February 20, 2025
Gas bag is actually a gas storage tank, his role is to store a certain amount of pressurized gas, ready for the scene of a sudden interruption of the gas source and lead to the valve can not be in a safe position of the temporary gas supply container. That is, in normal operation is not any role, only after the gas break will go through the gas bag to make up for the gas, so that the valve is in a fail-safe position.
Why choose pneumatic control valves with air bellows?
Generally larger valve caliber, selection will be encountered if the single-acting actuator, then the cylinder needs to be made very large, that is, the cost will be more expensive, in the market is also completely uncompetitive, and there is no need to do so. Therefore, the choice of double-acting cylinders to match the larger valves require a larger output force, plus air package can become similar to a single-acting cylinder. This will save a lot of cost, the valve installation space will also save a lot. Can also be in the intake air source suddenly stopped, to give a backup air source to ensure that the valve is used for a short period of time.
The main reason for choosing pneumatic valves with air packs is to improve the control accuracy and stability of the pneumatic system. Pneumatic valves are mainly responsible for regulating gas flow and controlling the stroke and force of pneumatic actuators, while air packs play the role of damping and buffering, which can smoothly control the changes in speed and force of pneumatic actuators. Therefore, the use of air packs can effectively reduce the shock and vibration in the pneumatic system and improve the regulation accuracy and stability of the system.
Air packs are usually connected to pneumatic valves through hoses or other connectors. The air pack is filled with gas, one to the pneumatic valve and the other to the air pressure source. The pneumatic valve is connected to the air pack through a hose, and the air pressure source is connected to the inside of the air pack through another pipe. In this way, the movement of the pneumatic valves is transmitted to the air pack, while pressure changes in the air pack smoothly regulate the movement of the pneumatic valves. With this connection, the air pack can effectively reduce the pressure pulsation in the pneumatic system and improve the stability and reliability of the system.
How is the air bellows connected to the pneumatic control valve?
Gas package as a temporary gas supply role after the site break, need to be connected to the site after the break can be given to the cylinder to make up the channel.
In order to be able to see more clearly, the following examples: double-acting cylinder configuration gas package (mainly through the solenoid valve solenoid valve control, gas or power failure position of the valve to be in the full closed or fully open situation)
Schematic diagram of the connection between air bellows and pneumatic control valve
AF is filtering pressure reducing valve; SV is magnetic valve (2-position 5-way); AB is air control valve; LV is lock valve; QB is air bag; CV is one-way check valve; SUP is compressed air inlet.
①Normal operation: the solenoid valve to control the valve fully open or fully closed through the solenoid valve gain or loss of power.
② only power failure: solenoid valve all the way to the air supply channel is connected to the cylinder, so the valve can be fully closed or fully open state, specifically according to the needs of piping.
③ only cut off the gas situation: after cutting off the gas, the solenoid valve with electricity, only one channel is and the cylinder want to pass, if it happens that the solenoid valve control is in the fully closed position, it happens that the gas packet connected to the gas control valve vent is to the cylinder so that the valve closes the direction of the valve, then the valve will be closed. If not, the valve may stay in any position.
④Both power and air: In this case, the fault position of the valve can be in the fully closed or in the fully open state, which can be piped according to the need.
Pneumatic control valve is a control valve model powered by a gas source. Compared with the electric control valve, the use of the requirements of the working conditions of the site to have a gas source, which adds limitations to the use of pneumatic control valves. But because the pneumatic control valve itself has explosion-proof performance, and there are two kinds of air open and air closed for different working conditions. Safety performance is much higher than the electric control valve. So in many working conditions is the user's control valve model.
Selection of pneumatic control valve acting mode is mainly to choose air open or choose air closed. Air-open pneumatic control valve that with the increase in signal pressure and open, in the gas source failure or no signal pressure when the valve automatically return to the closed state. Air-closed type regulating valve is the opposite of air-open type regulating valve. So in many working conditions the role of pneumatic control valve form of choice is particularly important. Here is how to choose the pneumatic control valve role form.
First of all, from the safety point of view of process production. In the signal pressure interruption, should ensure the safety of equipment or operators. If the regulating valve in the signal interruption is in the open position when the harm is small, then you should choose the gas open type; Conversely, the gas off type. For example, the heating furnace fuel gas or fuel oil to use gas-open control valve. There is no pressure signal should be cut off into the furnace fuel, to avoid the furnace temperature is too high and cause accidents. To regulate the flow of process media into the equipment control valve, if the medium is a flammable medium should be used gas open type, to prevent explosion. Another example, the carbonization of fertilizer plant fixed sub-tower level control valve, in order to ensure that when an accident occurs, the control valve can be in the fully open position, so that the fixed sub-tower will not be full of liquid level with water, resulting in high-pressure machine accidents, should be considered to use the gas shut-off type of control valve.
Then consider the characteristics of the medium. If the medium is easy to crystallize the material, to choose the gas shut-off type to prevent clogging. Heat exchanger by regulating the flow of the carrier to maintain the outlet temperature of the cold medium. If the temperature of the cold medium is too high, it will coking or separation, affecting the operation or damage to the equipment, then the regulating valve should choose the gas open type.
Also from the perspective of ensuring product quality and minimizing economic losses. In the event of an accident, minimize raw material and power consumption, but to ensure product quality. For example, in the distillation tower control system, feed control valve commonly used gas-open type, no air pressure on the closure, stop feeding, so as not to waste; back to the flow control valve can be used to gas-off type, in the absence of a gas pressure signal to open, to ensure that the return flow; when adjusting the amount of steam used for heating and the top of the tower when the product, but also use the gas-open type.
