User question
Usually, the gas in the gas cylinder needs to be regulated to a relatively low pressure through a pressure reducing valve before it can be connected to the MFC. When the pressure of the gas cylinder is too low, it is necessary to replace the gas cylinder. But some customers find that the MFC has been damaged after replacing it with a new gas cylinder. Why is this?
Working principle of pressure reducing valve
Firstly, we need to understand the working principle of the pressure reducing valve.
A manual pressure regulating valve opens the valve port by adjusting the amount of spring compression. Gas flows through the valve port to the rear end. When the outlet pressure gradually rises to the set pressure, the gas pressure that lifts the diaphragm upwards gradually increases until the spring force and outlet gas pressure reach equilibrium. If the gas cylinder is removed at this time and there is no high-pressure gas at the inlet, the spring force will cause the valve port of the pressure reducing valve to open to a relatively large degree. After connecting a new gas cylinder and turning on the cylinder switch, high-pressure gas suddenly enters the pressure reducing valve. Due to the rapid propagation of pressure in the gas and the relatively large opening of the pressure reducing valve, the high-pressure gas will instantly pass through the pressure reducing valve and be transmitted to the rear end. The pressure reducing valve diaphragm senses an increase in outlet gas pressure and gradually closes the valve port until it is completely closed. But in the moment just now, the high pressure was enough to reach the inside of the MFC, causing damage to the MFC sensor.
The correct method for replacing gas cylinders
Therefore, the correct way to replace the gas cylinder is to close the pressure reducing valve before replacing the cylinder. Alternatively, a shut-off valve can be connected after the pressure reducing valve, and the shut-off valve can be closed when replacing the gas cylinder to effectively protect the MFC and the entire system.
