How to calculate Gate valve closing time using an Hydraulic actuator?

[Arrayproducts]

Hi,
I would like to calculate the closing/opening time of a Gate valve using an hydraulic actuator. What are the input parameters required and what is the formula for this calculation?

Any suggestion and direction towards resources will be appreciated.

Thank you for your time and sharing your thoughts and wisdom.




Regards,
Suresh

http://www.arrayproducts.com

 

[gerhardl]

What do you actually need in closing time? Is closing time critical (either way) in your case?

On the emergency closing side you will often require very fast closing, perhaps in two steps, first one step to about 80% very fast, and rest slow to avoid water hammer. In other cases (large valves, long pipelines, high pressure) you will have to go, or wish to go, extreemly slow (three minutes to up to more than twice or triple the time) to avoid water hammer and pressure peaks higher than necessary for a perhaps 'lighter constructed' pipeline (cost reasons).

You have to start somewhere, and normally you will start with a given oil pressure from a 'normal' aggregate, select a cylinder diameter area (less the rod area on one side) to give a high enough force (P times A) to be sure to have sufficient force for all situations, especially sticking force when opening the valve after a long closed periode.

You know the stroke length (diameter of valve plus something small), and hence the volume.

The smallest restrictions (pipeline and/or solenoid valve real diameter or cv, and inlet/outlet openings integrated in the cylinder) for your 'normal' selected components are also known.

This will enable you to (somewhat approximate) calculate the closing time, or the actuator/piston supplier will be able to inform you, given the oil pressure. The reservoir have to be sufficient large to avoid significant pressure drop on input side under operation of the piston.

Too fast? (This is usually the case) : throttle down on input or output line, with hand operated throttle valves.

To slow? Increase pressure, and/or linesize, and/or reservoir, and/or aggregate capacity or solenoid cv. Change cylinder inlet/outlet borings?

For large rupture protection valves in high-pressure watermains or for hydroelectric turbine inlet valves with emergency shut-down, oil-hydraulic opening and fallweight closing with two step throtteling of the return oil is a common solution. Two reasons: not depending on electricity or other external force other than gravity, and fast and controlled closing.

Hope this roundabout answer will help you onto the right track!

 

[Arrayproducts]

Gerhardl,
Thank you for your response and providing me with some insight on the principle.I truly appreciate it.I should have provided more specific information earlier,my appologies.

The valve in discussion is mounted on a well head tree and carries well fluid.I have the force exerted by the valve that the actuator has to overcome in order to open/close. I also know the force this actuator can exert.The actuator is fed from a hydraulic supply of 207 bar running Castrol Transacqua fluid.I can find out the feed line piping information such as diameter and distance if necessary.

The intention is to estimate the fluid flow to the actuator and the time taken to close/open the valve.

I hope I have explained it enough this time.






Regards,
Suresh

http://www.arrayproducts.com

 

[gerhardl]

Sorry for the late response, but a warning: it seems from the application very important that the calculation is correct. In my opinion it could be very difficult to guarantee any accuracy on this calculation.

The valve has to be tested in my opinion if no one (component sub-suppliers?) can give the information.

Sketch for a possible way:
Calculate for one side of the actuator, and disregard or guess at losses elsewhere (as an approximation):

Use volume on actuator on downstroke return side, find cv of narrowest escape opening (outport or solenoide valve if placed near actuator), guesstimate difference of pressure in and out, and calculate flowtime out for this.

Control: same approximation for opposite side of actuator if any differences.

 

[terje61]

A second/third/fourth warning:
- Whatever opening times you will find during FAT this will change by changes in temperature due to less/more resistance of all lubricated components and especially the viscocity of the hydraulic fluid.
- If a valve has not been operated for some time it will not go as fast as 10 strokes later due to sticking/settling of seals, clogging of small ports etc.
- The speed of a hydraulic actuator normally depends on the inlet pressure, which you state is 207 bar. How constant is this pressure? In my experience the inlet pressure is fluctuating continuously because the hydraulic demand changes all the time. You could use a regulator, but people on-site have the tendency to "optimise" the setting.

Conclusion:
There will always be a large inaccuracy in your predictions. I would consider 10% more or less stroking time a very good estimate.

 

[Arrayproducts]

Thank you gerhardl and terje61 for sharing your wisdom. I truly appreciate your time.

terje61: The information that I have currently is, 207 bar comes from a hydraulic supply. I don't have anymore details.

You all have a great weekend and happy July 4th if you are in USA.

Regards,
Suresh

 

[dcasto]

we always make the bleed oricife variable so we can adjust time during scheduled inspections of such valves. Variable orifice, a needle valve with a tywrap (car seal) on it.