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Analysis of directing-acting steam reciprocating pumps

-Indicator pressure diagram: Discharge from pump is pulsating and changes

only when speed of pump is changed. Often air

chamber is connected on pump discharge to

provide more even flow by evening out pressure

surges. The pump consists of steam cylinder end in

line with liquid cylinder end, with a straight rod

connection between steam piston and pump piston

or plunger. These pistons are double acting which

means that each side pumps on every stroke.

Another construction style is the power pumps

which convert rotary motion to low speed

reciprocating motion using a speed reducing gear.

Power pump can be either single or double-acting.

A single-acting design discharges liquid only on

one side of the piston or plunger. Only one suction

and one discharge stroke per revolution of the

crankshaft can occur as shown in figure. The

double-acting takes suction and discharges on both

sides of the piston resulting in two suctions and

discharges per crankshaft revolution. Power pumps

are generally very efficient and can develop high

pressures. These pumps are more expensive than other pump types.

-A Single Cylinder Reciprocating Pump Capacity:

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For a Triplex Pump:

Prove analytically that:

Qmax/Qmean=π/3=1.047

(as given in above figure).

In the next figure, we note

that the constant K=Qmax.

If we examine the figure,

We see that the total Q has

a repeated cycle every 60o.

We can get Qmean by doing

integration for the function

of Q(θ) over any 60o

part

part and divide by that base

of length L = 60 * (π /180)

So, we can write:

����� ∗ L = (�� + ��)�� �� ����� ∗ L = (��)�� �� ����� ∗ L =���

��

��

� (�� + ��)��

���

���

By doing the first integral, ����� ∗ L = � � sin � �� + � sin(� − 240)�� ���

����� ∗ !� = [−� #�$� ]��� − [� cos(� − 240)]��� = −K[(cos60 − cos0)] − K[(cos(−180) − cos(−240)] = K

So we get: Qmean= 3K/π ; but since Qmax= K

The ratio is therefore: Qmax/Qmean= π/3 = 1.047 as shown on the figure.

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