# How to estimate the torque required to use a valve handwheel?

30 September 2020

### What is torque anyway?

Even though we all went through our "Physical Science" classes in junior high and high school and vaguely remember the "moment of a force" or "torque", this physical magnitude has often become quite blurred in our minds, and is often confused with a force or power.

And yet it is involved in many activities, whether professional (turning a steering wheel, turning any machine, tightening any screw or bolt) or leisure (who has never pressed pedals?). Nevertheless, when it comes to defining it and even more so to measuring it, it is not always easy...

Tools are available to measure torque. For example, torque spanners, which are widely used in the tightening or mechanical trades. But when it comes to knowing the torque required to open or close a system (usually a valve) using a handwheel, it is more difficult to find a means of measurement.

### Why measure the torque required to operate a valve handwheel?

Knowing the torque required to open, close or "unblock" a valve is important to assess the condition of the valve, its evolution over time and to define a possible need for maintenance. It also indicates what means will be needed to operate the handwheel. Can one operator handle it without any problem, does it take two people, does it require special means... ?

To increase efficiency and avoid the risk of accidents, fatigue and occupational diseases, more and more industries are choosing to use portable valve actuators. It makes possible to divide the time required by 10 or 20, without any effort for the operator and without any risk for the equipment.
However, it is still necessary to choose the appropriate actuator, especially in terms of torque. In fact, the torque that will be applied during the operation is not determined by the portable valve actuator, but by the handwheel itself.

If a handwheel requires a torque of 150 Nm to be handled, it is imperative that the chosen actuator is capable of handling it. Its maximum torque should be higher than that required to leave a "margin" that will allow it to be used within a "comfortable" range. On the other hand, an actuator, however "torquey" it may be, will never develop more than the torque required by the steering wheel. It may go faster or slower depending on its power, but the torque developed will remain 150 Nm. There is therefore no point in choosing an actuator with the highest possible torque that is unrelated to the torque demanded, just make sure that it has sufficient margin to pass any hard points.This is important because:

- An actuator capable of delivering high torque will be bigger, heavier, slower and more expensive. It only makes sense to use it if the required torque is actually high.

- An actuator with low torque will be lighter, faster and cheaper, but will be unable to move a handwheel that is too difficult to move, or to close a valve correctly that requires high torque to close completely.

It is therefore important not to make a mistake when equipping yourself with this type of device, and therefore to know the torque required for the handwheels you wish to manipulate.

### A quick and simple tool for estimating the torque of a steering wheel

Here we offer you a simple tool to estimate the torque required for your steering wheels. The torque being the product of the force applied by the distance between the pivot and the point where this force is applied, it can be estimated simply as follows:

- What is the radius of the steering wheel used?
- What is the difficulty for an operator to turn the steering wheel?
- Can he turn it easily with one hand (with an applied force not exceeding 5 kg, i.e. about 50 Newton)?
- Can he turn it easily with two hands (max. 5 kg per hand)?
- Can he turn it with two hands and a "reasonable" effort (max. 15 kg per hand)?
- Can he turn it with both hands but with difficulty? He has to put all his strength into it (up to 30 kg per hand)?
- Do you have to work in pairs (50 kg per operator, almost hanging from the steering wheel)?

If the handwheel is completely blocked and the torque required to unblock it exceeds 1000 Nm, the valve or reducer will probably have to be replaced. Applying an even higher torque would risk breaking the mechanism and making it unusable.

Take the 30 seconds needed to answer the questions on our  simple torque estimator and you will have an estimation of the torque required for your valves.

### Don't forget!

Of course, speed, number of revolutions to be performed and the desired duration of the operation are other elements to be taken into account before choosing the right portable valve actuator. You should also consider the maximum torque your valve and/or its handwheel will allow to ensure that the maximum torque developed by the actuator will not exceed the permissible torque. If this is the case, consider the "torque limiter" option available on most of our units.

If you have any questions, please do not hesitate to contact us.

We’ll make you eager to work with us !

Bruno Martin