is this the rigth forum? (valve turbulence problem)

[DavidCR]

We have a hydro power pipe where the spherical ball when closing is inducing strong vibrations downstream. Is this the right forum to make such a question?. Or would you please recommend other?, which one?

 

[vpl]

If your concern is about the valve, this is the right forum. If your concern is the vibrations in the piping (what is commonly called "water hammer" even if your fluid isn't water), then you might try forum378.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[gerhardl]

To give a full answer, 'all' details are necessary. The vibrations could be caused by one of several single causes, or two or more in combination.

Some few points to check out to start you off:

1. Pressure class of valve equal to static pressure plus 20% for pressure peaks?

2. Ball valve anchored and supported separately? Piping and equipment before and after valve supported and mounted not to transfer weight or not allowed forces to valve?

3. Is the ballvalve constructed for the purpose, and able to handle the actual water speed? (Simple ball-valves might not be constructed for forces enacting when closing above a certain given speed) In most cases at least trunnion mounted, or better double eccentric ball valve.

4. If this is a turbine inlet valve (with or without arm and weigtload to close), are the actuator forces sufficiently strong enough to close properly? (Not 'riding' on the 'almost closed' flow?)

5a. Are the actuator and actuator mounting supported directly on valve?

5b. If the actuator is mounted on the valve with external support in addition (for instance on walls or floor) will external support, plus actuator movement transfer forces, give an influencing skew torque to valve body (in addition to correct torque to spindle)?

6. Are all pipeline components aligned?

7. Any abrupt pipe components after the valve (bends etc)?

8. If this is outlet or bypass valve (also elsewhen): swingings could come from to high throtteling under certain circumstances if the valve is not constructed strong enough for this. The throtteling could give cavitation conditions (vacuum by high speed) and swingings when reentering to 'normal pressure'. (Other type of valve and/or special air inlet necessary)

8. Actuator speed and control OK?

Hope theese hints will help you!

 

[DavidCR]

It´s a 80inch diam. spherical. valve of a hydroelectric project penstock the pressure is high (3000ft water head). The valve is a special design and includes a expansion joint, but it looks that the joint expansion is not doing its work or there is a special unexpected turbulence problem that we have to study and we are looking for ideas to consider.

I´ll make the ? in the other forum.

Thanks a lot.

 

[stanier]

I think you have the wrong type of valve. I would expect that the valve would be a cone dispersion type. It is not surprising you have this cahllenge before you.

http://www.andritz.com/ANONID5D4DD4...s-and-services-large-hydro-valves-cone-valves

http

http://www.hydrostec.com.br/catalogos/D30-31-0-I.pdf://

http://www.chryssafidis.com/english/items.php?catid=234

Just google "cone dispersion valves".

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

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

 

[gerhardl]

I got an 'aha!' experience from staniers answer. I agree! If penstock in this case means outlet to a very low, near atmospheric pressure, you will have cavitation and strong vibrations if you have even a short pipeline stretch downstream.

To avoid this you need an expert to check your piping layout.

Main solutions:

1. Cone outlet valve (as stanier advices) directly to free air.

2. Needle valve,with vaned ring, either directly (without even a short pipeline downstream) or alternatively direct air inlet after the valve with abrupt increased pipe diameter (need specialist calculation and layout) (Best for exact regulation, can be throtteled exact in a very wide range)

3. Double eccentric ball valve, (not normal ball valve) direct to free air, without pipeline, but in this case what about forces in waterjet after valve? No throtteling.

http://erhard.de/index.php?ALakecomesintobeing

http://erhard.de/index.php?Needle-Valve-valves

http://erhard.de/index.php?Ball-valve-Valves-Water-

All theese solutions will be acceptable for very high flow speed, and valve diameter might perhaps be selcted considerably lower than present.