Trichy Bastard
Well-Known Member
After considering some of the numbers to do with water hammer, I see that the pressure spikes can be 5x or more momentary pressure (5x140psi)= 700psi!!! I know it's only for fractions of a second- but will I be really wearing on my diaphram in the accumulator tank like this? What's the real world experience?
Quote from Cav's thread- which he quoted from another source that is now a dead link:
Quote from Cav's thread- which he quoted from another source that is now a dead link:
INTRODUCTION TO WATER HAMMER:
Quick closing valves, positive displacement pumps, and vertical pipe runs can create damaging pressure spikes, leading to membrane damage, pipe-work, diaphragms, seals and gaskets meters and gauges.
Liquid for all practical purposes is not compressible, any energy that is applied to it is instantly transmitted. This energy becomes dynamic in nature when a force such as quick closing valve or a pump applies velocity to the fluid.
Surge or water hammer, as it is commonly known is the result of a sudden change in liquid velocity. Water hammer usually occurs when a transfer system is quickly started, stopped or is forced to make a rapid change in direction. Any of these events can lead to catastrophic system component failure. Without question, the primary cause of water hammer in process applications is the quick closing valve, whether manual or automatic. A valve closing in 1.5 sec. or less (depending upon valve size and system conditions),
can cause an abrupt stoppage of flow. The pressure spike (acoustic wave) created at rapid valve closure can easily be as high as five (5) times the system working pressure. Unrestricted, this pressure spike or wave will rapidly accelerate to the speed of sound in liquid, which can exceed 4000 ft/sec. It is possible to estimate the pressure increase by the following formula
Simplified Water Hammer Formula: P = (0.070) (V) (L) / t + P1
Where P = Increase in pressure
P1 = Inlet Pressure
V = Flow velocity in ft/sec
t = Time in sec.(Valve closing time)
L = Upstream Pipe Length in feet
An example of pressure hammer when closing a solenoid valve, with a 50 ft long upstream pipe connection:
L = 50 ft
V = 5.0 ft / sec( recommended velocity for PVC piping design)
t = 40 ms(solenoid valve closing time is approx. 40-50 ms)
P1 = 50 psi inlet pressure
therefore, P = 0.07 x 5 x 50 / 0.040 + P1
or P = 437.5 psi + P1
Total Pressure (Spike) = 437.5 + 50 = 487.5 psi
As can be seen from the above, the pressure spike is approaching 10× the original system pressure which demonstrates the potentially catastrophic effect of water Hammer in an extreme case