Common faults and troubleshooting of hydraulic press directional control valve

Update:03 Dec 2021

Due to the difference in neutral function, diameter and […]

Due to the difference in neutral function, diameter and control mode, hydraulic directional control valves have many varieties, but their principles are similar. In practical applications, electromagnetic (liquid) directional valves are the most widely used.

The common faults and troubleshooting of electromagnetic reversing valve in installation and use are as follows.

1. The AC solenoid coil is burnt out

a. Insulation of the coil is poor, which causes the inter-turn disconnection and burns. The coil must be replaced.

b. The supply voltage is higher than the rated voltage of the electromagnet, causing the coil to overheat and burn.

c. The power supply voltage is too low, so that the electromagnet current is too large, causing overheating and burning the coil.

d. The axis of the electromagnet core and the axis of the valve core are too poor in coaxiality, and the armature cannot be attracted, causing overheating and burning. At this time, the electromagnet should be disassembled and reassembled to the specified accuracy.

e. The electromagnetic force cannot overcome the movement resistance of the spool, causing the current to be too large, causing the coil to overheat and burning. Generally, the solenoid valve should be disassembled and checked carefully and resolved.

1. Whether the spool cannot be pushed because the pop valve is too hard.

2. Whether the valve core is stuck by dirt or impurities and cannot be pushed.

3. Whether it cannot be pushed because the push rod is bent.

4. Whether the valve body is deformed because the solenoid valve is installed on the bottom plate, the contact surface is uneven or the screw is not fastened uniformly.

5. Is it due to excessive back pressure at the oil return port?

f. The length of the push rod is too long. After pushing the spool in place, there is still a certain distance between the solenoid armature and the pull-in, so that the current is too large and the coil is overheated and burned.

When the user replaces the electromagnet by himself, the above-mentioned problems are often prone to occur. If the installation distance of the electromagnet after replacement is shorter than the original, and the armature pull-in stroke is in compliance with the specified requirements and consistent with the original electromagnet, then after assembly with the valve, the phenomenon that the armature stroke is greater than the stroke of the push rod pushing the spool will occur. It will cause the armature to fail to close and cause noise, jitter, overheating or even burnout.

If the replacement electromagnet has a longer installation distance than the original, after assembly with the valve, the effective stroke of pushing the spool will be shortened due to the increased distance from the push rod, which will reduce the opening of the valve and increase the pressure loss. Large, affect the movement speed of the actuator plum. Therefore, when the user replaces the electromagnet by himself, he must carefully measure whether the elongation of the push rod matches the armature stroke and cannot be replaced at will.

g. The commutation frequency is too high, and the coil is overheated and burned.

1. This phenomenon also occurs with AC electromagnets; DC electromagnets generally will not burn out due to the above-mentioned failures.

2. The spool does not move, the electromagnet is energized and does not change direction; the electromagnet is de-energized and does not reset

a. The valve core is stuck by burrs, burrs, garbage, etc.

b. The installation bottom plate of the plate valve is warped and uneven. After the fastening screw of the valve body is tightened, the valve body is deformed and the valve core is stuck.

c. The return spring is broken or stuck.

d. For solenoid valves with dedicated drain ports, the drain port is not connected to the fuel tank, or the back pressure of the drain line is too high, causing the spool to become "stuffy" and cannot be displaced.

e. The installation position of the solenoid valve is incorrect, the axis is not horizontal, but inclined and vertical, so the reversing or resetting cannot be in place due to the weight of the valve core and core iron.

f. If the spring is too hard, the spool cannot be moved or pushed in place; if the spring is too soft, the spool cannot be reset automatically after the solenoid is disconnected.

g. The working temperature is too high, and the valve core is thermally expanded and jams the valve body hole.

h. The solenoid is damaged.

3. The noise during commutation is due to the poor pull-in of the electromagnet armature, mainly due to the following reasons.

a. The pull-in end face of the iron core or armature is adhered to by contaminants.

b. The contact surface between the armature and the iron core is uneven or has poor contact.

c. The solenoid push rod is too long or too short.

4. Oil leakage on the bottom of the plate valve installation

a. The surface of the mounting base plate should be ground, the flatness error should not be greater than 0.02ram, and no convexity; the surface roughness should be greater than Ra8um.

b. The tightening force of the tightening screws is uneven.

c. The screw material is not heat-treated alloy steel screws. After replacing them with ordinary carbon steel screws, they are stretched and deformed and become longer due to the action of oil pressure, resulting in gaps in the joint surface and oil leakage.

d. The o-shaped sealing ring of the solenoid valve joint bottom surface is damaged or aging failure.

5. Oil leakage from dry valve a. The o-shaped sealing ring at the push rod is damaged. After the oil enters the electromagnet, it is often drained from the end face of the emergency manual push rod.

The two ends of the solenoid valve core are generally drain cavity L or oil return cavity o. Check whether there is excessive back pressure and the cause of back pressure. Pay attention to the oil tank air filter can not be blocked and cause the pressure in the oil tank.

6. The suction and release of the wet electromagnet is too slow. There is a bleed screw at the back of the electromagnet. When the electromagnet is tested, there is air in the magnetic hydraulic cylinder. If it is off, it will be compressed and form damping, making the armature slow. During the test run, the air screw should be unscrewed to exhaust the air, and the seal should be tightened when the oil is full.

Seven, the solenoid valve is selected correctly, but the oil flow path does not actually match the graphic symbol. This is a very easy problem when using the solenoid valve, which requires our attention and understanding. The same problem often occurs during the use and installation of manual, hydraulic and electro-hydraulic directional valves.

In the previous content about the function of the solenoid reversing spool valve, we have introduced a variety of spool structures of the solenoid valve. We should know that the standard symbol, which only represents the code of one type of valve, is nominal. , But not the structural code of the specific valve. There will be a gap between them.

Due to the special spool structure of the product, or the spool has been installed in the opposite direction during assembly, the actual oil flow path of the same type of valve often does not match the design required graphics. If the above problems are found, the two-position valve can be solved by turning the valve core or the electromagnet and related parts. For the three-position valve, the usual method of changing the electrical circuit is adjusted to solve·

If it still cannot be adjusted, when the process is not complicated, it is necessary to adjust the position of the working oil chamber pipeline or add a transition oil plate to solve the problem.

In order to avoid the occurrence of the above phenomenon, experienced hydraulic technicians often carry out simple non-disassembly inspections when buying hydraulic valves and before installing them. Now take the plate-type connection valve as an example and introduce it as follows.

a. Use your fingers or other objects to temporarily block all the oil outlets of the solenoid valve.

b. Find out the positions of P, A, B, T(O), L and other cavities on the joint surface of the valve. Generally, near the mouth of each cavity, the letters of the cavity (or cast letters) are printed with acid marks. If the handwriting is unrecognizable, it should be compared with the product sample to identify the relevant cavity.

c. First check the function of the spool valve in the initial position of the various valves and whether it meets the requirements for use. For example, the valve slide valve function is O type, when injecting clean oil into the P cavity, the oil does not flow into the other cavity ports. After being filled, it only overflows from the P cavity, and then to the A cavity, B cavity, T cavity, etc. Injecting clean oil, the situation is the same, it can be regarded as. Type machine slip. If it is H type, after injecting oil from P cavity (or from any cavity of A, B, T), you can see that the oil will be reflected from the A, B, and T cavity at the same time, until all the cavity ports are filled with oil .

d. Push the "manual emergency push rod" at the end of the solenoid valve to make the solenoid valve in different working positions, and then follow the sequence of a to check whether the oil passage is correct.

e. Recognize or adjust.