Liquid Dynamics - Pulsation Analysis, Diagnostics, and Software Models

Consider suction acceleration head ("A.H.") losses and how much discharge "A.H." your system will generate.
Estimate, how smooth will it be, with no dampeners at all.

Before specifying a smoother system, you may wish to estimate how much improvement you need from the system, as it will be. The calculation below is a rule of thumb that covers pressure pulsation generated to overcome system resistance to pump flow fluctuation only.

Explanation

Pressure pulsation generated by a system resisting flow fluctuation from your pump mostly depends on the mass of your liquid that has to follow the variations in velocity from your pump, the "flow fluctuations". This need to create head, or pressure, is often referred to as system "mass acceleration head". Flow "friction" also plays a part (see friction page) depending on system pipe size choice. To "visualize" what has to happen, first establish the weight of your liquid that has to fluctuate. Then consider the speed at which you intend to run your pump. The mass and time available for velocity change is where your system generates the pressure pulsation excitation. How much this is dissipated or amplified by the characteristics of your piping design controls how much pulsation your system will cause.

Necessary information to estimate acceleration head pulsation.
SG Specific Gravity - Grams per Cubic Centimeter, gm/"cc", gm/cm3 Conversion from Lbs. / Ft3, divide by 63
L Length of pipe in feet - Ft.
Q Volumetric flow rate - US Gallons per hour. Consider 1 US Gallon to equal 3.8 Liters
N Number of displacements per minute. RPM x Number of displacers per rev.
ID Average Internal Diameter of the pipe that is full of the liquid.
Z A figure of relative decrease in "pulsatiousness" by number of displacers - examples are
crank driven plungers.
Note: SG, L & ID have nothing to do with the pump.

Relationship

= Addition to system pressure, peaks from accelerated head. Or on a suction supply system, the pressure loss that will prevent the pump from filling.

Typical values of "Z" for reciprocating sine motion driven machines.

1 For simplex (Single piston, plunger, or maybe reciprocating oil to move a diaphragm)
2 For duplex (Two plungers, etc. Flow still comes to a halt as one displacer takes over from the
other)
4 For triplex (Three plungers, etc. Flow still comes to a near halt unless the volumetric efficiency is well above 75%)
6.5 For quadruplex (Four plungers, etc. phased at 90 - Sounds better, but chances of resonance
are worse)
9 For Quintuplex (Five displacers, overlap even with hot compressible liquids at high pressure)
18 For Septuplex (Seven displacers, smoother flow than a "Quin", but the frequency is high and
may match the natural vibration frequencies or the acoustic or the mass oscillation frequencies of short pipe nodes)

For two displacers or more where the drive is a linear oscillation, from fluid power, the value for "Z" may be more than doubled. How much more, depends on the dwell that occurs on direction changeover. This is more affected by drive fluid compressibility than valve design.

Two Examples

In these two examples, the pumped flow rate, stays the same, the "jerk-rate" - number of modulations per minute, and everything else stay the same, except pipe length " L".
pulsation analysis - example
The formula is from general industry use by Milton Roy and Foster Wheeler, etc. The "Z" factors are modified from empirical experience since 1963.

Note: increased pipe length gives more pulsation. Therefore, pulsation depends on the system. Similarly, changing the density of the liquid or the diameter of the pipe will change the pulsation.

Pumps make flow, but systems make pressure, pressure pulsation is a system response to flow fluctuation, and a system responsibility, not a pump vendor liability. Nor is the pump vendor necessarily qualified to address system piping and valve response pressure pulsation. Please call 1-888-DAMPERS, not the pump vendor.

Note:

As pulsation depends on pipe system length, diameter and the specific gravity of the system liquid, determining a dampening need without taking system details into consideration, is likely to lead to a less than suitable specification.