Actuator thrust calculation

[JackGardener]

Hi,

I wish to know if we can able to achieve class V shutoff with a spring and diaphragm actuator on a 900# globe control valve.
Application is Gas lift.

A colleague of mine told, best is select vendor offering piston with spring return actuator, as S&D actuator may not have thrust to achieve class V shutoff at 125bar shutoff pressure.

It is a multistage pressure reduction application. (60 to 30 bar, 30 to 15 bar and 15 to 5 bar).

Some vendors say, there is no relation between DP shutoff and ability of actuator to close at that pressure and it will work fine.

Experts please share which actuator I should choose - S&D actuator or piston/spring return.

Thanks
Jack

 

[mk3223]

The actuator size and type are based on the static and dynamic forces as needed for the control valve. These forces may be associated with the valve types, i.e. globe, ball, or butterfly, etc., friction forces from packing or seals, pressure differential across the valve, required thrust or torque, etc.
So, your colleague could be right for using the 900# globe valve with a piston actuator.

 

[gerhardl]

Hello JackGardener,

My view is as follows:

There are two main factors deciding a tight shutoff of any valve with any actuator.

The first is the quality of the valve and the ability to repeatedly, over the expected maintenance-free time, to keep closed with a closing force within the expected/calculated range.

The second factor is the actuators ability, in the same way, to supply the necessary force.

Your question is then if a certain type of valve has this quality combined with a certain type of actuator. The answer is yes if the actuator can give the necessary force repeatedly over time, and would not directly depend on actuator type.

However, if you compare an actuator with spring closing with an actuator with diaphragm closing, the diaphragm closing will be depending on more mechanical factors functioning at the same time than the spring closing one: gas to be present in right amount and with correct pressure, diaphragm to be ok, functioning sealings, solenoid valves, etc.

A diaphragm closing actuator would thus require more extensive quality and failsafe considerations to be within necessary quality limits than a spring operated one.

If all else equal, spring closing would be the natural choice.