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Explanations A through F

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"Controllers" of Pulsation

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LDi Catalog Printable PDF P4, P5, P6, P7, P8, P9

The danger is that the pipe system will generate a frequency that it amplifies.Cannon

1. Find the effective compressibility for the system.
2. Determine the speed of pressure transfer for "softness".
3. Feet per second or Meters per second = Frequency/Hz.
  feet pipe run meters pipe run

4. Compare System Hz. with pump Hz. and Pipe XY&Z natural shaking Hz.
5. Where there is coincidence, or at a power of, any of them, at any temperature, or for any one nodal length, your pipes are a problem

Piped Liquid The speed of the fastest projectile (2800 feet per second) is half the speed of pressure transfer (5600 feet per second) in a cold liquid de-gassed in a hard pipe.
Rate of pressure transfer a.k.a. "acoustic velocity".

Easy to prove - Change the pressure, measure it a mile away a second later.
But your flow rate is between 3 ft / sec and 25 ft / sec so flow fluctuation could be addressed with a bottle on a "T".
Pressure is 250+ times faster than flow, so:
Pressure pulsation can not be addressed without interception.


It doesn't matter how much you have to begin with, what counts is how much the system turns it into.
Large pipes - with no delta "P" do not scrub out pressure waves - are potential amplifiers.


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Pulse interception plus flow fluctuation reduction
Or just use one of our connections, if all you want is volume accumulation.
Then save a "T", and use the second connection for flush, drain, relief valve, or the PI tap.


It's too simple, trying to pass through a sudden increase to a larger diameter dampens high frequency pressure pulsation (large relative to system pipe diameter).

Pressure waves go 500 mph in hot gas, but travel 3500 mph in cold liquid.
A "T" piece could not intercept them.


LDi Page 6

Truth proof about discharge pulsation
Pipe systems cause pulsation. Hard systems destroy pumps.

Same pump, no pulsation
No Pulsation
Same pump, lots of pressure pulsation
Lots of Pressure Pulsation

Pumps make flow fluctuations, Systems convert them to pressure pulsation.
As truth is defined by "what if-what if not" you proved to yourself that pipe systems make pressure pulsation.

When we were seventeen and could run a 1/4 mile in 60 seconds, our pumps could work because our veins and arteries were soft and "dilatable".
400 Meters
When we die in bed with out boots on, and the quack say "of natural causes", his pronouncement is simply that our "pump" was tired because our "pipes" became hard.
StethoscopeAmortAmort Sign

Restrictions make systems "hard". Hard systems kill pumps.


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Pulse damping - infested with "witchcraft"?
How much pulsation was there before the "pulsation dampener" was fitted?
And how much after fitting the single connection "pulsation dampener".
It can be impossible to know, without data capture at kHz and very fast response characteristic transducers.
Can a human eye see above 30 Hz? Or a 20 ms response gauge measure a 1450 meters / sec pressure pulse go by?

Spring weight
Inside Gauge
How fast they shake, how far they swing depends on the weight and the spring - not on what excites them.

Eight gauges connected to the same point at the same time, which to believe?

With glycerin and choke
With glycerin, no choke
No glycerin but with choke
No glycerin, no choke
Gauges connected through a capillary
175 PSI
100 PSI
300 PSI
Gauges connected through a 1/2" pipe
400 PSI
450 PSI
25 PSI
225 PSI

Gauge Photo


LDi Page 8

Suction side pulsation
The problem - absorbed air or gas
"Started" for Reciprocating pumps means each suction stroke.

When a pump is started, there is an instant pressure fall at the pump end of the system.
Unless intercepted, a negative pressure wave travels back up stream to the point of supply.

Pressure Fall
The sudden pressure reduction causes gasses to come out of solution. They form bubbles, which join then act as springs between slugs of liquid.

The slugs are excited into oscillation by the rebounding negative wave. The slugs then alternately slam then starve the pump suction. The higher the pressure the harder the slam.

Air / gas out of solution

Excited Mass
Excited mass oscillation between two springs

If the pump has suction check valves, they are knocked open when they should be closing. (see "VE" below)


The force from the mass velocity of the slugs is more than check + spring
Check Spring
Volume is good, force is bad
Do not increase force / pressure

When you are thirsty, you lift and pour the liquid in, you don't force a pressurized hose down your throat!
The biggest enemy of good volumetric efficiency for a reciprocating pump, is too much pressure on the suction side.

"VE" - Volumetric efficiency falls, and pulsation shakes the pipes, which causes even more pressure pulsation.
Shaking Pipe
See Page 8 item A


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Suction side pulsation
The answer - 2 do's and 2 don'ts

"Started" for reciprocating pumps means each suction stroke.

Suction Supply System

Close Coupled
Local suction volume elasticity is an essential.

Forced Gas
2. Do not insert orifices or restrictions they will cause wave rebounds at a higher frequency, and cause frothing.

Orifice Orifice Orifice


Oil the hinges, put the child on the swing, and press with 1/2 an ounce (14 grams) Then press with 1/2 oz again and again The effects are cumulative Soon catastrophe Pressure pulsation can be like that too It depends on system frequency response. 1 psi from the vortexes of the discharge connection 1 psi + 1 psi - system pipe return pulse 3300 miles per hour 1 psi + 20 psi – and again several times per second Faster than a bullet 1 psi + 200 psi - after a few seconds Very soon fatigue or burst Reciprocating engine Muffler “T’d” off the pipe – lots of noise Would you put a silencer on a branch line / “T” piece? Trying to pass through only a small increase in diameter – a lot less noise Attempting to go through a much larger diameter increase – quiet as a mouse small diameter large diameter Barrel, short in, same pump, no pressure pulsation, short out, barrel Barrel, long suction system, same pump, lots of pressure pulsation, long discharge system, barrel Your pump and the 400 meters Inside a gauge: Tube spring, Mechanism weight, Hair spring 175 psi 100 psi 300 psi zero psi 400 psi 450 psi 25 psi 225 psi Gauge photos above taken at this instant Can you believe a gauge? Triplex pump at 68% volumetric efficiency with “pulsation dampener” on a “T” Suction supply system instability is easier to prevent than to allow and try to cure. 1. Provide the pump with a local source of volume at minimal pressure so that the mass to be accelerated is negligible. The volume must be able to change without a pressure fall. 2. Interceptors are “close coupled” De-couple the supply column from negative pressure changes De-couple = intercept by pass-through plus direction change. 1. Do not force gasses into solution with nitrogen or air pads, they will come straight out when the pump starts and increase the instability discussed in the problem. Orifice – makes bubbles Flow controls Restriction – choke the flow


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