How to prevent the fire of pneumatic actuator?

If the air actuator housing is aluminum, it is difficult to prevent the use of paint, because aluminum has a low melting point (1033~1150℉), which is higher than the melting point of the hydrocarbon mixture flame, and the parts will fail and the valve will not close.

A pneumatic actuator is an actuator that uses air pressure to drive the opening and closing or adjusting the valve. It is also called a pneumatic actuator or a pneumatic device, but it is generally called a pneumatic head. This article explains the various technical requirements of the pneumatic head.

The actuator and the adjustment mechanism of the pneumatic actuator are a unified whole, and its actuators are diaphragm, piston, fork and rack. The piston has a long stroke, which is suitable for requiring greater thrust; and a thin-film travel, which can only directly drive the valve stem. The fork-type pneumatic actuator has the characteristics of small torque, small space, and the torque curve is more in line with the torque curve of the valve, but it is not very beautiful; it is often used in high-torque valves. The rack-type pneumatic actuator has the advantages of simple structure, stable and reliable operation, safety and explosion-proof, etc., and has a wide range of applications in the production process under high safety requirements such as power plants, chemical industry, and oil refining.

When compressed air enters the pneumatic actuator from nozzle A, the gas pushes the double pistons to move in a straight line to both ends (cylinder head), the gear on the piston rotates 90 degrees counterclockwise, and the valve opens. At this time, the gas at both ends of the gas is discharged from the B pipe nozzle. On the other hand, when compressed air enters both ends of the pneumatic actuator from B port, the gas pushes the double column to move linearly in the middle, and the rack on the piston drives the gear on the rotating shaft to rotate 90 degrees clockwise, the valve closure. At this time, the gas is discharged from the middle of the pneumatic actuator and the A pipe. The above is the standard transmission principle. According to the user's needs, the pneumatic actuator can be installed in the opposite direction according to the standard driving principle, that is, choose to rotate clockwise to open the valve and counterclockwise to close the valve. Single-acting (spring return type) pneumatic actuator One nozzle for the air inlet, B pipe nozzle for the exhaust hole (the nozzle of the B pipe should be equipped with a muffler). The pipe nozzle enters the valve to open the gas, while the spring releases the valve by the spring.

In order to make the valve close the fire in time, in the case of easy fire, the internal spring and diaphragm of the iron type pneumatic actuator should be used, because the melting point of the diaphragm is low, so the fire, the film will be damaged quickly, and then the spring moves to make the valve in the closed position Location. Severe fires can alter the properties of metal components, causing the metal to soften, lose its tempering properties, and some metals actually melt. There is a direct relationship between the magnitude of the spring force and the tempering characteristics. Whether the remaining spring force after combustion is sufficient to maintain the valve position, the pneumatic actuator needs to conduct a combustion test to prove it.

In order to keep the pneumatic actuator still running, the spring must be protected from flame annealing. A more practical and effective way to protect the spring is to use flame-retardant coatings, pneumatic clamps on butterfly valves. We can apply materials containing epoxy resin to the actuator to expand and thin it so that the actuator can operate normally.

In a burn test, the actuator was able to operate for 42 minutes despite flame temperatures as high as 1400 to 1700°F thanks to the coating's protection. The test was conducted using a 1600 lb spring cast iron actuator, about 7 feet long, with a 12 inch cylinder bore, and fired with 9 propane torches. During the entire combustion process, the spring in the pneumatic actuator circulates once per minute, and the output torque of the spring after combustion is only reduced by 6%, mainly due to the reduction in bearing precision and the increase in friction through the clip-type butterfly valve.

Test results have shown that the fire-resistant coated springs are not affected by combustion flames and the piston and connecting rod seals remain sealed. After the test is completed, the actuator is immersed in cold water to simulate the sudden cooling effect of the high temperature shell. The test results show that the internal components of the actuator and actuator do not change due to the sudden cooling performance. The fireproof intumescent coating is poured and can be done on site, taking care not to rub the seals as this would impede repairs. When the coating dries, it forms an impenetrable seal.