Created on:2022-02-17 08:51

Troubleshooting of cartridge valve

Troubleshooting of cartridge valve

(1) When designing cartridge valve system, attention should be paid to the change of load pressure and the impact of impact pressure on, and corresponding measures should be taken, such as increasing shuttle valve and one-way valve.

(2) In order to avoid the wrong action of the valve core caused by pressure impact, try to avoid the situation that several cartridge valves use the same oil return or oil drain circuit.

(3) The action control of cartridge valve is not as accurate and reliable as others.

The two-way cartridge logic valve is composed of four parts: cartridge, pilot control valve, control cover plate and block. The causes of faults and troubleshooting methods also focus on these four places.

The valves set in the pilot control valve part and the control cover plate are exactly the same as the general conventional small flow solenoid directional valve, pressure regulating valve and throttle valve. Therefore, the faults caused by the pilot valve can be analyzed and eliminated with reference to the maintenance methods of the pilot valve. There are many forms of plug-in logic units, but there are no more than three types: slide valve type, cone valve type and pressure reducing valve core type. In principle, both have the functions of opening or closing the valve port. Structurally speaking, it is shaped like a check valve, so you can also refer to the maintenance method of the check valve. In addition to the above, the common faults of two-way cartridge valve are as follows.

1. The "on" or "off" logic performance is lost, and the valve does not act

When this fault occurs, the cartridge valve in the opposite direction does not reverse; For the pressure valve, the performance is pressure control failure; For the flow valve, it shows the failure of regulating the flow.

The main reason for this kind of failure is that the valve core is stuck, either in the open (fully open or semi open) position or in the closed (fully closed or semi closed) position. In this way, it cannot be closed when it needs to be closed and cannot be opened when it needs to be opened, thus losing logic performance.

When the two-way plug-in (logic unit) works normally, as shown in Figure 133, it is set to "+" when there is control pressure oil input in cavity x, and to "" when there is no control pressure oil input but through the oil pool. Under normal conditions, the output (a-b) is "-" or "+" respectively. There is no oil or oil output in the main oil circuit, that is, a to B are "blocked" or "connected". When this fault occurs, no matter whether the input is "+" or "-", the output is always "+" or "-", and there is no logical relationship. The specific causes and troubleshooting are as follows.

(1)       Cause analysis.

1) The dirt in the oil wedges into the fit gap between the valve core and the valve sleeve and locks the main valve core in the "on" or "off" position.

2) Due to machining error, the geometric accuracy of the outer circle of the valve core and the inner hole of the valve sleeve is out of tolerance, resulting in hydraulic clamping. This situation is often ignored by maintenance personnel, because the hydraulic clamping phenomenon only occurs in the working process. If there is taper and out of roundness between the outer circle of the valve core and the inner hole of the valve sleeve, the valve core will be stuck due to the radial unbalanced force caused by the pressure oil entering the annular gap. After pressure relief or disassembly for inspection, the valve core is often flexible without jamming.

3) The matching clearance between the valve core and the valve sleeve is too large, the internal leakage is too large, and the leaked oil enters the control chamber, resulting in the disordered input state.

4) The input of control chamber x is faulty. The input of control chamber x comes from the pilot control valve and the control cover plate. If the pilot control valve, such as the directional valve does not change direction and the pilot pressure regulating valve does not adjust pressure, it is bound to make the control pressure oil in the control chamber (chamber x) of the upper chamber of the main valve out of control, and the logic relationship of the input is destroyed, then the output is bound to be disordered.

5) There are burrs on the edges of the valve core or valve sleeve, or the outer cylindrical surface of the valve core is pulled during assembly and use, and the valve core is stuck.

6) The valve sleeve is embedded in the valve body (integrated block), and the inner hole is deformed due to the tight fit of the outer diameter; Or the valve core is stuck due to the small matching gap between the valve core and the valve sleeve.

(2) Troubleshooting.

1) The insert (logic unit) shall be cleaned and the oil shall be replaced if necessary.

