Hydraulic Press

Sequence Valve Circuits of Hydraulic Press

Sequence Valve Circuits of Hydraulic Press

Estimated reading time: 18 minutes

Problem 1: How the sequence circuit is implemented

1. Circuit with different loads to automatically control the action sequence of cylinders

Figure 1-1 shows two cylinders with the same piston area but different working loads. The sequence of action is 1 in and 2 in when the piston moves forward; 1 in and 2 in when the piston moves backward.

Sequence Valve Circuits of Hydraulic Press
1-1 Circuit for automatic control of cylinder action sequence with different loads

2. Sequential action circuit using sequence valves

In the circuit, in Figure 1-2 a sequence valve is used to make the cylinders work in the sequence 1-2-3-4. In a sequential operation circuit with sequence valves, the setting pressure of the sequence valve must be greater than the maximum operating oil pressure of the cylinder on the previous stroke, otherwise, a pre-action phenomenon (i.e. the previous stroke is not yet terminated and the next stroke is actuated) will occur.

Sequence Valve Circuits of Hydraulic Press
1-2 Sequential action circuit using sequence valves

3. Sequence circuit with the cam-operated reversing valve

Figure 1-3 shows a sequence circuit using a cam-operated four-way reversing valve. The start time of the next sequence action can be determined by changing the position of the ram on the piston rod and the cam-operated reversing valve. The sequence of action is shown by the arrows on the diagram.

Sequence Valve Circuits of Hydraulic Press
1-3 Sequence circuit using cam-operated four-way directional valves

4. Circuit with continuous reciprocating action

The clamping cylinder in Fig. 1-4 is operated by a manual reversing valve. After clamping the workpiece, the pressure oil is transferred to the reciprocating working cylinder through the sequence valve and is reciprocated by itself. When the clamping is released, the manual reversing valve is restored and the working cylinder stops operating.

Sequence Valve Circuits of Hydraulic Press
1-4 Continuous reciprocating action circuit

5. Sequence circuit using sequence cylinders

Figure 1-5, A cylinder for the piston rod fixed, cylinder simple movement; B cylinder for the cylinder simple fixed, piston rod movement. To complete the action sequence: 1YA get power, 1-A cylinder to the right, 2- B cylinder downward movement; 2YA get power, 3-A cylinder back to the left movement, 4-B cylinder back to upward movement.

As shown in Figure 1-5, from the electromagnetic reversing valve directly to the pipeline of cylinder B, series into the check valve, only allow the B cylinder discharge oil flow through, and into the B cylinder pressure oil must be through the sequence of cylinder A, because the position of the A cylinder piston to the B cylinder into the pipeline to close the role of the first after the start. When the cylinder piston stroke ends, only then open the oil circuit to the B cylinder, thus making the A. B cylinder achieve sequential action.

Sequence Valve Circuits of Hydraulic Press
1-5 Sequence circuit using sequence cylinders

6. Sequence circuit for electrical control

In the electrical control sequence circuit Figure 1-6, with limit switches and electromagnetic reversing valve to manipulate better, the electrical device is flexible, automatic manipulation quickly. When the stroke is finished, the limit switch A is triggered to de-energize the solenoid-operated reversing valve 2, and the right-hand cylinder works in the direction of arrow 4.

The sequence valve is installed in series in the oil circuit of each cylinder so that during the movement of one cylinder, the pressure drop of other cylinders will not be affected.

Sequence Valve Circuits of Hydraulic Press
1-6 Sequence circuit of electrical control

Problem 2: Improper sequential action

In the example of a system with an improperly selected sequence valve shown in Figure 1-7, the hydraulic pump is a dosing pump, and the circuit to which hydraulic cylinder A belongs is an inlet throttling speed control circuit. The load of hydraulic cylinder A is 1/2 the load of hydraulic cylinder B. A sequence valve 4 is set in front of hydraulic cylinder B, and its pressure setting is 1MPa lower than that of relief valve 2. The sequence of hydraulic cylinder action is required to be completed after the action of cylinder A and then the action of cylinder B. However, when the hydraulic pump is started and the electromagnetic reversing valve is energized, the left position works, the hydraulic cylinder A and B act at the same time, can not realize the sequence of A cylinder first action, B cylinder after action.

As the hydraulic cylinder B before the installation of the direct control sequence valve, also known as internal control sequence valve. When the relief valve overflows, the system working pressure has reached the pressure to open the sequence valve. With this type of sequence valve, the hydraulic cylinder B can only be operated without first acting, but not afterward.

