Hydraulic Press

7 Questions About Directional Control Valve You Should Know

Directional valve

Estimated reading time: 21 minute

Question 1: The Specification of The Directional Control Valve of The Hydraulic System of The Pipe Expander

Figure 1-1 shows the hydraulic system of a 600-ton pipe expander used in a factory. It can realize the action cycle of vertical cylinder fast down, sealing control cylinders on both sides synchronously fast forward, mold sealing one vertical, side cylinder pressurization-two cylinders synchronously rewind the mold opening and the vertical cylinder quickly retreats the mold opening action cycle.

Figure 1-1 The hydraulic system of a 600-ton pipe expander

Figure 1-1 The hydraulic system of a 600-ton pipe expander

When the solenoid 2DT is energized, the electromagnetic directional valve 10 is switched to the left position, and the hydraulic pump 1—the left position of the electro-hydraulic directional valve 8—the left position of the valve 10—the double hydraulic control check valve 13—the rodless cavity of the vertical cylinder 19, The vertical cylinder 19 quickly descends and seals the mold.

When the mold sealing pressure reaches the specified value, the electric contact pressure gauge 14 sends out a signal, the solenoid 2DT is cut off, 1DT, 5DT, 6DT are energized, and the hydraulic oil passes through the valve 8 to the right and the shunt valve 9—the electromagnetic reversing valve 11 to the right— The left position of the electromagnetic reversing valve 12-the double hydraulic control check valves 16 and 18 enter the rodless chambers of the side cylinders 20 and 21 respectively, and the cylinders on both sides fast forward and seal the mold synchronously.

When the mold sealing pressure reaches the specified value, the electric contact pressure gauge 17 sends a signal, the ultra-high pressure hydraulic-pressure 15 and 2~/ move backward at the same time, and respectively inject high-pressure oil into the rodless cavity of the vertical cylinder 19 and the side cylinders 20 and 21 to achieve Output 6MN (600tf) pressing force.

When the electromagnets 1DT, 4DT, 7DT are energized, the cylinders on both sides will retreat and open the mold synchronously. When the end of the stroke is reached, the stroke will open and a signal will be sent. The electromagnet 1DT is de-energized and the 3DT is energized, and the vertical cylinder quickly moves upward to open the mold.

In order to improve work efficiency and reduce power consumption, the system adopts pressure compensation variable axial piston pump 1 to achieve low-pressure and high-speed operation of vertical cylinders and side cylinders, and high-pressure and low-speed operation during mold sealing. The specifications of the three hydraulic cylinders are the same.

Figure 1-2

Figure 1-2

The vertical cylinder and the side cylinder move slowly. The vertical cylinder moves down quickly for 70 seconds, and the side cylinder moves forward quickly for 60 seconds. The return time is longer, resulting in extremely low production efficiency.

It can be seen from the working principle of the system that the vertical cylinder’s rapid downward movement and the side cylinder’s rapid forward movement are performed independently. A hydraulic source provides flow, and its operating speed is determined by the output flow of the hydraulic pump 1. When the vertical cylinder and the side cylinder are running quickly, because there is no load, the working pressure of the system is very low at this time and the pressure compensation variable hydraulic pump outputs at full flow.

The hydraulic cylinder moves slowly and the running time is too long, indicating that the actual flow input to the hydraulic cylinder is too small. This may have the following two situations:

  • The volumetric efficiency of hydraulic pump 1 is too low, causing the actual maximum flow output of the pump to be too small.
  • The system pressure loss is too large so that the pump is in a constant power variable adjustment condition and cannot output at full flow.

It is verified by inspection that the volume loss of hydraulic pump 1 is not large, and the volumetric efficiency has not decreased. It is inferred from this that the latter may cause problems in the system.

From the above analysis, it can be seen that when the hydraulic cylinder is running fast, the total partial pressure loss caused by the oil passing through the hydraulic valves is very large, especially the pressure loss through the electromagnetic reversing valve and the two-way hydraulic lock is the largest, which greatly exceeds their rated pressure Loss value. The total partial pressure loss of the hydraulic valve is combined with the pressure loss along the pipeline and the partial pressure loss, which will inevitably increase the working pressure of the system and reduce the actual output flow of the pump, thereby reducing the operating speed of the hydraulic cylinder. Slow, the running time becomes longer.

