Oil pressure abnormality case

1. Case background:

Recently, a screw compressor at a chemical industry site was running for about 1 hour, and the oil pressure continued to rise to 4.8 bar. The normal oil pressure requirement of this model is about 3.0 bar, and it is equipped with an axial force balance plate, which is sensitive to oil pressure deviation. On-site personnel tried to adjust through the oil pressure regulating valve, but the regulating valve failed and the oil pressure could not drop back.

High oil pressure will not trigger an interlock alarm in the control logic of this model, but long-term high oil pressure will affect the oil temperature and heat dissipation, and affect the axial force balance, posing a risk of equipment damage.

2. Preliminary analysis

After receiving the feedback, our service engineer made the following judgment:

·  If the oil pressure deviates from the normal value and the regulating valve does not respond, it means that the regulating valve itself is abnormal, and it is most likely that the valve core is stuck.。

·  Common causes of jamming include: foreign matter blocking, spring damage, and assembly errors.

·  Since the unit has just been in operation and the oil system has not had similar problems before, it is priority to suspect foreign matter intrusion.。

3. Processing process:

Follow the engineer's instructions on site and perform the following steps:

1. After stopping the machine to ensure that the system pressure is relieved, disassemble the oil pressure regulating valve;

2. Completely disassemble the oil pressure regulating valve and check the status of each internal part;

3. After disassembly, it was found that the space between the valve core and the valve body was blocked by white plastic fragments, making the valve core unable to move;

4. Thoroughly clean the valve core, valve body and all internal flow channels, and remove plastic debris;

5. Reinstall the regulating valve according to the standard torque and restart the machine.

Results: After starting up, the oil pressure stabilized at around 3.0bar, the regulating valve returned to normal regulating function, and the fault was eliminated.

4. Fault summary analysis

The white plastic fragments were identified at the scene and came from the sealing strip torn off when the lubricating oil barrel was opened. During the process of filling lubricating oil, the sealing strip fragments entered the oil tank with the oil. After being sucked into the oil pump, they passed through the oil line and finally got stuck at the valve core of the oil pressure regulating valve, causing the valve core to become stuck.

Direct lessons:

1. Irregular operation of opening the cover of the oil drum is the direct root cause of this failure;

2. The cleaning inspection before adding lubricating oil is not standardized, and the surrounding foreign matter must be cleaned up;

Precautions:

5. Understand the oil pressure regulating valve

The oil pressure regulating valve used in this model is essentially a direct-acting piston type relief pressure stabilizing valve. Its functions are as follows:

·  When the oil pressure exceeds the set value (such as 3.0 bar), the high-pressure oil pushes the piston to move and gradually opens the oil return port. The excess lubricating oil flows back to the oil tank and the oil pressure drops.

·  When the oil pressure is lower than the set value , the spring pushes the piston back, gradually closing the oil return port, and the oil pump continues to pressurize to maintain the system oil pressure.

This valve is a key protection component of the compressor lubrication system. It can not only prevent excessive oil pressure from damaging the oil seal, but also prevent insufficient lubrication caused by excessive oil pressure.