# Tool Pressure + Tank Pressure Relationship -- Is my Understanding Wrong?



## crosis (Sep 12, 2021)

I own a cheap Husky Air Compressor (Model: 0100211A) ...











*My Understanding of Air Compressors*

Now I'm no expert with air compressors but i am aware of the Tank Pressure Gauge and the Tool Pressure Gauge ;P . My understanding is when the air compressor is charging the Tank Pressure gauge will keep rising until the cut-off point (98 PSI, factory set) then cut-in come time to charge up (60 PSI, factory set). The Tool Pressure gauge will also climb to the point where the Air Pressure Regulator is set (mine is set for 50 PSI).

Furthermore, when the tool pressure gauge starts to fall the tank pressure side will compensate by topping up the tool pressure side so as to maintain the constant regulated pressure; so if the tool pressure starts to dip below 50 PSI then the tank pressure side will *promptly* compensate by moving some pressure over into the tool pressure side raising it back up to 50 PSI whereas the tank pressure side falls accordingly. Is this accurate?


*Usage*

During usage my Tank Pressure is at 98 PSI and Tool Pressure is at 50 PSI. When i hold down the wand to use up the tool pressure as expected the tool pressure drops quickly. The Tank Pressure, however, slowly drops. Its not until the tool pressure is at about 20 PSI and Tank Pressure has fallen to 60 PSI before the motor kicks in ...











When the motor kicks in the Tank Pressure Gauge slowly rises, however, the Tool Pressure Gauge remains at 20 PSI ...











*My Problem*

I was expecting the Tool Pressure Gauge side to maintain a constant 50 PSI but in actuality the tool pressure falls to 20 PSI without any help from the tank pressure side. The tool pressure side will not increase past 20 PSI even after the tanks side has fully topped up; I must manually adjust the regulator knob to allow more air in to get the tool side back up to 50 psi. Also, during tests, i'm able to drop the Tool Pressure side to 45 PSI while the Tank Pressure side remains at 98 PSI -- no movement. Again i was expecting some pressure sharing from the Tank side to the Tool side to raise it back up to 50 PSI. Not happening.

*Is my understanding of how air compressor work inaccurate or is my cheapo unit faulty?*

Thanks.


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## Marlin (May 25, 2015)

Very simple, the flow rate of your "wand" exceeds the flow rate of your regulator.

Try this: Hold down the lever on your want just enough to allow a little flow, enough that you can hear it but only a slight flow, you will see that the tool pressure gauge stays at 50 until the tank pressure goes down to 60 and the compressor kicks on.

Continuing holding the valve, you will see the tool pressure gauge will stay at 50 while the tank pressure climbs and eventually the compressor shuts off.

The restriction you are seeing may or may not be problematic, do you really have a need for that high of a flow rate at the tool, even including a standard blowgun?

If it is a problem, look for too small of fittings at the inlet of the regulator or maybe too small of a regulator.

If you think about it, even the largest regulator with the highest flow rate will see no or little pressure in the outlet if the glow rate is high enough.

I have a tiny little artist's airbrush air compressor. Using an airbrush, it can maintain set outlet pressure even with the airbrush operating continuously. The compressor has an air tank about one quart in size. The tank pressure stays higher than the desired tool pressure at all times.

But, if I put a blow gun on the end of the hose instead of an airbrush, I can reduce both gauges to near zero in about 3 seconds.

It's simple, you are exceeding the designed specifications of your compressor, probably nothing wrong with it at all.


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## iowagold (Jan 22, 2020)

you have to match the CFM of the compressor AND the regulator AND the fittings AND the hose to exceed the tool cfm..

best way is to look at the cfm of each tool and if you are to use only one tool at a time
that is the number you need for matching the rest of the system

i like to factor 2x the required cfm on every thing when doing a system.
that way you do not have to buy it twice.

for most home garage shops 3/4 ID line works for the feed lines to the outlets at the point of use.
pm if you need links for good systems.


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