Fast acting valve to simulate water hammer

[samfaulder]

Hi all,

I'm currently looking to design a rig capable of recreating water hammer I.e. The pressure pulse created when a shut off valve is closed rapidly which then propagates upstream of the valve.

I therefore require a very fast acting valve (aiming for 20ms) for a 1.5" dia pipe. What are the best options for this? I am able to accommodate any type of actuation but have so far been struggling to find a valve that can shut this quickly.

I also need the valve to be very repeatable and have consistent closure times to assess the effect of various pipe geometry changes on the pressure pulse magnitude. Being able to measure the closure time would be an added benefit (maybe through inbuilt limit switches?) but I appreciate this may not be possible.

Any advice would be much appreciated.

 

[crshears]

Hmmm...

Over-centre toggle device that snaps valve closed very rapidly? Toggle could be driven by an appropriate electic motor...

Hydraulically actuated valve similar to that which is used to actuate high-voltage circuit breaker plungers?

Cost-benefit questions also come into play...how much can you justify budgeting for this?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[samfaulder]

Cost shouldn't be an issue. Should have mentioned that this will be with a pretty substantial flow rate of 3L/s if that makes much difference.

Our main enemy is time so an off the shelf solution would be fantastic.

 

[Compositepro]

Standard swing-check and ball-check valve seat very rapidly and are perfectly capable of creating water hammer. The problem is keeping the valves open until some reverse flow velocity has been reached. Mount a ball-check valve so the the valve is open when the ball is down. The valve will stay open until the fluid velocity is enough to lift the ball. As the ball lifts it will have little to no effect on the flow until it seats, and you will then get water-hammer. An excess flow valve is another option. A swing-check valve with an external lever connection can also be used to manually trigger its operation.

 

[gerhardl]

On the special valveside: valves for emergency closing for instance in case of dust or chemical explosions in pipelines. Cost: very high. Have not checked myself, but try FIKE and competitors. Search emergency closing, fast acting valves in general.

Another idea: Manual operated 90 degree valve where lever is operated by separate, large, weight loaded free-swinging pendulum released from an exact given horizontal position each time. (Not sure this will give closing time sought)

 

[Compositepro]

Perhaps I should elaborate on my previous answer. If you are trying to create water hammer, no other valves will be any more effective than the standard check valves I mentioned. The ball or swing moves with the flow while closing so there is no throttling that occurs during closing. When the ball seats it comes to a very sudden stop, and so does the fluid. So, while the actuation process may not be supper fast, the water-hammer cannot be made any greater.

 

[georgeverghese]

Take a look at the simplified formula for pressure surge created by liquid hammer in a pipe : there are other parameters that affect the max pressure rise other than closing time on this valve. By suitable selection of these other parameters, a less challenging time for this valve closure may be obtained. Right now, 20millisecs on a DN40 valve sounds next to impossible to me, and difficult to verify also ( response lag time from time of closing signal initiation to the time when the valve actually starts moving may be >> than 20millisecs)

 

[samfaulder]

Hi all,

Thanks very much for your responses. Definitely some things to look at.

- With a check valve, would closure time not be dependent on flow rate? I require the valve to be as a repeatable between tests as possible as we will be testing a variety of flow rates.

- I have been wondering about mecahnical solutions such as the pendulum idea but again something we could buy off the shelf would be preferable.

- As for changing other parameters, this will form part of the testing but I require a closure rate similar to that of the system I'm trying to simulate, 20ms is aspirational so a valve closure time below 100ms will probably suffice, providing it is repeatable.

 

[samfaulder]

I've been looking at spring return valves i.e. with a dead man's handle which would be great in terms of simplicity - could just have a pin to hold back the handle and release when desired, however I have no idea how quickly they would close. Does anyone have any experience with these valves and their capability? Thanks agian.

 

[stanier]

Why not consider a two stage closing butterfly valve? After all they are most likely to cause water hammer in any system. At 90% closed the flow is almost full flow. Hence you only have to close the last ~10 degrees to simulate a fast closing valve.

Alternatively you could use an explosive charge similar to used in car airbag or ejector seat deployments.

ôThe beautiful thing about learning is that no one can take it away from you.ö
---B.B. King

http://waterhammer.hopout.com.au/