Figure 1-3

Figure 1-3

Conclusion: The main cause of system problems is improper selection of the specifications of the electromagnetic reversing valve and the two-way hydraulic lock.

The best way to solve this problem: select the electromagnetic directional valve and two-way hydraulic lock with appropriate specifications, and replace the corresponding components in the system, thereby reducing the partial pressure loss of the hydraulic valve.

When selecting a hydraulic valve to form a hydraulic system, in addition to considering the proper function of the selected hydraulic valve, it is also necessary to consider that its specifications should meet the performance requirements of the system. The improper selection of component specifications in this example will cause slow movement of the main and side cylinders and affect the normal working performance of the system, but will also cause excessive resistance loss, resulting in large energy loss and increased oil temperature.

Question 2: Selection of The Type of Directional Valve in The Hydraulic System of The Press Machine

Figure 1-4 shows the hydraulic system of a stretch-bending machine designed and manufactured by a certain factory, which can realize the stretching and bending of the profile. Operate the manual reversing valve 2. The oil enters the rodless cavity of the stretching hydraulic cylinders 4 and 5 through the left position, and the pistons of the stretching hydraulic cylinders 4 and 5 move forward to carry out the stretching process of the profile. When the required stretch rate is reached, the manual reversing valve 3 is then operated to connect to the circuit in its left position, and the oil enters the rodless cavity of the bending hydraulic cylinder 6 to bend the profile. After bending and shaping, the workpiece is unloaded, and the bending hydraulic cylinder 6 and the stretching hydraulic cylinders 4 and 5 are retracted, thereby completing a profile stretching and bending action cycle. The system pressure is set by overflow valve 1. After improvement, the hydraulic system adopts an electromagnetic directional valve and electromagnetic overflow valve, as shown in Figure 1-4(b).

Figure 1-4 The hydraulic system of the bending machine 1-overflow valve;  2,3-manual reversing valve; 4,5-stretching hydraulic cylinder; 6-bending hydraulic cylinder

1-overflow valve; 2,3-manual reversing valve; 4,5-stretching hydraulic cylinder; 6-bending hydraulic cylinder
Figure 1-4 The hydraulic system of the bending machine

Existing problems: The system adopts an electromagnetic overflow valve, which has obvious effects on reducing power consumption and reducing oil heating and leakage. However, when the stretching and bending actions begin, there is obvious hydraulic shock, accompanied by equipment flutter, which affects the quality of the product.

The electromagnetic reversing valve selected has the same specifications as the original manual reversing valve. The only difference is the reversing operation method. What is the problem?

The electromagnetic reversing valve changes the working position of the valve by using the suction force of the electromagnet to push the spool relative to the valve body. It switches quickly and the reversing time is short. Therefore, hydraulic shock will inevitably occur when the reversing valve is switched. The manual reversing valve is used to manipulate the lever and push the spool to move relative to the valve body to change the position. It does not switch as quickly as the former. It gradually opens or closes the valve port. It has the effect of throttling and damping, so it has an impact on the hydraulic pressure. Has a buffering effect. Therefore, the commutation stability of the modified system is poor.

Using the same specification electro-hydraulic reversing valve instead of the electromagnetic reversing valve can eliminate the hydraulic shock. At the same time, it also has the advantages of flexible operation of the electromagnetic reversing valve and easy automatic program control. The hydraulic system after further transformation is shown in Figure 1- As shown in 2(c). Adjusting the electro-hydraulic reversing valve controls the damper in the pressure oil circuit to adjust the reversing time, thereby improving the stability of the reversing.

This example illustrates: For hydraulic equipment that requires high commutation stability, it is advisable to use an electro-hydraulic directional valve or a controllable commutation time.

The manual reversing valve constitutes the hydraulic system.

Question 3: The Hydraulic Valve Problem of The Hydraulic System of The Lifting Platform

Figure 1-6 shows the hydraulic system of a lifting platform made by a factory, which can realize equipment lifting, lowering, and stopping at any position.

