Motor-Operated control valves??? it's proper??

[TAGE]

Dear All
I'm a mechnical engineer in the power plant. I'd like to know that if i can use motor actuator for the control valves (regularing purpose, not on-off purpose).Normally we use the pneumatic actuator for this kind of control; such as desuperheater, feed water system and so on. Even though I know the motor actuator of which technologies have highly been developed but I'm not quite sure that whether it's proper for regulating purposes or not, you guys are electrical engineers and i do hope that there would be someone making me for clarity of this my concern.

Thanks indeed and best regards

 

[dbaird]

Gemu offers motorized control valves. Check:

http://www.gemu.com/Opening.htm

David Baird
mrbaird@hotmail.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[Barry1961]

There are a lot of motor actuated valves out there in the petroleum industry. They are much more reliable in cold enviroments. I don't have any data on this but I am sure that a properly sized gearmotor will out last a air cylinder.

RACO makes a extremly rugged line of electric actuators but they cost a bunch. I think they are doing some valve stuff also.

Barry1961

 

[candu6]

Control valves move alot. This can be a problem with a motorized valve because you may wear out the motor starter quickly.

 

[btrueblood]

Dunno about motor starters, a lot of the newer motorized actuators use DC step motors that are switched by solid state electronics. There are also battery backup systems available that allow for "fail safe" operation, e.g. return valve to closed position in event of power failure or loss of signal.

 

[buzzp]

I would do it based on knowing all the details.

Its probably not important, but electric acutators operate slower than pneumatic.

 

[TAGE]

Thanks so much for all suggestions
In fact, I thought like what you suggested, what I'm concerned is we cannot do fail safe operations if power has gone as well as the life time of the motor actuator over the frequently-regulating operation but i really have no idea why the main contractor who is being awarded the project really wants to supply this type of actuator since, in my view, the cost of motor actuator is probably higher than the pneumatic actuator!!?? (I might be wrong) i'm not sure that if we consider overall an instrumentation-compressed air system (Higher capacity of compressors, piping and pneumatic actuators), we might need more investment for pneumatic system than power lines and motor actuators, don't we?

Regards

 

[kensea]

TAGE
It may pay to consider the environmental conditions that the intended actuator is going to be installed in and if the presence of electrical energy is ok. Recently we had an actuator explode, through an insufficent IP rating for process environmental conditions, ingress of moisture and some other nasties caused a build up hydrogen gas, sparking ignited the gas, and KARBOOM!, actuator cover in a million bits. Although the actuator itself did not fail and continued to operate fine, the safety risk was unacceptable. Some actuators can be confrigured to fail open or closed (for signal loss) depending on your process requirements and depending on process conditions have in-built mechnical redundancy (for power loss) to facilitate this. A 0-20mA control loop could be utilised where 4-20mA operates the 0-100% control and 0-4mA simulates broken wire/signal loss and will drive the valve to a fail safe position. Depending on the scope of works, instrument air can be expensive, only an indepth study of process requirements, operating conditions, process environmental conditions, safety targets, area/location regulatory requirements, long-term maintenence goals...etc will give an idea of pro's and con's vs cost/eff. between pneumatic/electrical control systems.
Kensea

 

[buzzp]

TAGE, all the stuff you mention (air compressor capacity) and the things mentioned by all posters needs to be considered in your decision.

 

[NYedison]

1)Pneumatic Actuators have been proven for this type of application. It is easy to operate,maintain and test the pneumatic actuators. These can be set for the desired fail safe position. It certainly has a lead over electric actuators.

2)For your application (Power Plant)Relaible supply of instrument air is always available in the power plant.

3) For desuperheater and feed water control valve, the duty is severe than the furnce draft and other application.

4) Electric actuators are being used for the regulating duty as well. However,due to the speed(gear box), torque, power supply and safety considerations the selection of the actuator is a difficult task. They are available in all voltage frequency, speed range.