Hi I'm a new helper here in Portland Or. And I was asked to find the answer to a question. The question was to find out the meaning of AP/AF and EP/EF for pump units. Not just that one unit is outside the tank and the other is immersed. But instead what the A and the E actually stand for with Dover. After researching the Rotary lift company and Dover I have found a whole series of pump units with two letter designations. First the Rota-flow pumps that were designated RP and RF which stood for Rota-flow passenger and Rota-flow freight (Dover Parts Catalog). Then after that came the Dover series DP and DF, which DP stands for Dover passenger. After that came A, C, and E series pump units. Which all of them came in a P or F configuration (Dover parts catalog). If anybody has any insight that would great because I can't find anything on line or anywhere else.