2) Check the accuracy of relevant parts and repair or reconfigure the valve core if necessary.

3) Refit or replace the valve core and valve sleeve to make the matching clearance between the valve core and valve sleeve appropriate.

4) Check and eliminate the faults of pilot valve (such as pilot solenoid valve) or pilot control elements (such as shuttle valve, one-way valve, pressure regulating valve, etc.) installed in the control cover plate to make the input signal normal.

5) Check the position of the burr at the edge of the valve core or valve sleeve, and take measures to remove the burr.

6) Carefully check and deal with it as appropriate.

2. It cannot be closed reliably and opened in reverse

As shown in Figure 134 (a), when 1dt and 2DT are powered off, the control chambers X1 and X2 of the two logic valves are connected with the control oil. At this time, both logic valves should be closed. However, when cavity P is unloaded or suddenly drops to a lower pressure, and there is still a relatively high pressure in cavity a, valve 1 may be opened, cavities A and P are connected reversely and cannot be closed reliably, while the outlet of valve 2 is connected to the oil tank, so there will be no reverse opening problem.

The solution is to adopt the method shown in Figure 134 (b): install a shuttle valve at the connection of two control oil ports, or install two check valves reversely, so that the control oil of the valve is introduced not only from chamber P, but also from chamber a. When PP > PA, the pressure control oil from cavity P closes the logic valve 1, and the shuttle valve steel ball (or one-way valve L) closes the path between the control oil cavity and cavity a; When p chamber is unloaded or suddenly depressurized, and P ^ > PP, the control oil from a chamber pushes the shuttle valve steel ball (or I.) to close the control oil from P chamber. At the same time, it is connected with the control chamber of logic valve through solenoid valve, so that the logic valve is still closed. In this way, no matter what happens to the pressure of chamber P or chamber a, it can ensure the reliable closing of the logic valve.

When the shuttle valve is not tightly sealed due to dirt stuck or the steel ball (or valve core) of the shuttle valve is strained, the reverse opening fault will also occur.

134

3. The logic valve cannot be closed to maintain pressure, which is not good

Generally, the pressure maintaining circuit can be used for pressure maintaining. The hydraulic control one-way valve with slide valve reversing valve as the pilot valve shown in Figure 135, or the hydraulic control one-way valve with slide valve hydraulic reversing valve as the pilot valve, can only be used in the system with no pressure maintaining requirements and low pressure maintaining requirements. If it is used in the pressure maintaining system, it will m present the fault of poor pressure maintaining. Because in the hydraulic control check valve shown in Figure 135, although the main valve is closed, some oil still leaks to the oil tank or another oil chamber. As shown in Figure 135 (a), when 1dt is powered off and PA > Pb, although the conical surface of the main valve core can be reliably sealed between cavities A and B, and there is no leakage under normal conditions, part of the pressure oil of the control oil from cavity a will leak to the oil tank through the annular gap of the pilot solenoid valve (between the valve core and the valve body), Another part of the pressure oil will be discharged to chamber B through the annular gap between the cylindrical guide surfaces of the main valve, so that the pressure of chamber a gradually decreases and can not maintain the pressure well. As shown in Figure 135 (b), when 2DT is powered off and Pb > PA, the main oil circuit is cut off. Although there is no leakage between cavities A and B, part of the pressure oil in cavity B also leaks to the oil tank through the annular gap of the pilot solenoid valve (or hydraulic directional valve), so as to gradually reduce the pressure in cavity B. Of course, the situation in Figure 135 (b) is slightly better than that in Figure 135 (a), and the pressure maintaining effect is slightly better. Because there is no pressure oil in chamber B leaking into chamber a through the gap between the cylindrical guide surfaces, but neither of them can strictly and reliably maintain the pressure.

In order to achieve strict pressure holding requirements, the slide valve type pilot solenoid valve shown in Figure 135 can be changed to use the hydraulic control check valve with external control as the pilot valve, as shown in Figure 136. Both cases can ensure that there is no internal leakage between cavities A and B, and there will be no leakage through the pilot slide valve, so it can be used in the hydraulic system with high pressure holding requirements. In addition, the following reasons also affect the pressure holding performance.

