Common Faults and Troubleshooting Methods for ATOS Pressure Reducing Valves

Brand

ATOS/Italian Atos

Application Areas

Environmental Protection, Bio-industry, Petroleum, Pharmaceutical/Biopharmaceutical, Comprehensive

ATOS Gear Pump, ATOS Axial Piston Pump, ATOS Vane Pump, ATOS Hydraulic Cylinder

ATOS pressure reducing valves reduce the inlet pressure to a desired outlet pressure through adjustment, and rely on the energy of the medium itself to automatically maintain a stable outlet pressure. From a fluid mechanics perspective, a pressure reducing valve is a throttling element with variable local resistance. That is, by changing the throttling area, the flow velocity and kinetic energy of the fluid are changed, resulting in different pressure losses, thereby achieving the purpose of pressure reduction. Then, relying on the adjustment of the control and regulation system, the fluctuation of the downstream pressure is balanced with the spring force, so that the downstream pressure remains constant within a certain error range.

Common Faults of ATOS Pressure Reducing Valves

(1) The outlet pressure is almost equal to the inlet pressure, and there is no pressure reduction. This fault is manifested as: the inlet and outlet pressures of the pressure reducing valve are close to equal, and the outlet pressure does not change with the rotation of the pressure regulating handle. The causes and troubleshooting methods are as follows. ① Burrs on the countersunk groove edge of the main valve core or valve body hole, or dirt stuck in the gap between the main valve core and valve body hole, or out-of-tolerance dimensional tolerances of the main valve core or valve hole, cause hydraulic jamming, locking the main valve core in the maximum opening (max) position. Due to the large opening, the oil pressure is not reduced. In this case, deburring, cleaning, and repairing the valve hole and valve core precision can be used to resolve the issue, depending on the specific situation.

② An overly tight fit between the main valve core and valve hole, or roughening of the valve hole or valve core during assembly, can also cause the valve core to jam in the maximum opening position. In this case, a suitable clearance can be selected. The clearance for J-type pressure reducing valves is generally 0.007～0.015mm. Before fitting, the valve hole can be appropriately ground before fitting the valve core.

③ Blockage of the short damping hole or valve seat hole of the main valve core results in the loss of its automatic adjustment function. The main valve spring force pushes the main valve to the maximum opening, becoming a straight-through unobstructed flow, with the inlet pressure equal to the outlet pressure. The damping orifice can be cleared using a φ1.0mm steel wire or compressed air, followed by cleaning and reassembly.

④ For J-type pressure reducing valves, the damping element with the damping orifice is pressed into the main valve core. During use, it may be pushed out due to insufficient interference fit. After being pushed out, the pressure in the inlet and outlet chambers becomes equal (no damping), and the upper and lower force areas of the valve core are equal. However, there is a spring in the outlet chamber, so the main valve core is always in the maximum opening position, making the outlet pressure equal to the inlet pressure. In this case, the damping element with a slightly larger outer diameter needs to be re-machined and re-pressed into the main valve core.

⑤ For JF-type pressure reducing valves, the drain hole is plugged with an oil plug at the factory. When this oil plug is not unscrewed and the valve is used, oil is trapped in the upper chamber (spring chamber) of the main valve core, causing the main valve core to be in the maximum opening without pressure reduction. The same applies to J-type pipe valves. This phenomenon will also occur in J-type plate valves if the L port is not connected to the oil sump when the mounting plate is designed.

⑥ For J-type tubular valves, it's easy to install the valve cover incorrectly (90° or 180° off) during disassembly and repair, blocking the external drain port and preventing oil drainage, causing the same oil trapping phenomenon as above, resulting in the main valve remaining at its maximum opening without pressure reduction. Simply install the valve cover in the correct orientation during repair.

⑦ For JF-type pressure reducing valves, incorrect top cover orientation will cause the output oil hole to connect with the drain hole, resulting in no pressure reduction; this must also be noted.

(2) The outlet pressure is very low; even tightening the pressure regulating handwheel does not raise the pressure.

① The pressure reducing valve's inlet and outlet ports are reversed: for plate valves, this is a design error in the mounting plate; for tubular valves, it's an incorrect connection. The inlet and outlet ports of the J-type pressure reducing valve are exactly opposite to those of the Y-type relief valve. Users should pay attention to the stamped markings (Pl, P2, L, etc.) near the oil ports on the valve, or consult the hydraulic component product catalog; incorrect design and connection are unacceptable. ② If the inlet pressure is too low, the pressure output from the outlet will be even lower after passing through the throttling orifice of the pressure reducing valve core. In this case, the cause of the low inlet pressure should be investigated (e.g., a faulty relief valve).

