5 preguntas sobre la válvula de retención que debe saber

Tiempo de lectura estimado: 12 minuto

Check Valve

Question 1: The Pressure Relief Method of The Hydraulic Control Check Valve

1. When there is backpressure at the outlet of the hydraulic control check valve, the external drain type should be selected, and the internal drain type can be selected in other cases. For the hydraulic system of the lifting platform, due to poor design considerations, the external leakage hidráulico control check valve should be used, but the internal leakage type is selected, resulting in strong vibration and noise in the system.

2. The internal drain type can be used in the oil circuit where the oil flow is reversed and there is no backpressure. Otherwise, the external drain type is used to reduce the pressure of the control oil. The external drain type must return pressure without pressure, otherwise, it will offset part of the control pressure.

3. The internal leakage and external leakage hydraulic control check valves are respectively used in the occasions where the backpressure of the oil flow in the reverse outlet cavity is low or high to reduce the control pressure. As shown in Figure 1-1(a), the hydraulically controlled check valve is installed at the back of the check valve, and the oil flow in the reverse oil cavity is directly connected to the tank. The backpressure is very small, and the internal drain structure can be adopted. The hydraulic control check valve in Figure 1-1(b) is installed in the front of the one-way throttle valve, and the reverse oil outlet cavity is returned to the tank through the one-way throttle valve. The backpressure is very high, and it is advisable to adopt an external leakage structure.

4. In Figure 1-1, if the B cavity is connected to high-pressure oil, and the A cavity cannot establish a large back pressure (such as directly connected to the oil tank), the hydraulic control check valve with the unloading spool is used, because the unloading After the loading spool is opened, the flow area at the unloading valve is very small, the pressure of the high-pressure oil source in the B cavity still cannot be relieved, and the high pressure still acts on the upper cavity of the main spool, pressing the main spool on the valve seat, In this way, the control piston still needs a large control oil pressure to open the main spool.

5. When the hydraulic control check valve draws the spool away from the control piston, allowing the reverse oil flow to pass until the control oil is removed, the control piston returns, and the spool is renewed and closed, the oil in the piston cavity is controlled. It must be discharged from the control port. If the control oil circuit returns to the oil back.

6. If the pressure is high and the oil discharge is not smooth, the control piston cannot return quickly, and the closing speed of the valve core will also be affected. This is not enough for the system that quickly cuts off the reverse oil flow. For this reason, a hydraulically controlled check valve with an external leakage structure can be used, as shown in Figure 1-2, to introduce pressure oil into the external leakage port to force the control piston to return quickly.

Question 2: The Opening Pressure of The One-way Valve

1. The opening pressure of the one-way valve depends on the stiffness of its built-in spring. Generally speaking, in order to reduce the flow resistance loss, a check valve with a low opening pressure should be used as much as possible; on the other hand, for the control pressure necessary to maintain the electro-hydraulic directional valve, the check valve is used as a back pressure valve. In order to ensure sufficient back pressure, a check valve with a high opening pressure should be selected.

2. When selecting the hydraulic control check valve, the control pressure required by the hydraulic control check valve should be considered. In addition, the influence of the system pressure change on the control oil circuit pressure change should also be considered to avoid accidental opening.

3. Pay special attention to whether the opening pressure of the hydraulically controlled check valve has a “negative pressure effect” in the locking circuit of the two-way hydraulic lock. This “negative pressure effect” will cause the jumping motion phenomenon and vibration of the actuator.

4. The hydraulic control check valve circuit design should ensure that the reverse oil flow has sufficient control pressure to ensure the opening of the spool. As shown in Figure 1-3, if there is no throttle valve, when the three-position four-way reversing valve switches to the right passage, the hydraulic pump supplies oil to the upper cavity of the hydraulic cylinder, and at the same time opens the hydraulic control check valve, the cylinder piston The rapid drop of the load weight causes the pressure to drop due to insufficient oil supply from the hydraulic pump to the upper cavity of the hydraulic cylinder, that is, the control pressure of the hydraulic control check valve is low, so that the hydraulic control check valve may be closed and the piston stops falling. Subsequently, under the condition that the flow continues to be replenished, the pressure rises again, and the control oil opens the hydraulic control check valve again. In this way, due to the opening and closing of the hydraulic one-way valve, the lowering of the piston of the hydraulic cylinder is intermittent, resulting in low-frequency oscillation.

5. Precautions for the use of the filling valve. The function of the filling valve is to replenish oil from the oil tank (or filling oil tank) to the hydraulic cylinder or system to avoid the phenomenon of suction. The filling valve with control can also play a role in rapid oil discharge.

6. In order to avoid the phenomenon of suction, when selecting the filling valve, its diameter cannot be too small. When the liquid-filled tank is not under pressure, the flow rate of the liquid-filled valve should be limited to 1.5-2.5m/s. When the liquid-filled oil tank is under pressure, the flow rate can be appropriately higher.

7. In order to prevent shock and vibration in the hydraulic system during the return stroke, when a controllable filling valve is used, the appropriate control pressure or the appropriate time for the control oil should be selected. Generally, when the filling valve is forcibly opened, the pressure in the hydraulic cylinder should be lower than 2 to 4 MPa.

Question 3: Check Valve Installation

1. When installing, check the direction of the valve inlet and outlet, otherwise, it will affect the normal operation of the hydraulic system, especially the one-way valve used at the pump outlet. If installed in the reverse direction, the pump may be damaged or the motor may be burned out.
2. The in-line valve avoids piping when the inlet and outlet ports are not identified, as shown in Figure 1-3. Pipe-type valves have as few as 2 ports and as many as 5-6 ports. In the case of unidentified port names, sloppy piping will often cause serious consequences, such as malfunction of the lighter ones and accidents for the more severe ones.

