to the check valve assembly 10 which is located in line in the pipe 22 and positioned in a vertical orientation just below the lower most position 40 of the stem 38 of the mushroom pop up valve 34 see fig2 3 and 4 as shown specifically shown in fig2 the check valve assembly is located between the vertically oriented end 44 of inlet pipe 22 and the lower end 46 of outlet portion 37 of the pipe assembly the check valve assembly includes a body 50 for housing the check valve mechanism an outlet coupler 52 and an inlet coupler 54 in the illustrated embodiment the couplers are adapted to be mated with complementary ends in the pipes 22 and 37 however it should be understood that any suitable coupling mechanism could be used such as by way of example welding in operation when the pipe 22 is pressurized the check valve 10 opens and the pressurized fluid flows through the check valve and into the pipe 37 this lifts the mushroom pop up valve 34 into engagement with the mushroom gasket 36 for closing off the abrasive chamber 19 from the pressure 20 see fig1 and 3 when the pressure in pipe 22 is relieved gravity permits the mushroom valve to retract into the pipe 37 with the mushroom head substantially closing off the upper end of pipe see fig1 3 and 4 however during the blow down period small amounts of abrasive may enter into the pipe 37 and as the system is depressurized abrasive material can backflow into the system outside of the tank 11 causing malfunction or damage the check valve 10 substantially reduces the likelihood of back flow from pipes 37 and 20 into the external system.