So I am going to admit it here...I do not know how to set the output pressure on a compressor

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Forum topic by JNP posted 05-27-2012 08:05 PM 3218 views 0 times favorited 24 replies Add to Favorites Watch
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113 posts in 2601 days

05-27-2012 08:05 PM

I am a relatively smart individual and can usually figure things out pretty quickly…this however, has me stumped. May just be one of those “red-mist” issues when you can’t see the clear solution due to rage but…

I have a porter-cable 150 psi compressor. I just bought a HVLP gun that says DO NOT EXCEED 40 PSI.
I see the pressure valve on the compressor and know that you pull it out and turn it to change and push it in to lock but how do you set a specific pressure?

The manual just says to:
Pull the valve out , turn counterclockwise to it’s stop and push knob in.
Turn on the unit, pull knob out and turn the valve clockwise to increase pressure. When it reaches the desired pressure push the valve in to lock.

Okay, valve is pulled and turned counterclockwise to it’s stop and pushed back in.
Unit is turned on…(it immediately starts to build pressure even with the valve pulled out and all the way counterclockwise). Pressure builds (without having to turn the knob clockwise) and when it registers 40 psi I push it back in…and…nothing. The motor continues to run(and never shuts off), I can hear air bleeding off but it is holding at 120 psi.

Can someone please dumb this down to kindergarten level? What the heck am I missing?

Thank you! Jeff

-- Jeff

24 replies so far

View a1Jim's profile


117115 posts in 3600 days

#1 posted 05-27-2012 08:30 PM

It could be a defective pressure valve or if it has two valves your adjusting the wrong one.

-- wood crafting & woodworking classes

View higtron's profile


237 posts in 2700 days

#2 posted 05-27-2012 08:37 PM

you should have two gauges one is for the tank pressure which should always reach a max psi in your case 120psi. the second gauge is for the regulated pressure it’s the one you turn, it regulates the pressue that is fed to your sprayer this pressure stays constant no mater what the tank pressure is. So if your regulated pressure reads 40psi the tank pressure rises, and falls independent of the regulated pressure. Good luck
P.S if the regulated pressure is changeing than something is wrong with your compressor, in the back of the owners manual ther will be a list of autherized repair shops pick one nearest your area, I’ve always had good luck with these repair shops, and I’ve always felt like I got a fair shake.

-- A friend will help you move, a good friend will help you move a body

View JNP's profile


113 posts in 2601 days

#3 posted 05-27-2012 08:38 PM

Well Jim, there is one gauge right on the tank with no adjustments there. That I assumed would be tank pressure. The other gauge is right next to the adjustment valve. It may just be a defective valve. Time to get out the hammer and start hitting the valve to unstick it! :-)

-- Jeff

View Infernal2's profile


107 posts in 2220 days

#4 posted 05-27-2012 08:58 PM

I agree, it sounds suspiciously like a broken valve. Luckily most of those valves are rather easy to replace since they are usually just a dial valve mounted on a brass T. However, if you can’t absolutely replace it, you can simply stick a MIP or FIP fitting on another brass nipple with the slip in post on one end and a tool site pressure regulator on the other and then run your hoses as normal.

Something like this….

View MrUnix's profile


6764 posts in 2222 days

#5 posted 05-27-2012 09:01 PM

If the compressor motor continues to run and never shuts off then you have more problems than just being able to set the output pressure!

Try this: turn the output regulator all the way off and connect your HVLP gun. Turn on the compressor and allow it to reach maximum pressure, at which time it should automatically shut off. If it doesn’t, then you either have a defective pressure switch or a serious leak somewhere. After it shuts off, your tank gauge should be reading max pressure (140-150psi if that is what your compressor is rated for), and your output gauge should read zero. If all is good up to this point, then all you need to do is start turning your output regulator until the gauge on it reads 40 psi and lock it down.

Let us know how it goes!


-- Brad in FL - In Dog I trust... everything else is questionable

View JNP's profile


113 posts in 2601 days

#6 posted 05-27-2012 09:07 PM

The unit will turn off if I have the pressure valve turned clockwise and locked. It is when I have it dialed at a point less than full that it doesn’t shut off. It seems as it is continues to try to bleed down but the motor won’t stop.

When the motor stops both gauges are reading 150 psi. I’ll try one more time, then get a replacement valve.

Thanks all!

-- Jeff

View Mark Shymanski's profile

Mark Shymanski

5621 posts in 3736 days

#7 posted 05-27-2012 09:21 PM

From my experience with compressors I’ve learned that you sometimes have to vent air downstream of the output pressure gauge in order for them to read correctly. This usually applies when decreasing pressure, so may not apply here.


