Fisher 627WH pressure regulator, used in anhydrous ammonia service. This valve was originally going to see up to ~750 psig and drop it down to 300 psig, but now is only seeing about 150 psig. I am seeing excessive pressure drop across it, ~100 psig! It doesn't make any sense, the valve should be wide open and only see minimal pressure drop (<5 psig). But regulator is not a reducing valve. A pressure regulator usually has a loaded spring to determine the rated regulated pressure. If a valve was designed to give 300 psig when the inlet is 750 psig it will the regulated pressure as long as the flow rate will be under some flow rate value if larger flow rate is needed the inlet pressure should be increased to keep the 300 psig regulated pressure. you can not just change the inlet pressure to 150 without readjusting the spring to a new desired load. Even if the spring allows regulating to 145 psig you will not receive much flow when the inlet pressure is 150 psig. The inlet/regulated pressures are function of the flow too.

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