SPX H PRESS. Valve

Running it at 300 psi is within spec. The adjustable range on this regulator goes from 300 up to 10,000 psi, so that lower end is a legitimate operating point, not just a floor they listed for legal reasons. It also holds whatever you set it to within 3% across repeated cycles, so even at the low end you're getting consistent, repeatable pressure rather than something that drifts around on you.

This in-line pressure valve is designed for use with either single- or double-acting cylinders, letting you tweak the operating pressure below the pump's relief valve setting.