(1) The fitting cone of the valve core and the valve sleeve is not tight, resulting in internal leakage between cavities A and B.

(2) The O-ring seal on the outer cylindrical surface of the valve sleeve fails to seal.

(3) Leakage caused by poor internal casting quality on the valve body (such as gas}l crack, shrinkage, etc.) and leakage on the connecting surface of the manifold block. It can be handled on the basis of analyzing the causes according to different situations.

(4) The "on" and "off" speed of logic valve is too fast or too slow (too fast will cause impact, and too slow will cause action delay), and all components of the system cannot act in coordination

The switching speed (time) of the main valve core of the cartridge unit is related to many factors. Such as control mode, working pressure and flow, oil temperature, control pressure and flow, spring force, etc. For the same valve, its opening and closing speed is also different; In addition, improper design, use and adjustment will cause the switching speed to be too fast or too slow, as well as the resulting faults such as impact, vibration, action hysteresis, action disharmony and so on.

For the directional valve element with external control oil supply, the main determinants of the opening speed are the pressure PA and Pb in chamber a and chamber B and the flow resistance of the oil drain pipe (to the oil tank) in chamber x (c). When PA and Pb are very large and the oil discharge in cavity x is very smooth, the difference between the up and down force of the valve core will be very large, so the opening speed will be very fast, resulting in great impact and vibration. The solution is to install a one-way throttle valve on the oil discharge pipeline of chamber x to improve and adjust its flow resistance, so as to reduce the opening speed. On the contrary, when PA and Pb are very small and the oil drainage in chamber x is not smooth, the pressure difference between the upper and lower action of the valve core is very small, so the opening speed is very slow. At this time, it is necessary to appropriately increase the throttle valve installed on the oil drainage pipe of control chamber x to make the oil drainage in chamber X smooth, as shown in Figure 137 (a).

The main factors affecting the closing speed of externally controlled directional valve elements are the difference between control pressure PX and PA or Pb, control flow and spring force. When the difference is very small and the valve is closed mainly by spring force, the closing speed is relatively slow, otherwise it is faster. To improve the closing speed, it is necessary to increase the control pressure, such as using sufficient flow, separate control pump to provide sufficient pressure control oil and other measures; When the difference is large and the closing speed is too fast, a throttle valve can also be added to the oil inlet pipeline of chamber x to reduce PX and control the flow, so as to reduce the closing speed, as shown in Figure 137 (b).

For the internal control pressure valve element, its opening speed and time mainly depend on the working pressure of the system, the size of the damping hole on the valve core and the spring force, as well as the flow resistance of the oil discharge pipeline in the control chamber. When used as a two position two-way valve, as when unloading the electromagnetic relief valve, if they open too fast under high pressure, they will cause impact and vibration. The solution is to add a one-way throttle valve on the oil discharge pipe to adjust the oil discharge resistance to change the opening speed. The closing speed is mainly related to the damping hole and spring force. Since the internal control type is mainly composed of pressure valve elements, the closing speed is required in order to obtain the stability under pressure regulation and other working conditions. The closing time of the existing pressure valve is generally a few tenths of a second. If you need to be faster, you can only increase the damping hole and strengthen the spring force, but this in turn will affect the opening time of the valve and other performance of the pressure valve, which must be taken into account.

In addition, the size of the pilot device also has a great impact on the switching speed of the valve, so the model of the pilot valve must be determined according to the size (diameter) of the cartridge valve it controls and the required switching speed.

