Overhung impeller

In this group, the impeller or impellers are mounted on the extreme end of the shaft in a cantilevered condition hanging from the support bearings. This group of pumps is also subdivided into a class known as motor-pumps or close-coupled pumps where the impeller is directly mounted onto the motor shaft and supported by the motor s bearings. 

In this group the impeller or impellers are mounted onto the shaft with the bearings on both ends. The impellers are mounted between the bearings. These types of pumps are further divided into single stage (one impeller) or multi-stage pumps (multiple impellers). 

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Figure 3-48. Upper limits of specific speeds for single suction overhung impeller pumps handling dear water at 85°F at sea level. (By permission, Hydraulic Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps, Hydrauiic Institute, 13th ed., 1975.)...

SPECIFIC SPEED, N. = RPM VGFM FOR SINGLE SUCTION OVERHUNG IMPELLER PUMPS... 

Vapor is circulated by means of a cold blower and insulated ducting. The vapor flow rate is measured by an orifice plate, situated upstream of the fan, with the appropriate length of straight section before and after it. A flow smoother is provided at the inlet to the metering section. The present fan, consisting of a copper-bladed overhung impeller mounted on a stainless steel shaft, will deliver some 78,000 ft /hr of oxygen vapor measured at -183 C, with a head of 30 in. of water, i.e., approximately 250,000 ft /hr at NTP. 

Some impeller is attached at the end of pump shaft. This is overhung impeller. Overhung impeller pump is also classified as close coupled, where the impeller is mounted directly to the driver shaft, or separately coupled, where the impeller is mounted on a pump shaft. 

ARR. 2 SWSI For belt drive or direct connection. Impeller overhung. Bearings in bracket supported by fan housing. 

ARR. 4 SWSI For direct drive Impeller overhung on prime mover shaft. No bearings on fan Prime mover base mounted or integrally directly connected. 

ARR. 9 SWSI For bell drive Impeller overhung, two bearings, with prime mover outside base... 

Note Although between bearing first stage impellers may result in superior rotor support, certain applications which require superior suction performance may benefit from an overhung first stage impeller arrangement. 

Close-coupled vertical in-line single-stage overhung pumps shall be designated pump type OHS. Close-coupled pumps have their impellers mounted directly on the driver shaft. (Does not meet all the requirements of this international Standard, see 5.2.)... 

Centrifugal single-stage overhung, process type impeller cantilevered beyond bearings capacity varies with head... 

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