Electric linear actuator for control valve
Electric linear actuator for control valve
(OP)
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
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





RE: Electric linear actuator for control valve
Motorized valves
Beta 1.1
Characteristic life (hrs)
Life low 17,000
Life avg 25,000
Life hi 1,000,000
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RE: Electric linear actuator for control valve
PABW
RE: Electric linear actuator for control valve
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RE: Electric linear actuator for control valve
Rexa makes an electraulic unit that is the standard of the industry. Jordan make industrial-quality electrics for rising-stem control valves. There are a lot of small electrics out there for HVAC-type applications, and there are a lot of gate-valve actuators (limitorque, Rotork, Auma, Biffi) than can be fittied with positioner cards. THe gate valve actuators doen't use roller screws but in my experience a bronze thrust nut with ACME thread.
RE: Electric linear actuator for control valve
PABW
RE: Electric linear actuator for control valve
If it is only one valve, why not go ahead and try it. If the service is critical, why not try a valve on a less critical service.
In any case, it doesn't take that much time to change a valve/actuator.
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RE: Electric linear actuator for control valve
How big an actuator is this? Is this a aeroderivative machine? The fuel valve on an aero engine is a very different animal to the fuel valve on a frame machine, principally in the size and mass of the moving parts. Continous modulation will put a lot of dynamic force on the actuator as it accelerates and decelerates the valve. Depending on your loop tuning this may be quite aggressive to maintain adequate control of the turbine. Ask the vendor to warrant the life of the actuator for your specific application. The cycle life he quotes could be with little or no mass attached to the actuator.
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RE: Electric linear actuator for control valve
We have been using the electric actuator on our turbine fuel valve for over 10 months now. Since it does operate in essentially the same small area, I was concerned about thread wear, which we will check in October. So far we have seen no change in performance, and have been very pleased with the results. I was asking if anyone else had used an actuator like this one and had comments on its long term reliability. The technology is very different from what we are using so I’m not sure how to even schedule maintenance on it.
I’m going ahead with the second application, and will let you know how this turn out.
PABW
RE: Electric linear actuator for control valve
I'm following this with great interest because we're in the middle of a trial installation of a Rexa electro-hydraulic actuator to the IGVs of one of our turbines. Our fuel valves are all electro-hydraulic, as are the eight main valves on our steam turbines. We consistently find calibration errors of less than 0.1% on a 40mm stroke gas valve after a year in service. An error as large as 0.1% is unusual. We're hoping the Rexa unit will come close to these reliability levels - I'll post findings in a new thread next year once I have some data.
The ballscrew idea is something which we discounted on reliability grounds, perhaps a little unfairly, and I'm trying not to focus on only one technology. Your experiences are thus very interesting. Is the actuator a self-contained package? Would you mind posting a URL for the manufacturer?
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I don't suffer from insanity. I enjoy it...
RE: Electric linear actuator for control valve
Just to clarify - the actuator we are using on the fuel valve has a roller screw, not a ball screw. My understanding is that ball screws for valve control is not a good idea for the same reasons you stated - reliability.
The fuel valve actuator has a separate drive, not self contained. The actuator I'm considering for a different application is self-contained but I don't see info on the web yet. Rep tells me it's new.
Manufacturer for both is Exlar www.exlar.com
PABW
RE: Electric linear actuator for control valve
The foregoing assumes that yours is a modulating application. If it is a on/off application, then any old actuator will do. But if it is going to modulate, you better get an actuator from the class of devices that can meet that modulation rate. The Rexa certainly can, the Jordan can in most models, Beck can. Electrohydraulics are going to leak some day. Can't say when, but they will leak. If that is a problem, go strictly electric.
I know people who love any of the above, and I know people that hate all of the names I mentioned and that have been discussed here.
If you are going to operate at a fairly constant point, be concerned about what JimCAsey related about the wear at that point.
rmw
RE: Electric linear actuator for control valve
Do you mean 3600 starts per hour?
I don't know of any actuators that can do 3600 starts a minute.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Electric linear actuator for control valve
rmw
RE: Electric linear actuator for control valve
RE: Electric linear actuator for control valve
Actuators like this are pretty costly, since they need a separate amplifier to ‘drive’ the motor via a resolver or encoder. (Basic motion control stuff) This new one however includes the amplifier in the same housing as the actuator, and the price is considerably less. It hasn’t shipped yet, but I’ll keep you posted on my results. If it works and doesn't show thread wear, I won't look at a electro-hydraulic again.
PABW
RE: Electric linear actuator for control valve
If temperature is not an issue, then this is unimportant.
rmw
RE: Electric linear actuator for control valve
Does your application require a fail safe action? Can the roller screw electric actuator provide it?
It does look very interesting. Thank you for sharing this with us.
RE: Electric linear actuator for control valve
PABW
RE: Electric linear actuator for control valve
RE: Electric linear actuator for control valve
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.
RE: Electric linear actuator for control valve
The UPS only needs it to power this actualtor for a few seconds to get it to postion, then engage a break.
PABW