We are specifying 84" x 144" sluice gates in one of our projects and we expect very high torque and thrust required for the actuator to pull up the gate under a head of 40ft water. What type/brand of electric actuators do you suggest?

The height of the cylinder actuator (either pneumatic or hydraulic)  will be within inches of the height of the electric actuator.
With the valve open, the lead screw will have to pass through the electric actuator and stick up into the air. (probably inside a fixed protection tube)
So you can have a 144" stroke cylinder, or a 144" long ACME- threaded actuating screw.  

A pneumatic cylinder will presumably run on your plant air system, so typically that means you can have 80 psi you can count on.  

A hydraulic actuator typically draws from a 1500 psi system,
So the relative areas of the pneumatic vs hydraulic are almost 20:1 (or a 4.3:1 diameter ratio, neglecting the (important) cross-sectional area of the actuating rod)

If you need fail action, you can use a pneumatic accumulator about the size of a tank car, or a hydraulic accumulator which would be much smaller, or you could use an electrical failsafe which would be basically batteries and an inverter, and comparatively quite compact. 

Speed can be an important spec.  Electrics usually operate at only 12-15" per minute.  If this stroke is 144", it might take 10 minutes to open.  Likewise, if there is a power failure it may be necessary to maintain control of the valve.  A hydraulic accumulator can handle multiple strokes after power is lost.  This accumulator would push fluid into the hydraulic actuator.

However, hydraulic actuators can be tall.  If there is a height issue, electrics may be the way to go.

The height of the cylinder actuator (either pneumatic or hydraulic)  will be within inches of the height of the electric actuator.
With the valve open, the lead screw will have to pass through the electric actuator and stick up into the air. (probably inside a fixed protection tube)
So you can have a 144" stroke cylinder, or a 144" long ACME- threaded actuating screw.  

A pneumatic cylinder will presumably run on your plant air system, so typically that means you can have 80 psi you can count on.  

A hydraulic actuator typically draws from a 1500 psi system,
So the relative areas of the pneumatic vs hydraulic are almost 20:1 (or a 4.3:1 diameter ratio, neglecting the (important) cross-sectional area of the actuating rod)

If you need fail action, you can use a pneumatic accumulator about the size of a tank car, or a hydraulic accumulator which would be much smaller, or you could use an electrical failsafe which would be basically batteries and an inverter, and comparatively quite compact. 

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