The reciprocating motion of the plunger in the diaphragm metering pump in the hydraulic chamber through the diaphragm is passed to the liquid between the plunger and the diaphragm. In order to maintain the normal movement of the diaphragm to hydraulic cavity closed space liquid (usually with hydraulic oil) the volume remains constant. So as to ensure the volume formed by the movement of the diaphragm is always equal to the stroke volume of the plunger in order to keep the pump flow stability; but in the actual operation process of pump in the plunger seal will inevitably cause leakage at the same time, there may be a gas into the hydraulic chamber.
In addition, when the volume of oil filling or discharge excessive line pressure rises accident it may change the hydraulic fluid, thus affecting the flow stability, reduces the measurement accuracy of the pump. In order to solve the problem of how to stabilize the measurement accuracy of metering pump metering pump flow, how stable, using the three valve device actually refers to the so-called the combination includes three functions of compensation, discharge and safety protection device or device supporting the hydraulic chamber, according to its principle is divided into different automatic compensation and forced compensation two three valve device.
The automatic compensation three valve device is widely used in diaphragm metering pump, especially when the suction height is required, it can only use this compensation device. The three valve device is made up of three separate safety valves, relief valves and replenishing valves.