The Pipeline Shock Prevention People
Pump Start-up surge, Valve closure shock, Pump shutdown back flow bang.
Large vessels for high pressures with matching bladders, diaphragms, gas bags, and bellows, for over a third of a century.
ShockGuard Ltd. offer shock alleviators. | Please phone USA 910-270-2737
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Thought for today-and tomorrow
"Rigid pipes in a house, bang if you shut a faucet fast, if you close it slowly - no bang - so shock levels dependon speed / time.
How it works:
Pump Startup surge.
The peak value of the surge is found from a). How fast [time taken for] the pump spin up. b). The mass of the the liquid in the pipe ahead of it, which has to be accelerated away in order of the pump to be able to cause flow. c). The peak will be reduced according to the softness of the pipe wall, and the compressibility of the liquid with its level of entrained and absorbed gas, and the temperature. Hot liquids are softer.
Also, if the pipe is small, causing a high velocity, pressure drop / scrubbing action / Reynolds number effect, it will reduce the peak by the end of the pipe. The "hammer" frequency comes form pipe length and wave speed. Wave speed, or pressure transfer from place to place in a liquid system, is faster than a bullet.
A cure for start up pressure surge is a bypass back to suction, close the bypass off progressively - slowly produce increasing load over a longer time. A similar solution is, to allow time delay before all of the liquid in the system has to be accelerate, by installing an accumulator - sometimes called a hammer arrestor or shock alleviator. They do not arrest shocks or alleviate them - these vessels prevent pressure surges.
Pump cut out or "backflow" Shock.
Although a pump may stop, the liquid it has been pumping goes on flowing away from the pump, a vacuum is made. The vacuum causes back flow. When this void is collapsed the instantaneous dead stop of the liquid cause enormous hammer. If you can't use a vacuum breaker or bypass circuit, a correctly sized accumulator will help fill the void and decelerate the backflow over time, when the void has been collapsed.
Valve Closure Water Hammer.
The information needed to solve water hammer is the same as pump surge above, except that it is for liquid column deverlartion not acceleration, and the time, is time for valve to close. If you can not close the valve more slowly, you will need to address water hammer.
Please remember always, dynamics are time dependent. In Waterhammer,, Surge and Shock the answers will be of suspect benefit unless an accurate figure of TIME was used. We must calculate with dt.
E-mail the figures for your problem to
Excitational frequencies, from the pressure wave speed or "acoustic velocity", not only depend on the exact lengths of all pipe nodes in the system, but also on the effective compressibility of the system. "Effective", combines pipe wall elasticity and liquid compressibility with entrained and adsorbed gasses. All of which change with Temperature.
Many analysis ranges will be needed unless temperature, gas absorption, and entrainment remain constant. It is nearly always less expensive to prevent a pressure disturbance with one of our "alleviators", than to make "acoustic" models.
Explanation, how Shock & Surge prevention works
Shock alleviators do not alleviate shock, nor do surge alleviators alleviate surge. SurgeGuard, JumboFlex, and Floatolator all work in the same way. They provide a soft place, so that the pump does not have to instantly accelerate all the liquid in the system when it starts. Similarly, they provide a place into which flow can continue, for a time, against increasing resistance, when a a valve has been slammed.
In both cases, because time has been increased, peak pressure generation is decreased. In short, they all PREVENT the peak pressure from being generated. They are all preventors, they do not alleviate something that has happened. In USA Phone Toll Free 1-888-326-7377
Understanding How it Works
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