Pressure Pulsation Dampeners for Transients and their Interception
The purpose of these analogies is not absolute definition, it is to assist in "visualizing" the different phenomena.
Shake a pipe, generate a pressure pulse.
Turn a pulse instead of reflecting it.
. Dissipate a transient, why increase the frequency?
. Importance of smaller pipes.
Changes in diameter - Orifices, Eccentric and "Conc" reducers, the 7 Degree taper.
Accumulator, Orifice Reactive Resonator, or a true Pulsation Dampener.
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 host, 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 DEFERENCE BETWEEN PUSHING LIQUID IN A PIPE, AND PULLING A PIPE ALONG A VOLUME OF LIQUID, in terms of liquid pressure.
REFLECTION MAKES YET ANOTHER FREQUENCY*
Whereas a long rad 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".
There are different stiffnesses for each of these direction change methods There stiffnesses impact the pipe mechanical vibration frequencies.
When the 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. This is "good" to the extent that it is NOT increasing the load on the pump, by imposing an orifice against pump delivery.
"High frequency transients"
LIQUID CHAMBERS ALONE WILL COST TOO MUCH & BE HUGE THE PROBLEM IS THAT THE PULSE MAY HAVE A SUBSTANTIAL VOLUME as well as pressure amplitude. When the duration of a pulse is sustained for a measurable length of TIME, the pulse will have VOLUME, it will not simply be a TRANSIENT. The volume of the dampener vessel required to provide sufficient LIQUID COMPRESSIBILITY will be between 10,000 & 100,000 times the volume of the pulse, depending on the pulse characteristics
1. As high frequencies die away relative to the ratio of diameters, your dampeners will be smaller and more efficient when you keep you pipe sizes down. 2. Even more important is that the smaller the pipe, the more dissipative it is, so the pipe will scrub out some pulsation.
3. Additionally, a dissipative pipe system will not become a pulse amplifier. UNFORTUNATELY YOU CAN NOT JUST STEP THE PIPE DIAMETER DOWN, THE STEP WILL RETURN THE PULSE.
A pressure occurrence - travels at MACH 5, and sees any reduction in cross sectional area that is steeper than an included angle of 7 degrees, AS A “BRICK WALL”. Nearly all of a pressure spike can be caused to go into a dampener from a large diameter pipe by compressing it down a 7° taper.
An orifice makes it harder for the pump. It reflects the pulsation, but helps to protect the pipe system.
A gas bag, makes the system soft, which is good for the pump. The residual pressure pulses go past, no good for the pipe.
A true dampener helps the pump AND protects the system. There are dampeners available that follow the logic of pump dynamics and of acoustics. In essence a dampener is 1. large diameter, 2. multi ported, and 3. has elasticity. An orifice resonator is bad for a pump. Soft accumulators do not protect pipes.
For more information about this and other pressure pulsation related topics go to Liquid-Dynamics.com.