③ If the downstream circuit load of the ATOS pressure reducing valve is too small, the pressure cannot be built up. In this case, consider connecting a throttling valve in series downstream of the pressure reducing valve.

④ Poor contact and lack of tightness between the pilot valve (cone valve) and the valve seat mating surface due to dirt accumulation; or severe scratches on the pilot cone valve, out-of-roundness of the valve seat mating hole, or gaps, causing a lack of tightness between the pilot valve core and the valve seat hole.

⑤ During disassembly and repair, the cone valve may be missing or not installed in the valve seat hole. In this case, check the assembly and sealing of the cone valve.

⑥ The long damping orifice on the main valve core is blocked by dirt, as shown in Figure 3-21. Oil in chamber P2 cannot flow into the main valve spring chamber through the long damping orifice e. The feedback pressure from the outlet chamber P2 cannot be transmitted to the pilot cone valve, causing the pilot valve to lose its regulating function on the main valve outlet pressure. After the damping orifice is blocked, the main valve P1 chamber 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). Therefore, when the outlet pressure is very low, it can overcome the force of the balance spring and close the pressure reducing valve throttling orifice ymin. This causes the inlet pressure p1 to drop significantly to p2 through the ymin throttling orifice, preventing the outlet pressure from rising. The long damping orifice should be kept clear.

⑦ The pilot valve spring (pressure regulating spring) is incorrectly installed as a soft spring, or it may be deformed or broken due to spring fatigue, causing the p2 pressure to be unable to be adjusted higher, only reaching a low set value, which is far below the maximum regulating pressure of the pressure reducing valve.

⑧ The pressure regulating handle cannot be fully tightened due to thread damage or insufficient effective depth, preventing the pressure from reaching the maximum.

⑨ Poor sealing between the valve cover and valve body, resulting in severe oil leakage. This may be caused by a missing or damaged O-ring, loose tightening screws, or end-face flatness errors during valve cover machining, typically resulting in a convex perimeter and a concave center.

⑩ The main valve core is stuck in a small opening position due to dirt, burrs, etc., causing low outlet pressure. Cleaning and deburring are necessary.

(3) Unstable pressure, large pressure fluctuations, and sometimes high noise.

According to relevant standards, the pressure fluctuation of a J-type pressure reducing valve is ±0.1 MPa, and for a JF-type it is ±0.3 MPa. Exceeding these standards indicates large pressure fluctuations and unstable pressure.

① J-type and JF-type pressure reducing valves are pilot-operated, and the pilot valve is interchangeable with the relief valve. Therefore, the causes and troubleshooting methods for large pressure fluctuations can be found in the relevant sections on relief valves. ② When the pressure reducing valve is used beyond its rated flow rate, the main valve often oscillates, causing the pressure reducing valve to become unstable. In this case, the outlet pressure cycles through "pressure increase-decrease-re-pressure increase-re-decrease," so it is essential to select a pressure reducing valve of the appropriate model and specifications.

③ High back pressure at the drain port L can also cause large pressure fluctuations and instability. A separate return line should be used for the drain pipe.

④ Spring deformation or poor stiffness (due to poor heat treatment) leads to large pressure fluctuations. A qualified spring should be replaced.

(4) The outlet pressure automatically increases 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 electro-hydraulic directional valves or externally controlled sequence valves. When the electro-hydraulic directional valve or externally controlled sequence valve reverses or operates, the outlet flow of the pressure reducing valve becomes zero, but the pressure still needs to maintain the previously set pressure. In this case, because the valve outlet flow is zero, only the pilot flow flows through the pressure reducing port. Because the pilot flow rate is very small, generally within 2 L/min, the main valve pressure reducing port is almost fully closed (with a very small opening). The pilot flow rate exits through the triangular groove or inclined cone surface. If the main valve core fit is too loose or wear is excessive, the leakage will increase. According to the flow continuity theorem, this leakage must also flow from the main valve core damping orifice. That is, the flow rate through the damping orifice consists of both the pilot flow rate and the leakage. Since the damping orifice 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), to increase the flow rate through the damping orifice, the hydraulic pressure in the lower chamber of the main valve will inevitably increase. Therefore, when the pressure reducing valve outlet pressure is set, if the outlet flow rate is zero, the outlet pressure will increase due to the main valve core fit being too loose or wear being excessive.