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The FE Petro STP -MLD leak detector is a three position, pressure - sensing, piston operated valve designed to continuously monitor the piping by indicating any leakage in the piping between the discharge and the submersible pump and the solenoid valve in a service station dispenser. When the submerged pump is turned on after the system pressure has dropped significantly below the normal static system pressure, three GPH (at 10 psi) is metered through the STP -MLD into the piping system. If a leak is present that equals or exceeds this amount, as much product escapes from the system as is metered through the STP -MLD. Under this condition, pressure cannot build up in the piping system. When a nozzle is opened, a poppet in the STP -MLD moves to a position that restricts the flow to 2 GPM. This is the indication to the operator that a leak is present. If there are no leaks, pressure rapidly builds in the system forcing the STP -MLD to open to the full -flow position. In a system with no leaks, it takes approximately three seconds for a complete test. No further line testing takes place until the line pressure drops significantly below the normal static system pressure. v 1. The Tripped or Bottom 2. Leak Sensing Position 3. Non -Leak or Full Flow Position In this position the system pressure Position When the system is less than 1 psi, the has increased to approximately 12 psi This position allows full flow. The piston and poppet are in the and all the flow must travel around poppet will remain in approximately "bottom" or "tripped" position. In this the metering pin which limits it to this position as long as the system position of the poppet, product flows approximately a 3 GPH rate (at 10 psi). pressure remains at about the through the horizontal hole in the pop- If there is a leak in the system which pumping pressure. If the pressure in pet and around the metering pin at a will allow leakage to exceed this amount, the system drops when the pump is rate of approximately 2 GPM the line pressure will not build beyond turned off, either due to thermal flow into the delivery line when the this point and the valve will remain in contraction of the product or due to a submersible pump is running. In the leak sensing position with the main leak, the piston moves downward and normal operations the piping remains flow blocked. If there is an attempt to the poppet engages and seals inside full of fluid and when the submersible dispense while the valve is in this posi- the cage at about 3 psi, or approxi - pump is turned on, with a flow rate of tion, the line pressure will drop to less mately 10 feet of head, in gasoline. 2 GPM through the poppet, pressure than 1 psi, the piston will respond, and Any time the pump is turned on after builds rapidly and the poppet moves to the poppet will return to Position 1 the seal on the poppet is inside the the leak sensing position. where 2 GPM will flow to the dispensers. cage, a line test will be performed. Leaks smaller than 3 GPH will be indi- cated by the STP -MLD taking longer than three seconds to open completely because some of the flow leaks out of the system and the rest builds pressure. — _ _ _ = r If there is no leakage in the system, f the small flow around the metering pin FE Petro, Inc. ■ 4805 Voges Road `— increases the line pressure and in P.O. Box 139 ■ McFarland, WI 53558 approximately three seconds the piston (608) 838-8786 ■ Fax: (608) 838-6433 will move the poppet to Position 3.