

2.1 PART-LOAD POWER CONSUMPTION AND ALLOWED PART LOAD STEPS COMSEL

To determine the allowed partload steps for the design conditons and the corresponding partload power consumption refer to software program Comsel.

2.2 CYLINDER NUMBERING

Fig. 2.2-1 Cylinder numbering Grasso 68S

2.3 CAPACITY CONTROL

Table 2.3-1 Capacity control steps

2.4 CONTROLS SINGLE STAGEIn case the compressor will be controlled by a micorprocessor-based control device, the pressures, temperatures, switches and solenoid valves as mention in the picture below have to be controlled.

Fig. 2.4-1 Controls for single stage compressors

Table 2.4-1 Legend single stage control system

2.5 CRANKCASE OIL LEVEL SWITCH

General

In case two or more compressors operate in parallel on one common oil reservoir or oil separator, Grasso can supply an oil level switch.

Selection and Data

• To be fited on crankcase

Qyt

Cyl

ind

ers

Cap

acit

y %

Rem

arks

Cyl

ind

ers

Sole

no

ids

5

40 2 + 5 -

80 1 + 2 + 4 + 5 B

100 1 + 2 + 3 + 4 + 5 A + B

6

33 2 + 5 -

66 1 + 2 + 4 + 5 B

100 1 + 2 + 3 + 4 + 5 + 6 A + B

1 Compressor

3 Oil separator

4 Suction pressure header

7 Discharge pressure header

8 Oil pump

9 Oil pressure regulator

10 Solenoid valves for capacity control

11 Capacity control mechanism of the compressor

12 Crankcase oil level switch

13 Cylinderhead temperature sensor

14 Compressor drive motor

16 Solenoid valve oil return protection

19 Oil separator oil level switch

B To capacity control mechanism of the compressor



PI2010/v008

• Auxiliary relay required (not included)• Wiring: If 'Low oil level' and 'Compressor is running'

then 'solenoid valve open'

Standard scope of supply

• Oil level switch

Options• Mounting

Fig. 2.5-1 Float switch wiring diagram

Table 2.5-1 Legend

2.5.1 DETAILS CRANKCASE OIL LEVEL FLOAT SWITCH

Fig. 2.5-2 Crankcase oil level float switch

1 Oil level float switch

2 Auxiliary relay (not included)

3 Solenoid valve (not included)

4 Oil return from oil separator or liquid rectifier

N Neutral

L Live

Legend

A Float switch housing

B Oil level float switch

C Oil sight glass



PI2010/v008

2.6 WATER COOLED CYLINDER HEADS AND COOLING WATER REQUIREMENTS

GeneralGrasso can supply a cylinder head water cooling system in order to increase the field of application in fulload and partload.

If water cooling will be applied, the option discharge temperature protection is compulsory.

Effect of water cooling

Water cooling means cylinder head cooling. Even during full-load operation the overall compressor housing temperature will be favourably influenced by applying water cooling, and also enlarging the original total field of application in comparance to compressors without water cooling.

Application requirements

The water cooling system, consisting of special cylinder head covers and the interconnecting rubber hoses, has been designed for a maximum water pressure of 20 bar.

The actual water flow for different values of water inlet temperature and depending on the operating conditions to and Tc (evaporating and condensing temp.) should be such, that the water outlet temperature does not exceed 53 oC and the discharge gas temperature, measured in the cylinder head, is not higher than Tc + 155 oC.

Hints and tips

1 It is recommended to apply a closed water recirculation system via a separate heat exchanger in order to prevent deposits inside the cooling water channels which could restrict the free flow of water.The cooling water used should be non-aggressive (not causing corrosion, e.g. sea water or brackish water should not be used at all) and with an water inlet temperature not lower than 10 oC in order to prevent premature condensation of refrigerant in the cylinder heads which may result in liquid hammer and possible damage to the compressor.

2 Provision should be made to interrupt the waterflow when the compressor stops, preferably by means of a solenoid valve.During long periods of compressor standstill at low ambient temperatures the cooling water should be drained off from the cylinder heads and oil cooler or an anti-freeze agent should be added to the cooling water in order to prevent freezing of the cooling water.

In case alternative waterflow connections are required (e.g. when expected pressure drop seems to be too high), Grasso has always to be consulted.

Normally, water flows in series through the cylinder heads. In case of some compressor types, the water flow might be split into two paralles circuits. Each circuit results into lower pressure drops. Consult always Grasso for more detailed information.

