Home / Case / Experience / Common faults and troubleshooting methods of air pressure reducing valve
The reasons for this failure and the troubleshooting methods are as follows:
① Because there are burrs on the main valve core or the edge of the sinking groove of the valve body hole or there is dirt stuck in the gap between the main valve core and the valve body hole, or because the shape and position tolerance of the main valve core or valve hole is out of tolerance, Hydraulic clamping occurs, and the main valve core is stuck at a position with a larger opening (max).
Due to the large opening, the oil is not decompressed. At this time, according to the above situation, deburring, cleaning and repairing the accuracy of the valve hole and valve core can be taken to eliminate it.
② Due to the tight fit between the main valve core and the valve hole, or roughening of the valve hole or the valve core during assembly, the valve core is stuck at a large opening position, and a reasonable clearance can be selected at this time. The fit clearance of J-type pressure reducing valve is generally 0.007-0.015mm, and the valve hole can be properly ground before matching, and then the valve core can be matched.
③ The short damping hole of the main valve core or the blockage of the valve seat hole loses the automatic adjustment function. The spring force of the main valve pushes the main valve to a larger opening and becomes straight through without hindrance. The inlet pressure is equal to the outlet pressure. The damping hole can be blown through with φ1. Omm steel wire or compressed air, cleaned and reassembled.
④ For the J-type pressure reducing valve, the damping part with the damping hole is pressed into the main valve core, and it may rush out due to insufficient interference during use. After rushing out, the pressure of the oil inlet chamber and the oil outlet chamber are equal (without damping), and the upper and lower force areas of the valve core are equal, but there is a spring in the oil outlet chamber, so the main valve core is always in a relatively large opening position, so that The outlet pressure is equal to the inlet pressure. At this time, it is necessary to reprocess the damper with a slightly larger outer diameter and re-press the main valve core.
⑤JF type pressure reducing valve, when leaving the factory, the oil drain hole L is blocked with an oil plug. When the oil plug is not screwed out and used, oil will be trapped in the upper chamber (spring chamber) of the main valve core, resulting in a large opening of the main valve core without decompression. The J-tube valve is the same. This phenomenon will also occur if the J-type plate valve does not connect the L port to the oil pool when designing the mounting plate.
⑥For the J-type tubular valve, it is easy to install the valve cover in the wrong direction (wrong 90° or 180°) during disassembly and repair, so that the external oil discharge port is blocked and the oil cannot be discharged, resulting in the same oil trapping phenomenon as above, which makes the main valve Top at a larger opening without decompression. When repairing, just assemble the valve cover in the right direction.
⑦ For the JF pressure reducing valve, if the top cover is installed in the wrong direction, the output oil hole will communicate with the oil drain hole, resulting in no decompression, so attention must also be paid.
① The oil inlet and outlet ports of the pressure reducing valve are reversed: the design of the mounting plate is wrong for the plate valve, and the connection is wrong for the pipe valve. The oil inlet and outlet of the J-type pressure reducing valve are just opposite to the oil inlet and outlet of the Y-type relief valve. When users use it, please pay attention to the steel stamp marks (Pl, P2, L, etc.) near the oil port on the valve, or refer to the catalog of hydraulic components, and do not design or connect wrongly.
② The pressure at the oil inlet is too low, and the output pressure from the oil outlet is even lower after the pressure reducing valve core throttles the port. At this time, the cause of the low pressure at the oil inlet should be found out (such as a failure of the relief valve).
③ The downstream circuit load of the pressure reducing valve is too small. If the pressure cannot be established, it can be solved by connecting a throttle valve in series downstream of the pressure reducing valve.
④ Poor contact between the pilot valve (cone valve) and the mating surface of the valve seat due to dirt retention; or the pilot cone valve is severely scratched, the seat fits out of circle and has a gap, causing the pilot valve core to Does not fit tightly with the seat hole.
