Electric linear actuator for control valve 1

[PABW]

Hi,
I have a sliding stem valve application where running air will be difficult. I’m thinking of using a linear electric actuator similar to what we have on our turbine fuel valve. (Ball screw, or roller screw I think – we replaced an old hydraulic 10 months ago) My only concern is thread wear, which so far has not been a problem. (It will be inspected this fall – but I can’t wait that long) A local rep has shown me a design that includes an integrated controller in a nice small package, but he had no reliability data other than motion control applications. Anyone have thoughts on reliability with this type of actuator on a control valve?

PABW

 

[JLSeagull]

A reliable power source does not make a valve fail in a safe manner. The UPS may provide some duration between an event and a blackout. The energy is lost once the batteries are drained whether after five minutes or eight hours. Other things exist between the UPS and the valve stem.

A spring provides stored energy that rarely fails. I regard spring opposed diaphragms and pistons as fail safe actuators. For my comfort zone, gas-over-oil or stored pressurized hydraulic media connected via tubing to a vane or other non-spring design is not fail safe regardless of the tricked out solenoid circuitry or hydraulic hand-pumps. I require the force of the spring. This is a bit rigid considering that I accept pilot operated pressure relief valves. I have seen offshore platforms with the gas-over-oil shutdown valves on 36 NPS risers. I think that stored pressure for actuating media places the entire platform at serious risk during a fire. Only a spring-opposed actuator fits my criteria of fail-safe.

Further argument could address that valve stems and springs break too. Life.

 

[PABW]

Sorry I wasn't more clear. I wanted the valve to go to a known position under failure, but I didn't need an actual fail 'safe'.
The UPS only needs it to power this actualtor for a few seconds to get it to postion, then engage a break.

PABW