Well, being the manipulator removable, so you can attach other thing to the valve shaft, you have so much options.
You could use a coupled rotary actuator to the shaft by the means of a shaft coupler. There's many types, this is a simple one, but you probably would not get the actuator axle full aligned with the valve shaft, so a coupler that permits some misalignment is desirable, like these:
rubber shaft coupler http://www.abssac.co.uk/uploads/products/cat_pp651_coupling%20jaw%202.jpg
Every coupler has its specifications and types of misalignment it will support.
You can use a belt or chain transmission too. Then you need to attach a pulley or sprocket to the valve axle.
Chain and sprocket transmission
Synchronous belt transmission
A possible problem with these two option is the lateral force the transmission could put on the valve shaft, as it has not made to support this, it probably will wear. One way to overcome this is to use a shaft coupler to a bearing with the transmission, so the lateral force will be supported by the bearing.
For actuating the valve, you can use a couple of options.
- A stepper motor.
- A DC brushed-motor with a reduction gearbox like this
The gears are show for illustration purposes, they are normally enclosed.
There's many types of reduction gearbox too, I will not extend into this on this answer.
You probably need some way of knowing the position of the valve shaft (feedback). It can be a multi-turn potentiometer for simple analog output.
RC servo motor
If the valve needs less than 1 turn you can try to use an RC servo-motor, they have a DC-brushed motor, a reduction gearbox, a potentiometer for feedback, and a control circuit. You then feed with the angle position in a signal modulated by a technique know as PWM. Along the fact that the valve will operate at less than a 360° angle, you need to be sure the torque of the RC servo motor will be superior to the needed. Also metal gears and shaft will provide a more robust system, considering the torque.
@DiegoCNascimento the image can be used with credits
Here's a final assembly possibility. You should be sure the pipe could support the forces involved with a safety margin, if not, use the wall mount supports.
Note: some valves main axles will go up or down when rotated, if this is the case the mechanical coupler should support this.
I do not assume any responsibility by any damage or injure in the mounting of this, the user should have plenty attention he/she is working with high-temperature and high-pressure parts that can pose danger.