Figure 1-5

Figure 1-5

When 2DT is energized, oil-electromagnetic reversing valve 5 right position-hydraulically controlled check valve 7-plunger cylinder 8 lower cavity-plunger moves upwards-the weight is lifted. When the 1DT is energized, the oil-hydraulic control check valve 7-electromagnetic reversing valve 5 left position-throttle valve 4-oil tank, the plunger moves downwards-the weight drops. The descending speed of the weight is controlled by the throttle valve 4, and the descending stop position is controlled by the hydraulically controlled check valve 7. When the 3DT is energized, oil-hydraulic pump 1-relief valve 2-oil tank (unloading).

There is a problem: when the weight is descending, it emits beat-like vibration and noise.

All hydraulic components in the detection system are normal, so the problem of the system is not caused by the failure of the component itself. In the system, a throttle valve is used to adjust the descending speed of the plunger cylinder, so when the oil flows in the reverse direction, the hydraulic control check valve outlet pressure is backpressure. The control oil pressure is still the setting value of the overflow valve 6, so the force balance of the valve core is broken, the valve core drops to close the valve port, and the pressure in the oil outlet cavity becomes zero. At this time, the control oil pressure set by the overflow valve 6 opens the hydraulic control check valve again, the oil flows in the reverse direction, and backpressure is generated in the reverse oil outlet cavity, and the hydraulic control check valve is closed again. This was repeated so that the plunger cylinder was lowered and stopped intermittently, and vibration and noise were emitted at the same time.

Figure 1-6 Hydraulic system of lifting platform 1-hydraulic pump;2,6-overflow valve; 3,5-electromagnetic reversing valve;4-throttle valve; 7-check valve; 8-plunger cylinder

1-hydraulic pump;2,6-overflow valve; 3,5-electromagnetic reversing valve;4-throttle valve; 7-check valve; 8-plunger cylinder Figure 1-6 Hydraulic system of lifting platform

Solution method

  • Increase the control oil pressure. Increasing the setting pressure of the relief valve 6 means increasing the minimum control pressure, which can reduce vibration and noise within a certain range of the descending speed of the plunger cylinder, but is disadvantageous for saving the power of the control part.
  • Change the setting of the throttle valve. Set the throttle valve above the hydraulic control check valve to make the hydraulic control check valve reverse the backpressure of the oil chamber to zero. This helps eliminate vibration and noise, but increases the power consumption when the plunger cylinder rises.
  • Select the appropriate hydraulic valve. Choosing a hydraulically controlled check valve with an external drain port can eliminate vibration and noise.
  • The problems exposed in the system are caused by the improper selection of component types. When selecting a hydraulic control check valve, in addition to knowing its function as a hydraulic lock, you must also understand its structure type. When there is backpressure, you should choose a hydraulic control check valve with an external drain.

Question 4: The Hydraulic Valve Control Oil Pressure of The Crane Spreader Positioning Hydraulic System

Figure 1-7 shows the positioning hydraulic system of the container crane spreader, which can realize the movement and positioning of the container spreader. The hydraulic cylinder 5 is required to travel left and right in the horizontal direction and be accurately positioned at any position, without drifting or shifting, and its movement speed should be adjusted. In order to meet the positioning requirements of the spreader, an external leakage type (with a load relief valve core) dual hydraulic control one-way valve 4 is set at the oil inlet and outlet ports of the hydraulic cylinder 5 to lock the hydraulic cylinder. Because of the four one-way valves, the oil can flow through the speed control valve in the same direction no matter the piston moves to the left or right, so the reciprocating speed of the piston is equal, and the system working pressure is set by the overflow valve 1.

Since the neutral function of the reversing valve 2 in the system is O type, when the reversing valve 2 is switched to the neutral position, the oil circuit between the hydraulic cylinder 5 and the reversing valve 2 is closed, and a certain pressure is still maintained, namely The control oil circuit of the hydraulic control check valve still has pressure, so that it cannot be closed immediately. The hydraulic control check valve is not closed until the control oil circuit pressure oil is relieved due to the internal leakage of the reversing valve. Therefore, there is still a period of time from when the reversing valve is in the neutral position to when the piston stops moving, and the hydraulic cylinder cannot be positioned accurately.

