Motorised Valve or Pneumatic Valve is Best

Try Siemens valve actuators, we have 50-60 on property and none failed in 13 years.

http://www.buildingtechnologies.siemens.com/bt/us/Products__and__Systems/hvac_products/HVAC_components/valves/Pages/valves_landingPage.aspx

Electrically operated valve. If the there is any distance from the power sources. Conduit and wire is less expensive the black pipe or air line. Cost of the valves are about the same. With pneumatics you may have to provide some air treatment and regulation(psi) which is extra cost. With pneumatics if compressor goes down you lose function if electric you don't. If electrical power goes down you lose both anyway.

Now whats the function of the valve it mat make a difference?

Is this a test?

ozzb is right.

Normally you have more control with electrical signals than Pneumatics. U can also control the flow with a motorised valve and PID control system.

For Motorised valves, you have 2 types:

Gate Valve and Butterfly Valve.

i prefer gate valve as its life is longer than butterfly valve. However, the availability depend on the size of pipe you are using.

For quick response, pneumatic is likely to be best. Otherwise, I would tend toward electrically motorized. It depends on how rapidly the process may fluctuate.

The only data given, water @ 35-40C doesn't affect the selection.

You want an on-off valve, a modulating valve? You want a fail open/close/as is operation? Valve size? Which system and differential pressure? Stroke time is essential? All this and similar data will give you the thrust/torque you need to move the valve and this will assist you in the selection, usually motor operators have a higher force rating, but most of them are for on-off actuation (modulating function need a different motor power/size). Air operated are used for both applications (on-off and modulating). The later need more instrumentation (positioners, maybe volume boosters...)

Kind regards

We use electrically motorized valves in larger and plastic lines for throttling flow and to reduce the effect of (water hammer). The electric valves we have are designed to return to a safe position in the event of a power failure by spring action. Pneumatic valves would be a good choice in hazardous locations where flammable vapours may be present.