The Structure Design and Operating Principle of the Pressure Relief Valve (Part One)

In the water pump pipeline system, when the pump is suddenly stopped, the check valve at the outlet of the pump is quickly closed, causing the circulation flow rate in the valve outlet pipeline to suddenly drop, and generating shock pressure from reverse flow. The sudden change in speed will cause the shock pressure wave transmission, and the transmission speed is very high, which can increase the pressure of the valve outlet section to several times higher than the rated pressure. This is the so-called water hammer in the pipeline, which can make the valve or pipeline break and cause an accident. In order to avoid this kind of accident, people currently use valves with delayed closing characteristics, such as two-stage closing butterfly valves, hydraulic control valves with two valve plates, check valves with slow closing, etc., to delay the closing of the valve. Through the pump and rotor components, a part of the water returns to achieve the purpose of pressure relief to eliminate water hammer pressure. However, because the pressure is relieved for a long time, the reverse flow impacts the impeller of the pump for long, which speeds up the reversal of the pump rotor components. The pump rotor components and the motor rotor components connected to them will be damaged after a long time. In order to solve the above problems, it is necessary to design an automatic pressure relief valve installed on the bypass pipeline, which can lead the reverse flow to the pump inlet within the pressure relief time, that is, the pressure relief and reverse flow no longer passe through the pump rotor components to complete the pressure relief. The pressure relief valve can be closed automatically after pressure relief, which completely solves the problem of reversing of the pump caused by reverse flow and pressure relief and achieves the purpose of effectively eliminating water hammer.
  
Structural design
The valve consists of a valve body, a hydraulic cavity, a hydraulic pipe a and a hydraulic pipe b. The valve body is a four-way pipe with a hydraulic drive rod, a lower valve plate and an upper valve plate. The two ends of the hydraulic drive rod are threaded. The lower part of the valve body is connected with the bottom bonnet by connecting screws. The upper and lower sides of the valve body each have a water inlet and outlet connected to the pipeline. The middle of the valve body which is near the upper water inlet and outlet has a sealing seat. The upper valve plate is connected to the hydraulic transmission rod by welding, and the lower valve plate is connected with the hydraulic transmission rod through a nut and a thread at one end of the hydraulic transmission rod. The upper part of the valve body is connected with the hydraulic cavity through a flange. The hydraulic cavity is composed of a hydraulic cavity seat, a hydraulic cavity cover, a hydraulic cavity body and a piston, and they are connected to the valve body through a screw and nut. There is a hydraulic cavity seat cover on the hydraulic cavity seat, and the piston is in the hydraulic cavity. The hydraulic transmission rod is connected to the piston by a nut of a hydraulic cavity seat cover and a thread at one end of the hydraulic transmission rod. The piston divides the hydraulic cavity into an upper cavity and a lower cavity. There is an O ring on the piston. The O ring is compressed and sealed with the inner wall of the hydraulic cavity, so that the upper and lower cavities of the hydraulic cavity are completely separated. A through hole is opened on the hydraulic cavity cover, and the hydraulic pipe a is connected with the upper cavity of the hydraulic cavity by the through hole. The hydraulic cavity seat is provided with a through hole, and the hydraulic pipe b is connected with the lower cavity of the hydraulic cavity by the through hole.
 
Install O rings on the upper valve plate, lower valve plate and hydraulic cavity seat cover, and install sealing gaskets on the matching surface between the hydraulic cavity cover and hydraulic cavity, the hydraulic cavity and hydraulic cavity seat, the hydraulic cavity seat and valve body. Install a filter and a regulating valve micro check valve on the hydraulic pipe a, and install a filter and a regulating valve on the hydraulic pipe b. The hydraulic cavity seat is provided with a through hole, and a hydraulic pipe c is connected through the through hole. A micro check valve is installed on the hydraulic pipe c and a bleed plug screw is installed above the hydraulic cavity cover. A bleed plug screw is installed on the hydraulic cavity cover, which can be used to release the gas in the upper cavity of the hydraulic cavity. The hydraulic cavity is composed of the hydraulic cavity seat, hydraulic cavity cover, hydraulic cavity, diaphragm upper plate, diaphragm and diaphragm gland. The diaphragm upper plate, diaphragm and diaphragm gland are in the hydraulic cavity; and the diaphragm upper plate is on the diaphragm; the diaphragm gland is under the diaphragm. The hydraulic transmission rod is connected to the diaphragm gland, the diaphragm and the diaphragm upper plate by a nut and a thread at one end of the hydraulic transmission rod and passes through the hydraulic cavity seat cover. The hydraulic cavity cover, the diaphragm and the hydraulic cavity are connected by screws and nuts. The diaphragm divides the hydraulic cavity into upper and lower cavities and completely isolates the upper and lower cavities.