This is the best pressure relief valve out there for the cost. Took advice from another review and put a little keg lube on the rubber seal and it seems to hold pressure very consistent. Other versions of this stick badly and do not come apart to add lube (CR series brass version). Spin top to adjust the pressure. I'm using it for my fermenter and simply boil the whole thing prior to fermentation. When close to full open (just before it unscrews completely) it holds 2-3 PSI. So far I have only tried mounting vertical.
Best low cost option for a spunding valve. At low pressures (1-4 psi) the precision is not perfect as the re-seal point is is probably +/- 1 psi but at higher pressures (> 7 psi) it is perfect. I have found that it is not critical to be exact at < 5 psi for early fermentation as long as it reseals above 0 (which it always does) to maintain positive pressure in order to avoid air entering the fermneter. In later stages for carbonation it is perfect.
If you're looking for a PRV that varies from lowish (~5psi) up to about 40psi, and you want it to reseal once it drops below your setpoint, then this is the PRV you want! All stainless constructions with only one small BUNA rubber O-ring that functions as the sealing point. Give that rubber a super light coat of keg lube and this PRV is highly capable of resealing just below the setpoint. And just to be perfectly clear, the top third unscrews from the base assembly and this is how you adjust the pressure setpoint.