I got a new air compressor for Christmas, a real upgrade.

Now for my old one.....it is a small 6 gallon with an operating/tank max pressure of 125 psi. The 1/4" npt pressure relief valve was relieving at about 60 psi. I want to replace it, but the only ones in town are 115 psi, which would not allow the compressor to set itself, and 200 psi which is way too much (the tank pressure gage shows the red zone starting at 125 psi. I will have to order, but want to order the correct size. I know 125 SOUNDS like the right choice but have read reviews that these sometimes relieve just below what they are spring set for. I long ago lost the manual, and it is an inexpensive import given to me 10+ years ago.

Has anyone here had to replace theirs? If so, did you go over a little on the relief valve setting so that the compressor would set properly?

Go over a bit, 130-150 psi will be fine, is there an ASME stamp on the tank or just the tag? Odds are that the tank would actually be rated for min 150 psi per industry standards, given its a piston and fairly small it might even be rated for 200 psi. The tag/gauge kit is a CYA move by the manufacturer.

Double check the offline pressure and MAWP of the tank are both 125 PSIG. Not positive about low cost imports, but I suspect the tank will be stamped with a slightly higher number

Ideally you'll want your PSV 10% (or more) above your offline pressure, but you may be limited by the MAWP of your tank. I agree that 115 and 200 are not good choices.

Sorry I'm not much help.

Also keep in mind the "rating" is max pressure for normal operating conditions, most PRVs on standard 125psi screw compressors will be set (about) 10% above the receivers ASME stamp. In other words, you won't be making a bomb if you have it set for 150-175 PSI.

You can use a proportional relief device and adjust it to your desired set pressure. I've used ones from swagelok but they are probably a little pricey brand new for what you want to do. But you can probably find a lightly used one on eBay.

I sell compressors for a living, I got way too excited when I saw this thread... Anybody want to learn about variable speed drive compressors?

Yes, and please detail energy savings payback and life of equipment increase. Don't tell me how much the vfd will cost if (when) it goes, or how hard I have to run it to actually see energy savings. #copco

Well the new Neos drive did solve a lot of problems...

Cheap relief valve typically relieve at +/- 10% of the "set" pressure. So a 125 psi valve will relieve between 112 and 137 psi.

Also as someone else suggested, why not get an adjustable relief valve. and just dial it in to whatever you want