Couplings Type

Couplings for pumps usually fall in the category of general-purpose couplings. General purpose couplings are standardized and are less sophisticated in design. The cost of such coupling is also on the lower side. In addition, there are special purpose couplings that can be used on turbo machines and are covered by the API 671 specification.

In these couplings, the flexible element can be easily inspected and replaced. The
alignment demands are not very stringent. The couplings fitted on pumps usually fall inany of the five types mentioned below.
These are:
1. Gear coupling
2. Grid coupling
3. Disk coupling
4. Elastomeric compression type
5. Elastomeric shear type.

Shaft couplings

A shaft coupling transfers torque between two in-line, or nearly in-line, rotating shafts. The magnitude of the torque in the shafts is equal, although slipping and disengagement can cause speed variations. In its simplest, and perhaps oldest form, the coupling acts as a means of joining shafts. Another function is to join two shafts which are not necessarily in perfect alignment with each other. The coupling in this case must be capable of absorbing such misalignment. Modern couplings,
between pump and driver, must be capable of rapid disassembly.

Baseplates

Pump units are mounted on baseplates to allow the unit to be bolted down. Unless otherwise stated, baseplates are designed for mounting on concrete foundations and to be supported over the whole length by grouting. The pump supplier must be aware if a baseplate is intended for mounting on structural steelwork with intermittent supports. The design of the baseplate side members may need adjusting to preserve alignment. If the baseplate is to be grouted in with epoxy grout rather than concrete, a special paint finish will be required on the contact surfaces. If the baseplate is to be welded down to structural steelwork the pump supplier should be informed.

Pump Priming System

FOOT VALVES
A foot valve is a form of check valve installed at the bottom, or foot, of a suction line.When the pump stops and the ports of the foot valve close, the liquid cannot drain back to the suction well if the valve seats tightly. Foot valves were very commonly used in early installations of centrifugal pumps. Except for certain applications, their use is now much less common.

PRIMING CHAMBERS
Chamber primer is a tank with a bottom outlet thatis level with the pump suction nozzle and directly connected to it. An inlet at the top of the tank connects with the suction line. The size of the tank must be such that the volume contained between the top of the outlet and the bottom of the inlet is approximately three times the volume of the suction pipe. When the pump is shut down, the liquid in the suction line may leak out, but the liquid in the tank below the suction inlet cannot run back to the supply. When the pump is started, it will pump this entrapped liquid out of the priming chamber, creating a vacuum in the tank. The atmospheric pressure on the supply will force the liquid up the suction line into the priming chamber.

PRIMING INDUCTORS
If a separate source of liquid of sufficient capacity and pressure is available, it can be used to fill the suction line of the pump to be primed through the use of an inductor. For water, the pressure must be equal to about 4 lb/in2 for each foot (90 kPafor each meter) of head necessary to prime the pump, measured from the lowest liquid level in the sump from which priming must be accomplished to the top of the pump. The amount of liquid necessary depends on the pressure.

CENTRAL PRIMING SYSTEMS
If there is more than one centrifugal pump to be primed in an installation, one priming device can be made to serve all the pumps. Such an arrangement is called a central priming system. If the priming device and the venting of the pumps are automatically controlled, the system is called a central automatic priming system.