Pressure Relief Valve Four Major Structures And Maintenance

- Apr 11, 2018-

(1) The outlet pressure is almost equal to the import pressure, no decompression

    This failure phenomenon manifests itself as follows: the pressure at the inlet and outlet of the relief valve is nearly equal, and the outlet pressure does not change with the rotation adjustment of the pressure regulator handle. The causes and exclusion methods are as follows.

    1 There is burr on the main valve core or on the edge of the body bore sink groove or there is dirt in the gap between the main valve body and the valve body hole, or due to the tolerance of the main valve core or valve hole position tolerance The hydraulic pressure is generated and the main spool is stuck at the maximum (max) position. Due to the large opening, the fluid is not decompressed. At this time, according to the above conditions, the method of removing the burr, cleaning and repairing the valve hole and the valve core can be separately adopted.

    2 Because the main spool and the valve hole are too tight, or when the valve hole or spool is pulled when assembling, the spool will be stuck at the maximum opening position, and a reasonable clearance can be selected at this time. J-type pressure reducing valve with a clearance of 0. 007 ~ 0. 015mm, equipped with a suitable grinding valve hole, and then with the valve core.

    3 The main spool has a short orifice or a seat hole that is blocked and loses its ability to automatically adjust. The main valve spring force pushes the main valve to the maximum opening and becomes straight and unobstructed. The inlet pressure is equal to the outlet pressure. The orifice can be blown with φ1. Omm wire or with compressed air and cleaned and reassembled.

    4 For the J type pressure reducing valve, the damping element with orifice is pressed into the main valve core. During use, it may be flushed out due to insufficient amount of interference. After rushing out, make the pressure in the oil inlet chamber and the oil outlet chamber equal (without damping), and the upper and lower force areas of the valve core are equal, but the oil outlet chamber has a spring, so the main valve core is always in the position of maximum opening, making the outlet The pressure is equal to the inlet pressure. In this case, rework the damper with a slightly larger outer diameter and re-press the main spool.

    5JF type pressure reducing valve, factory drain valve 孑 L is plugged with an oil plug. When the oil plug is not used for screwing out, the main valve core upper chamber (spring chamber) is trapped in oil, causing the main valve core to be at maximum opening without decompression. J-tube valve is the same as this. The J-plate valve can also cause this phenomenon if the mounting plate is not designed to connect the L-port to the oil reservoir.

    6 J-type tube valve, it is easy to install the valve cover in the wrong direction (wrong 90 ° or 180 °), so that the outer drain port blocked, can not drain, resulting in the same phenomenon of trapped oil, so that the main valve The maximum opening without decompression. When repairing, assemble the bonnet assembly direction.

    7 For the JF type pressure reducing valve, if the direction of the top cover is wrong, the output oil hole will be in communication with the drain hole, causing no decompression, and care must be taken.

    (2) The outlet pressure is very low. Even if the pressure regulator hand wheel is tightened, the pressure will not rise.

    1 Relief valve inlet and outlet ports reversed: The plate valve was designed with a mounting plate in error, and the tube valve was taken over with an error. The inlet and outlet ports of the J type relief valve are just opposite to the inlet and outlet ports of the Y relief valve. When using, please pay attention to the mark (Pl, P2, L, etc.) stamped on the valve near the oil port of the valve, or consult the hydraulic component catalog. Do not design errors or errors.

    2 The pressure at the inlet is too low. After the orifice of the pressure reducing valve is reduced, the pressure output from the outlet is lower. At this time, the reason for the low pressure at the inlet (for example, overflow valve failure) should be ascertained.

    3 Pressure relief valve downstream circuit load is too small. The pressure cannot be established. At this time, consider connecting the throttle valve downstream of the pressure reducing valve.

    4 The contact between the pilot valve (valve valve) and the valve seat mating surface due to dirt retention and poor contact, not close; or serious scratches on the pilot cone valve, valve seat with 孑L out of round, there is a gap, causing the pilot valve core Not in close contact with valve seat hole.

    5 Leaking poppet or poppet valves are not installed in the valve seat hole during the repair. In this regard, check the poppet valve assembly or sealing conditions.

    6 The long orifice on the main spool is blocked by dirt. As shown in Figure 3-21, the oil in the P2 chamber cannot flow into the main valve spring chamber through the long orifice e. The feedback pressure in the outlet chamber P2 is not transmitted to the pilot cone. On the valve, the pilot valve loses its regulating effect on the outlet pressure of the main valve. After the orifice is blocked, the main valve P. The cavity loses the effect of oil pressure p3, making the main valve a direct-acting spool valve with very weak spring force (only the main valve balance spring), so when the pressure at the outlet is very low, the effect of the balance spring can be overcome. Force to make the throttle valve throttle off a small ymin, so that the inlet pressure p1 ymin throttle by a large step down to p2, so that the pressure on the outlet can not come. The long orifice should be open.

