The Classification of Pressure Relief Valve
1. Acting-type pressure relief valve: the simplest pressure relief valve. It is with a flat diaphragm or bellows. Because it is an independent structure, there is no need to install an external sensor line downstream. It’s the smallest and the most economical one among the three sanitary pressure relief valves discussed here. It is specially designed for medium and low flow amount. The accuracy of direct acting pressure relief valve is typically +/- 10% of the downstream set point.
2. Piston-type pressure relief valve: This type of pressure relief valve combines two kinds of valves–the pilot valve and the main valve–into one. The design of the pilot valve is similar to that of the direct acting pressure relief valve. The exhaust pressure from the pilot valve acts on the piston, causing the piston to open the main valve. If the main valve is large and can’t be opened directly, this kind of design will use the inlet pressure to open the main valve. Therefore, compared with direct acting pressure relief valve, at the same pipe size, this kind of pressure relief valve has a higher capacity and accuracy (+/- 5%). As with the direct acting pressure relief valve, the inside of the pressure relief valve senses the pressure, there’s no need for an external installation of the sensor line.
3. Diaphragm-type pressure relief valve: in this type of pressure relief valve, double diaphragm replaces the piston inside the inner pilot pressure relief valve. This increased diaphragm area can open a larger main valve, and at the same pipe size, its capacity is greater than that of the inner pilot piston pressure relief valve. In addition, the diaphragm is more sensitive to pressure changes, its accuracy can be up to +/- 1%. Higher accuracy is due to the positioning of the downstream sensor line (outside the valve), where there is less turbulence in gas or liquid. This kind of pressure relief valve is very flexible, different types of pilot valves such as pressure valve, temperature valve, air load valve, solenoid valve can be used with it.