If the circuit is improved, as shown in Figure 1-7 b, the direct control sequence valve 4 is replaced by a remote control sequence valve, and the remote control circuit of the sequence valve is connected between hydraulic cylinder A and the throttle valve, so that the opening and closing of the sequence valve is determined by the load pressure of hydraulic cylinder A, independent of the inlet pressure of the sequence valve. Therefore, the control pressure of the remote control sequence valve is adjusted to a slightly higher pressure than the load pressure of hydraulic cylinder A, to achieve the sequence of cylinder A acting first and cylinder B acting later. The action process is: start the hydraulic pump to adjust the pressure in front of the relief valve, electromagnetic reversing valve energized left position work, pressure oil part through the throttle valve into the hydraulic cylinder A. Push cylinder A movement, part of the pressure oil by the relief valve overflow back to the tank. When hydraulic cylinder A movement to the end, its load pressure quickly increases and reaches the control pressure of the remote control sequence valve, the remote control sequence valve main oil circuit is connected, the hydraulic cylinder B starts the action.

Sequence Valve Circuits of Hydraulic Press
1-7 Example of a system with improperly selected sequence valves
1-Constant pump  2-Relief valve  3- Solenoid valve  
4-Sequence valve   5-Governor  6,7- Check valve

Problems:

The control oil circuit of the remote control sequence valve cannot be connected in front of the throttle valve; the setting pressure of the relief valve in the hydraulic system should be set according to the load pressure of hydraulic cylinder B, otherwise, it will not be able to eliminate the above-mentioned fault. The reason is that the load of hydraulic cylinder B is 2 times the load of hydraulic cylinder A. The working pressure of hydraulic cylinder B is the highest pressure of the hydraulic system, so the working pressure of the whole hydraulic system should be adjusted according to the normal action of hydraulic cylinder B.

Problem 3: Mismatch of pressure setting values

1. Mismatch between the pressure setting value of the relief valve and the sequence valve

In the system shown in Figure 1-8, the hydraulic pump is quantitative, and the sequence valve 5 controls the hydraulic cylinder 6 after hydraulic cylinder 7 has moved to the end of its movement: The sequence valve 4 controls the hydraulic cylinder 6 when the hydraulic cylinder 7 returns to its initial position and then starts the return movement. The slow movement of hydraulic cylinder 6 was found in the system. The common reasons for the slow speed are that the flow rate of the hydraulic pump does not reach the required value, serious leakage inside the reversing valve, serious leakage inside the hydraulic cylinder, etc., but for. The above system faults were checked and were not among the common causes of the above faults.

Sequence Valve Circuits of Hydraulic Press
1-8 Example of a circuit with mismatched pressure setting values
1-Dosing pump  2-Relief valve  
3-Solenoid-operated reversing valve
4,5-Sequence valve  6,7-Hydraulic cylinder

When checking the return pipe of the relief valve, it was found that when the hydraulic cylinder 6 was in motion, a large amount of oil flowed out from the return pipe and the relief valve started to overflow, thus indicating that the pressure setting of the relief valve and the sequence valve did not match. If the pressure of the relief valve is also adjusted according to this value, the relief valve will also start to overflow when the sequence valve is opened. If the pressure of the relief valve is adjusted higher than the sequence valve, but the higher value is not enough, when the hydraulic cylinder 6 in the process of moving when the external load increases, that is, the hydraulic cylinder 6 working pressure reaches the pressure of the relief valve, the relief valve will start to overflow, the movement of the hydraulic cylinder 6 will slow down. Therefore, the pressure of the relief valve should be adjusted to 0.5~0.8MPa higher than the pressure of the sequence valve, so that they match each other, to exclude such failure.

2. One-way sequence valve control of the sequence action circuit pressure adjustment is not appropriate

As shown in Figure 1-9, the cause of the sequence action is improper pressure adjustment. The correct adjustment method is: after moving the valve 6 adjustment pressure should be higher than the working pressure of cylinder 4 0.8 ~ 1MPa; valve 3 adjustment pressure should be higher than the working pressure of cylinder 5 backward action three 0.8 ~ 1MPa, to avoid the working pressure fluctuations in the system to make the sequence valve misoperation.

Sequence Valve Circuits of Hydraulic Press
1-9 Sequential action circuit controlled by one-way sequence valve
1-Relief valve  2-Directional valve
3,6-One-way sequence valve  4,5-Hydraulic cylinder

3. The pressure matching problem of each component

The design of the sequential action circuit controlled by the pressure relay is a problem, taking the system of two cylinders as an example, and setting the sequence cycle according to action one – action two an action three an action four.

