A term used to describe a suction pumping system where the following are true:
1) There is only one check valve located immediately below the pump.
2) The pump is at a higher elevation than the tank
3) The piping slopes continually back to the tank.
Suction pumping systems incorporating these features are “safe” because leaks in the piping will result in a loss of prime but not release of product outside the primary containment.
See also PEI/RP900.