⑤ During disassembly and repair, the cone valve is missing or the cone valve is not installed in the seat hole. In this regard, the assembly or tightness of the poppet valve can be checked.
⑥ The long damping hole on the main valve core 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 damping hole e, and the feedback pressure of the oil outlet chamber P2 cannot be transmitted to the pilot cone On the valve, the pilot valve loses its ability to regulate 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, so that the main valve becomes a direct-acting slide valve with weak spring force (only the balance spring of the main valve), so when the pressure of the oil outlet is very low, the function of the balance spring can be overcome Force the throttle of the pressure reducing valve to close ymin, so that the pressure of the oil inlet p1 is greatly reduced to p2 through the ymin throttle, so that the pressure of the oil outlet cannot be increased. The long orifice should be unobstructed.
⑦ The pilot valve spring (pressure regulating spring) is wrongly installed as a soft spring, or due to long-term deformation or breakage due to spring fatigue, the p2 pressure cannot be adjusted high, and it can only be adjusted to a certain low value, which is far lower The maximum adjustment pressure of the pressure reducing valve.
⑧ The pressure regulating handle cannot be screwed to the bottom due to thread strain or insufficient effective depth, so that the pressure cannot be adjusted to a higher level.
⑨ The seal between the bonnet and the valve body is poor, resulting in serious oil leakage. The reason may be that the O-ring is missing or damaged, the compression screw is not tightened, and the flatness error of the end face occurs during the processing of the valve cover, which is generally convex around and concave in the middle.
⑩ The main valve core is stuck in the small opening position due to dirt, burrs, etc., so that the outlet pressure is low. Can be cleaned and deburred.
According to relevant standards, the pressure swing of the J-type pressure reducing valve is ±0.1MPa, and that of the JF type is ±0.3MPa. If the pressure exceeds this standard, the pressure swing is large and the pressure is not stable.
① J-type and JF-type pressure reducing valves are pilot-operated, and the pilot valve and relief valve are common. Therefore, the cause of large pressure swing and the elimination method can refer to the relevant parts of the relief valve.
② When the pressure reducing valve is used under the rated flow rate, the main valve oscillation phenomenon often occurs, which makes the pressure reducing valve unstable. At this time, the pressure at the oil outlet appears a cycle of "boosting, then stepping down, then boosting, then stepping down" , so be sure to choose a pressure reducing valve suitable for the model and specification.
③The oil drain port L is subjected to a large back pressure, which will also cause large pressure swings and unstable pressure. The oil drain pipe should return the oil separately.
④The deformation or stiffness of the spring is not good (poor heat treatment), resulting in large pressure fluctuations, and qualified springs can be replaced.
In some decompression control circuits, the outlet pressure of the decompression valve is used to control the control oil pressure of the electro-hydraulic directional valve or external control sequence valve. After working in the direction or direction, the flow rate at the oil outlet of the pressure reducing valve becomes zero, but the pressure still needs to maintain the original set pressure. In this case, since the valve outlet flow is zero, the flow through the decompression port is only the pilot flow.
Since the pilot flow is very small, generally within 2L/min, the main valve decompression port is basically close to the fully closed position (the opening is very small), and the pilot flow flows out from the triangular groove or inclined cone surface. If the main valve core cooperates If it is too loose or worn too much, the leakage will increase.
According to the flow continuity theorem, this part of leakage must also flow from the damping hole of the main valve core, that is, the flow flowing through the damping hole is composed of two parts: pilot flow and leakage, and the area of the damping hole and the oil pressure in the spring chamber of the main valve (the oil pressure in the spring chamber is determined by the pre-compression of the adjusted pressure regulating spring), in order to increase the flow through the damping hole, the oil pressure in the lower chamber of the main valve will inevitably increase.
Therefore, when the outlet pressure of the pressure reducing valve is adjusted, if the outlet flow rate is zero, the outlet pressure will increase due to the loose fit of the main valve core or excessive wear.
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