If you’re dealing with unplanned shutdowns or persistent alarms on your high-pressure PET compressor, you’re not alone. Whether you’re an on-site technician or plant manager, having a reliable fault guide is crucial for staying online and productive.
This practical guide helps you troubleshoot common faults across all Belliss & Morcom WH compressor models, including:
WH28
WH29
WH35
WH40
WH45
WH50
These robust units power countless PET packaging lines worldwide—but even the best machines need attention now and again. Read on to learn how to identify, understand, and fix the most common compressor faults before they become costly failures.
Common Startup Issues
Pressure, Flow & Valve-Related Faults
Temperature and Cooling System Problems
Mechanical Noises and Vibrations
Electrical & Instrumentation Faults
Prevention Tips to Reduce Repeat Failures
1. Unit Will Not Start
Emergency stop engaged
Safety switch activated (e.g. low oil pressure, water flow, high temperature)
Incorrect phase rotation or blown control fuses
Faulty starter or isolator
The motor is not receiving a signal from the panel
2. Trips Immediately After Starting
The oil pump is not building pressure
Incorrect oil level or unsuitable oil type
The water supply valve is closed or blocked
Control circuit fault or overloaded starter
3. Low Delivery Pressure
Open the bypass or drain valve
Leaks in the air system
Suction valve not fully closed
Excessive valve or ring wear
4. Relief Valve Frequently Blowing
The delivery pressure switch is set too high
Blocked cooler or discharge pipe
Faulty unloader or malfunctioning actuator
5. Interstage Pressure Off-Spec
Valve issues in the previous stage
Blocked or fouled intercoolers
Worn or damaged piston rings
6. High Final Air Temperature
Poor water flow (below 24 m³/h)
Dirty or blocked aftercooler/intercoolers
High ambient or water inlet temperature
Valve leakage or ring wear
7. High Oil Temperature
Low oil level or degraded oil
Oil cooler fouled or bypassing
Cooling system fault
8. High Water Outlet Temperature
Restricted flow in cooling water lines
Incorrect pressure in the water supply
Excessive ambient heat
9. Strange Noises
Bearing wear (crosshead, crankshaft, etc.)
Valve plate movement or failure
Loose pistons or worn guides
10. Excessive Vibration
Mounting bolts are loose or uneven
Pipe strain from rigid connections
An imbalanced flywheel or worn motion components
11. Starter or Motor Trips
Voltage fluctuations or phase loss
Overload tripping too early
Motor winding failure
12. Faulty Readings or No Indication
Sensor drift or failure
Pressure gauge damaged or out of calibration
Faulty wiring in the control panel
Monitor daily: Log pressure, oil level, air temps, and water flow for trend spotting.
Use high-quality parts: Aftermarket doesn’t mean low-grade—ours are engineered to OEM tolerances.
Service valves regularly: Valve wear is a common cause of pressure and flow issues in all WH units.
Stick to service intervals: Follow manufacturer guidance for changing rod packings, piston rings, and oil.
This guide applies to all Belliss & Morcom WH-series compressors, including:
WH28, WH29, WH35, WH40, WH45, and WH50
These models share common design architecture, safety systems, and maintenance principles, making this fault-finding guide your go-to reference for the entire range.
At DLJ Compression, we supply precision aftermarket parts and offer technical support for all WH-series compressors. Whether you’re troubleshooting suction valve issues, replacing worn packings, or planning a major overhaul, we can help.
– Service kits available for all WH models
– Fast response and expert diagnosis
– Global supply of WH-compatible parts
Reach out today, and keep your PET production line running smoothly.
