I have a steam radiator at home and it has a valve similar to the picture below.

enter image description here

Please note that the valve doesn't have grooves on top to attach things to.

I want to build something to turn it on and off depending on the temperature at certain points in the room.

I have that taken care of but cannot find a way to attach a actuator(actuator is the right word in the context I guess?) to turn the valve in both directions.

Also It is a rented apartment so I would like to avoid making any modifications to the radiator itself.

  • $\begingroup$ There's no screw on the valve that lets you change the manipulator on the top? Normally that valves require a high torque, and so the mechanical join should be up to that torque. $\endgroup$ Jan 24, 2014 at 15:44
  • $\begingroup$ Sorry for the late reply but I just checked and yes the manipulator can be removed!!Also the valve seems to be fairly free and requires very less effort to open and close.Even with the manipulator removed, what am I supposed to replace it with? $\endgroup$
    – SteveIrwin
    Jan 25, 2014 at 1:01
  • $\begingroup$ well that's good, I added an answer then. $\endgroup$ Jan 25, 2014 at 3:14
  • $\begingroup$ If you don't have the ability to machine a part to fit, a hacky way is to buy a similar manipulator in a plumbing/hw shop and glue a gear or a pulley to it. You can then mount the entire "assembly" on. If this isn't clear I can try to draw it up... $\endgroup$
    – Guy Sirton
    Jan 25, 2014 at 7:18
  • $\begingroup$ @GuySirton I have the ability to machine simple parts.I would like to see that assembly drawing you mentioned here.Thanks. $\endgroup$
    – SteveIrwin
    Jan 26, 2014 at 19:48

2 Answers 2


Well, being the manipulator removable, so you can attach other thing to the valve shaft, you have so much options.

Mechanical coupling

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
chain and sprocket transmission

Synchronous belt 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.

Electro-mechanical actuator

For actuating the valve, you can use a couple of options.

  • A stepper motor.
  • A DC brushed-motor with a reduction gearbox like this

DC brushed-motor with gearbox show
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.

  • $\begingroup$ Great ideas. I would avoid the coupling due to alignment issues, as you mention. You can also use a largeish gear and a smaller drive gear. Do you have some ideas though about how the OP can mount his motor? $\endgroup$
    – Guy Sirton
    Jan 25, 2014 at 7:11
  • $\begingroup$ @GuySirton thanks. I tried to use images for the transmission that showed the reduction in the sprocket or pulley :) Maybe a bit more clear. Anyway I will try to avoid this because of lateral force on the valve axis, so I think a coupler will be more interessing, I don't think aligning it will be dificult, just making a support that can be adjusted, but there's one thing I forget at writing I will add later, that is some valves axis tend to go up or down, if it the case a shaft coupler that tolerate this misalignment would solve the issue. I will try to add a idea for the support later. $\endgroup$ Jan 25, 2014 at 15:25
  • $\begingroup$ @DiegoCNascimento Excellent answer.However I searched online but couldn't find a coupler.Perhaps a link would be great.Also I would like to know more about adding a support for the motor.I have access to a small workshop and can machine simple parts.Thanks for helping out though. $\endgroup$
    – SteveIrwin
    Jan 26, 2014 at 19:44
  • $\begingroup$ @Stevelrwin well I search for shaft coupler will return lots of options, should not be difficult to get one. I will try to post anything about the support $\endgroup$ Jan 26, 2014 at 20:07
  • $\begingroup$ Well, now there is a sketch of the assembly. $\endgroup$ Jan 27, 2014 at 3:31

If the valve has enough traction with a rubber band1, you can use one to control the valve as in the image below.

enter image description here

To make sure the rubber band doesn't start falling over time due to gravity, you could attach a half-circular plate under the valve, so the rubber band wouldn't slowly slide down as it would rest on that plate. Note that the amount of the pressure on the plate should be very small, since the rubber band is quite stretched to provide enough stretch for rotation, so a not so strong glue might do the trick for that plate.

1 This both depends on the material it's made of and quite importantly, how much torque is required to turn the valve.

  • $\begingroup$ Well, I think that is really difficult for these valves. I don't know these, but by the OP post, I think they require a large amount of torque. Also my suggestion to the drawing: The motor should be put in smaller diameter than the manipulator of the valve and near it, this would put more rubber on the circumference of the valve. Also too much lateral force and the valve could wear fast. $\endgroup$ Jan 24, 2014 at 18:21
  • $\begingroup$ @DiegoCNascimento, thanks for the pointers. I'm actually a software programmer, so my knowledge of mechanics is rather limited. $\endgroup$
    – Shahbaz
    Jan 24, 2014 at 18:22

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