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

Operating principles and functions
The bypass hydraulic pressure relief valve with the above-mentioned structure is used in the  fluid pipeline system. It is installed on the bypass pressure relief pipeline on the outlet side of the pump and check valve to obtain the following functions and use effects:
When the pump is in the starting state, the pressure in the lower cavity of the hydraulic cavity connected with the hydraulic pipe is higher than the pressure in the upper cavity of the hydraulic cavity connected to the hydraulic pipe. Under the action of the pressure difference, the piston moves upward and drives the lower valve plate to move upward through the hydraulic transmission rod. For the time being, liquid enters the lower water inlet and outlet, and outflows from the upper water inlet and outlet through the valve body. When the piston moves upwards and drives the lower valve plate upward through the hydraulic transmission rod until the lower valve plate touches the sealing seat in the valve body, the O ring on the lower valve plate is compressed to have a sealing effect. At this time, There is no liquid flows in the upper water inlet and outlet and the lower water inlet and outlet. The pump and piping system are in normal working condition. The hydraulic pipe connected to the hydraulic cavity cover can speed up the liquid flow in the hydraulic cavity, so that this process can be carried out quickly.

When there is a sudden power failure, the check valve is automatically closed. At this time, the pressure in the upper cavity of the hydraulic cavity is greater than the pressure in the lower cavity of the hydraulic cavity, and the piston moves downward under the action of the pressure difference and drives the lower valve plate to move downward. The sealing ring loses its sealing function, and liquid flows into the upper water inlet and outlet and is discharged from the lower water inlet and outlet through the valve body. Meanwhile, the upper valve plate simultaneously moves  downward under the drive of the hydraulic drive rod until it touches the sealing seat in the valve body. The O ring is compressed to have a sealing effect. At this time, the liquid flow in the upper water inlet and outlet is stopped, and the hydraulic effect is eliminated. The time from when the lower valve plate and the upper valve plate moving downwards at the same time, and the O ring losing its sealing effect to the O ring obtaining the sealing effect is the pressure relief time. The sealing gasket is used to ensure that the liquid in the hydraulic cavity does not leak, and that the liquid in the valve body does not leak. The O ring on the hydraulic cavity seat cover is used to isolate the liquid in the hydraulic cavity and the valve body. In order to adjust the pressure relief time, a regulating valve is installed on the hydraulic pipe. The pressure relief time can be adjusted by controlling the inflow and outflow speed of the liquid in the upper and lower cavities of the hydraulic cavity through the regulating valve. A filter is installed on the hydraulic pipe to filter impurities in the liquid to ensure cleanliness in the hydraulic cavity. A micro check valve is installed on the hydraulic pipe, which can be used to throttle the water flow in the upper cavity of the hydraulic cavity. The valve is flexible and the closing time is adjustable. The fastest time is 15 seconds and the slowest time is 348 seconds. A micro check valve is good for eliminating the water hammer for complex pipeline systems. And the problem of delayed closing of the two-stage check valve and reversing of the pump caused by reverse flow is completely solved.
 
Applications
Three types of pressure relief valves with diameters of 80mm, 150mm and 300mm and a nominal pressure of 1.6MPa have been designed and manufactured, which are used in tap water, metallurgical cooling circulating water and petrochemical cooling circulating water pipeline systems. After nearly one year of operation, the pressure relief valve has been proved to be flexible and have a adjustable closing time. For complex pipe systems, the pressure relief valve has a good effect on eliminating water hammer, and completely solves the problems of delayed closing of the two-stage check valve and reversing of the pump caused by reverse flow. It shows that the valve structure and performance design are feasible, and the parameter selection is accurate. The bypass hydraulic control pressure relief valve is installed on the bypass pipeline on the outlet side of the check valve in the main pipeline, and is used in conjunction with the check valve. Use the pressure liquid in the pipeline to obtain drive and automatic control, which completely solves the traditional problem of reversing of the pump rotor part caused by two-stage close valves to eliminate the water hammer pressure. The pressure relief valve is suitable for eliminating water hammer pressure in various complex pipelines because of its adjustable closing time, which is a new type of pressure relief valve with popularization and application value.