PUMPS

A pump uses the mechanical energy produced by its prime mover to move liquid from one point to another. The pump moves the liquid by either pushing, pulling, or throwing. Pumps are often named or classified by the action that causes fluid movement; for example, diaphragm or centrifugal.

Regardless of its design or classification, each pump has a power end and a liquid end. The power end is some form of prime mover, such as an electric motor, internal combustion engine, or steam turbine. In steam-driven pumps, the power end is often referred to as the steam end. The basic purpose of the power end is to develop the mechanical motion or force required by the liquid end.

In the liquid end, mechanical motion, developed by the prime mover, is exerted on the liquid. This part of the pump must allow for suction (where the liquid enters the pump) and for discharge (where the liquid leaves the pump). The liquid end is often referred to as the pump end, the water end, or the oil end to show the nature of the substance pumped.

Diaphragm Pump

The diaphragm pump (fig. 14-33) uses a flexible diaphragm to move liquid. The prime mover is usually a small gasoline engine with an eccentric connecting rod arrangement that converts rotary motion to reciprocating motion. On the suction stroke, the diaphragm is drawn upward into a concave configuration. This movement of the diaphragm results in a partial vacuum that causes the suction ball valve to

Figure 14-33.-Diaphragm pump.

unseat (and at the same time keeps the discharge ball valve seated) and to admit liquid to the pump cylinder. On the discharge stroke, the diaphragm is pushed downward forcing the trapped liquid out through the discharge valve. Thus the liquid is made to move by the reciprocating motion of a flexible diaphragm.

Since the diaphragm forms a tight seal in the pump cylinder between the liquid being pumped and the rest of the pump and driving mechanisms, there is little danger of liquid abrasion or corrosion of moving parts behind the diaphragm.

NOTE: Diaphragm pumps are especially well-suited for pumping mud, slime, silt, and other wastes or heavy liquids containing debris, such as sticks, stones, or rags.

Liquid strainers are fitted at the suction inlet to prevent large objects from fouling the suction and discharge valves or possibly damaging the diaphragm.

You may have to use the diaphragm pump for such duties as dewatering trenches where sewer lines or waterlines are to be laid, dewatering cofferdams or cave-ins, or repairing breaks in water or sewage lines. Two of the most popular types of diaphragm pumps are the mud hog (closed discharge) and the water hog (open discharge).

The mud hog is for jobs that require pumping heavy and thick liquids that must be discharged at a distance away from the pump. The pump is fitted with discharge hose connctions, and the ball valves and chambers are designed to prevent fouling by sticks, stones, or rags.

The water hog is used for pumping thinner or less viscous liquids. It can handle liquids containing sand, gravel, or mud. The discharge outlet from the water hog is open to permit free flow and to increase discharge capacity. The liquid is discharged directly at the pump. A discharge hose, however, can be fitted to the pump if desired, but the hose connection can reduce the efficiency of the pump.

You must know the operation of the diaphragm pump. Since nearly every job presents a different problem, you may have to vary the operating procedure to fit the individual job.

Before starting the pump, place the suction line and screen in the liquid to be removed by the pump. Construct a trough to drain the pump discharge away from the pump.

OPERATION.- Start the engine first. If the pump does not pick up the liquid in a minute or two, check the suction line for leaks. You can do this by pouring water over the hose connections. In the event there is a leak, air bubbles will appear.

Should the connections be tight and no leaks appear, check the diaphragm for cracks or punctures. If the diaphragm is damaged, it has to be replaced. A mechanic inspector must make any further inspections.

INSPECTION.- Because of the nature of the liquids handled by diaphragm pumps, inspection during pump operation becomes particularly important. Inspect the suction inlet strainer often to avoid accumulations of debris that reduce suction efficiency. Most diaphragm pump installations also permit easy access to the suction and discharge ball check valves. These valve mechanisms should also be inspected frequently to detect scoring, fouling, and improper valve seating.

NOTE: Sand, gravel, and other material can corrode the diaphragm and ball check valves; expect these parts to require the most frequent operator inspections.