How to choose the right torque limiter when operating valves?

"I'll take the 'torquey' one! "That's what you often hear from customers who are using a portable valve actuator for the first time.

It's easy to imagine that a stuck or very difficult valve is the primary reason for purchasing such a tool. However, this is not necessarily the best reason to use a portable valve actuator, and it may even be a bad idea if the maximum torque developed by the actuator is greater than the maximum torque that the valve, its gearbox or its actuator (handwheel) can handle! In this case, beware of breakage!

What is the maximum torque that can be applied to a valve handwheel?

The easiest way is to refer to the valve specifications (when available) and find the M.A.S.T. (Maximum Acceptable Stem Torque). If you don't have this information, you have to go gradually, with rotation tests in one direction and then in the other, and hope that the material will hold! In any case, a completely blocked valve actuator is often a sign that it is time to replace the valve itself...

How to be sure not to exceed the maximum torque applied to a valve handwheel?

A torque limiter integrated in the portable actuator should be used. There are several systems of torque limiters, from the simplest to the most sophisticated. But in any case, it is important to choose the right one, and especially the one that will be correctly sized to obtain the necessary torque, but not too much!

Make sure your portable actuator is capable of achieving the desired torque. Indeed, there is no need to choose a torque limiter if the actuator itself cannot deliver this torque.

Use stall torque, when possible

The first and simplest torque limiter is therefore the maximum torque that the actuator can reach.

In the case of a pneumatic actuator, this "stall" torque is itself modifiable according to the operating pressure, and does not pose any problem to the actuator, which can be brought "to stall" as often as necessary without causing any damage to the actuator itself. For modec actuators (HL83 range), the values of the stall torque at 4, 5 and 6.2 bar are indicated in the catalogue and a simple linear extrapolation between these values will give a sufficiently accurate idea of the stall torque.

In the case of a gas actuator, there is also a maximum torque at which the motor will stall.

In the case of a portable electric actuator, wired or battery powered, the problem is different. In fact, an electric motor is very likely to be damaged when it is brought to stall. So you can't rely on this method to limit torque.
We can therefore see that although this "method" has the advantage of simplicity, it lacks precision and can cause significant problems, especially with electric actuators

MC89 and JA73 modec battery electric actuators: use the integrated torque limiter

The Modec MC89 (easy and standard duty) and JA73 (standard and heavy duty) ranges of battery powered portable actuators incorporate torque limiting systems by default, which already meet the majority of requirements.
The MC89 has an electronic system for setting the maximum torque which ensures that the machine will stop as soon as the chosen torque is reached. There is therefore no risk of breakage, either for the valve or its operating element, or for the actuator.
The JA73 has an intelligent clutch system that allows the maximum torque to be set at 100%, 80%, 60%, 40% or 20% of the maximum torque indicated in the catalogue. When this torque is reached, the clutch disconnects the engine from the integrated gearbox and the device stops although the engine is still running.

These intelligent systems allow the setting of a maximum torque on our electric actuators, without risk.

Adjustable mechanical torque limiter

The systems described above are effective in most cases, but sometimes greater precision is required, or the adjustment range must be continuous rather than stepwise. Also, the gas portable actuators (PY68) do not have a maximum torque setting system.

To meet these specific needs, modec has developed a mechanical adjustable torque limiter, which can be fitted as an option to any portable actuator in the range, and which allows manual adjustment of plus or minus 40% in relation to a median value. Once the set torque is reached, the motor disconnects from the gearbox, instantly cancelling the cut exerted by the actuator on the maneuvering element.

Be careful, when selecting your torque limiter with a set range, remember the following simple but important things (and pardon the obvious!):

- Below the minimum adjustable torque (40% below the selected median value), there will be no way to limit the torque!
- Even if the actuator has the potential to deliver high torque, this torque will not be able to exceed the upper torque setting limit (40% above the selected median value) because the limiter will always trip before!

Regardless of the type of modec portable actuator selected, there is a solution to control the torque and thus guarantee the safety of the equipment.