Surge Water Hammer Effective Valve closure time

[Sawsan311]

Dear All,

I have been looking into the subject for surge water hammer impacting design parameters. For systems with actuated valves we tend to consider the valve closing time based on a typical value of 1 in / sec. However, I came across the principle of effective valve closure time which in fact represents the critical last 25% of the valve closing time of a gate valve for example. Some design standards consider surge evaluation for full bore actuated valves based on the effective valve closing time. If we consider so, then we would conservatively estimate the valve closing time i.e. too fast closing and hence directly impacting the surge pressure.
Appreciate your views on whether total valve closing time is the influential in surge analysis or the effective valve closure time.. what is the phenomena behind having this effective valve closing time most critical?

Thanks

 

[LittleInch]

Some design standards consider surge evaluation for full bore actuated valves based on the effective valve closing time.

Err care to tell us which ones?

The closure characteristic of the particular valves installed are part of the transient analysis programs and for sure, many types of valves only really start to have an impact on flow in the last 25 to 30% of closure.

I have seen different closure speeds used on valves sothat the initial 75% is fas and the last 25% a lot slower. Not easy to do but can be done.

There is a negative pressure puls going back from the moment the valve starts to move, but it depends where your surge is really coming from - pressure waves back into the pump or from the cessation of flow.

But without knowing which these "standards" are I can't really say.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

For a lot of valves the restriction isn't proportional to the position.
Think ball or plug valves where the last 25% of closing motion may be 2/3 of the restriction.
On cooling system valves we commonly use soft closers in order to slow down that last 25-30% of flow restriction.
Opening is another issue. Sometimes if you open too slowly and there is little backpressure you can cause very high stresses or even cavitate the valve. Unless we saw a reason to do otherwise we tried to open to roughly 50% restriction quickly, and then ease on open from there.

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P.E. Metallurgy

 

[Sawsan311]

Thank you all for your great responses,

I would like to understand why the last % opening of the valve represent the most critical for the water hammer or surge considering the closure of the well will not only cause a negative pressure cavity downstream the valve but also a pressure wave propagating on the upstream pipeline system by sonic velocity and liquid compressibility effect as well the line packing effect..

Thanks

regards