Change the original system with the O-type reversing valve to the Y-type reversing valve. The improved system is shown in Figure 1-7. Due to the Y-type neutral function of the reversing valve, when the reversing valve is in the neutral position, the control oil circuit of the hydraulic control check valve is immediately connected to the oil tank, and the pressure drops rapidly, so the hydraulic control check valve can be closed in time and locked tightening effect. 

1-Overflow valve; 2-Manual reversing valve; 3-Speed regulating valve; 4-Hydraulic control check valve; 5-Hydraulic cylinder
Figure 1-7 The positioning hydraulic system of the container bridge crane spreader

1-Overflow valve; 2-Manual reversing valve; 3-Speed regulating valve; 4-Hydraulic control check valve; 5-Hydraulic cylinder
Figure 1-7 The positioning hydraulic system of the container bridge crane spreader

Question 5: Selection of Hydraulic Valve Type For Accumulator Speed Increasing Circuit

The hydraulic equipment made by a factory is shown in Figure 1-8. Due to the long intermittent time and the high-speed movement of the actuators, an accumulator is used as an auxiliary power source and used in conjunction with a hydraulic pump with a small flow rate. When the manual reversing valve 5 is in the neutral position, the hydraulic cylinder 6 stops and the hydraulic pump 1 charges the accumulator 4 through the one-way valve 2, and the accumulator stores energy at this time. When the pressure of the accumulator reaches a certain set value, the pilot-operated external control sequence valve 3 for unloading is opened, so that the pressure oil output by pump 1 flows back to the tank through valve 3, and pump 1 is in the unloading state. When the left or right position of valve 5 is connected to the circuit, pump 1 and accumulator 4 simultaneously supply oil to the hydraulic cylinder 6 to make it move quickly. The set pressure of sequence valve 3 in the loop is higher than the maximum working pressure of the system to ensure that all the flow of pump 1 enters the system during the working stroke.

1-Hydraulic pump; 2-One-way valve; 3-Sequence valve; 4-Accumulator;5-Manual reversing valve; 6-Hydraulic cylinder
1-Hydraulic pump; 2-Check valve spool; 3-Unloading relief valve body; 4-Accumulator; 5-Manual reversing valve; 6-Hydraulic cylinder; 7-Plunger; 8-Pilot valve Spool; 9-Adjusting screw; 10-Pilot valve spring; 11-Main valve spring; 12-Main valve core; 13-Center hole; 14-Damping hole
Figure 1-8 Accumulator speed increasing circuit

1-Hydraulic pump; 2-One-way valve; 3-Sequence valve; 4-Accumulator;5-Manual reversing valve; 6-Hydraulic cylinder
1-Hydraulic pump; 2-Check valve spool; 3-Unloading relief valve body; 4-Accumulator; 5-Manual reversing valve; 6-Hydraulic cylinder; 7-Plunger; 8-Pilot valve Spool; 9-Adjusting screw; 10-Pilot valve spring; 11-Main valve spring; 12-Main valve core; 13-Center hole; 14-Damping hole
Figure 1-8 Accumulator speed increasing circuit

When the oil pressure from the accumulator drops due to the leakage at the pilot valve port, the pilot valve spool is closed, the main valve spool is also closed, and the unloading channel of the hydraulic pump is cut off, so the above sequence occurs The phenomenon of repeated opening and closing of the valve. Through the above analysis, it is concluded that the reason for the problem of the system is that the pilot-operated external control sequence valve is selected as the unloading valve.

