WE ARE DESIGNING A GAS RECOVERY SYSTEM FROM A PROPANE REFRIGERATION LOOP.PROPANE VAPORS RECOVERED WILL BE REINJECTED IN A BOIL-OFF SYSTEM TO BE COMPRESSED AND LIQUEFIED AGAIN WITH VAPORS COMING FROM STORAGE TANKS.THE TIE-IN POINT IS LOCATED AT ABOUT 100 M FROM THE RECOVERY POINT IN THE BOIL-OFF COLLECTOR IN WICH PRESSURE MUST NOT EXCEED 0.15 KG/CM2.THE RECOVERED GASES PRESSSURE VARIES FROM 5 TO 3 KG/CM.THE OPERATION TAKES ABOUT 30 MINUTES BY MEANS OF A RSTRICTION ORIFICE.AT THE INJECTION POINT, A PRESSURE CONTROL VALVE MUST DECREASE THE PRESSURE TO ABOUT 0.15 KG/CM2 WHATEVER PRESSURE OR FLOW WILL CHANGE.THE CONTROL VALVE MUST GIVE 0.15 KG/CM2 AT THE OUTLET EITHER PRESSURE IS 5 - 4 - 3 KG/CM2, AND FOR VAIRABLE FLOWRATE.I'M ASKING IF SUCH VALVES EXIST, IF YES HELP TO GET SPECIFICATIONS AND DESIGN CALCULATION METHOD AND A SCHEMATIC FOR THE CONTROL LOOP.Nothing you asked for sounds much different from a regulator, otherwise known as a pressure reducing valve. Normally regulators have "droop" or proportional band of about 10% of their range, but pilot-operated regulators can be much tighter. Or, you could go for a control valve, with a positioner in a full control loop with a pressure transmitter monitoring the downstream poressure for a pressure controller that outputs to the valve. The control loop can give you better steady-state accuracy, but will probably not be as quick as the regulator on a sharp transient.

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