"My compressor won't build pressure any more" is one of the most common questions about compressed air. In most cases, the cause is simple and can be found in a few minutes. Here are the checks to make, from the simplest to the most technical.
Safety first: before opening a cover or removing a part, switch off the power supply, lock it out and release the air from the air receiver. A compressor can restart on its own as long as it is powered.
The diagnosis in one table
| What you notice | Likely cause | What to do |
|---|---|---|
| Pressure drops quickly when the compressor stops, even with no tool connected | Leak in the network, a fitting or the drain | Look for leaks with soapy water or by listening, with the machine stopped |
| The compressor runs non-stop but never reaches the cut-out pressure | Consumption higher than the flow, or a major leak | Compare the tools' consumption with the compressor's actual flow |
| Filling the air receiver takes longer and longer | Clogged intake air filter | Clean or replace the air filter |
| The compressor stops before the expected pressure | Pressure switch or set point incorrectly adjusted | Check the cut-out pressure set on the pressure switch or controller |
| Piston compressor - the motor runs but the pump struggles | Loose or worn belt | Check the belt tension and condition |
| Piston compressor - air comes out of the intake filter | Faulty cylinder valve | Have the valves checked |
| Screw compressor - it runs but does not load | Intake valve not opening, or a fault reported | Read the message shown on the controller |
| Large amounts of water come out of the drain and the usable volume seems reduced | Air receiver full of condensate | Drain the air receiver and check the automatic drain |
1. Look for leaks
This is the number one cause. A leak makes the pressure drop as soon as the compressor stops, and forces it to run longer to compensate. Do the following test: build up pressure, close all tools, and watch the pressure gauge. If the pressure falls while nothing is consuming air, there is a leak.
Listen to the network when it is quiet, or apply soapy water to fittings, quick couplings, hoses and the drain: bubbles show the leak. Our article on how to detect and repair compressed air leaks details the method, and the leak cost calculator shows what they are costing you.
2. Compare consumption with flow
A compressor cannot deliver more air than its flow. If you have added a tool, a blow gun that stays open or an extra workstation, consumption may simply exceed what the machine produces: the pressure tops out below the set point.
Add up the consumption of the tools used at the same time and compare it with the compressor's actual flow at your working pressure. The configurator does this calculation. If the compressor is undersized, the answer is not to raise the pressure but to increase the flow.
3. Clean the air filter
A clogged intake filter chokes the compressor: it draws in less air, so it compresses less. Filling takes longer and longer. The filter is checked at every service and replaced as soon as it is blocked. On our screw compressors, the first service takes place at 500 hours, then every 1,500 hours, and the controller shows the reminder. For piston compressors, see when to service a piston compressor.
4. Check the settings
The compressor stops at the cut-out pressure set on the pressure switch (piston) or on the controller (screw). If this set point has been changed, the machine stops earlier than expected. Also check that the pressure you want does not exceed the machine's maximum pressure: an 8 bar compressor will never deliver 10 bar. Our article on calculating your compressor pressure helps you choose the right set point.
5. Causes specific to piston compressors
- The belt: when loose, it slips and the pump turns more slowly. When worn or cracked, it must be replaced.
- The valves: an intake or discharge valve that does not close properly lets air flow back. Typical sign: air coming back out through the intake filter.
- The piston rings: as they wear, air passes between the piston and the cylinder. The compressor runs hotter, uses oil and produces less air.
6. Causes specific to screw compressors
On a screw compressor, the electronic controller monitors pressure, temperature and operating hours. Read the displayed message first: it points the diagnosis straight in the right direction. An intake valve that stays closed, a faulty pressure sensor or a clogged air/oil separator are among the possible causes. These jobs are for a technician.
When to call after-sales service
If leaks, the filter, the settings and consumption have been ruled out, or if the controller shows a fault, contact after-sales service. Before calling, note the model, the operating hours, the pressure reached and any message displayed: the diagnosis will be all the quicker.