Sequence Valve Circuits of Hydraulic Press
1-10 Sequential action circuit controlled by pressure relays
1-Clamping cylinder  2-Feeding cylinder  
3-Two-position four-way solenoid valve 4,7- Check valve  
5-Pressure reducing valve  6-Three-position four-way solenoid valve
8-Overflow valve 9-Hydraulic cylinder  10-Suction filter
11-Two-position two-way solenoid valve   12-Speed control valve  
13- Pressure relay (1YJ)

Figure 1-10 shows a sequential action circuit with two pressure relays. The main fault in this circuit is that the sequential action is incorrect, i.e. it does not cycle in the manner of action one – action two – action three – action four. The causes of bad activation and the methods of elimination are as follows. The adjustment pressure of each valve is not appropriate or changes for some reason in the course of use.

For example, to prevent the pressure relay 1YJ from sending a false signal before the clamping cylinder 1 reaches the end of the clamping stroke, the adjustment pressure of 1YJ should be 0.3 to 0.5 MPa greater than the clamping pressure of the clamping cylinder, and to ensure that the cylinder 2 is not fed first before the workpiece is reliably clamped, the adjustment pressure of the pressure reducing valve 5 is 0. 3 to 0.5 MPa higher than the adjustment pressure of 1YJ; the adjustment pressure of the relief valve 8 The adjustment pressure of relief valve 8 should be 0.2~0.3MPa higher than the adjustment pressure of valve 5 and 0.3~0.4MPa greater than the maximum working pressure of cylinder 2. 2YJ should use the loss of pressure to send a signal.

Problem 4: Simultaneous speed and sequence control problems

1. The problem of the control method of the sequence valve

For circuits with simultaneous speed and sequence control, the control method of the sequence valve should be carefully considered.

Sequence Valve Circuits of Hydraulic Press
1-11 Selection of the control method of the sequence valve
1-Clamping cylinder  2-Feed cylinder  3-Sequence valve 4-Pressure valve  5-Workpiece

Take the circuit shown in Figure 1-11 as an example, the design requirements: clamping cylinder 1 clamps the workpiece 5 before the feed cylinder 2 can act and. The speed of the clamping cylinder 1 is required to be adjustable. Figure 1-11 (a) To control the speed of the clamping cylinder 1 through a throttle valve, the pressure valve 4 must be a relief valve (normally open pressure valve) and the circuit must be a constant pressure circuit, the pressure force of which is regulated by the pressure valve 4. Thus, the opening pressure p of the sequence valve 3 can only be p2 ≤ pi, so the feeding cylinder 2 can only act first or together with the clamping cylinder 1 (without considering the difference in load between the two cylinders), which does not achieve the intended purpose. The sequence valve in Fig. 1-11 (b) is controlled in an external way, i.e. the secondary (control) pressure is not led by the primary pressure, but by the throttle valve outlet. In this way when the clamping cylinder 1 in the process of movement, due to the throttle valve must exist differential pressure, the secondary pressure is always less than the primary pressure, until the clamping cylinder 1 clamping workpiece stop movement, the secondary pressure is equal to – – secondary pressure, the feeding cylinder 2 only to start action, to achieve the required sequential action.

2. Improper adjustment parameters of the relief valve and sequence valve lead to the failure of the sequence action to meet the requirements

Sequence Valve Circuits of Hydraulic Press
1-12 Double-cylinder sequential action hydraulic system for special-purpose machine tools
1-Hydraulic pump   2-Pressure valve   3-relief valve   4,5-Hydraulic cylinder

As shown in Figure 1-12 for special machine tool double-cylinder sequential action hydraulic system. Due to improper adjustment parameters of the relief valve and sequence valve, resulting in hydraulic cylinder 4 movement speed can reach the design value, while the speed of hydraulic cylinder 5 then the predetermined low. The reason for the above problem: because the pressure valve 2 should not open when open, the flow of the pump will be diverted, that is, the relief valve 3 set to open the pressure value is lower than the sequence valve through the hydraulic pump when the full flow of the highest pressure value or relief valve 3 set to open the pressure value is equal to or slightly higher than the sequence valve open through the hydraulic pump when the full flow of the highest pressure value, the hydraulic cylinder can not run at full speed or speed when large and sometimes small, therefore, Therefore, to set the pressure of relief valve 3 to 0.5~0.8MPa higher than the highest pressure after the sequence valve is opened, the problem of the system can be solved.

Problem 5: Variable load circuit design problem

Sequence Valve Circuits of Hydraulic Press
1-13 Design system of the variable load circuit
1-Dosing pump  2 -Indiscriminate flow valve  
3-Electromagnetic directional valve 4,5-Remote control valve  
6,7- Check valve  8 Hydraulic cylinder

In the system shown in Figure 1-13, hydraulic pump 1 is a dosing pump and the three-way four-way electro-hydraulic reversing valve is a Y-type.

