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. Here we discuss the key considerations to take into account when choosing a torque limiter.
Too much torque can cause serious damage to the valve, and often results in it needing to be replaced. Torque limiters are designed to ensure that torque never reaches these critical levels, and can help protect expensive machinery.
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 maximum acceptable stem torque (MAST). If you don’t have this information, you have to go gradually, with rotation tests in one direction and then in the other. 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, and it is important to choose the right one.
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, the stall torque is itself modifiable according to the operating pressure, and can be brought to stall as often as necessary without causing any damage to the actuator itself.
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.
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.
The JA73 has an intelligent clutch system that allows the maximum torque to be set at 100, 80, 60, 40 or 20 per cent of the maximum torque indicated in the catalogue. When this torque is reached, the clutch disconnects the engine from the integrated gearbox.
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 allows manual adjustment of plus or minus 40 per cent in relation to a median value. Once the set torque is reached, the motor disconnects from the gearbox.
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.
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