Another method is to add a buffer as shown in Figure 138, which can be used to automatically control the speed of opening and closing the valve, so as to effectively eliminate the impact during unloading of the hydraulic pump. When the buffer valve core is in the original position, the overflow valve is in the unloading state. When chamber K is closed by the solenoid valve (the solenoid iron is energized), the overflow valve is closed and the system is boosted. Under the action of oil pressure, the left end of the valve core moves to the right against the elastic force of the spring and presses on the spring seat at the right end. At this time, the conical surface of the valve core only has a small flow area between the cavities X. and X, forming a liquid resistance, which can be adjusted by adjusting the screw. When the solenoid valve is powered off, the pressure in the upper chamber of the overflow valve is slowly relieved to the oil tank through the damping of the buffer. At the same time, the pressure at the left end of the valve core decreases rapidly due to the connection of the oil tank. Under the action of the spring, the valve core moves to the left, the flow area between chamber X1 and chamber x2 also gradually increases, and the pressure in the upper chamber of the overflow valve decreases faster, Thus, the lifting (opening) speed of the overflow valve spool begins to be very slow, and then gradually becomes faster, that is, the pressure relief is slow when the system pressure is at high pressure and fast when the system pressure is at low pressure, so as to effectively eliminate the impact during the unloading of the hydraulic pump and properly control the unloading time.

138.139

5. The closing time of the valve core is too long, which is much longer than the opening time, especially the large diameter( Ф 63~ Ф 100mm) valve

By pilot solenoid valve 2 (normally Ф 63~ Ф In the circuit (see Figure 139) that controls the opening and closing of two-way cartridge valve 1 (100mm diameter), when valve 2 is energized and valve 1 is opened, the opening time is short because the pressure PA and Pb are much greater than PX (≈ 0); When closing, because the pressure of the upper and lower cavities is basically balanced, it is mainly closed by the spring force of the upper cavity (x cavity), and the closing time is longer; Increasing the spring stiffness is beneficial to shorten the closing time, but it will increase the overflow resistance of the valve port, which is generally not desirable; Adjusting throttle valve 3 can change the pressure difference between the upper and lower chambers of the valve core and the inlet and outlet flow into chamber x, so the opening and closing time can be adjusted. When valve 3 is opened, the opening and closing time can be shortened, otherwise it will be prolonged. Setting valve 3 is beneficial to prolong the opening and closing time and reduce the reversing impact during opening, but it is contradictory to speeding up the valve closing speed; The hydraulic force mainly plays the role of closing when the valve core has a small opening (0 ~ 1.0mm), which has nothing to do with the flow direction; The friction of the main valve core always hinders the opening and closing.

In addition, the oil supply mode (external control and internal control) of cavity x is different, and the opening and closing time is also different. The closing time of the valve core is the shortest because the pressure of the external control oil is stable and independent of the load; During internal control, the closing resistance of port a oil supply is greater than that of port B oil supply, so the closing time of port a oil supply is longer.

The solution is to use the fast two-way cartridge valve circuit, as shown in Figure 140. Since valve 1 is a large diameter valve( Ф 63~ Ф 100mm), if the small drift diameter is still used( Ф 6~ Ф 10mm) solenoid valve as a pilot valve will cause great over-current resistance to the pilot solenoid valve due to the particularly large pilot flow, so it can not realize the rapid opening and closing of the main valve. Therefore, this circuit adopts the form of two-stage pilot control. A two-way cartridge valve 2 with a diameter of 16mm is added between the main valve L and the pilot solenoid valve 3 as the second stage pilot control to meet the overflow requirements of large control flow. Its working principle is as follows.

The control mode adopts internal control. When solenoid valve 3 is powered off, the control oil from port a enters the control chamber (upper chamber) of secondary pilot valve 2 through damping hole 4 and the right position of valve 3 to close it; The other way enters the A. port of valve 2 through check valve 5 and damping hole 6, and the other way enters the control chamber of valve 1 through check valve 7. At the same time, the oil from port B also enters the control chamber of valve 1 through check valve 9. Since valve 2 is closed, main valve l also closes quickly. When the solenoid valve is energized, the valve 2 opens quickly first, resulting in a sharp drop in the pressure in the control chamber of valve 1. Therefore, the valve 1 opens quickly under the action of system working pressure oil.

