Created on:2022-03-14 13:05

Brief introduction and key points of speed regulating valve

Brief introduction and key points of speed regulating valve

1. Working principle of speed regulating valve

The speed regulating valve is a combined valve composed of constant differential pressure reducing valve 1 and throttle valve 2 in series, as shown in Figure 88. The throttle valve is used to regulate the passing flow, and the constant differential pressure reducing valve automatically compensates for the influence of load change, so that the pressure difference before and after the throttle valve is a constant value, which eliminates the influence of throttle valve load change on flow. The differential pressure reducing valve is connected in series with the throttle valve, and the left and right chambers of the differential pressure reducing valve are communicated with the front and rear ends of the throttle valve respectively. Set the inlet pressure of the pressure reducing valve as P1 and the outlet pressure as P2. After passing through the throttle valve, it will be reduced to P3. The size of P3 is determined by the load F of the hydraulic cylinder. When the load f changes, P3 and the differential pressure P1-P3 at both ends of the speed regulating valve change accordingly, but the differential pressure P2 - P3 at both ends of the throttle valve remains unchanged. For example, when f increases, P3 increases, the hydraulic pressure in the spring chamber of the pressure reducing valve core increases, the valve core moves to the left, the opening x increases, and the pressure reducing effect decreases, which increases P. as a result, the differential pressure P2 - P3 remains unchanged. Vice versa, so that the flow through the speed regulating valve remains constant.

The travel limiter is used to limit the opening of the pressure reducing port and prevent a large amount of oil from passing through the pressure reducing port when the system is restarted, causing the hydraulic cylinder to rush forward (known as the phenomenon of starting forward rush), reducing the processing quality and even damaging the parts. Among the newly developed products is a pre control (or external control) speed regulating valve, which is filled with control oil in the left chamber of the pressure reducing valve to prevent the pressure reducing port from opening too large when it is not working. From the structure of the speed regulating valve, the pressure reducing valve and throttle valve are generally arranged vertically. The throttle valve part has a flow regulating handwheel, and the pressure reducing valve part can be attached with a travel limiter.

2. Structure of typical speed regulating valve

(1) Temperature compensation speed regulating valve. The speed regulating valve eliminates the influence of load change on flow, but the influence of temperature change still exists. Therefore, in order to solve the influence of temperature change on flow, temperature compensated speed regulating valve should be used in the system with high requirements for speed stability. The structure of the temperature compensation speed regulating valve is basically similar to that of the ordinary speed regulating valve, except that the former is connected with a temperature compensation rod on the valve core of the throttle valve, as shown in Figure 89. When the temperature rises, the flow will increase. However, since the compensation rod is made of PVC plastic with large temperature expansion coefficient, it will also increase with the increase of temperature, so that the valve port will be reduced, otherwise it will be opened larger, so the flow can be kept basically unchanged (the flow change will not exceed 10% in the range of 20 ~ 60 ℃).

88.89

(2) Structure of ordinary speed regulating valve. Figure 90 shows the structure of ordinary speed regulating valve (plate connection). The pressure reducing valve and throttle valve in the speed regulating valve adopt valve core and valve sleeve structure. The flow of the speed regulating valve is regulated by the regulating part of the throttle valve, and the pressure difference before and after the throttle valve is compensated by the pressure reducing valve. China's QF speed regulating valve (nominal pressure is 32Mpa) is such a structure.

90

Figure 91 shows the structure of a two-way speed regulating valve (plate connection). The valve is mainly composed of adjusting knob 1, valve body 2, throttle valve core 9 installed in valve sleeve 3 and pressure compensator 6. The pressure oil flowing from port a to port B is controlled at orifice 8. The throttle opening can be adjusted by knob 1. Pressure compensator 6 installed behind the throttle port is used to compensate for the change of outlet pressure of the valve. Spring 7 compresses pressure compensator 6 and throttle spool 9 respectively. When no oil flows through the valve, the spring compresses the pressure compensator to make it open. Once the oil passes through the valve, the pressure oil from a generates a force on the pressure compensator through the throttle hole 5, and the pressure compensator 6 acts until the forces on it balance with each other and reach a set position. If the pressure of port a increases, the pressure compensator moves to the closed position until the force on it is balanced again. Due to the constant "follow-up action" of the pressure compensator, the speed regulating valve can obtain a constant flow. The 2FRM speed regulating valve of Bosch series is of this structure.

The technical parameters of speed regulating valve are shown in the table below.

Technical parameters of medium and high voltage speed regulation products

model

通径(mm)

大工作压力(MPa)

额定流量

(L/min)

DF

10 20 32

14

42240

Q

2 10 20 25 32

31.5

25200

 

3. Application of speed regulating valve

The advantage of speed regulating valve is stable flow, while the disadvantage is large pressure loss. It is often used in the quantitative pump oil supply throttle speed regulation hydraulic system with large load change and high requirements for speed control accuracy, and sometimes it is also used in the volume throttle speed regulation hydraulic system with oil supply. In the oil supply throttle speed regulation hydraulic system, it can cooperate with the overflow valve to form a series throttle (inlet throttle, outlet throttle, inlet and outlet throttle) and parallel (bypass) throttle speed regulation circuit or system. The circuit schematic diagram can be obtained as long as the throttle valve in the throttle speed regulation circuit is replaced by the speed regulation valve.

4. Precautions for use

(1) The speed regulating valve (without one-way valve) can not be used in the reverse direction, otherwise the differential pressure reducing valve will not function as a pressure compensator.

(2) In order to ensure the normal operation of the speed regulating valve, it should be noted that the working differential pressure of the speed regulating valve should be greater than the minimum differential pressure △ Pmin of the valve. The minimum differential pressure △ Pmin of the high-pressure speed regulating valve is generally 1MPa, while the minimum differential pressure △ Pmin of the medium and low-pressure speed regulating valve is generally 0.5MPa.

(3) After the flow is adjusted, the position shall be locked to avoid changing the adjusted flow.

(4) when working near the minimum steady flow rate, it is recommended to set up a pipeline filter at the inlet side of the timing valve to avoid obstruction of the valve and affect the stability of the flow.

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