about load sensing proportional valve, electrical control

The load-sensitive electronically controlled Proportional Valve developed by GRH began in the early 1990s and is the first load-sensitive electronically controlled proportional valve with independent intellectual property rights in China. The engineering expert and manufacture technology expert are all from the United States. The core equipment is the same as that of foreign counterparts. The electric proportional pressure reduction valve and core components are imported to ensure that the performance and quality can completely replace equivalent load sensing electronic control proportional valves.

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Load-sensitive proportional multi-way directional valve is widely used in construction machinery, agricultural machinery, and mobile industries due to its better energy saving, proportional control, easy remote control, and stepless control independent of load changes, which can meet the characteristics of multiple actuators working at the same time under different loads. In this study, based on the analysis of the principle of the load-sensitive proportional multi-way valve, some problems that should be paid attention to in the use of the valve are explained in detail in combination with its internal structure characteristics.

The main difference between the load-sensitive proportional multi-way valve in the variable pump system and the quantitative pump system is that it does not contain a three-way pressure compensator. The schematic diagram is shown in Figure 2. This is due to the load-sensitive proportional multi-way valve of the variable pump system. When the variable pump is used, the load pressure signal Ls is introduced into the variable mechanism of the variable pump, so as to realize the control of the flow pressure without adding a three-way pressure compensation valve.

Analysis of several problems that should be paid attention to in use

1. The problem of pressure regulation of the load-sensitive proportional multi-way valve of the quantitative pump system

In the quantitative pump + load-sensing proportional multi-way valve system, the pressure valve safety valve, three-way pressure compensator, secondary relief valve, etc. in the system are coupled with each other. If the user does not have a thorough understanding of the working principle of the valve or is not professional . The pressure adjustment is more difficult.

Generally, the supplier will adjust the pressure and flow according to the user's requirements. However, this setting value is based on the theoretical value in the design stage. The user often has more or less deviation from the design value in the actual application or on-site debugging.

This requires the user to re-adjust the pressure or flow value of the multi-way valve that has been connected to the hydraulic system of the whole machine. In the system, the set pressure of the safety valve is higher than the set pressure of the secondary relief valve. Safety valve, which plays the role of safety protection in this multi-way valve system, is normally closed. Since the reversing valve is in the neutral position, as shown in Figure 3, the pressure oil P is not connected to the load pressure outlet groove. And the load sensitive oil circuit has no pressure, that is, no LS pressure signal is introduced into the spring cavity of the fixed differential relief valve. If the pressure is greater than the fixed differential pressure (9bar), the pressure can be unloaded through the fixed differential relief valve, so that the outlet pressure of the pump cannot be established.

To adjust the pressure of the safety valve, one of the reversing valves must be placed in the A position or the B position. At this time, the pressure oil port is connected with the load pressure outlet groove, the A port or the B port is blocked. or when the actuator of a certain path is in the limit position or stuck, the secondary relief valve is adjusted to the maximum to provide sufficient pressure signal, and the load pressure signal can be obtained in the multi-way valve (system). And the differential relief valve can be introduced. In this way, under the combined action of the load pressure and the spring force, the valve port of the differential relief valve tends to be closed, so that the outlet pressure of the pump is established, and the relief valve relief pressure can be set. For the secondary relief valve, after adjusting the safety valve, the pressure of the secondary relief valve can be adjusted.­­

2. Analysis of problems that should be paid attention to , when using load-sensitive proportional multi-way valve with variable pump

Generally speaking, when the main valve is in the neutral position, the LS signal oil circuit of the flow controller (load sensitive regulating valve) should be in the unloaded state to reduce the circulation loss. Without this pressure relief, the pump in the non-reversing position would still operate at the full residual flow and pressure set by the pressure regulator, which is not allowed. Since some reversing valves do not have this unloading oil circuit design, some pressure-flow controllers have an internal bypass/I, lone L or throttle valve between the LS signal inlet and the pressure relief outlet. Since most of the load-sensing proportional multi-way valves have the function of LS unloading when they are in the neutral position, they can only be used with DFRl type pumps, otherwise the function failure will be caused due to the excessive discharge of the control oil. This is due to the fact that there is a 0.8-diameter damping hole L in the LS oil circuit inside this type of multi-way valve, and the flow provided is limited, about 2 IMmin. The principle of the neutral position LS unloading of the load-sensitive proportional multi-way valve of the variable pump system is shown in Figure 4, which is a partial oil circuit diagram in the schematic diagram.