3. When piping between pipe-type hydraulic components, avoid incorrect thread forms and size parameters, as shown in Figure 1-5. In hydraulic piping, with the increase of imported components, there are more thread standards encountered, such as ordinary threaded cylindrical pipe thread, 60°tapered thread, metric tapered thread, American thread, inch thread, etc., and the pitch and other dimensional parameters are also different. If you do not pay attention when piping, it is easy to cause random buckling and loosening, and the consequences are more serious.

Flow Control Valve

The flow valve controls the flow by changing the opening area of the orifice, thereby controlling the movement speed of the actuator.

Flow valves include throttle valve, one-way throttle valve, stroke throttle valve, speed control valve, stroke speed control valve, one-way speed control valve, overflow throttle valve, delay valve, diverter valve, collector valve, etc. many types. Among them, the throttle valve is the most basic flow valve, and most of the others are developed to overcome a certain aspect of the throttle valve. When the throttle opening of the throttle valve has a constant rise, when the load changes, the oil pressure difference between the throttle valve inlet and outlet also changes, and the flow rate through the throttle valve also changes. Therefore, the movement speed stability of the actuator is required to be higher. On occasions, a speed control valve is needed. The speed control valve uses the principle of load pressure compensation to compensate for the change in the pressure difference between the inlet and outlet caused by the load change so that the pressure difference basically tends to be a constant. The pressure compensation component is usually a fixed differential pressure reducing valve or a fixed differential overflow valve, so the speed control valve is called a fixed differential pressure reducing speed valve or a fixed differential overflow speed regulating valve.

Question 4: The Structure of The Throttle Valve Port

1. Sinking groove-shaped orifice. Mainly used in slide valve structure, its structure is simple and has ideal linear characteristics. The valve port should be processed by wire cutting.

2. Due to the radial gap, the sealing performance is not good when fully closed, and due to the small hydraulic radius, it is easy to cause blockage when the flow is small.

3. Cone valve-shaped orifice. Good air tightness, simple manufacture, and good sensitivity for small flow.

4. Its hydraulic radius is small, and it is easy to cause blockage when the opening is small.

Rectangular orifice. The partial opening form equivalent to the undercut groove shape has good linearity and better sealing performance than the undercut groove shape.

T-shaped orifice. Through the combination of rectangular orifices with different widths, different valve port gains can be achieved for large and small flow rates. At a small opening, the valve port has a larger hydraulic radius, so the stability of the small flow is good.

5. The workmanship is not satisfactory enough. Axial triangular groove-shaped orifice. When the spool moves axially, it changes the size of the flow area. This kind of orifice has a simple structure, good manufacturability, medium hydraulic diameter, small and stable flow rate, and large adjustment range. Since several triangular grooves are evenly distributed in the circumferential direction, the radial forces are balanced with each other, so when adjusting The required force is also small. This is a currently widely used orifice structure. The throttling channel has a certain length, and the change of oil temperature has a certain influence on the flow.

6. Round orifice. The circular orifice is opened on the shaft sleeve, which is easy to process. When the valve core moves in the axial direction, the opening of the valve is changed. The small flow rate is stable and the resistance is good.

The orifice is easy to change during high-pressure work, and the characteristics of the initial section are not good, but the linearity is acceptable when the opening is large. In order to improve the adjustment performance of the initial section, it is sometimes designed as a T-shaped compound valve port, and the narrow square port is used for adjustment when the opening is small.

Question 5: Throttle Valve Flow Adjustment Problem

The main problems in the use of the throttle valve are flow regulation failure, unstable flow, and increased internal leakage.

Flow Regulation Failure

The main reason for the failure of flow regulation is that the valve core is stuck in the radial direction. At this time, it should be cleaned to remove the dirt.

Unstable Flow

1. Throttle valve and one-way throttle valve When the orifice is adjusted and locked, the flow is sometimes unstable, especially when the flow is small. This is mainly caused by loosening of the locking device, partial blockage of the orifice, increased oil temperature, and load changes. At this time, measures should be taken to tighten the locking device, filter the oil, strengthen the oil temperature control, and make the load change as small or unchanged as possible.

2. The flow adjustment range should meet the maximum and minimum flow requirements of the system, and the flow adjustment range of the flow control valve should be greater than the flow range required by the system. Special attention should be paid to the minimum stable flow of the selected valve when selecting the throttle valve and speed control valve to meet the requirements of the minimum stable speed of the actuator.

3. The maximum flow can meet all flow ranges in a working cycle, and the flow through the flow control valve should be less than the rated flow of the valve. Like the pressure control valve, the main specifications of the low and medium pressure flow control valve models of the Guangyan Institute are the rated flow, while the medium and high-pressure series flow control valves are given the diameter, and different diameters are allowed. For the flow rate, please refer to the relevant product samples. In fact, if the pressure loss requirements are not strict, the flow through the flow control valve can be slightly greater than the rated flow in the sample.

4. Flow control accuracy, whether the selected valve can meet the flow accuracy to be controlled, even if it can meet the performance indicators provided in the full range of the system, but it is also noted that the control accuracy of the flow control valve is very poor when the flow is small.

5. The change of system pressure must be within the rated pressure of the valve, and the possible pressure range of the system should be considered to select the flow control valve.

Increase in Internal Leakage

It is mainly caused by excessive wear of the sealing surface, and the valve core should be replaced.

In addition to the problem of the throttle valve, the stroke throttle valve, and the one-way stroke throttle valve are also common in that the spool reaction force of the stroke throttle valve is too large, which is mainly due to the radial jam of the spool and the plugging of the drain port. Therefore, the drain ports of the stroke throttle valve and the one-way stroke throttle valve must be connected back to the fuel tank separately.