Vertical Pumps

Vertical-shaft pumps fall into two classifications: dry-pit and wet-pit. Dry-pit pumps are surrounded by air, and the wet-pit types are either fully or partially submerged in the liquid handled.

Vertical Dry-Pit Pumps Dry-pit pumps with external bearings include most small, medium, and large vertical sewage pumps, most medium and large drainage and irrigation pumps for medium and high heads, many large condenser circulating and water supply pumps, and many marine pumps. Sometimes the vertical design is preferred (especially for marine pumps) because it saves floor space. At other times, it is desirable to mount a pump at a low elevation because of suction conditions, and it is then also preferable or necessary to have the pump driver at a high elevation. The vertical pump is normally used for large capacity applications because it is more economical than the horizontal type, all factors considered.

Many vertical dry-pit pumps are basically horizontal designs with minor modifications (usually in the bearings) to adapt them for vertical-shaft drive. This is not true of small-and medium-sized sewage pumps, however. In these units, a purely vertical design is the most popular. Most of these sewage pumps have elbow suction nozzles (see Figures 102 through 104) because their suction supply is usually taken from a wet well adjacent to the

FIGURE 102 Section of a vertical sewage pump with end-suction (elbow) and side discharge (Flowserve

FIGURE 102 Section of a vertical sewage pump with end-suction (elbow) and side discharge (Flowserve


FIGURE 103 An installed vertical sewage pump similar to that shown in Figure 102 (Flowserve Corporation)

Centrifugal Pumps Dismantle
FIGURE 104 Vertical sewage pump with a direct-mounted motor (Flowserve Corporation)

pit in which the pump is installed. The suction elbow usually contains a handhole with a removable cover to provide easy access to the impeller.

To dismantle one of these pumps, the stuffing box head must be unbolted from the casing after the intermediate shaft or the motor and motor stand have been removed. The rotor assembly is drawn out upward, complete with the stuffing box head, the bearing

FIGURE 105 Vertical bottom-suction volute pumps installed in a sewage pumping station (Flowserve Corporation)

housing, and the like. This rotor assembly can then be completely dismantled at a convenient location.

Vertical-shaft installations of single-suction pumps with a suction elbow are commonly furnished with either a pedestal or a base elbow (refer to Figure 102), both of which can be bolted to soleplates or even grouted in. The grouting arrangement is not desirable unless there is full assurance that the pedestal or elbow will never be disturbed or that the grouted space is reasonably regular and the grout will separate from the pump without excessive difficulty.

Vertical single-suction pumps with bottom suction are commonly used for larger sewage, water supply, or condenser circulating applications. Such pumps are provided with wing feet that are bolted to soleplates grouted in concrete pedestals or piers (see Figure 105). Sometimes the wing feet may be grouted right in the pedestals. These must be suitably arranged to provide proper access to any handholes in the pump and to allow clearance for the elbow suction nozzles if these are used.

If a vertical pump is applied to a condensate service or some other service for which the eye of the impeller must be vented to prevent vapor binding, a pump with a bottom single-inlet impeller is not desirable because it does not permit effective venting. Neither does a vertical pump employing a double-suction impeller (see Figure 106). The most suitable design for such applications incorporates a top single-inlet impeller (see Figure 107).

If the driver of a vertical dry-pit pump can be located immediately above the pump, it is often supported on the pump itself (refer to Figure 104). The shafts of the pump and driver may be connected by a flexible coupling, which requires that each have its own thrust bearing. If the pump shaft is rigidly coupled to the driver shaft or is an extension of the driver shaft, a common thrust bearing is used, normally in the driver.

Although the driving motors are frequently mounted on top of the pump casing, one important reason for the use of the vertical shaft design is the possibility of locating the motors at an elevation sufficiently above the pumps to prevent the accidental flooding of the motors. The pump and its driver may be separated by an appreciable length of shafting, which may require steady bearings between the two units. Subsection 6.3.1 discusses the construction and arrangement of the shafting used to connect vertical pumps to drivers located some distance above the pump elevation.

Bearings for vertical dry-pit pumps and for intermediate guide bearings are usually antifriction grease-lubricated types to simplify the problem of retaining a lubricant in a housing with a shaft projecting vertically through it. Larger units, for which antifriction bearings are not available or desirable, use self-oiling, babbitt steady bearings with spiral

Altitude Suction Guide
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