Question 6: The Hydraulic Valve Problem of The Hydraulic System of The Butyl Rubber Coating Machine

In recent years, hollow glass doors and windows have been widely used due to their good heat insulation, sound insulation, anti-frost and sealing properties, and long service life. Butyl rubber is the first seal through aluminum hollow glass doors and windows. It is solid at room temperature and becomes semi-fluid when heated to 110~140℃. The glue can be extruded to realize glue application under the pressure of 12~15MPa. . Butyl coating is an indispensable link in the production process of aluminum hollow glass doors and windows. The butyl rubber coating machine is special equipment designed and manufactured for this process. It heats, pressurizes, and extrudes the butyl rubber to evenly coat the middle of both sides of the aluminum spacer. Process requirements: The butyl rubber must be evenly coated and not cut off to ensure the performance of the hollow glass doors and windows.

1-Hydraulic pump; 2-Overflow valve; 3-Three-position four-way electromagnetic reversing valve;
4-Hydraulic control check valve; 5-Hydraulic cylinder; 6-Butyl rubber cylinder;
7-Accumulator; 8-Electric contact pressure gauge
Figure 1-9 Schematic diagram of the hydraulic system of a butyl rubber coating machine

1-Hydraulic pump; 2-Overflow valve; 3-Three-position four-way electromagnetic reversing valve;
4-Hydraulic control check valve; 5-Hydraulic cylinder; 6-Butyl rubber cylinder;
7-Accumulator; 8-Electric contact pressure gauge
Figure 1-9 Schematic diagram of the hydraulic system of a butyl rubber coating machine

The composition of the hydraulic system of the butyl rubber coating machine is shown in Figure 1-9. The systems are shown in Figure 1-9 and Figure 1-9 has been applied in practice, and the principles of the two are similar. Now take Figure 1-9 as an example for illustration. The working principle is: when the 1YA is energized, the left position of the reversing valve is connected to the circuit, and the hydraulic cylinder 5 moves from right to left to extrude the butyl rubber for gluing. When the pressure in the rodless chamber of the hydraulic cylinder rises to the upper limit value of the electric contact pressure gauge 8, the pressure gauge contact sends a signal to de-energize the solenoid 1YA, the reversing valve is in the neutral position, and the hydraulic pump is closed at the same time, and the hydraulic cylinder is replaced by the hydraulic pressure. The one-way valve 4 and the accumulator 7 are controlled to maintain pressure. When the pressure in the rodless chamber of the hydraulic cylinder drops to the lower limit set by the electric contact pressure gauge, the pressure gauge sends a signal to energize the 1YA, and the hydraulic pump supplies oil to the system again to increase the pressure in the rodless chamber, thereby causing the hydraulic cylinder The pressure remains within the required working range. When the piston of the hydraulic cylinder reaches the predetermined position before the endpoint, the electromagnet 2YA is energized, the right position of the reversing valve is connected to the circuit, the hydraulic cylinder moves from left to right, and the piston rod retracts. It should be pointed out that the hydraulic cylinder 5 and the butyl rubber cylinder 6 are installed on the same horizontal line and fixed on the bracket respectively. The space between the two is used to fill the solid butyl rubber.

Problems in the hydraulic system of the butyl rubber coating machine: During the operation, it was found that the butyl rubber was unevenly applied, and the extruded glue flow became finer and thinner until the flow stopped, and the performance of the hollow glass doors and windows produced did not meet the requirements. The system is shown in Figure 1-9 shall be protected.

In the pressure performance test, when the hydraulic pump is not turned on and the manual control 1YA is energized, the pump reversal phenomenon also occurs. It is found that the two circuits shown in Figure 1-9 have certain defects: in the pressure holding stage, the energy storage The hydraulic oil in the hydraulic cylinder enters the rodless cavity of the hydraulic cylinder, but because the reversing valve adopts the M-type neutral function, the oil in the rod cavity of the hydraulic cylinder cannot return to the tank, that is, the oil return is closed, causing the piston of the hydraulic cylinder to be unable to move. The glue cannot be squeezed out so that the glue flow becomes smaller and smaller until the flow stops at the end. For the system shown in Figure 1-9, when the hydraulic pump is not working and the left position of the reversing valve is turned on, the high pressure of the hydraulic oil in the accumulator causes the high-pressure oil to flow back into the hydraulic pump, causing the pump to reverse. Turn.

