This does not allow all the pipping to be monitored and is not acceptable. UST suction systems use a positive displacement pump at or near the point of end use to draw the product from the tank to the pump. Typical suction lines operate at a vacuum of 3 to 5 psi. When the pump is shut off or a hole or break develops, suction is interrupted, product may flow backwards through the pipe, away from the dispenser and towards the tank. One or more check valves may be located in the pipe to prevent flow backwards through the pipe.
Product is held in the pipe between the check valve and the pump.
Product in the pipe between the tank and a check valve may drain back into the tank if there is a loss of vacuum. Requirements will depend on which type of suction piping you have. With safe suction below-grade piping is sloped so that the pipe's contents will drain back into the storage tank if the suction is released. Also, only one check valve is included in each suction line and must be located directly below the suction pump. In either case, the check valve must be visible in the dispenser pump immediately below the pump itself.