Introduction of throttle valve

Introduction of throttle valve

Throttle valve is the flow control valve with the simplest structure but the most widely used. It often cooperates with overflow valve to form various throttle speed regulation circuits or systems for quantitative pump oil supply. According to different operation modes, the throttle valve can be divided into manual regulating ordinary throttle valve, stroke stop or cam and other mechanical moving parts operating stroke throttle valve, etc; The throttle valve can also be combined with other composite valves such as one-way throttle valve and one-way travel throttle valve.

Figure 80 shows the structure and graphical symbols of the throttle valve. The hydraulic oil flows in from the oil inlet P1 and flows out through hole a, the axial triangular groove at the left end of valve element 1, hole B and oil outlet P2. The valve core 1 is always close to the end of the push rod 2 under the action of spring force. The cone of the valve core l where the orifice is located is usually provided with 2 or 4 triangular grooves. Adjust the hand wheel 3 to move the push rod along the axial direction, so as to change the flow area between the oil inlet and outlet, and then adjust the flow.

The throttle valve has the advantages of simple structure, small volume, convenient use and low cost. The regulating range of the throttle valve port is large, the flow has a linear relationship with the pressure difference before and after the valve port, and has a small stable flow, but the flow channel has a certain length, and the flow is easy to be affected by temperature and load. Therefore, it is only applicable to the hydraulic system with little change in temperature and load or low requirements for speed stability.

The experiment shows that when the throttle valve works in a small opening area, although the pressure difference △ p between the front and back of the valve and the oil viscosity u remain unchanged, the flow QV flowing through the valve will fluctuate periodically. With the gradual reduction of the opening, the change of flow pulsation will intensify, and even intermittent cut-off will occur, resulting in the complete loss of working capacity of the throttle valve. The above phenomenon is called the blockage of throttle valve. The main causes of blockage are: ① the dirt in the oil blocks the flow port, that is, the dirt is blocked and washed away, resulting in flow pulsation; ② The adsorption of polarized molecules in oil and metal surface leads to the formation of adsorption layer on the surface of throttling gap, which changes the size and shape of throttling port.

The blockage of the throttle valve makes the flow of the throttle valve unstable when working under a small flow, resulting in the crawling of the actuator. Therefore, there should be a minimum flow limit for the throttle valve to work normally. This limit is called the minimum stable flow of the throttle valve, which limits the minimum stable speed of the actuator when used in the system.

The technical parameters of medium and high pressure throttle valves are shown in the table below.

Technical parameters of medium and high pressure throttle valve products