    7 pilot valve spring (pressure regulating spring) is wrongly installed into a soft spring, or due to spring fatigue caused permanent deformation or broken and other reasons, resulting in p2 pressure adjustment is not high, can only be adjusted to a certain low value, this value is far below Relief valve maximum regulation pressure.

    8 The pressure regulator handle cannot be tightened to the maximum due to the strained or effective depth of the thread.

    9 The seal between the valve cap and the valve body is bad and there is a serious oil leakage. The reason may be O-ring leaking or damage. When the compression screw is not tightened and the bonnet is finished, flatness error occurs. Generally, it is convex around and concave in the middle.

    10 The main spool is stuck in a small opening position due to dirt, burrs, etc., which results in low outlet pressure. Can be cleaned and deburred.

    (3) No regulation, large pressure swing, and sometimes high noise

    According to the provisions of the relevant standards, the J-type valve pressure swing is ± o. lMPa, JF is ±o. 3MPa, more than this standard for the pressure swing large, no pressure.

    Type 1J and JF type pressure reducing valves are pilot type. Pilot valves and relief valves are common. Therefore, the causes of large pressure swings and their elimination methods can be referred to the relevant parts of relief valves.

    2 When the pressure reducing valve is used in excess of the rated flow rate, the phenomenon of main valve oscillation often occurs, so that the pressure reducing valve is not stabilized. At this time, the pressure at the outlet pressure appears a cycle of “boost-buck step-by-step pressure step-up and step-down repeatedly”. , so be sure to choose the appropriate type of pressure relief valve.

    3 If the back pressure of the drain port L is large, the phenomenon of large pressure swing and non-regulation will also occur. The drain pipe should be returned to the oil alone.

    4 Spring deformation or stiffness is not good (heat treatment is not good), resulting in pressure fluctuations, you can replace the qualified spring.

    (4) The pressure at the outlet increases automatically after the working pressure is set

    In some decompression control loops, the outlet pressure of the pressure reducing valve is used to control the size of the control hydraulic pressure of the electro-hydraulic reversing valve or the external control sequence valve. When the electro-hydraulic reversing valve or the external control sequence valve is changed After or after work, the flow rate of the pressure relief valve outlet port becomes zero, but the pressure still needs to maintain the original set pressure. In this case, because the valve outlet flow is zero, the flow through the decompression port is only the pilot flow. Since the pilot flow is very low, generally within 2L/min, the main valve decompression port is basically close to the fully-closed position (minimum opening degree), and the pilot flow is discharged from the triangular groove or tapered conical surface, if the main valve core cooperates. If it is too loose or worn too much, the leakage increases. According to the flow continuity theorem, this part of leakage must also flow from the main valve orifice, that is, the flow through the orifice consists of the pilot flow and leakage, and the orifice area and the spring pressure of the main valve spring chamber Unchanged (oil pressure in the spring chamber is determined by the pre-compressed volume of the regulated pressure-regulating spring). In order to increase the flow through the orifice, the pressure in the lower cavity of the main valve will inevitably increase.

    Therefore, when the pressure at the outlet of the pressure reducing valve is set, if the outlet flow is zero, the outlet pressure will increase due to the main valve core fitting too loose or excessive wear. Fault phenomenon: unstable pressure fluctuations

Failure analysis:

    1. The air is mixed with air 2. Damper hole is sometimes blocked

    3. The roundness of the slide valve and the inner hole of the valve exceeds the regulation, causing the valve to get stuck

    4. The spring is deformed or stuck in the slide valve, making the slide valve difficult to move or the spring being too soft

    5. The ball is not round, the ball does not fit well with the valve seat, or the poppet valve is installed incorrectly

    Method of exclusion:

    1. Exclude air in oil

    2. Clear the orifice

    3. Research valve hole and slide valve

    4. Replace spring

    5. Replace steel ball or remove poppet valve adjustment

    Symptom: The secondary pressure is not rising

    Failure analysis:

    1. Leakage

    2. Poor valve and seat bad contact

    Method of exclusion:

    1. Replace seals, tighten screws, and ensure uniform torque

    2. Repair or replace

    Symptoms: Can not afford to reduce pressure

    Failure analysis:

    1. Drainage port is disconnected; drain line is connected to return line and return pressure

    2. Main spool in the fully open position

    Method of exclusion:

    1. The drain pipe must be separated from the return pipe and returned to the tank separately

    2. Repair and replace parts. Check the oil