Waterflow requirements

Water inlet; always cylinder number 1 .

Water outlet; always highest cylinder number

1 Waterinlet temperature < Tc-7 K2 Wateroutlet temperature < 53 oC3 Discharge gas temperature < +155 oC4 Mimimum required water flow is based on water

outlet temperature approx. 53 oC

2.6.1 WATER TREATMENT

Since water qualities can differ greatly, it is stronly recommended to consult a water treatment specialist, to avoid extensive damage.

Industrial water mostly contains dissolved or solid components which cause corrosion or deposit or encourage algal growth. The water for the compressor cooling should be treated chemically to reduce undesired effects like increasing extra maintenance costs due to additional expenditure for the removal of dirt coats or the replacement of corroded parts.



PI2010/v008

Check the water quality of the coolant and heat carriers. Do not exceed the values indicated for the various substances as mention in Table 2.6-1.

Table 2.6-1 Substances

If additives or cooling brines are applied, it is absolutely necessary to check if the materials used are compatible.

The addition of substance in inadmissible concentrations is inhibited.

If condenser brines are used, it is also necessary to check whether the inhibitors are still thermally stable at the desired compressor temperatures.

Appearance Colourless, clear, no forming of sediments

pH value 7 - 8.5 -

Electrical conductivity < 1000 10-6 s/cm

Chloride < 250 mg/l

Sulphate <240 mg/l

Nitrate < 50 mg/l

Ferrum < 0.2 mg/l

Free carbonic acid < 20 mg/l

Manganese < 0.2 mg/l

Ammonia < 2 mg/l

Free chlorine < 0.5 mg/l

Total hardness < 1.78 mol/m3

Acid capacity < 1.07 mol/m3



PI2010/v008

2.6.2 COOLING WATER REQUIREMENTS

Table 2.6-2 Minimum cooling water flow Grasso 8S

Table 2.6-3 Pressure drop Grasso 8S

Example calculation pressure drop

a Grasso 47S, Tc=+40 oC, Actual water flow = 10.0 liter/min;

b 10.0 liter/min = 0.6 m3/ hc Actual pressure drop = (0.6/1.8)2 = 0.111 bar

2.7 CRANKCASE HEATER

Recommended for all compressors and all conditions of operation.

General

During standstill of the compressor, refrigerant may dissolve in the oil charge of the crankcase or it may even condense, both due to an increase of crankcase pressure, a decrease of crankcase temperature and/or possible temperature differences between crankcase and evaporator.

Excessive foaming of oil in crankcase, can occur when starting the compressor after a long period of standstill with relatively low oil temperature which may result in damaging the compressor by a lack of lubrication.

Low oil temperatures may also cause a high oil viscosity, which may result in troublesome starting.

Selection and Data standard heater

• Refer to table.• Engine room temperatures below 20 C.• Wiring: If 'compressor NOT running' then 'element is

energised'.

Standard scope of supply

• Heater element (mounted, not wired).

Fig. 2.7-1 Standard crankcase heater

Mentioned power in Watt; Standard voltages are 110-120 V and 220-240 V.

2.7.1 HEATER FITTING DETAIL

The standard crankcase heater is fitted into a sleeve so can be exchanged while compressor is in operation.

Table 2.7-1

2.8 STOP VALVES, CHECK VALVES AND FLANGES SUCTION AND DISCHARGE CONNECTIONS

Refer to “Main Dimensions and Space Requirements” to determine DN connections

General

Grasso can deliver (straight through) stop valves to suit suction and discharge connections.It is strongly recommend to apply suction and discharge stop valves.

Standard scope of supply• Stop valves (not mounted)

Options

• Additional set of flanges (not mounted)• Check valves for discharge connections (not

mounted)• Welding stop valves, check valves and mating flanges

Number of cylinders

Minimuma cooling water flow (liter/min)

a. Low water outlet temperature is recommended; Higher waterflows results info lower water outlet temperatures.

Tc=+35 oC Tc=+40 oC Tc=+45 oC Tc=+50 oC

5 + 6 7.5 8.5 12.5 21.0

Number of cylinders Kv (m3/h)Approx. pressure drop

(bar) at Tc=40 oC

5 + 6 1.8 0.08 (8.5 liter/min)

Legend

CE Cable entry

RC Removable cap to protect connections

Number of compressor

cylinders

Installed power of heater element Dimension L (mm)

5-6400

(Thermostatically controlled)

400

reciprocating compressors for industrial refrigeration series … documents/grasso... ·...

Documents