Water Hammer 1

[ECD40]

Does anyone know how the 0.070 factor in the Water Hammer pressure formula is derived? I get a lower number when introducing the water density and 'g' into the formula to get the units to cancel out to lb/inch squared. Please see attachment.

 

[1503-44]

If the pipe is not well anchored, it could easily be a chihaugua, all noise, no bite. On the other hand it might be a Wolf.
The easiest way to rough check that is to CHECK FLOW VELOCITIES.
If they're all less than 10fps, probably no worries.
If they're 10-15fps, could be trouble.
If they're over 20 fps, could be dangerous, depending on your pipe design pressure and safety factors. And you probably need to be slow them down.
30 or above, look out. That's trouble for sure.
NOTE, THOSE ARE GENERAL RULES OF THUMB.
They can make for broken pipes, if there is a lot of gravitional effects, ups and downs, like in a mine.
Not doing a difficult analysis because it's difficult is a very poor excuse. If you have any velocities over 20, you need to do it.



Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[FacEngrPE]

I suggest you look at pump check valves as a potential shockwave generator.

When a pump stops, the loss of pump discharge flow causes the check valve to close, In the case of a mine pump the discharge pressure is relatively high, This high discharge pressure will drive the reverse flow velocity much higher than the design flow velocity, making the calculation method above unlikely to reflect the correct physics.

You can try check valves that close fast enough that reverse flow is prevented, as suggested in the linked pages:

https://blog.craneengineering.net/topic/water-hammer.

Sometimes adding air chambers to the system will dampen or eliminate water hammer.

 

[pierreick]

Hi,
Let you try Joukovsky's equation using your favorite search engine.

https://www.ajdesigner.com/phpwaterhammer/maximum_pressure_head_equation.php

Note: 1/144 is the coefficient you are looking for, pay attention to your unit system (British).
BTW, it's 0.007 not 0.07
Good luck
Pierre

 

[ECD40]

Some great comments and suggestions - much appreciated. We think that we may have some air leaked into the system, which can also be a source of water hammer. We are checking at the minesite and I'll keep you posted. Thanks everyone.

 

[TiCl4]

Not to derail the thread...

The largest safety factor I've ever heard of is for crane wire cables (4).

but for what it's worth steam hoses will typically have a safety factor of 10.

 

[1503-44]

Never messed with those and I think I don't want to.

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."