(I) The outlet pressure is almost equal to the inlet pressure, and the pressure is not reduced
This fault phenomenon is manifested as: the inlet and outlet pressures of the pressure reducing valve are almost equal, and the outlet pressure does not change with the rotation adjustment of the pressure regulating handle. The causes and troubleshooting methods are as follows.
1. Because there are burrs on the edges of the main valve core or the countersunk groove of the valve body hole, or dirt is 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 the valve hole exceeds the tolerance, hydraulic clamping occurs, and the main valve core is stuck at the maximum opening (max) position. Due to the large opening, the oil does not reduce pressure. At this time, according to the above situation, the methods of deburring, cleaning and repairing the valve hole and valve core accuracy can be adopted to eliminate it.
2. Because the main valve core and the valve hole are too tight, or the valve hole or valve core is roughened during assembly, the valve core is stuck at the maximum opening position. At this time, a reasonable gap can be selected. The matching clearance of the J-type pressure reducing valve is generally 0.007~0.015mm. 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 valve seat hole is blocked, and the automatic adjustment function is lost. The main valve spring force pushes the main valve to the maximum opening, becoming straight through without obstruction, and the inlet pressure is equal to the outlet pressure. The damping hole can be blown through with φ1.Omm steel wire or compressed air, and then 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 be flushed out during use due to insufficient interference. After flushing out, the pressure of the oil inlet chamber and the oil outlet chamber is equal (no 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 the maximum opening position, so that the outlet pressure is equal to the inlet pressure. At this time, the damping part with a slightly larger outer diameter needs to be reprocessed and re-pressed into the main valve core.
5. For the JF-type pressure reducing valve, the oil drain hole is blocked with an oil plug when leaving the factory. When the oil plug is not screwed out and used, the main valve core upper chamber (spring chamber) is trapped with oil, causing the main valve core to be at the maximum opening without reducing pressure. The J-type tubular valve is the same. If the J-type plate valve is designed to install the mounting plate without connecting the L port to the oil pool, this phenomenon will also occur.
6. For J-type tubular valves, 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 leakage port is blocked and the oil cannot be discharged, causing the same oil trapped phenomenon as above, causing the main valve to be at the maximum opening without reducing pressure. When repairing, just install the valve cover in the right direction.
7. For JF type pressure reducing valves, when the top cover is installed in the wrong direction, the output oil hole and the oil leakage hole will be connected, resulting in no pressure reduction, which should also be noted.
(II) The outlet pressure is very low, and the pressure cannot rise even if the pressure regulating handwheel is tightened
1. The inlet and outlet oil ports of the pressure reducing valve are connected in reverse: for plate valves, the mounting plate design is wrong, and for tube valves, the pipe connection is wrong. The inlet and outlet of the J-type pressure reducing valve are just opposite to those of the Y-type relief valve. When using, please pay attention to the steel stamp marks (Pl, P2, L, etc.) near the oil port on the valve, or check the hydraulic component product catalog. Do not design or connect incorrectly.
2. The oil inlet pressure is too low. After passing through the throttle port of the pressure reducing valve core, the pressure output from the oil outlet is even lower. At this time, the reason for the low oil inlet pressure should be found out (for example, the overflow valve is faulty).
3. The load of the downstream circuit of the pressure reducing valve is too small, and the pressure cannot be established. At this time, you can consider connecting a throttle valve in series downstream of the pressure reducing valve to solve the problem.
4. The pilot valve (cone valve) and the valve seat mating surface have poor contact and are not tight due to the retention of dirt; or the pilot cone valve has serious scratches, the valve seat mating hole is out of round, and there is a gap, causing the pilot valve core and the valve seat hole to not fit tightly.
5. During disassembly and repair, the cone valve is missing or the cone valve is not installed in the valve seat hole. In this regard, the assembly or tightness of the cone valve can be checked.
6. The long damping hole on the main valve core is blocked by dirt, and the oil in the P2 chamber cannot flow into the main valve spring chamber through the long damping hole e. The feedback pressure of the oil outlet chamber P2 cannot be transmitted to the pilot cone valve, causing the pilot valve to lose its regulating effect on the main valve outlet pressure. After the damping hole is blocked, the main valve P. The chamber loses the effect of the oil pressure p3, making the main valve a direct-acting slide valve with a very weak spring force (only the main valve balance spring). Therefore, when the oil outlet pressure is very low, the force of the balance spring can be overcome to close the throttle port of the pressure reducing valve to ymin, so that the oil inlet pressure p1 is greatly reduced to p2 through the ymin throttle port, so that the oil outlet pressure cannot rise. The long damping hole should be unobstructed.
7. The pilot valve spring (pressure regulating spring) is mistakenly installed as a soft spring, or the spring fatigue causes permanent deformation or breakage, etc., resulting in the p2 pressure not being able to be adjusted high, and can only be adjusted to a certain low fixed value, which is much lower than the maximum regulating 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 the pressure cannot be adjusted to the maximum.
9. The seal between the valve cover and the valve body is poor, and there is serious oil leakage. The cause may be the missing or damaged O-ring, the tightening screw is not tightened, and the end face flatness error occurs during the valve cover processing, which is generally convex around and concave in the middle.
10. The main valve core is stuck in a small opening position due to dirt, burrs, etc., resulting in low outlet pressure. It can be cleaned and deburred.
(III) Unstable pressure, large pressure swing, and sometimes loud noise
According to the relevant standards, the pressure swing of J-type pressure reducing valve is ±o.1MPa, and that of JF-type is ±o.3MPa. Exceeding this standard means large pressure swing and unstable pressure.
1. J-type and JF-type pressure reducing valves are pilot-operated, and the pilot valve and the relief valve are common, so the causes and elimination methods of large pressure swing can refer to the relevant parts of the relief valve.
2. When the pressure reducing valve is used at a flow rate exceeding the rated flow, the main valve oscillation phenomenon often occurs, making the pressure reducing valve unstable. At this time, the oil outlet pressure appears a cycle of "increase pressure, reduce pressure, increase pressure again, and reduce pressure again", so it is necessary to select a pressure reducing valve of suitable model and specification.
3. The back pressure of the oil drain port L is large, which will also cause large pressure swing and unstable pressure. The oil drain pipe should return oil separately.
4. The spring is deformed or the stiffness is not good (the heat treatment is not good), resulting in large pressure fluctuations. Qualified springs can be replaced.
(IV) The outlet pressure increases automatically after the working pressure is set
In some pressure reducing control circuits, the outlet pressure of the pressure reducing valve is used to control the control oil 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 switched or works, the outlet flow of the pressure reducing valve 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 pressure reducing port is only the pilot flow. Since the pilot flow is very small, generally within 2L/min, the main valve pressure reducing port is basically close to the fully closed position (very small opening), and the pilot flow flows out from the triangular groove or the inclined cone surface. If the main valve core is too loose or worn too much, the leakage will increase. According to the flow continuity theorem, this part of the leakage must also flow from the damping hole of the main valve core, that is, the flow through the damping hole is composed of the pilot flow and the leakage, while the damping hole area and the main valve spring chamber oil pressure remain unchanged (the spring chamber oil pressure is determined by the pre-compression of the adjusted pressure regulating spring). In order to increase the flow through the damping hole, it is inevitable to cause the oil pressure in the lower chamber of the main valve to increase. Therefore, when the outlet pressure of the pressure reducing valve is adjusted, if the outlet flow is zero, the outlet pressure will increase due to the main valve core being too loose or worn too much.