an Engineering & Service Bulletin

Technical Topics

J.H. WRIGHT & ASSOCIATES

ACCELERATION HEAD AND SURGE SUPPRESSION

I'm sure very few readers of these papers have thought about (or really cares) what happens to the liquid on the suction side of diaphragm or piston type pumps. Of more concern is the fact that these pump types can produce severe pulsations which can shake loose piping, ruin gages and make flow meters worthless.

Diaphragm or piston type pumps utilize check valves on the suction and discharge, which open and close with each stroke. Therefore, the liquid in the suction piping moves with a stop and go motion. All this acceleration requires energy and you don't recover it from the deceleration. As a matter of fact, acceleration loss can and often does become a real factor in decreasing the NPSH available to the point of pump cavitation.

Unfortunately, or fortunately, depending on how you look at it, these pumps can handle vapor pretty well so the pumps just keep on going. Diaphragm life is reduced and other maintenance problems develop.

The solution to this acceleration, stop, accelerate problem is a very simple device called a suction stabilizer.

Basically, the air (or other gas) pad above the flexible diaphragm dampens out the pulsations of the liquid caused by the starting and stopping against the pump's suction valves.

These devices are specifically designed and sized for suction liquid stabilizing, they are not accumulators such as those found in hydraulic circuitry. Poor results will be experienced if one tries to use an accumulator.

Therefore, if you are experiencing high maintenance costs and poor diaphragm life on your pumps, try a suction stabilizer first. Then if the discharge pulsations are still objectionable, install a pulsation dampener on the pump discharge. These are very similar in design to suction stabilizers and work about the same way. The combination will reduce your discharge pulsations by 90 to 95%!

Both these devices are available in a wide choice of materials and elastomers.

One last thought - do you have any quick closing valves installed on long piping runs as a safety system? Water hammer might cause a pipe rupture worse than your original problems if you don't arrange some sort of shock absorption. These same devices can be used. If you'd like to learn more about this subject mark the attached "Bingo" card and I'll mail you a really excellent article by an engineer with 19 years of pulsation dampening experience.

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