The pilot valve 3 in Figure 6 140 adopts a small-diameter ball valve, which reverses faster than the slide valve solenoid valve and has no leakage. The damping hole 4 is used to adjust the closing speed of the valve 2, and the damping hole 6 is used to generate the opening differential pressure of the valve 1 and can adjust the closing speed of the valve 1; Throttle valve 8 is used to adjust the opening speed of valve 1; Check valves 5 and 9 respectively allow the control oil at ports a and B to enter the control chamber of valve 1 and prevent the reverse flow of liquid flow.

The pilot cartridge valve 2 is equipped with a stroke regulator. Adjusting its opening can change the opening and closing speed of valve 2 and the oil discharge flow of valve l control chamber, so as to adjust the opening and closing stability of valve 1 and slow down the reversing impact of hydraulic system.

The quick opening and closing circuit of the main valve shown in Figure 141 has the same working principle as figure 140. It can also make the reversing (closing and opening) time very short. The control circuit is slightly simpler, but the opening and closing time adjustment function is worse.

140.141

6. The large flow two-way cartridge electromagnetic overflow castration cannot be completely unloaded

This phenomenon means that when the electromagnet of the electromagnetic relief valve is powered off (normally open) or powered on (normally closed), the pressure of the relief valve cannot be reduced to the lowest, but maintains a relatively high pressure value, and the unloading pressure of the system is high. The causes and troubleshooting are as follows.

(1)       The main valve core is stuck in the small opening position due to dirt or burr, and the unloading pressure is high; If it is stuck in the closed position, it will not unload at all. At this time, it can be cleaned to make the main valve core move flexibly.

(2)       The stiffness of the return spring of the main valve core is too large, which is beneficial to the closing, but it brings the problem of not going under the unloading pressure. At this time, the main valve core return spring with low stiffness should be replaced.

(3) According to the information, the size of the main valve core damping hole (or bypass damping hole) should be smaller than the size of the damping hole in the valve cover, while the cartridge valves produced at present are of the same size.

7. When cartridge valve is used as pressure relief valve, the pressure relief speed is too fast, or the pressure relief speed is too slow

This fault actually contains a pair of contradictions: if the pressure is relieved too fast, there will be impact, and if there is no impact, it can only slow down the pressure relief speed. At this time, the circuit shown in Figure 142 can be used. When the pressure relief is just opened (at this time, the pressure is high), the speed is slow, and then the pressure drops a little and then quickly relieves the pressure. This contradiction can be solved.

The three-stage pilot control is adopted in the circuit, which can achieve slow pressure relief (avoid impact) and then rapid large amount of oil discharge and pressure relief. It is a fast two-way cartridge valve group with slow opening speed first and then fast opening speed. Its working principle is as follows.

When solenoid valve 3 is powered off, the control oil from port a of valve 1 passes through damping hole 4 and then enters the control chamber of valve 2 (secondary pilot control valve) through the right position of valve 3 to close valve 2; The other way enters the control chamber of hydraulic directional valve 8. When the control pressure oil is lower than the spring force of the hydraulic valve, the hydraulic valve resets under the action of the spring force, so that the oil in the control chamber of valve 7 is discharged back to the oil tank, and valve 7 is opened; The other way enters the control chamber of valve 1 through damping hole 5 and ports B1 and A1 of valve 7. Since valve 2 is closed at this time, valve l also closes quickly under the action of spring force and large flow mainly controlled by valve 7. At the same time, with the increase of port a pressure of valve 1, valve 8 switches under the hydraulic action of increasing pressure. The control oil originally enters the control chamber of valve 1 through ports B1 and A1 of valve 7, and then enters the control chamber of valve 7 through hydraulic valve 8 to close valve 7.