Figure 1-10 is the schematic diagram of the improved hydraulic system of the butyl rubber coating machine. The central function of the reversing valve adopts K-type. In the pressure-holding stage, the hydraulic cylinder has a rod cavity to return oil, and the piston of the hydraulic cylinder can continue to move from left to right depending on the pressure of the accumulator so that the glue can be applied.

Even and no cut-off occurs. At the outlet of the pump, a one-way valve is added to effectively prevent the reversal of the hydraulic pump caused by the backflow of high-pressure oil in the accumulator.

Figure 1-10 Schematic diagram of the improved hydraulic system of the butyl rubber coating machine

Figure 1-10 Schematic diagram of the improved hydraulic system of the butyl rubber coating machine

Question 7: The Central Function of The Reversing Valve of The Hydraulic System of The Vertical Mill Hydraulic Machine

The working principle of the vertical mill is shown in Figure 1-11. The left and right ends of the grinding mill are respectively connected with the piston rods of the left and right hydraulic cylinders.

The lift of the grinding wheel is controlled by the expansion and contraction of the piston rod of the hydraulic cylinder. In the grinding process, on the one hand, the hydraulic system provides sufficient pressure to the grinding wheel; on the other hand, the grinding wheel rotates, the grinding wheel rotates under the action of the abrasive, and the rotary movement of the grinding wheel is realized by the motor through the belt drive. The material in the grinding disc moves to the periphery of the grinding disc due to the centrifugal force enters the channel, and the material is crushed under the pressure and shear of the grinding machine.

Figure 1-11 Working principle diagram of vertical mill

Figure 1-11 Working principle diagram of vertical mill

The hydraulic system of the vertical mill hydraulic machine is an important part of the vertical mill, mainly composed of an oil cylinder, accumulators, hydraulic pipeline, hydraulic station, and other components. Its main function is to apply enough pressure to the grinding wheel to crush the material. The working principle of the system is as follows.

As shown in Figure 1-12, when the 1DT is energized, the left position of the reversing valve is connected to the circuit, the hydraulic cylinder 4 moves from up to down, and the grinding wheel moves down through the pressure provided by the hydraulic system. When the pressure in the rodless cavity of the hydraulic cylinder 4 rises to the upper limit of the electric contact pressure gauge 5, the pressure gauge contact sends a signal to de-energize the solenoid 1DT, the reversing valve is in the neutral position, and the hydraulic cylinder 4 is powered by the accumulator. 6 The leakage compensation system is working in the pressure-holding state; when the pressure of the rodless cavity of the hydraulic cylinder drops to the lower limit set by the electric contact pressure gauge 5, the contact of the electric contact pressure gauge 5 sends out a signal again, so that the 1DT is energized, and the hydraulic pump. The output hydraulic oil is sent to the system again.

The system is supplied to increase the pressure of the rodless cavity so that the pressure of the rodless cavity of the hydraulic cylinder is kept within the required working range. When the 2DT is energized, the right position of the reversing valve is connected to the circuit, the hydraulic cylinder has a rod cavity to enter the oil, and no rod cavity returns oil, and the piston rises. When both 1DT and 2DT are powered off, the system is in a neutral state as shown in the figure.

1-Hydraulic pump; 2-Overflow valve; 3-Three-position four-way electro-hydraulic directional valve; 4-Hydraulic cylinder; 5-Electric contact 6-Accumulator; 7-Motor; 8-Check valve; 9-Hydraulic control check valve
Figure 1-12 Hydraulic system of vertical mill hydraulic machine

1-Hydraulic pump; 2-Overflow valve; 3-Three-position four-way electro-hydraulic directional valve; 4-Hydraulic cylinder; 5-Electric contact 6-Accumulator; 7-Motor; 8-Check valve; 9-Hydraulic control check valve
Figure 1-12 Hydraulic system of vertical mill hydraulic machine

2 thoughts on “7 Questions About Directional Control Valve You Should Know

  1. Simon says:

    Thanks for your paper, by the way, can you please send me the hydraulic press machine manual?

    1. Grace says:

      Yes, can you tell me which machine’s manual,and how much Ton you bought?Then we will send the fittest manual to you.

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