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Just what is "back pull-out" design? Pump manufacturers and users commonly use the term to describe designs which allow the pump bearing frame and impeller to be backed out of the volute without disturbing the pump piping connections. This concept should offer easy disassembly for maintenance and impeller trim.
But there’s much more to true back pull-out.
In some so-called back pull-out designs, the volute moves with the piping when the bearing assembly is removed from the volute. Not only is this dangerous for maintenance personnel, but it’s a nightmare for reassembly. An integrally cast support and mounting foot located directly beneath the pump volute prevents volute movement--and makes maintenance an easy, fast, one-man operation.
In addition, the coupling must be a center drop-out or spacer type in a true back pull-out pump. This design allows removal of the bearing frame and rotating element without disturbing the motor. If the coupling is a solid type, the motor must be moved to allow removal of the bearing frame.
For true back pull-out, the pump assembly must have:
- Construction which permits the bearing frame and impeller to be easily backed out of the volute.
- Rigid mounted, foot supported volute
- Center drop-out or spacer type coupling
Overhung volutes… solution or problem?
Some manufacturers have designed their general purpose end-suction pumps with interchangeable volutes between their close-coupled and base-mounted units. While this provides a manufacturing and inventory advantage to the pump company, it’s a disservice to the user. This volute, when installed, will be in an over-hung position -- unsupported, although connected to suction and discharge piping.
Without solid support beneath the volute, pipe weight alone will cause distortion which can cause premature failure of the bearings, mechanical seal, sleeve, shaft and even the impeller.
Although some overhung pumps may be disassembled without disconnecting the volute from the suction/discharge piping, the pumps are not true back pull-out. Since the volute is not securely fastened to the mounting base, it will take the full weight and strain of the piping when the power or bearing frame and rotating element are removed. Consequently, the volute will move and usually a significant distance. It will take at least two men and sufficient equipment to practically "jack up the building" to reposition the volute in its original position and reassemble the pump. A very time-consuming, costly and unnecessary ordeal!
Overhung base-mounted end-suction pumps are susceptible to other problems on hot water pumping applications. Shortly after start-up, the system piping will expand. The pump volute will move, and, as a result, pump failure will prematurely occur because of distortion and misalignment.
These problems can be avoided by making sure the end-suction pump you specify has true back pull-out design.
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End-suction overhung design |
Base-mounted end-suction design |
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Designed with the user in mind
The Bell & Gossett 1510 end suction pump is designed with the user in mind. It is a true back pull-out centrifugal pump with an integral heavy duty one-piece casting and mounting foot directly beneath the pump volute. When maintenance is required, no volute movement will occur, at any time. Original alignment will remain. There’s no need to "jack up the building" for reassembly. The bearing assembly and rotating element simply slide back into the volute because the volute and piping have not moved from their original position.
True back pull-out saves a lot of time and money
A true back pull-out pump lets personnel get to the heart of the maintenance task easily. The center of the coupling assembly will drop out. The volute will stay in place. The bearing assembly will slide out and back in easily. Piping connections and the motor need not be disturbed.
Specify and use B&G true back pull-out end-suction base-mounted pumps. The difference can save a lot of time and money.