When solenoid valve 3 is energized, first valve 2 opens quickly, but the opening is very small. Valve 1 controls the oil in the chamber to drain a small amount through the throttle port of valve 6 and the small overflow path of valve 2, so that valve 1 opens slowly under the upper and lower pressure difference. Therefore, port a of valve 1 only slowly relieves pressure from port B at the beginning. When the pressure of port a (i.e. the control pressure of valve 8) is lower than the spring force of hydraulic valve 8, valve 8 resets and works in the lower position. Valve 7 opens because the control chamber is connected to the oil tank. Therefore, a large amount of oil in the control chamber of valve 1 is discharged into port a of valve L through port B and damping hole 5 of valve 7. At this time, valve 1 is like a differential cylinder, and the valve l spool is lifted up quickly and opened to the maximum, so as to realize rapid pressure relief.

From the analysis of working principle, it can be seen that when the pressure at port a is high, the opening time of valve 1 is long, and after the pressure drops, the opening time of valve L is short (open quickly), so as to realize slow unloading under high pressure and avoid the generation of impact pressure, while rapid unloading under low pressure and rapid pressure relief. The total pressure relief time is still short.

8. It cannot be self-locking and the cartridge valve cannot be closed firmly

This fault is similar to fault 2. If there is a slight fault, the cartridge valve will open and cannot be closed, which means it cannot be self-locking.

In order to maintain the self-locking ability of the cone valve, the existence of the control pressure must be maintained, and the phenomenon that the self-locking cannot be caused by the excessive fluctuation of the oil source of the control pressure must be prevented. To solve this problem, we should mainly consider the design carefully and take precautions. Refer to figure 143 for the selection mode of control oil. Figure 143 (a) is selected when PA > Pb; Figure 143 (b) is selected when Pb > Pa; Figure 143 (c) shows that sometimes PA > Pb and sometimes Pb > PA are selected; Figure 143 (d) and (E) show that the valve can be selected when the pressure fluctuation of PA and Pb is too large to ensure reliable valve locking; Figure 143 (E) connect the two oil delivery ports of shuttle valve S1 and S2. One is connected to external control oil source PC and the other is connected to working oil circuit B or a. When the pressure of the control oil source PC is lost, the A or B oil circuit can be supplemented; When PC and the main oil supply circuit PA all lose pressure, the pressure Pb generated by the gravity of the actuator (hydraulic cylinder) or other external forces can also be used to close the cone valve. Shuttle valve S2 itself is a pressure comparator. Figure 143 (a), (b) and (c) are internal control oil supply, figure 143 (d) is external control oil supply, and figure 143 (E) is internal and external control combined oil supply.

9. Faults caused by improper recombination of logic valve control function

A logic unit has three control functions: direction, pressure and flow. In order to simplify the structure and reduce the size, a logic unit (cartridge valve) can play the role of "one valve with multiple functions" and "one valve with multiple functions" in the work, so as to carry out the composite control of functions. However, "one valve with multiple functions" does not mean that a cartridge valve can carry out the combination of multiple control functions arbitrarily. Certain principles must be observed, otherwise it will bring congenital faults, It doesn't even work. The combination of "one valve with multiple functions" on a cartridge valve can be divided into the following two cases.

(1) Compound at the same time.

A hydraulic resistance can control its opening to change the hydraulic resistance, and then control the flow direction, pressure and flow. For the directional valve, when the hydraulic resistance R = 0, it is circulation, and when r = ∞, it is closed, which belongs to on-off control; For pressure valve and flow valve, under certain conditions, an opening corresponding to hydraulic resistance corresponds to a pressure or flow value, which belongs to constant value parameter control. The two control methods are different.

1) The directional valve and pressure valve can be controlled at the same time. As shown in Figure 144, the cartridge valve control chamber is connected with a pilot pressure valve. Therefore, while the pressure oil flows from P → a, the cartridge valve automatically adjusts to a certain opening to control the pressure in front of the valve and realize the simultaneous control of flow direction and pressure parameters. However, the hydraulic control check valve and pressure valve cannot be combined at the same time. Figure 145 (a) shows a plug-in hydraulic control check valve. When the K port is not connected with human control oil, a → B, but B is not connected with a, which is the function of check valve; When a control oil is supplied to port K, a → B, B → a, the hydraulic control check valve operates normally. Add a pilot pressure valve for compound control, as shown in Figure 145 (b). When the hydraulic directional valve is in the normal position, a → B, and pressure control can be realized. B is not available and a is applicable. However, when the control pressure oil is introduced into port K, a → B, and there is pressure control, but B is not connected to a, so the compound control of hydraulic control check valve and pressure valve cannot be realized, and the pressure regulation failure occurs.