-- "Checking for square? What madness is this! The cabinet is square because I will it to be so!" Jeremy Greiner LJ Topic#20953 2011 Feb 2

View Gregn's profile


1642 posts in 3006 days

#8 posted 05-27-2012 09:28 PM

Have you tried letting the tank pressure up and then adjusting your regulator to 40 PSI?

I Always let my tank pressure up before I adjust my regulator to the desired pressure. If your trying to adjust your regulator first the compressor will run till the tank pressures up. If that doesn’t work then I agree that you have a bad valve.

-- I don't make mistakes, I have great learning lessons, Greg

View MrUnix's profile


6764 posts in 2222 days

#9 posted 05-27-2012 09:40 PM

Mark brings up a good point.. and that is why I suggested closing the regulator before turning on the compressor (so everything starts at zero psi). But if everything shuts off and holds at 150 psi, decreasing the pressure on the regulator should not cause the motor to start back up.. that would indicate loss of tank pressure, so something is definitely out of whack. If you do determine it is the regulator, an alternative would be to get an external regulator and filter unit. Leave the stock regulator cranked open all the way and regulate pressure with the external one. As a side benefit, the filter will remove any water/impurities in the line that would ruin your paint job. Even if you do replace the regulator, you will probably want a filter anyway for painting.


-- Brad in FL - In Dog I trust... everything else is questionable

View RussellAP's profile


3104 posts in 2310 days

#10 posted 05-27-2012 09:42 PM

There is a lot of ambiguity in your post. Just to make sure I understand, the gauge on the right is tank pressure and will continue until the tank is at 150 psi.
The gauge on the left is the output pressure and is adjustable.
The knob with (+ – ) regulates your output pressure.
The tank will continue to fill no matter what output pressure you pick. It will go off around 150 PSI. This has no effect on the output pressure though unless of course the tank pressure is less then 40 psi. A simple way to tell if the gauge is working is to turn the output pressure down and feel the air coming out of the hose, then turn it up to max and see if it blows harder. You might also put a small gauge at the end of the hose to further regulate the pressure to 40psi just before the HPLV gun. When you pull the trigger on the gun, the gauges won’t be all that accurate due to the pressure going from static to dynamic, but if you’re concerned about the gun, simply dial it down to 30 psi static.

-- A positive attitude will take you much further than positive thinking ever will.

View Sawkerf's profile


1730 posts in 3091 days

#11 posted 05-27-2012 10:15 PM

I don’t have a PC compressor, but I think that Russell has it backwards. The brass fittings on the right are hose connectors so my money says that the gauge on the right is the outlet pressure. The gauge on the left would be the tank pressure.

You dial in your desired pressure with the knob in the center. The push and pull action is just a “lock” and isn’t really necessary. Clockwise rotation should move the right gauge down to whatever setting you want. Counterclockwise rotation raises the setting.

FWIW, that compressor may have trouble keeping up with a HVLP rig. They use a lot of air and the tank drains pretty quickly. I also don’t recommend using a 1/4” air hose – it just won’t pass enpugh air. My setup won’t run on anything less than 3/8”.

-- Adversity doesn't build reveals it.

View JNP's profile


113 posts in 2601 days

#12 posted 05-27-2012 10:34 PM

This is the compressor have. The gauge you see is the output gauge. The tank pressure gauge is on the left side of the tank by the release valve.

Brad and Mark, I think there is a problem. When I turn the valve all the way to the left, toward the ”-” and click it down the reading escalates as the motor runs. There is quite a bit of air leaking out of the valve and the motor won’t stop unless I turn it all the way to the right, toward the ”+” and lock it down. If I do that and the motor stops, I can then turn the valve back to the left but it just bleeds off very slowly. The gauge drops as the pressure bleeds off.

-- Jeff

View RussellAP's profile


3104 posts in 2310 days

#13 posted 05-27-2012 11:18 PM

Sawkerf, my mistake, I have a Stanley Bostitch and the gauges are opposite from that one.

-- A positive attitude will take you much further than positive thinking ever will.

View dhazelton's profile


2771 posts in 2320 days

#14 posted 05-27-2012 11:22 PM

Is there a brass relief valve that is partially out from it’s seated position? 150 psi is it’s cutoff pressure no matter what and will always shut off there. You should look in the manual for the pressure that it switches on at. Turning the dial gives you your final output pressure at the hose. I think you have a leak, or as I said a faulty relief valve that is letting air escape hence the machine never switches off because it never gets a chance to get up to cutoff pressure.

View dbhost's profile


5723 posts in 3255 days

#15 posted 05-27-2012 11:35 PM

Are you trying to use a Pancake compressor to run an HVLP gun? My 8 gallon compressor BARELY works for my HVLP… I wouldn’t even consider a smaller compressor…

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