The figure shows the neutral Ls unloading oil circuit. It can be seen that the LS is unloaded in the neutral position, and the oil circuit is cut off when it is in the reversing position.

The main internal structure of the main valve of a load-sensitive proportional multi-way valve is shown in Figure 5. When the valve core is in the neutral position, LS is introduced into the annular groove through the flow channel on the valve body. The hole 1, hole 2, hole 3 and the undercut groove are communicated with the oil return channel R, and finally Ls is introduced into the return oil and released.

3. Conversion of load-sensitive proportional multi-way valve in quantitative pump and variable pump system

The fact that the load-sensitive multi-way valve in the quantitative pump system is converted into a variable pump load-sensitive multi-way valve is to make the three-way pressure compensator in the former fail, but it does not affect other oil circuits. The most direct method is to take out the spring from the three-way pressure compensator, and use a gasket to deaden the valve core so that the valve core cannot move. If the function of this device in the system and its internal structure principle are understood, it can be known that there is an M5 damper in the three-way pressure compensator. Figure 6 is the working principle diagram of the three-way pressure compensation valve. If this damper is replaced with M5 screws. In this way, the control pressure that makes the valve core tend to be opened can be cut off, and the three-way pressure compensator can be always in a closed state, making it invalid, so as to achieve the purpose of switching between the two.

4. Problems that should be paid attention to in terms of technical characteristics of load-sensitive proportional multi-way valve

1) Appearance design and technological features

At present, most of the load-sensitive proportional multi-way valves on the market are of sheet-type structure; the valve body manufacturing process includes two types: cast valve body and steel machined valve body.

(1) For steel parts machined valve body: the advantages are compact design, high integration and small volume. This is because the valve body is machined from steel, which is smaller in size but higher in strength than castings. The disadvantage is that the flow channels are machined, and there is no smooth transition between the channels, so the local resistance loss of the fluid is large; the calorific value is large and the efficiency is low. Secondly, compared with the cast valve body, the steel machined valve body has a large amount of machining and high cost, resulting in a high price of the whole valve;

(2) For the cast valve body: the advantage is that the mass production cost is low and the amount of machining is small; the casting flow channel is smoother and the pressure loss is small. The disadvantage is that the volume is large and the casting process is complicated.

2) Theoretical and technical characteristics

In a word, the load-sensing proportional multi-way valve is a complex hydraulic product with certain technical difficulties that integrates load-sensing technology, electro-hydraulic proportional technology and cartridge valve technology. It has certain energy saving, easy remote operation or wireless remote control, design The theory is mature, the product performance is relatively stable, and it has a high reputation in the field of construction machinery. However, this valve also has the shortcomings of unsatisfactory compensation characteristics and low accuracy due to the influence of some factors such as hydraulic power and the fluctuation of spring setting pressure when the initial state of the internal hydraulic compensator, which has been used for more than 30 years, is fully open. And technical limitations such as no anti-flow saturation function. A company's LUDV multi-way valve has the function of resisting flow saturation. In addition, the electro-hydraulic load-sensitive load port independent control multi-way valve mentioned in the literature [2] has more ideal control accuracy and energy saving.

in conclusion

The load-sensing proportional multi-way valve is not a simple, single control element, but a highly integrated (hydraulic) system composed of multiple cartridge elements with different functions coupled with each other with specific pressure and flow regulation characteristics. The detailed explanation of the problems that should be paid attention to the use of the valve, the discussion of some unconventional application, and the analysis of the overall technical characteristics will help users to have a deep understanding of the valve principle, the function of each cartridge element and the main internal structure. Thereby, the correctness and rationality of the hydraulic system design and on-site debugging and fault handling methods of the whole machine are improved. The analysis of its technical characteristics can provide a certain reference for designers to rationally select the valve.