Harbor Freight Compressor Regulator isn't regulating?

by Peter
(Leesburg, FL USA)

Have a cheap H/F compressor rated for 4.5 SCFM @ 90psi, tool is rated 4 SCFM @ 90psi.

With the reg set at 90 and tank pressure reading 120, when I trigger the tool (impact driver) pressure immediately drops to 60 and stays there even after the compressor kicks in at 95psi about 8 seconds later.

Have set the reg to 90 (from 0 as I've read here) while the tool is running and this results in a "wide open" regulator, 120psi when tool is off.

(Same issue with blowgun, just less of a drop)

Will I damage the tool starting it with 120?

Do I have a misunderstanding that a regulator should hold the preset pressure as long as there is that much or more behind it?

Could this be a flow issue from tank to reg? Thanks, Peter. BTW: I don't expect or need the compressor to continuously keep up with the tool.

Bill says...

Peter, good questions and good expectations.

The piece of info that you haven't provided is the demand in CFM of the impact driver. This type of tool is, as is a blow gun, huge compressed air suckers.

Your 4.5 CFM at 90 PSI may not even be enough to keep the driver running for a second or two before the entire line from the tank to the tool is void of air.

And yes, if your demand exceeds the supply in flow, the regulator will drop instantly when you trigger to the tool.

Tell me what the specs on the air tool say in a comment here. I suspect the compressor is far too small in both plumbing, regulator flow capacity, or HP to keep up.



Comments for Harbor Freight Compressor Regulator isn't regulating?

Click here to add your own comments

Jul 11, 2011
by: Peter

Will take your advice and try another regulator. Is there a difference in ability to regulate among differing brands and, if so, how does one shop this item? Will keep you posted with the results. I know this isn't a tool forum, but if I can't resolve the issue, do you know if the tool will be harmed starting with 120 psi? Wait a minute...if I can maintain 90 psi with the reg all the way open, doesn't that rule out a flow issue at least outside the reg?
Cheers to you and for your forum,


You need to check the specs on the tool to see its maximum operating pressure. I would hope that 120 PSI wouldn't hurt it, but can't be sure.

And, as you point out, if it's pulling more air than can be delivered, the pressure reaching the tool will be less than the tank pressure, for sure.

Good luck, and yes, do please keep us posted.


Jul 11, 2011
Maybe not the regulator...
by: Peter

Thanks for the speedy reply Bill. As noted in the second line of my original post the tool (impact driver) claims to use (an average) 4SCFM. I was aware of the high demand of these tools, but thought I'd at least momentarily be able to get 1/4 of the rated torque out of the driver (driver is rated at max 425 lb/ft and I'm using a torque wrench to finish the nuts to only 90). Compressor is a Central Pneumatic 67501, 2hp/8gal/125psi; the 1/2" impact wrench is also a CP, Item 94803. Hmmm...before I got this wrench, I borrowed a professional model and don't remember having a problem. I'll have to check what the specs are on that tool. Thanks again, Peter


Peter, my apologies. I overlooked that piece of info entirely. Old eyes, you know.

I still believe though that the tool is pulling more air than the compressor can deliver through the discharge line, and that's why the pressure drops on the regulator so dramatically.

Other than that, invest in a spare regulator to see if, in so doing, it is the regulator that's giving you grief.

Again, sorry about the oversight.



Click here to add your own comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Harbor Freight Compressor Issues.

Did I damage a seal or something?


When the compressor runs for about a minute, oil start to ooze out of the hole in the oil cap. It started ever since I put a wooden stick in the oil tank to measure the oil level, and when I touch the bottom of the oil tank, it sort of felt like it poked a hole through something. I did not use very much pressure when I put the stick in the reservoir, but I'm thinking I damaged or put a hole in a gasket or something. If this is what's causing the problem, how can I fix it and what parts do I need. Any help would be appreciated. My email, Despinda@gmail.com

Before I used the stick to measure the oil, the compressor worked fine. If I damaged something can you give me some kind of idea if I have to remove the head and replace something. Any instructions on how to get to the broken part would be greatly appreciated. help! Thank You Doug Espinda

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Harbor Freight Compressor Issues.