Air Compressor Pressure Drops During Operation

Is it behaving differently than it did in the past?

Here are some tips for troubleshooting...

Both previous questions are valid dude. What is your draw number and what is your supply number?

Somebody else may have tapped into your compressed air lines. Power theft is obnoxious but real. Trace all of the lines from your compressor and storage tank.

The one thing you can do is to use a stop watch to measure how long it takes for a known tool to turn ON the compressor and how long it takes for the compressor to turn OFF. A little math and comparison should tell where the problem lies. You might find that you just have a slow leak somewhere. Soapy water can find where a leak resides.

We really don’t have much to go on yet.

I’ve seen drastically underperforming compressors with air receivers holding about 50% water. Combine this with insufficient lube to even touch the sight glass and you get a sluggish and slow recovery, way too many cycles, and dirty air (as a bonus, all of the companion problems that come with dirty shop air). These two common maintenance issues would likely give the symptoms described in the (somewhat confused) thread title.

Yeah, we need our new member MalcAndCheese to tell us some more about what has been done so far, as well as more detail on equipment involved. I never considered an uninvited guest helping himself to my compressed air, but I suppose this could be.

Many (likely most) compressors can struggle to keep up with a single high-demand tool like a grinder or paint spray gun. 'We' implies multiple tools at once. Remember in 'Jaws' where they needed a bigger boat? Well...

Clearly the demand exceeds the supply which can also be caused by the head gasket leaking. I have found this to occur because newer compressors use and Aluminium head gasket. I have replaced the head gaskets on 3 separate compressors with Copper ones and the problem went away.

Maybe this is your problem which is not shown during the run up to normal unloaded pressure. Compare the CFM of the compressor against the summated tool load CFM by their nameplate.

Measure the CFM at the tool while it is running before you touch the pump – if the tank holds pressure with no demand but drops under load, you are normally looking at demand exceeding supply or a restriction between tank and tool, not a pump fault.

Three things that get missed:

• The intake element can look clean and still be restricted. Check its pressure drop rather than its colour, and make sure the intake hose or silencer is not collapsing under vacuum.
• Water in the receiver. A tank half full of condensate loses most of its usable storage, so the machine cycles far more often – drain it and confirm the separator/drain is actually working.
• Unloader or tank check valve leaking back to the head when the unit stops.

If it is a small single-stage unit feeding a grinder or a spray gun, it is probably simply undersized – 1–2 HP will not sustain the 6–9 CFM those tools draw.