comparison - electric v pneumatic actuator

Can any of you offer some insight to selection of an electric or pneumatic actuator for ON/OFF ball valve? The valves will need to be FAIL LAST STATE and both elec and air are readily available. What should be the deciding factors? Is pneu more reliable? Is elec more costly?

I generally prefer electric. Pneumatics can be cheaper IF you already have the compressor, drier, filter, etc. Frost can be a problem for outdoor mounted pneumatics. It used to be that you could get more precise control with pneumatics, but that's not generally the case now.

Actuators

Kerry actuators are self-contained electric hydraulic and can come with an accumulator for fail safe type operations. These actuators are very good and very reliable. Wide range of operating voltages AC and DC.
http://www.kerryactuator.com/

Roger

When was that?

Tom Jenkins said:

It used to be that you could get more precise control with pneumatics, but that's not generally the case now.

Click to expand...

All things being equal, a pneumatic system is much more difficult to precisely control.

Electric actuation is more expensive and generally much slower.

As pointed out above, electric actuation is more controllable and precise. Electric actuation is also probably more suited for temperature extremes like outdoor applications.

To have the "FAIL LAST STATE" condition, a motorized electric ball valve would be the best way to go... if you loose your OPEN and/or CLOSE signal to the valve it will remain in the last state it was in. To get the same operation in a pneumatic valve you need a air to open, air to close which is generally more expensive than the spring to close or open versions. Electric actuated gets more expensive when you try to have fail to close operation because you require a sensing circuit and battery pack to provide power to close or open the valve

Precise positioning?

Since the valve to be controlled is a quarter turn ball valve the only desirable states are OPEN and CLOSED. Ball valves are not used for throttling flow. This eliminates the "precise positioning" part of the discussion.

If plant air is available and the actuator will not be in a location prone to freezing, the pneumatic seems to me to be the better option. Even with a double acting actuator I believe it would be less expensive than the equivelant motor operator.

When selecting your FAIL LAST STATE/POSITION actuator, have a look at the newer type of actuator that does not require external solenoids to hold position upon air or signal loss. I have found that with the cost of the standard actuator plus the fail safe solenoids, is greater than a newer type actuator that has this function internally.

I replaced SMC IP6100 type actuators with the fail safe extras for the new IP7100 digital model at lesser cost.

The change out was a result of the failsafe relays/solenoids failing when exposed to heavy rain.