The compressor is simply too small for the job. More air is being used than the machine can produce. No fault, no leak -- just not enough compressor.

What you'll see

The compressor runs loaded 100% of the time and pressure still drops below setpoint during peak demand. It might recover during quiet periods but can't keep up when the factory is running at full production. The pressure swings between the load and unload setpoints -- or worse, drops below the load setpoint. This often creeps up slowly as new equipment is added to the system.
Before you assume this is the problem

Before deciding the compressor is too small, verify it's actually delivering its rated capacity. Close the outlet valve -- does it reach setpoint quickly? If yes, the compressor is healthy and it's truly a capacity issue. If it struggles even with the outlet closed, the compressor itself has a problem (inlet valve, separator, etc.). Also check for leaks -- fixing a 20% leak rate is like getting 20% more compressor for free.

Could also be:

See all causes of low pressure / can't reach setpoint →

How to diagnose

  1. The outlet valve test (again)

    Close the outlet valve. If the compressor quickly builds to setpoint and unloads, it's producing its rated capacity. The problem is that demand exceeds what it can supply. This test is the starting point for every low-pressure investigation.

    Result: Quick pressure buildup with valve closed = compressor is OK, demand is too high.

  2. Check what changed

    Did someone add a new machine? A new production line? A new blast cabinet? Even adding a few extra air tools can push a marginally-sized compressor over the edge. Ask the operators: when did the pressure problems start? What changed around that time?

    Result: New equipment coinciding with pressure problems = capacity issue confirmed.

  3. Monitor the load/unload cycle

    A healthy compressor with adequate capacity runs loaded maybe 60-70% of the time. If yours runs loaded 90-100% of the time and still can't maintain pressure, it's undersized. Some controllers display load percentage or duty cycle.

    Result: 100% loaded + pressure still dropping = not enough capacity.

How to fix it

  1. Fix leaks first

    Before buying another compressor, fix every leak in the system. In many factories, 20-30% of compressed air is wasted on leaks. Fixing them might be all you need. It's the cheapest 'capacity upgrade' there is.

  2. Install a larger air receiver

    A bigger receiver smooths out demand peaks. It won't increase average capacity, but it can handle short bursts of high demand that a smaller receiver can't buffer. This might be enough if the problem only occurs during brief peak periods.

  3. Add a second compressor

    If demand truly exceeds capacity after fixing leaks, you need more compressor. Adding a second machine (rather than replacing with a larger one) gives you redundancy and flexibility. Run one for base load, one for peaks. If one goes down, you still have the other.

Common mistakes

Don't increase the pressure setpoint to 'make more air'. Higher pressure means more energy consumption and more stress, but it doesn't increase the volume of air produced. The compressor delivers the same cubic meters per minute regardless of pressure setting. Also: an oversized dryer can cause significant pressure drop. If the dryer is too small compared to the airflow, pressure after the dryer drops even though the compressor is fine.

Parts & tools

No compressor parts needed -- this is a system sizing issue. Larger air receiver. Leak detection and repair supplies. Possibly a second compressor if the system is genuinely undersized.

Review safety precautions before starting →

This issue can also cause

  • High Energy Use Excessive power consumption or unexpectedly high electricity bills, often caused by control problems, air leak...