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PROCEEDINGS OF THE TWENTY-FOURTH INTERNATIONAL PUMP USERS SYMPOSIUM • 2008

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Piping vibration—Can result from improper piping support,

cavitation, or normal reciprocating pump hydraulic pulses

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Noisy operation—Most present when pump is cavitating

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Reduced capacity—Can result from fluid flashing. If it is, this is

an indication that the pumping chambers are filing up with gases

or vapors.

These factors contribute to reduced pump life, and are a

potential hazard to personnel and associated equipment. It is

possible to fracture a fluid cylinder and/or piping and damage the

pump drive end internals with high pressure surges occurring when

fluid is flashing or cavitating.

The following basic piping guidelines represent a combination

of Hydraulic Institute recommendations and criteria established by

experienced designers of systems containing reciprocating pumps.

While pump manufacturers cannot assume responsibility for the

piping system into which the pump is installed they can provide

valuable guidance that can aid system designs.

Figure 29. Flow Velocity in Suction Pipe Standard Weight

(Schedule 40) Steel Pipe Selection Curve.

Pump Suction Piping System

Piping should be laid out so no high points occur where vapor

The suction line velocity is based on an acceleration head of 0.7

pockets may form. Vapor pockets reduce the effective flow area of

feet per foot of suction line length and the acceleration head

the pipe and consequently make pump priming and operation

equation from the Hydraulic Institute Standard. For discharge line,

difficult. Vent any unavoidable high points and provide gauge and

a velocity not exceeding three times the suction line velocity is

drain connections adjacent to pump.

considered good practice.

Line Size

Acceleration Head

Many pump problems result from a suction line that is too small

After selecting the line size from above, it is necessary to

in diameter, or too long. Suction piping should be as follows to

calculate the total acceleration head (H

) in the suction line.

provide a smooth transition of fluid flow and result in reduced

As with centrifugal machines the NPSHA in the system must

piping friction losses:

always exceed pump NPSHR plus piping friction losses, but with

Be short and direct

reciprocating pumps a further consideration must be made with

respect to acceleration head.

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Be one to two sizes larger than pump suction connection. Use

Fluid inside the pump is accelerated and decelerated as a result of

eccentric type pipe reducers at pump with flat side up to avoid a

the reciprocating motion and suction valves opening and closing.

possible vapor pocket.

This accelerated and decelerated pulsation phenomenon is also man-

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Contain a minimum number of turns. Accomplish necessary

ifested within the suction pipe. The energy required to keep the fluid

turns with long radius elbows or laterals.

in the suction pipe from falling below vapor pressure is called accel-

eration head. The key influencing factors of the pump are pump

Figure 28 contains a chart to aid in the design of suction piping.

speed, plunger size, valve spring load and spring rate, valve lift, valve

From this figure determine the optimum suction velocity for

passage area, cylinder passage configuration, suction manifold con-

the appropriate machine and use this information in Figure 29

figuration, and power end connecting rod center to center of bearing

to determine the appropriate pipe size. This pipe sizing chart is

distance to throw radius ratio. While the key influencing factors for

based on Schedule 40 piping and the values should be adjusted

the suction piping are actual suction pipe length, mean flow velocity

accordingly for heavier schedules.

in suction line, and fluid being pumped. If sufficient energy is not

available, problems such as fluid flashing, cavitation, piping

vibration, noisy operation, reduced capacity, and reduced pump life

can occur. To calculate the H

required to overcome this phenomenon,

use the following empirical equation:

where:

= Head in feet (meters) of liquid pumped to produce required

acceleration

= Actual suction pipe length in feet (meters) not equivalent

length

= Mean flow velocity in suction line in feet per second (m/s)

= Pump speed in rpm

= Pump constant factor of…

0.200 for simplex double acting

0.200 for duplex single acting

0.400 for simplex single acting

0.115 for duplex double acting

Figure 28. Maximum Recommended Suction Line Velocity for

0.066 for triplex single or double acting

Pump Type.

0.040 for quintuplex single or double acting

"Positive Displacement Reciprocating Pump Fundamentals - Power And Direct Acting Types" By Herbert H. Tackett, Jr., James A. Cripe, Gary Dyson Page 10

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