144.145

2) Normally open pressure reducing valve and directional valve cannot be combined. As shown in Figure 146 (a), the two cavities of the normally open pressure reducing valve P. and R are always connected, so the closing control cannot be realized. Therefore, if the two are combined, the reversing function cannot be realized. If you want to realize compound, you must change the normally open pressure reducing valve into the normally closed pressure reducing valve structure to have the function of direction and pressure reduction.

3) The directional valve and flow valve can be combined at the same time without failure. As shown in Figure 147, while the cartridge valve controls the flow direction from P → a, a screw positioning device is used on the control cover plate to limit the opening amount of the valve core, that is, a cartridge valve is used to realize the simultaneous control of flow and flow direction.

146.147

4) In principle, pressure valve and flow valve cannot be combined at the same time, because the position of pressure control in cartridge valve system is basically fixed. For example, the overflow valve (pressure limiting valve), unloading valve, sequence valve and pressure reducing valve are in the oil inlet circuit of the system, while the back pressure valve is in the oil return circuit of the system, and the overflow valve, unloading valve and channel are connected in parallel, so the combination of each pressure pilot control to which cartridge valve is basically fixed and has no choice, otherwise it will fail or fail. In the circuit shown in Figure 148, the flow valve and channel are installed in series on the oil inlet or return circuit. At this time, if the pilot throttle valve and back pressure valve are installed on the oil return circuit (valve 2), when the electromagnet is powered off, valve 1 is closed, valve 2 is opened, a → o, and valve 2 is throttled and back pressure controlled at the same time. However, after analysis, it is found that when the opening of valve 2 is less than the opening amount limited by the throttling screw, it is the function of back pressure valve; When the opening of valve 2 is equal to (or slightly greater than) the opening amount limited by the screw, it is the throttling function, and the simultaneous control of throttling and back pressure cannot be realized, that is, the simultaneous combination of pressure and flow cannot be realized. At this time, the pilot throttle valve should be placed at the oil inlet to implement oil inlet throttling and return oil back pressure.

But the sequence valve is an exception, which can be combined with the flow valve, because the sequence valve is essentially an on-off valve, which uses the pressure signal to control the switch.

5)       Simultaneous compound control cannot be realized between pressure valves and flow valves.

(2) Sequence control. That is, several control functions such as flow direction, pressure and flow are realized by a cartridge valve in sequence, regardless of switch control (flow direction) or constant value control (pressure and flow). However, the sequence of compound control design should generally be flow direction → pressure → flow control, which can be controlled by different pilot valves at different times. As shown in Figure 149, the cartridge valve 1 is equipped with four pilot valves (solenoid valve 3, pilot pressure regulating valves 5 and 4 and throttle valve 6) for control, so it can have five control functions at different times: support (preventing the falling of self weight), pressure limiting, oil drainage, speed regulation and back pressure.

However, special attention should be paid to the form of throttle pilot control. Generally, there are two types of pilot control of cartridge throttle valve: limit type and throttle type. The throttle valve here can only be throttle type instead of limit type.

