Low Discharge Pressure in Your Air Compressor
When Your Compressor Runs, But Pressure Doesn’t Build
If your air compressor is running but your pressure gauge barely moves (or takes forever to build pressure) you’re likely dealing with a discharge pressure issue. This problem can show up in any compressor type, from reciprocating to portable rotary screw to stationary rotary screw units. Here’s how to troubleshoot the cause based on the kind of machine you own.
If You Have a Reciprocating or Portable Rotary Screw Compressor
These compressors tend to lose discharge pressure due to basic wear-and-tear or airflow restrictions. The good news: most of these fixes are quick and cost-effective.
What to Check:
- Dirty or Clogged Air Filter – A blocked intake restricts airflow into the system.
- Leaky Connections or Hoses – Even small leaks can keep pressure from building fully.
- Loose or Slipping Belts – If the motor is spinning but not transferring full power, output suffers.
- Faulty Check Valve – If it’s not sealing properly, air may leak back into the system.
- Worn Pistons or Valves (Recip Models) – In older reciprocating units, internal wear can reduce compression efficiency.
What to Do:
- Replace or clean your air filter regularly. Don’t wait for it to clog completely.
- Tighten hose clamps and use soapy water to find air leaks around fittings.
- Inspect and tighten belts; replace if they’re cracking or glazed.
- Remove the check valve and clean or replace it if it’s leaking.
- If internal wear is suspected, it may be time for a rebuild or component replacement.
If You Have a Stationary Rotary Screw Compressor
Low discharge pressure on a rotary screw system is usually more about controls, filtration, or internal flow issues. The system may be running, but it’s not delivering what it should.
Where to Look:
- Dirty Separator Element or Oil Filter – These restrict airflow and reduce system efficiency.
- Inlet Valve Malfunction – If the valve is stuck partially open or closed, air won’t flow correctly.
- Improper Pressure Switch or Controller Settings – The unit may be working against the wrong target.
- Air End Wear or Damage – Worn rotors can’t compress air efficiently.
- Demand Exceeds Capacity – The plant may be pulling more air than the machine is rated to deliver.
How to Fix It:
- Inspect the separator and oil filters; replace if they’re near end-of-life or clogged.
- Test the inlet valve to make sure it fully opens under load conditions.
- Check pressure switch and controller setpoints—reset to OEM specs if needed.
- Perform air end inspection if the unit has high hours or you suspect rotor wear.
- Verify system demand and consider adding a second unit or storage if needed.
Prevent Low Pressure Issues
For Reciprocating and Portable Compressors
- Change air filters regularly and store your compressor in a clean environment.
- Inspect hoses and fittings for leaks every month.
- Replace belts as part of your annual maintenance, even if they still “look fine.”
For Stationary Rotary Screw Compressors
- Follow a strict filter and separator change schedule based on runtime hours.
- Keep your controller parameters documented and periodically verify setpoints.
- Log airend hours and plan rebuilds before performance drops become noticeable.