Theory of Operation
The Liquid Controls MA-4 LPG Meter combines a positive displacement meter, differential valve, strainer, and vapor eliminator in one assembly.
The Liquid Controls vapor eliminator employs a sleeve-type valve that permits a “leak” flow of approximately 0.2 GPM from the vapor vent back to the supply tank. A 200-mesh strainer is incorporated in the vapor eliminator casting and is easily accessible by removing the strainer cover.
The Liquid Controls differential valve incorporates a piston-diaphragm type construction, with the piston moving away from its seat when at least 15 psi pressure (above product vapor pressure) is maintained at the meter outlet. The soft seat valve assures measurement accuracy by requiring 1) pump operation for delivery, 2) adequate back pressure to prevent product vaporization during measurement, and 3) blockage of flow when the vapor eliminator release valve opens.
Meter Installation
Meter - Install the meter assembly in dispenser cabinet to a secure base, using the supplied bracket on the meter housing and the “feet” located on the strainer assembly base. Make inlet and outlet connections at the flanged surfaces on the strainer and differential valve, respectively.
Vent Line - The vent line from the meter vapor vent to the vapor space on the supply tank should be 1/4-inch minimum inside diameter tube or pipe. A shut off valve must be installed in the vapor vent line to allow removal of the strainer or to service the meter. The vapor release vent line must be returned to the vapor space of the supply tank and normally should not be made common with the other vapor return lines or pump bypass lines. When properly installed, this line must permit free flow in either direction. If the valve in the vent line is closed the meter will not function. These instructions must be followed to maintain proper function of the differential valve.
