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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 I . The Tripped or Bottom Position When the system is less than 1 psi, the piston and poppet are in the "bottom" or "tripped" position. In this position of the poppet, product flows through the horizontal hole in the pop- pet and around the metering pin at a rate of approximately 2 GPM flow into the delivery line when the submersible pump is running. In normal operations the piping remains full of fluid and when the submersible pump is turned on, with a flow rate of 2 GPM through the poppet; pressure builds rapidly and the poppet moves to the leak sensing position. 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 2. Leak Sensing Position In this position the system pressure has increased to approximately 12 psi and all the flow must travel around the metering pin which limits it to approximately a 3 GPH rate (at 10 psi). If there is a leak in the system which will allow leakage to exceed this amount, the line pressure will not build beyond this point and the valve will remain in the leak sensing position with the main flow blocked. If there is an attempt to dispense while the valve is in this posi- tion, the line pressure will drop to less than 1 psi, the piston will respond, and the poppet will return to Position 1 where 2 GPM will flow to the dispensers. Leaks smaller than 3 GPH will he 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. If there is no leakage in the system, the small flow around the metering pin increases the line pressure and in approximately three seconds the piston will move the poppet to Position 3. 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. Ina 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. 3. Non -Leak or Frill h11ow Position This position allows full flow. The poppet will remain in approximately this position as long as the system pressure remains at about the pumping pressure. If the pressure in the system drops when the pump is turned off, either due to thermal contraction of the product or due to a leak, the piston moves downward and the poppet engages and seals inside the cage at about 3 psi, or approxi- mately 10 feet of head, in gasoline. Any time the pump is turned on after the seal on the poppet is inside the cage, a line test will be performed. FE Petro, Inc. ■ 4805 Voges Road P.O. Box 139 ■ McFarland, WI 53558 (608) 838-8786 ■ Fax: (608) 838-6433