Fault analysis and troubleshooting of pressure reducing valve
Fault analysis and troubleshooting of pressure reducing valve
1. The outlet pressure is almost equal to the inlet pressure without decompression
(1) Cause analysis.
1) For J-type pressure reducing valve, the damping part with damping hole is pressed into the main valve core, which may rush out due to insufficient interference in use. After flushing out, make the pressure of the oil inlet chamber and the oil outlet chamber equal (without damping), and the upper and lower stress 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 the position of maximum opening, so that the outlet pressure is equal to the population pressure.
2) For J-type tubular valve, it is easy to install the valve cover in the wrong direction (90 ° or 180 °) during disassembly and repair, so that the external oil drain port is blocked and the oil cannot be drained, resulting in oil trapping, so that the main valve is pushed at the maximum opening without decompression.
3) JF type pressure reducing valve, the oil drain hole is blocked with oil plug when leaving the factory. When the oil plug is used without screwing out, the oil is trapped in the upper chamber (spring chamber) of the main valve core, resulting in the maximum opening of the main valve core without decompression. J-type tubular valve is the same. This phenomenon will also occur if the I port is not connected to the oil pool when designing the mounting plate of J-type plate valve.
4) For JF type pressure reducing valve, when the top cover is installed in the wrong direction, the output oil hole will be connected with the oil drain hole, resulting in no pressure reduction.
5) Because there are burrs on the main valve core, or there are burrs on the edges of the countersunk groove of the valve body hole, or there are dirt stuck in the gap between the main valve core and the valve body hole, or 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 the position of the maximum opening (ymax), as shown in Figure 67. Due to the large opening, the oil does not depressurize.
6) The short damping hole or valve seat hole of the main valve core is blocked, and the automatic adjustment function is lost. The spring force of the main valve pushes the main valve to the maximum opening, which becomes direct and unimpeded, and the inlet pressure is equal to the outlet pressure.
7) Due to the tight fit between the main valve core and the valve hole, or roughening the valve hole or valve core during assembly, the valve core can be stuck at the maximum opening position. At this time, a reasonable clearance can be selected.
(2) Troubleshooting.
1) The damping parts with slightly larger outer diameter shall be reprocessed and re pressed into the main valve core.
2) When repairing, install the valve cover in the right direction.
3) Carefully check whether the oil drain hole is still blocked with an oil plug. If it is blocked, remove the oil plug in time.
4) Install the top cover in the right direction when repairing the valve.
5) According to the above situation, deburring, cleaning and repairing the accuracy of valve hole and valve core can be "eliminated".
6) During repair, the damping hole can be blown through with 10mm steel wire or compressed air, cleaned and reassembled.
7) Before fitting, the valve hole can be properly ground, and then the valve core can be fitted. For J-type pressure reducing valve, the fitting clearance is generally 0.007 ~ 0.015mm.
2. The outlet pressure is very low. Even if the pressure regulating hand wheel is tightened, the pressure cannot rise
(1) Cause analysis.
1) The contact between the pilot valve (cone valve) and the mating surface of the valve seat is poor and not tight due to dirt retention; Or the pilot cone valve is severely scratched, the matching hole of the valve seat is out of round, and there is a gap, resulting in the non tightness between the pilot valve core and the valve seat hole, as shown in Figure 68.
2) The long damping hole on the main valve core is blocked by dirt. As shown in Figure 69, the oil in P2 cavity cannot flow into the spring cavity of the main valve through the long damping hole e, and the feedback pressure of P2 in the oil outlet cavity cannot be transmitted to the pilot cone valve, so that the pilot valve loses the regulation effect on the outlet pressure of the main valve. After the damping hole is blocked, the main valve P3 loses the function of oil pressure R, making the main valve become a direct acting slide valve with weak spring force (only the balance spring of the main valve). Therefore, when the pressure at the oil outlet is very low, it can overcome the force of the balance spring and reduce the throttle of the pressure reducing valve by Ymin., In this way, the oil inlet pressure P1 passes through Ymin. The throttle port depressurizes greatly to P2, so that the pressure at the oil outlet does not rise.
3) During disassembly and repair, the cone valve is omitted or the cone valve is not installed in the valve seat hole.
4) The inlet and outlet of the pressure reducing valve are connected reversely: the installation plate of the plate valve is wrong, and the connecting pipe of the tubular valve is wrong.
5) The pilot valve spring (pressure regulating spring) is wrongly installed as a soft spring, or the P2 pressure cannot be adjusted high due to permanent deformation or fracture due to spring fatigue. As long as it is adjusted to a low fixed value, this value is far lower than the maximum regulating pressure of the pressure reducing valve.
6) The pressure at the oil inlet is too low. After passing through the throttling port of the pressure reducing valve core, the pressure output from the oil outlet is lower.
7) The main valve core is stuck at the position of small opening due to dirt and burr, so that the outlet pressure is low.
8) The load of the downstream circuit of the decompression chamber is too small to establish the pressure.
9) The sealing between the valve cover and the valve body is poor, resulting in serious oil leakage. The reasons 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 pressure regulating handle is stuck, the thread is strained or the effective depth is not enough, so it cannot be screwed to the bottom, so that the pressure cannot be adjusted to the maximum.
(2) Troubleshooting.
1) Carefully check the fit between the pilot valve (cone valve) and the valve seat. If there is damage, repair or replace it as appropriate, and carefully clean it during assembly.
2) The long damping hole shall be unobstructed.
3) Check the matching or sealing of cone valve.
4) When using, please pay attention to the steel seal marks (P1, P2, l, etc.) near the oil port on the valve, or consult the product catalogue of hydraulic components. Do not make wrong design and connection. The oil inlet and outlet of J-type pressure reducing valve is just opposite to that of Y-type overflow valve.
5) Replace the appropriate pilot valve spring (pressure regulating spring).
6) Find out the cause of low oil inlet pressure (e.g. overflow valve failure).
7) It can be cleaned and deburred.
8) It should be considered to connect the throttle valve in series downstream of the pressure reducing valve.
9) Check the sealing between the valve cover and the valve body and replace the O-ring in time.
10) Check whether the thread of the pressure regulating handle is damaged or the effective depth is not enough, and repair or replace it according to the actual situation.
3. Unstable pressure, large pressure swing and sometimes loud noise
According to the provisions of relevant standards, the pressure swing of J-type pressure reducing valve is ± 0.1MPa and that of JF type is ± 0.3MPa. Exceeding this standard means that the pressure swing is large and the pressure is not stabilized.
(1) Cause analysis.
1) When the pressure reducing valve is used beyond the rated flow, the main valve oscillation often occurs, which makes the pressure reducing valve
2) Spring deformation or poor stiffness (poor heat treatment), resulting in large pressure fluctuation.
3) J-type and JF type pressure reducing valves are pilot type, and the pilot valve is common with the overflow valve, so the willing cause of large pressure swing can be referred to the relevant parts.
4) Drain port I. If the back pressure is large, the phenomenon of large pressure swing and unstable pressure will also occur.
(2) Troubleshooting.
1) Replace and select the pressure reducing valve suitable for the model and specification.
2) Qualified springs can be replaced.
3) The troubleshooting method can refer to the relevant parts of the overflow valve.
4) The oil drain pipe should be returned separately.
4. Serious leakage
The cause of serious leakage is basically the same as that of overflow valve, which can be overhauled and eliminated by reference.
