Water hammer & valve closing time

[Prototyp]

I am planning a water systems (flow velocity ~2.5 m/s, max. 8 bar) consisting of a header and several branches connected to the header by butterfly or ball valves. These valves are electrical actuated with an opening/closing time of approximately 10 seconds. I would like to check in advance if a water hammer is likely to occur if a branch valve ist opened or closed but the calculation seems to be rahter complicated.

Are there any experiences or rules of thumb what opening/closing time of branch valves are required to prevent the header pipe from water hammer?

 

[LittleInch]

What's the size of the pipe / valves?

You will get some sort of pressure surge at that velocity, but 10 seconds may be just long enough to avoid it becoming an issue.

Do you have a pressure surge limit close to your 8 bar??

A lot depends on whether there are other flow paths available ( if there are that's a good thing) or not and where and how far away is the pressure source?

when your valve starts to close the pressure wave starts and bounces back off the source. If that bounce occurs before the valve is fully closed then it reduces the pressure surge.

Below about 3m/sec you are generally Ok and for most smaller size valves anything around 10 seconds is usually Ok as well.

BTW this would have been better in the pipelines and piping forum, but that's for next time.



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[Prototyp]

Thank you LittleInch,

I am not quite sure what you mean with pressure surge limit. The pressure rating of the piping is PN16.
The headers size is DN150 and the braches with the actuated valves are DN50. The pumps are located aorund 20 m away from the first branch and 120 m away from the most remoted branch.

What is your opinion, will there be pressure surge under these conditions and will it cause trouble?

 

[LittleInch]

You shouldn't have an issue.

Is the flow through one branch or many at the same time?

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

 

[Prototyp]

Usually many at the same time.

 

[HitokiriAoshi]

10 seconds to close a valve that small, i wouldn't worry about it. those lines run into issue with quarter turn when it snap closes.

Luke | Valve Hax |

https://valvehax.com/

 

[LittleInch]

With many flow paths at the same time you really won't have an issue with surge.

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

 

[gerhardl]

Hi Prototyp

I agree with above. Closing time, sizes, pressure, flow velocity and the common valve types should normally not give any problems.

Quite another issue is the actuator size and closing time selection. Is the relatively short closing time necessary? Often longer closing times are acceptable. This could give smaller higher geared/cheaper actuators and even less chance of pressure peak problems.

 

[Prototyp]

Thank you for your help.

Gerhard, it wouldn't be a problem if the actuation time is longer for example 60 seconds would be ok as well. I checked different suitable actuator/valve-combinations and the opening time varied between 10 and 30 seconds. Therefore I asked for pressure surges at 10 seconds actuation time.

 

[gerhardl]

OK.

I don't think you will have any problems at 10 sec. with a normal, good piping layout.

The thought was more at actuator cost and longtime maintenance cost (price/time), centered on what is available for precise actuators and controls at the market.

Good luck!

 

[goutam_freelance]

The surge becomes critical if the closing time is less than 2L/a s. Assuming 120 m length and about 1000 m/s wave velocity:

2L/a=2x120/1000=0.24 s

So if you have 10 s it is more than critical, so surge will be less. In any case for such smaller dia and small length pipes 10 s closing time is safe enough.