Liquid Dynamics International Ltd. - Piping System Analysis / Piping System Simulation

LDi – P2

A. Shake a pipe, generate a pressure pulse.
B. Turn a pulse instead of reflecting it.
C. Dissipate a transient, why increase the frequency.

The purpose of the analogies is not absolute definition, it is to assist in visualizing the different phenomena.

A. Shake a pipe, generate a pressure pulse.

Leave the end of the garden hose attached to a closed "tap" or faucet. Extend the hose uphill, and leave open but full of water. Hold the middle of the hose, then jerk it. Water spurts out. The jerk created pressure, if not, nothing would have come out. Similarly, shaking a pipe causes pressure pulsation in the liquid.

When the engine or motor attached to a pump, is not perfectly installed, the pipe attached to the pump will vibrate. This can be measured as liquid pressure pulsation. It will be significant when the shaking is along the axis of the pipe. There is no difference between pushing liquid in a pipe, and pulling a pipe along a column of liquid, in terms of liquid pressure.

B. Turn a pulse instead of reflecting it.

When the bend is gradual enough, a pressure wave can be carried round a corner without reflection.
A reflection makes yet another frequency
Whereas a long radius 90 will be better in terms of volume / mass flow, a pressure wave traveling over 5,000 kilometers per hour, will see it as a "brick wall", - just as it does with a "hard 90".
A 22.5 Degree + 22.5 Degree “scarf joint” a.k.a. “fabricated 45” reflects some and transmits some of a pressure wave.
Worst “hard 90”
There are different stiffnesses for each of these direction change methods.
These stiffnesses impact the pipe mechanical vibration frequencies.

C. Dissipate a transient, why increase the frequency.

Where Diameter of a vessel is 8 times the Diameter of a pipe, high frequency pressure pulse transients will have died away before they can bounce off the nearest point of reflection and find their way out into the rest of the system.
"High frequency transients"
Typical for vane and centrifugal pumps
This is "good" to the extent that it is not increasing the load on the pump by imposing an orifice against pump delivery.