a-Pulse Prediction

An example of a short & a long pipe

This demonstrate to your customer why it is in their best interests to provide you with the following minimum figures, or why they should enable you to obtain these figures from their pipe system designers.

SG = Specific gravity of fluid, Grams per Cubic Cm.

To convert from Lbs/Ft3, divide by approx. 63

L = Length in feet of system pipe full of the liquid.

ID = Average Inside Diameter of system pipe full of liquid.

ID divided by 2, then Squared, x Pi = cross section area

Cross Sectional Area

Cross Sectional Area x Length = volume
Volume x SG gives Mass to be accelerated

Q = Flow rate average, of the liquid in the pipe, Gallons Per Hour,
from which, with pipe ID, we learn the over time velocity -ft/sec

N = Strokes per minute. Total of all displacers RPM of the pump times
Number of plungers, etc. From which we learn the time available for the acceleration See NOTE

F = Factor for number of pistons or plungers that keep the mass moving The more there are, the more they will overlap, and the less jerky the flow will become, so that will cause less pulsation.

1 = simplex	(Single piston or plunger - may also be pushing oil to move a diaphragm)
2 = duplex	(Two plungers etc. - the flow will still come to a halt as one changes over to another)
4 = triplex	(Three, now there will be continuous flow, provided the volumetric efficiency is high enough)
6.5 = quadraplex	(Four, sounds better. But the problem is that such a low & even number maximizes the chances of resonance, so flow through interception becomes a necessity)
9 = quintuplex	(5, Good - overlap even at low volumetric efficiencies)
18 = septuplex	(7, Also good, BUT now the number of pulses per second is becoming high. High frequencies may easily match the high frequency of short pipe nodes. If this occurs what ever level of residual forcing pulsation you go down to, the system stands a good chance of amplifying the residual pulsation to a high level.

NOTE A known rate of acceleration of a known mass will require a given force, Lbs/In2,"PSI", to achieve that acceleration. Hence one may establish an approximate minimum level of expected pressure pulsation, before determining how much damping is required to get rid of that pulsation.
Answers as to size of a damper, which are not based on the length of the pipe etc., may be somewhat misleading.

a	b
SGa = 0.90	SGb = 0.90
La = 35 (Short Pipe)	Lb = 250 (Long Pipe)
Qa = 73.5	Qb = 73.5
Fa = 1	Fb = 1
Na = 70	Nb = 70
I.D.a = 1.0	I.D.b = 1.0
For the short pipe, a	For the long pipe, b
5.851 PSI	37.612 PSI
PSI above is: Pressure loss, negative pulsation, for a suction system -or- Positive pulsation, for a discharge system, that will be generated
Notice that (a) for a short pipe, and (b) for a longer pipe, with all figures the same, and only the length of the pipe changed, the level of pulsation is completely different. Therefore, the level of forcing action pulsation, depends entirely on the system figures, not on the pump - the pump parameters have stayed the same. When only the pump parameters are stated for a damper selection, the damper size will have to be for a near infinitely long pipe, or alternately the answer will be a guess. PulseGuard, Nov. 1998 Courtesy Milton Roy company and others for simple formulae.

	PULSE PREDICTION
	*All depends on your pipe length* "Positive pressure pulsation" or "Over Pressure" or "Acceleration Head", that will be caused by the need for repetitive acceleration of a mass of liquid.