A pneumatic control valve is a valve that works via compressed gas to limit a device, preventing overloads, explosions or any number of other harmful effects. Newer control valves work through sensors that monitor the internal conditions of a device. The most common gas present in a pneumatic control valve is compressed atmospheric air. In addition to compressed air, most pneumatic control valve gases have a small amount of vaporized oil that keeps the internal parts of the valve lubricated as it functions.
It is possible to find a pneumatic control valve on a huge number of different devices and machines. These valve types are very common in industrial and factory machinery, such as in manufacturing and processing machines. In addition, they are found on heavy-duty hand-held tools like rivet guns and inside residential and commercial machinery such as heating and cooling systems.
In nearly every instance of a pneumatic control valve, the valve requires a burst of compressed air to force a plug into a set position that stops a dangerous situation from occurring. This burst typically creates a mechanical reaction that forces the plug into an opening that prevents a gas or liquid from passing. Sometimes this process also reveals a secondary opening that allows the system to bleed off the blocked material.
These systems typically respond to abnormally high heat, pressure or flow rate. Any of these situations could result in damage to the device or even an explosion. In most modern equipment, these factors are monitored by an external system that also directly controls the pneumatic control valve. When any dangerous situation begins, the system is alerted to the problem and triggers the valve.
Older systems typically had a less high-tech method of monitoring problems. These systems had a wide variation based on overall design, but they typically worked via a test module inside the machine. In many cases, as temperature or pressure increased, a system inside the device would force air or water into a connected chamber. When the substance in the chamber hit a certain level, the device would trigger the valve, which would calm the system and drain the chamber. This process would then start all over again.
Most pneumatic systems used compressed atmospheric air. Nearly any other gas, with the exception of oxygen, poses a significant asphyxiation risk should the gas leak from the system. Oxygen, in nearly any concentration higher than that in the atmosphere, is so flammable that it would likely trigger an explosion when used.