# Compressor runs continuously?



## Dublak2

I bought my first air compressor based on suggestion here. I got a 10 gallon, 2.5hp, 125 psi.

if im going to use it on any given day I typically turn it on and let it run until the tank fills before i spray gun. Ive taped my line connections fairly well. I hear a tiny air leak at the tank valve.

my issue is that I hardly spray at all, maybe a couple minutes, and then the compressor needs to turn back on. Why? 10 gallon tank isn’t that tiny. The other thing that’s confusing is that when i open the tank release valve a ton of air spits out. So i know the tank is not empty when the compressor is switching on.

whys this thing running the whole time i spray? Cant i get some peace and quiet????


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## wingless

Welcome to the forum.

It sounds like the compressor pump is very small. What are the CFM ratings for the pump?

The pump operates to replenish air removed from the tank. The small leak sounds like a minor factor.

The spray gun has a specified air consumption. It would be something like 10 CFM at 40 PSI. What is the air consumption for the spray gun being used?

It sounds like air is being replenished MUCH more slowly than being used.

Get a bigger compressor to decrease the run time. Get a compressor that exceeds the consumption rate so there are never times where waiting is required to continue working.

Use a long air hose so the compressor noise is away from the user.


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## Dublak2

Gun is 6 CFM @ 40 psi and compressor is 6.2 cfm @ 40 psi and 5.3 cfm @ 90. Is that really all that far off?


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## wingless

Nope, those specs are on the edge for the continuously-operating compressor to keep up with the gun, eventually shutting off after gun usage, when the tank pressure is "happy" again.

If all is good, then the regulated air pressure should be maintained at the setpoint, such as 40 PSI, throughout the usage. Does the regulated pressure remain constant, or droop?

If a lower compressor operation duty cycle is desired / required, then a compressor w/ a much higher CFM is needed.

But, that setup is specified to be acceptable and that setup should never require waiting for air pressure to build before gun operation may resume. Are there times when waiting is required?


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## Dublak2

I have yet to experience any problems with the air pressure itself. Just that the compressor seems to kick on a lot. Fortunately my spray gun needs are that of a hobbyist so it’s not like im spraying every day, not even every week. Im just trying to troubleshoot and learn.


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## wingless

All sounds normal w/ this system, nothing to troubleshoot.

The pressure switch will kick on at something like 90 PSI and off around 125 PSI.

With the consumption and replenishment so close the compressor will not shut off until after consumption has stopped and the tank tops off.

That configuration is good. The compressor cycling on / off causes greater wear than continuous usage.


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## stevon

*10 gallon*

Dublak2,

I beleive what you hear is the head unloader feature of all compressors when you shut the pressure control switch off. This is to facilitate starting the electric motor with no back pressure to fight when you or the pressure switch turns the pump on. The check valve is a one way valve that commonly goes bad and if it does, air pressure will constantly leak out the head unloader until the tank is empty (causing constant cycling). I would keep a check valve handy as this is a maintenance item much like the air filter and is relatively cheap. IMO, unless you are using an airbrush, 10 gallons & 2.5 HP for spray equipment is very small, 5HP+ & 60 or 80 gallons with 10 CFM+ is what most would use to do car painting and bodywork. (large air consumption tools)

Stephen



Dublak2 said:


> I bought my first air compressor based on suggestion here. I got a 10 gallon, 2.5hp, 125 psi.
> 
> if im going to use it on any given day I typically turn it on and let it run until the tank fills before i spray gun. Ive taped my line connections fairly well. I hear a tiny air leak at the tank valve.
> 
> my issue is that I hardly spray at all, maybe a couple minutes, and then the compressor needs to turn back on. Why? 10 gallon tank isn’t that tiny. The other thing that’s confusing is that when i open the tank release valve a ton of air spits out. So i know the tank is not empty when the compressor is switching on.
> 
> whys this thing running the whole time i spray? Cant i get some peace and quiet????


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## stevon

wingless,

Yeah, running compressor at the limits of it's design will increase wear, produce more water output and cook the motor (overheat). There are constant run 100% duty designs that use an idle unloader or "pilot valve" to keep running motor and pump (unloaded) to cool the pump and motor in between fill cycles. You can convert any compressor by adding and using one of these devices. https://www.about-air-compressors.com/pilot-unloader-valves/ 


wingless said:


> Nope, those specs are on the edge for the continuously-operating compressor to keep up with the gun, eventually shutting off after gun usage, when the tank pressure is "happy" again.
> 
> If all is good, then the regulated air pressure should be maintained at the setpoint, such as 40 PSI, throughout the usage. Does the regulated pressure remain constant, or droop?
> 
> If a lower compressor operation duty cycle is desired / required, then a compressor w/ a much higher CFM is needed.
> 
> But, that setup is specified to be acceptable and that setup should never require waiting for air pressure to build before gun operation may resume. Are there times when waiting is required?


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## Dublak2

Is it difficult or expensive to install a pilot unloader valve? Not the handiest guy over here.


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## wingless

Dublak2 said:


> Is it difficult or expensive to install a pilot unloader valve? Not the handiest guy over here.


 Every compressor I've seen already has a unloader / check valve.

Every compressor I've seen would never start w/o an unloader valve.

The compressor will run until the pressure switch is "happy", then the motor stops running and an audible compressed air hiss noise exists for a few seconds. That air hiss noise is created by the unloader valve. That compressed air discharge permits the pump to start running against 0 PSI, instead of trying to start running against the tank pressure.


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## iowagold

I use the rule of double the compressor specs for the tool you run...
10 gallon tank is too small of a reserve...
at least on a piston compressor...

a 50 to 100 gallon system storage would work the best...
at least on permanent systems...

a 10 gallon tank works out to 1.33680556 cu foot...
so a 100 gallon reserve system is 13.3680556 cu foot...
and is about right for a small paint shop.
and use a 20 cu foot per min on the compressor, and a 28 cu foot per min works best!

and make sure your compressor is rated for continues run...
or is a comercial rated compressor..

most low cost compressors are not rated for the heat that the comercial units are..
plastic rings, etc...
yup they will melt down!!

always go over kill on your compressor and your compressor lines!!


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## stevon

wingless, 
A commercial solution designed to continuously run is the E-Max Pro series: 




Which is expensive and not the smallest package for a home garage. Converting a 2.5 or 3HP Comp with a 30 gal tank could work for the task at hand, but just barely lol. You would need to ask around compressor re-builders in person or on the phone and with a little plumbing skills you should be good to go! I did one years ago and bought my pilot valve from Graingers, followed the included instructions then added a small engine muffler to the vent port to reduce noise. 

Stephen



wingless said:


> Every compressor I've seen already has a unloader / check valve.
> 
> Every compressor I've seen would never start w/o an unloader valve.
> 
> The compressor will run until the pressure switch is "happy", then the motor stops running and an audible compressed air hiss noise exists for a few seconds. That air hiss noise is created by the unloader valve. That compressed air discharge permits the pump to start running against 0 PSI, instead of trying to start running against the tank pressure.


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## stevon

*Pilot*

wingless,

We are talking about a pilot valve. A special additional valve that allows motor and pump to run in an "unloaded" state running pump and motor while not compressing air but venting it into the atmosphere. This does not generate heat and pump flywheel fan cools the pump while internal motor fan cools the motor running at no load also not generating any heat. Thus cooling everything down. Added benefit is when pressure is demanded valve closes and flywheel and motor momentum helps start compressing air (less startup load)

Stephen 


wingless said:


> Every compressor I've seen already has a unloader / check valve.
> 
> Every compressor I've seen would never start w/o an unloader valve.


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