Ralph- Most any constant flow regulator will work with the Nelson A4 flowmeter (now produced and sold by Mountain High as the MH4). Pressure delivered is not much of a factor, as long as tubing on the inlet side of the flowmeter is clamped tightly enough to hold against whatever pressure the regulator delivers. I have seen some regulators that have an outlet pressure over 100 psi. Mountain High regulators are normally around 15 psi. I have both in stock. Contact me at: info at mmfabrication dot com