ESD valve- Hydraulic or Penumatic

[cam72]

Hi

For selection of ESD valve actuator supply, what are factors that decide whether ESD valve shall be hydraulic or pneumatic? What are advantages of Hydraulic valves?

Thanks.

 

[gerhardl]

Both fluids are utilized, and also with a third variant 'gas over oil' combined to give an assured oil pressure.

Different solutions are used, depending on a number of factors. One important factor is of course the cheapest commercial solution available ('common practice for size, process fluid (not actuator fluid), pressure class, valve type, size, speed of closure, and branch/application)

No firm rules can in my mind be set down, but you will find firm opinions if you start with an exact application and process type.

Some general tendencies (not firm rules) can be put down:

Smaller valves, air used elswhere -> air
Larger valves, hydraulic used elsewhere -> hydraulic
Faster movement -> air or fallweight closed hydraulic cylinders if larger valvetypes.
Slower or controlled movement -> trotteled air or better controlled (perhaps) hydraulic.
Valves on hydraulic operated machines -> hydraulic
Submerged -> hydraulic
Valves remote from electricity or sources for common air or oil hydraulics -> electric, battery backed, or handpumped hydraulics or battery backed electric. More seldom air.

 

[JLSeagull]

An advantage of a hydraulic systems would be the use 3000 psig fluid as the driving medium. This reduces the actuator size compared to 80 psig air.

Pneumatic actuators normally use air. Remote natural gas facilities can use the gas pressure as the driving force. Thus 1000 psig natural gas could reduce the actuator size too.

My preference is air unless there is an outstanding reason to deviate. Also, I like to point out that stored energy from a spring is very desirable for emergency shutdown. Double acting pistons don't meet my emergency shutdown criteria.

 

[itascot]

ESDV service actuation is "where at all possible" pneumatic.
The main reasons are fast exhaust of air = fast stroke, exhaust into atmosphere eliminates a discharge line back into a reservuoir (and possible back pressure/choking of exhaust).
Where extreme torque/thrust values are expected from actuator generally Hydraulic type is used, but when this is not available HPG actuators are used (High Pressure Gas) with pre-charged "power packs" at 180 or 220 Barg, reduced to around 65 Barg supply to actuators.
If you give exact details of where these are to be used, I can give precise information on possible solutions.
Ciao,

 

[gerhardl]

.. J.L. Seagull - I agree with all your points, except that an emergency shutdown valve also (as one example) can be a very large and high-pressure valve in a hydroelctrical plant for turbine water.

In this case oil hydralics are present for turbine inlet control and forces are so large that air alone for this reason is impractical, and that shutdown has to be controlled, normally in two steps to avoid water hammer, more easily controlled with oil and weightloaded closeddown, oil return throtteled.

... My point is that the wide use of 'ESD' makes it impossible to make generalisations.

(Your description is well suited and presice for small and medium-sized up to larger valves for general process emergency shutdown.)

Regarding spring operation for return: I agree if practical. If larger forces or very fast closing or controlled closing time is required double acting with backup pressurized reservoir (control possible both of inlet from reservoir and outlet from opening sylinder) is also commonly used, both for air or oil.

 

[hsbcn]

Here's a very useful thread on this same subject:

http://www.eng-tips.com/viewthread.cfm?qid=151777&page=10

Hope this helps!

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