The hydraulic cylinder 8 pushes the load W into motion. As the load is positive in the first half of the neutral position and negative in the second half of the neutral position, i.e. the direction of the load is the same as the direction of movement of the hydraulic cylinder, the sequence valves 4 and 5 are remote control sequence valves. When the hydraulic cylinder is pushing the load movement to the right, the hydraulic cylinder rodless chamber into the oil pressure of the oil circuit is large enough to open the remote control sequence valve 4, the hydraulic cylinder can push the load movement to the right. Conversely, when the hydraulic cylinder is pulling the load to the left, the hydraulic cylinder can only pull the load to the left when the hydraulic pressure in the hydraulic cylinder rodless chamber inlet circuit reaches a pressure that can open the remote control sequence valve 5.

Sequence Valve Circuits of Hydraulic Press

The problem with the system is that the hydraulic cylinder generates strong vibrations and shocks during the load movement. The remote control sequence valve is set in the system to avoid the failure of the hydraulic cylinder swinging sharply downwards when the load direction is changed during the pushing motion of the load. The reason for the vibration and shock of the hydraulic cylinder is that when the load swings downwards to the right past the neutral position, the pressure in the rodless chamber of the hydraulic cylinder decreases rapidly, resulting in the inlet pressure not being able to open the remote control sequence valve 4, so the remote control sequence valve 4 closes immediately, at this time when the hydraulic cylinder is moving rapidly to the right under the pull of the load, the oil in the rodless chamber is discharged rapidly to the outside, so when the remote control sequence valve closes, it produces violent vibration and shock, so that the load is swinging to the right is forced to stop the movement.

As the remote control valve closes, the hydraulic cylinder cannot return to the tank, so the pressure in the rodless chamber of the hydraulic cylinder increases rapidly, which causes vibration and shock. When the hydraulic cylinder rodless chamber of the fluid pressure increases so that its inlet pressure can open the remote control sequence valve 4, the hydraulic cylinder rodless chamber of the fluid straight through the tank, the load and sharply swing down to the right. This process repeats itself, so that vibration and shock are created. When the hydraulic cylinder pulls the load to swing to the left, the same vibration and shock phenomenon occurs when the load swings down to the left beyond the neutral position.

This failure is due to poor design and should therefore be improved as per Figure 1-13 b. Set throttle valves on the outlet lines of remote control sequence valve 4 and 5 respectively to regulate the speed of movement of the hydraulic cylinder. When the load is over the neutral position, i.e. the load direction and the hydraulic cylinder movement direction – the same, the oil in the hydraulic cylinder return chamber can not be unlimited back to the tank, but by the throttle valve regulation. When the throttle valve throttle port is adjusted, through the throttle valve flow Q by the following formula to determine.

Sequence Valve Circuits of Hydraulic Press

Q – Flow rate through the throttle, cm³/s

Cd – Flow factor, cm 0.5

A – Cross-section area of the throttle opening, cm²

ρ- Density of the oil, kg/cm³

P – the pressure difference between the front and rear of the throttle, N/ cm²

From the above formula can be seen, when A set, through the throttle valve flow Q and the throttle valve before and after the square root of the pressure difference Δp proportional to the pressure after the throttle valve is zero (because directly through the tank), so the greater the flow through the throttle valve, the greater the pressure of the hydraulic cylinder back to the oil chamber. In this way, when the direction of the load is the same as the direction of movement of the hydraulic cylinder, the oil in the return chamber of the hydraulic cylinder is under certain pressure, and this pressure changes with the adjustment of the throttle valve. Therefore, the pressure in the inlet chamber of the hydraulic cylinder will not drop rapidly under the condition of negative load, and the remote control sequence valve will not close. Therefore, in the process of load change from positive to negative, the hydraulic cylinder still moves smoothly due to the regulation of the throttle valve. At this time, the remote control sequence valve mainly plays a balancing role, so that the load can be in any position to stay stable. To ensure the hydraulic system. The hydraulic circuit system diagram for variable loads shown in Figures 1-14 can be used to ensure the smoothness and reliability of the system.

Sequence Valve Circuits of Hydraulic Press
1-14 System diagram of variable load hydraulic circuit

If the system design is not well thought out, one or another failure is bound to occur, even if the whole hydraulic system cannot work. Therefore, for systems subjected to alternating load directions, a careful analysis of the forces should be carried out before the hydraulic system is designed.

One thought on “Sequence Valve Circuits of Hydraulic Press

  1. Avatar of Tomas Tomas says:

    Please send us your hydraulic press catalog, thanks

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