Hello everyone,
I am designing some API 610 Pumps for off-shore use.
I have a doubt when to use overhungs pumps or between bearings pumps
I know that I have to use between bearings for high flows, but how high?
I would request proposals from a couple of different manufacturers. They may be incentivized to offer overhung options in order to be the low cost bid. I might go back and request proposals for between bearing double suction based on the NPSH margin (< 5 feet), Suction Specific Speed (>13,000) or Suction Energy (>240 x 10[sup]6[/sup]). A large, low rpm, between bearings pump would improve all three of those parameters. Then I would balance the higher installation cost and higher energy costs against better reliability and availability.
Low maintenance is nice when offshore.
Otherwise you don't give much information to decide between them.
Do you have a specific application in mind, or are you trying to frame a general rule of thumb?
Bearing configuration is selected by the pump designer to limit the effects of deflection and critical speed of the shaft and impeller. As the details of that subject are well above my pay grade, these links will better explain what you need to know than can I. Bearings on both ends of the shaft are far superior to controlling maximum deflection on the longer shaft pumps and that configuration must be selected when deflections of an overhanging impeller are too large, which might cause impeller contact with the casing.
It's horses for courses, what flowrates and heads are required, 10 gpm at 50 ft or 1000gpm 250ft. There is no rule of thumb, it's always (or should be) a considered engineering review,
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
