Introduction to pressure reducing valve

Introduction to pressure reducing valve

The pressure reducing valve is a pressure control valve that uses the pressure loss caused by the liquid flow flowing through the gap liquid resistance to make the outlet pressure lower than the inlet pressure. According to different regulation requirements, there are: a constant value pressure reducing valve used to ensure that the outlet pressure is a constant value; Constant differential pressure reducing valve used to ensure the constant pressure difference between inlet and outlet; A constant ratio pressure reducing valve used to ensure that the inlet and outlet pressures are proportional. Among them, the fixed value pressure reducing valve is the most widely used. Here, only the fixed value pressure reducing valve is introduced.

The pressure reducing valve is mainly used to reduce the oil pressure of a branch of the system, so that the same system can have two or more branches with different pressures. For example, when the clamping or lubrication branch in the system needs a stable low pressure, just connect a pressure reducing valve in series on the branch.

Fixed value pressure reducing valve is divided into direct acting type and pilot type, of which pilot type pressure reducing valve is widely used. Figure 61 shows the structural principle and graphical symbols of the pilot pressure reducing valve. The main components of the pressure reducing valve are the same as the overflow valve, and the shape is also very similar. The differences are: the structure of the main valve core is different. The main valve core of the overflow valve has two shoulders, while the main valve core of the pressure reducing valve has three shoulders; Under normal conditions, the oil inlet and outlet ports are normally closed and the pressure reducing valve is normally open; The oil overflow valve opened at the control valve port is from the inlet oil pressure to ensure the constant inlet pressure, and the pressure reducing valve is from the outlet oil pressure to ensure the constant outlet pressure; The oil in the spring chamber of the overflow valve is led to the oil return port (internal leakage type) in the valve body, and the oil at the outlet of the pressure reducing valve passes through the actuator. Therefore, the leakage oil is led back to the oil tank (external leakage type) separately.

As shown in Figure 61 (a), when the inlet hydraulic oil flows to the outlet through the main valve port (pressure reducing gap), the pressure is r. At the same time, the outlet hydraulic oil enters the lower chamber of the main valve core 7 through the channels on the valve body 6 and the end cover 8, and then passes through the damping hole on the main valve core 7 to the upper chamber of the main valve core and the front chamber of the pilot valve. When the load is small and the outlet pressure R is lower than the pressure regulating pressure, the pilot valve is closed, there is no liquid flow through the damping hole of the main valve core, the pressure of the upper and lower chambers of the main valve core is equal, the main valve core is at the lowest end under the action of the spring, and the valve port is fully open, which does not play the role of pressure reduction. If the outlet pressure P exceeds the set pressure of the pressure regulating spring with the increase of load, the pilot valve port will be opened, and the hydraulic oil at the outlet of the main valve will go to the upper chamber and pilot valve port of the main valve core through the damping hole of the main valve core, and then return to the oil tank through the oil drain. Due to the damping effect of the damping hole, there is a pressure difference (P2-P3) between the upper and lower chambers of the main valve. Under the action of the pressure difference, the main valve core moves upward against the resistance of the upper spring and plays the role of pressure reduction due to the reduction of the valve port of the main valve. When the outlet pressure P2 drops to the set value, the pilot valve core and the main valve core are in force balance at the same time, and the outlet pressure remains stable. The outlet pressure of the valve can be changed by adjusting the preload shrinkage of the pressure regulating spring, that is, adjusting the spring force.

Compared with overflow valve and sequence valve, the main characteristics of pressure reducing valve are: the oil that controls the opening and closing of valve port comes from the oil outlet, keeps the outlet pressure constant, the valve port is normally open, and the oil drain is connected to the oil tank separately.

Pressure reducing valve is widely used in clamping oil circuit, control oil circuit and lubricating oil circuit.

The technical parameters of pressure reducing valve are shown in the table below.