148.149

10. Pressure interference of median closed system

Figure 150 (a) shows the electro-hydraulic cartridge logic valve circuit of O-type intermediate function composed of three position four-way p-type solenoid valve as pilot valve and four cartridge valves 1, 2, 3 and 4. The control oil led from the main oil circuit enters the control chamber of four cartridge valves from X through the three position four-way solenoid directional valve of p-type intermediate function. Theoretically, when the electromagnetic directional valve is in the middle position, all cartridge valves (1, 2, 3 and 4) should be closed, and P, O, a and B are not connected with each other. However, interference problems often occur in practical work, and some two short-time communication still occur in the oil ports P, O, a and B4. For example, when the working conditions of P → B and a → o - the working condition of the left travel of the piston of the hydraulic cylinder transition to the middle position, the cavity a will be pressurized due to the inertia of the hydraulic cylinder, and the pressure Pa will rise more than px.

In this way, when cartridge valve 1 is opened, there is still oil flow of a → o, so that the system does not work normally or even cannot work. In order to avoid this kind of failure, the method shown in Figure 150 (b) can be adopted, that is, three check valves can be added. In this way, no matter what phenomenon occurs, the control oil p is always taken from the highest pressure among P, PA and Pb, so that when in the middle position and working position, the cartridge valves 1 ~ 4 will be in the correct state in strict accordance with the predetermined control, so as to prevent pressure interference.

150

11. Pressure and flow interference between main stage circuits

The interference of pressure and flow between main stage circuits is mostly solved by cartridge check valve and hydraulic control check valve, while the pressure interference between several pilot control valves of one cartridge valve or pilot control circuits of several cartridge valves needs to be prevented by adding check valve, shuttle valve, directional valve, etc.

Figure 151 shows the cartridge valve controlled by "reversing and pressure reducing", K1 is the pilot pressure reducing valve and K2 is the pilot electromagnetic reversing valve. When 1dt loses power, P → a, the pilot pressure reducing valve K1 works. In order to prevent the return oil of K1 from flowing directly back to the oil tank and make the pressure reduction ineffective, the check valve 3 must be added, otherwise the pressure reduction will not work; When 1dt is energized, the control oil enters the control chamber of cartridge valve through one-way valve and pilot pressure reducing valve to close cartridge valve 1 and realize a → o.

12. Pressure interference of throttle speed regulation system

Figure 152 (a) shows the inlet throttle speed regulation system. Cartridge valve 2 is equipped with pilot throttling control, and cartridge valve 5 is a differential relief valve, which is used as the pressure compensation valve of valve 2. At first glance, this circuit design is reasonable. However, it will have the fault of pressure interference: when the pilot directional valve works at the left position, the overflow throttle valve composed of P → a, B → o, valve 2 and valve 5 can work normally; However, when the pilot directional valve is in operation, there are p → B and a → o, then the control pressure of valve 5 is zero, valve 5 is opened, the system is unloaded and cannot work. In order to solve this pressure interference problem, connect chamber a and valve 5 control chamber with a shuttle valve, as shown in Figure 152 (b), so that the higher pressure of the two can be connected with the valve 5 control chamber, so as to ensure that when p → B and a → o, the valve 5 control chamber is connected with the control chamber of valve 2; When p → A and B → o, the control chamber of valve 5 is connected with chamber a. Thus, the above faults can be eliminated to ensure the normal operation of the system.

152

13. Noise and vibration

In the circuit shown in Figure 153, if the four cartridge valve models (diameter) choose the same size, noise and vibration will occur. The size of the two oil drain valves should be larger than the first gear valve, especially the diameter of valve a, otherwise vibration, noise and heating will be generated due to small overcurrent capacity. Especially when the piston rod is thick, carefully calculate the oil return flow from valve A and select the valve with sufficient flow capacity. At present, the diameters of the four logic valves in many equipment diagrams are mostly the same, which is wrong. The following table is the reference table of rated flow of logic valves with various diameters at present.

Rated flow of logic valves of various sizes

Diameter (mm)

16

25

32

40

50

63

80

100

125

额定流量

(L/min)

200

450

750

1250

2000

3000

4500

7000

10000

 

14. Internal leakage

If it is the circuit in Figure 154 (a), there is no way to solve the internal leakage problem from P1 to P2. It needs to be changed to the connection in Figure 154 (b), and the internal leakage is very small.

153.154

 

 

 

 

 

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