Back Pull-Out ANSI Pumps
What is a back pull-out pump? It is difficult to cut and weld piping and have flanges line up exactly where they are needed. This is why expansion joints should be utilized more than they are. As a result, it often takes two people with pry bars to get pump flanges and the flanges of the piping to line up so they can be secured together. Despite the fact that a flange more than 1/32” out of flat or out of parallel can cause pipe strain, it is all too common.
ANSI pumps like OnHandSupply.com, Goulds 3196, Summit 2196 and Griswold 311 are designed to allow the casing (volute) to stay in the piping system. The rest of the pump can be removed from the motor side of the pump.
This creates other issues. Either the motor has to be moved and later reset and realigned or a drop-out coupling is used. The drop-out coupling has a removable center, about 3” long. This center drops out and allows the pump to be pulled out from the casing (volute). The problem with this is that the overall length of the shaft is extended by the length of the drop-out section. Since the bearings are on one end of the pump in this overhung design, the possibility of shaft movement where the impeller is located increases.