When we choose a pneumatic control valve, we must first determine whether to choose air-open or air-close. This is the protection position when the control valve is cut off. If the process requires the valve to be opened when the air is cut off, select the normally open (air-closed) control valve. Otherwise, choose a normally closed (air-to-open) control valve. This is just a rough solution. If the process requires three-break protection of gas, power, and signal, the regulating valve needs to be equipped with some accessories to form a protection system to achieve the control requirements. These accessories mainly include retaining valves and solenoid valves. , Gas tank, etc. The following are the two position retention schemes of single-acting pneumatic control valves and double-acting pneumatic control valves.
This program is mainly composed of control valves, air-controlled reversing valves, positioners, self-locking valves, one-way valves, pressure reducing valves, gas storage tanks, etc. Its working principle is as follows:
When the air source of the control system fails (lose air), the self-locking valve (the function of which is opposite to that of the retaining valve) is automatically opened to cancel the control air source of the air control reversing valve. The slide valve of the air control reversing valve is in the spring Reset under the action of, one of the two air-controlled reversing valves is exhausted, the other is aired, and the one-way valve is closed. The gas source is supplied to the valve from the gas source stored in the gas tank, so as to realize the full valve Close or fully open. The conversion of fully closed or fully open can be realized by adjusting the connection mode of the air-controlled reversing valve.
If you want to realize the position retention of the pneumatic control valve, install a pneumatic position retention valve and change the pipeline connection, use the self-locking valve to directly control the position retention valve, and cancel the pneumatic control reversing valve, one-way valve, and gas storage tank.
If you want to ensure that the valve has several actions when the air source is cut off, the following solutions can be used.
This scheme consists of a gas storage tank, a one-way valve, a blocking valve, a stop valve, etc. Its working principle is as follows:
When the air source fails (loss of air), the one-way valve is closed, the lock valve loses air, the slide valve of the lock valve is reset under the action of the spring, the air path is reversed, the air source pipeline of the system is disconnected, and the storage is connected. In the gas tank pipeline, the gas storage tank supplies gas to the valve to ensure that the valve has several actions to achieve the purpose of continuous control. Due to the limited capacity of the gas storage tank, and the pressure of the gas source in the gas storage tank continues to decrease with the action of the valve, the gas storage tank cannot be used for a long time to supply air to the valve. The capacity of the gas storage tank for this plan should be larger than that of the general protection gas storage tank. In this scheme, when the gas source is cut off, the number of valve actions is related to the capacity of the gas storage tank.
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