Plunger Valve Troubleshooting

The plunger valve is a common type of valve used to control and cut off the flow of fluids, widely applied in various industrial fields. However, during its operation, plunger valves may experience various faults, affecting their efficiency. This article ATO industrial automation will discuss the causes of common plunger valve faults and methods for resolving them to help users restore normal operation as quickly as possible.

Insufficient or No Output Flow from Plunger Valve

1. Inadequate suction: This can occur due to excessive resistance in the suction pipeline or insufficient replenishment of hydraulic fluid. Causes may include high valve speed, low liquid level in the reservoir, air leaks in the inlet pipe, or clogged filter elements.
2. Excessive leakage: Large gaps and poor sealing in the valve can cause excessive leakage. This may be due to metal fragments or debris scratching the spool, oil leakage at the end face, poor mating of the one-way valve in the variable mechanism, or the presence of sand holes or scoring on the valve body and distribution plate. Identifying the source of foreign matter in the hydraulic oil inside the valve can help locate damaged components.
3. Small angle of the tilting plate: it results in lower valve displacement, which can be addressed by adjusting the variable piston to increase the tilt angle.

Non-Zero Output Flow at Midposition

In a variable directional plunger valve, the zero tilt angle of the tilting plate is considered the midposition, where output flow should be zero. However, sometimes the midposition may deviate from the midpoint of the adjustment mechanism, resulting in continuous flow output at midposition. This can be caused by a misaligned, loose, or damaged controller and requires recalibration, tightening, or replacement. Inadequate maintenance or wear of the damping device in the control piston can also cause this phenomenon.

Flow Fluctuations in Plunger Valve

Flow fluctuations in plunger valves can be attributed to various factors, often stemming from poor control of the variable mechanism. Possible issues include foreign matter entering the variable mechanism, scoring, abrasions, or damage on the control piston, insufficient amplifier energy, damaged components, or a poorly performing damping device for control pistons with springs. These problems can lead to unstable control piston movements and pressure fluctuations. Generally, troubleshooting such issues involves disassembling the hydraulic valve, replacing damaged parts, increasing damping, improving spring stiffness, and adjusting control pressure, among other steps.

Abnormal Output Pressure from Plunger Valve

Output pressure from the valve is determined by the load and is approximately proportional to input torque. Abnormal output pressure can manifest in two ways.

1. Low output pressure:
   When the valve is in a self-priming state, if there is air leakage in the oil inlet pipeline or significant leakage in the hydraulic cylinder, one-way valve, directional valve, etc. in the system, it will cause the pressure to not rise. This requires identifying the leak, tightening, and replacing the seal to increase the pressure. If there is a malfunction or low adjustment pressure in the overflow valve, and the system pressure cannot rise, the pressure should be readjusted or the overflow valve repaired. If the deviation between the cylinder body of the hydraulic valve and the port plate causes a large amount of leakage, and in severe cases, the cylinder body may break, the matching surface should be reground or the hydraulic valve should be replaced.
2. High output pressure:
   If the circuit load continues to rise and the pressure of the valve also continues to rise, it is considered normal. If the load is constant and the pressure of the valve exceeds the required pressure value for the load, hydraulic components outside the valve should be checked, such as directional valves, pressure valves, transmission devices, and return pipelines. If the pressure is too high, the overflow valve should be adjusted.

Vibration and Noise in Plunger Valve

Vibration and noise often occur together, posing risks to operators and environmental pollution.

1. Mechanical vibration and noise: Misalignment or interference between the valve shaft and the motor shaft, damaged bearings on the rotating shaft, damaged coupling joints, worn elastic cushions, and loose assembly bolts can generate noise. For high-speed or high-energy transfer valves, regular inspections, recording of amplitude, frequency, and noise levels for all components are recommended. When valve rotation frequencies match the natural frequency of pressure valves, resonance may occur, and it can be eliminated by changing the valve's speed.
2. Noise generated by fluid flow in the plunger valve pipeline: Noise can be produced due to factors like the inadequate size of inlet pipelines, low flow capacity or blockage in inlet filters, air ingress in inlet pipes, excessively high hydraulic fluid viscosity, low fluid levels causing inadequate suction, and liquid impact in high-pressure pipelines. Therefore, it is essential to design the reservoir properly and select the right filters, pipes, and directional valves.

Overheating of Plunger Valve

Excessive heating of plunger valves can result from two main causes. The first is mechanical friction-induced heating, which occurs due to components moving in a dry or semi-dry friction state, generating heat from mutual friction. The second cause is fluid friction-induced heating, where high-pressure oil leaks through various gaps into low-pressure chambers, leading to a significant loss of hydraulic energy converted into thermal energy. Properly selecting clearances between moving parts, reservoir volume, and cooling equipment can help prevent overheating and excessively high oil temperatures in the valve. Additionally, blockages in the return oil filter leading to high back pressure can also cause elevated oil temperatures and overheating of the valve body.

Oil Leakage from Plunger Valve

There are various reasons for oil leakage in a plunger valve:

1. Damage to the main shaft oil seal or defects, scratches, or other flaws in the shaft.
2. Excessive internal leakage causing increased pressure at the seal, which can damage or push out the oil seal.
3. Inadequately sized or excessively long drain pipes causing leaks at the seal.
4. Loose external oil pipe connections, damaged pipe joints, aging or cracked sealing gaskets.
5. Loosening of bolts in the variable control mechanism and seal damage.
6. Sand holes or poor welding in the cast iron valve shell.

The plunger valve is a critical component that plays an essential role in industrial production. While it offers numerous benefits, it is vital to understand and address its faults. By following the information provided in this article, users can better comprehend the causes of plunger valve malfunctions and employ appropriate solutions to safeguard and maintain these critical devices, ensuring their safe and efficient operation.