Submersibles

Submersibles

The multi-stage jet demonstrates the principle that a greater number of stages increases the pressure that the pump is capable of delivering.

This same concept underlies the design of the submersible pump, by far the fastest growing type used for water systems.

Every submersible has a series of stages arranged on a common shaft.

Each stage consists of an impeller, very similar to those used on basic centrifugal pumps, and a diffuser.

The diffuser's function is to convert water velocity into higher pressure and to channel the flow into the next stage.

Thus, a submersible pump consists of a series of stages connected to a single motor.

What distinguishes this type of pump from others is that the motor is submerged in the well, along with the pump.

By virtue of its multiple stages, the submersible pump generally delivers higher pressures than jet pumps of the same horsepower.

Consequently, such units are favored for deeper wells.

However, their high capacity (in terms of flow) and quiet operation—all moving parts are down in the well—offer advantages at any depth.

Classification of Submersible Pumps

There are numerous ways to classify submersible pumps. The most common are as follows:

1. Diameter

Since a submersible must fit down in the well, it must obviously have a diameter no greater than the well in which it is installed.

Thus submersible pumps can be classified as 4-in., 6-in., etc.

While pressure increases with the number of stages, delivery—i.e., output in terms of flow—is determined in part by the pump diameter.

For household use, most submersibles are of the 4-in. type.

2. Number of Wires

To operate submersible pumps, electrical cable must be run from the power source to the pump motor in the well.

Thus, these units can also be described by the number of wires used in the power cable.

Three-wire submersibles have the starting device (start capacitor and switch) in a control box above the ground.

The same is true of overload protection.

Two-wire subs have the starting controls and sometimes the overload protection built into the pump motor.

3. Motor Design

Submersibles are also classified according to the design of the pump motor.

There are three basic types:

A. Hermetic Motors

In this design, the stator and rotor windings are made of conventional wire, then sealed in a plastic matrix.

The entire part is then hermetically sealed in metal, giving rise to the terms "canned" or "potted" for the windings of these hermetic motors.

With the electrical parts so sealed, the motor can run freely under water; indeed, well water flowing through the motor serves as both lubricant and coolant.

B. Oil Filled Motors

A second design involves "open" or unsealed motor windings—rotor and stator—which are lubricated by oil.

A reservoir of oil, kept under pressure either by spring loading or by gravity, keeps water from leaking into the motor spaces.

C. Non-Hermetic Water-Filled

A third design involves "open" or non-hermetic windings similar to the oil-filled motor.

In this case, however, the windings are insulated with a waterproof, flexible material.

In this design water serves as both lubricant and coolant.

However, because of the insulation on the windings, it cannot short out the electrical circuits.

Other Pump Types

Piston Pump

This is a form of reciprocating pump in which the action of a piston alternately sucks water into a pumping chamber and then forces it out into the system.

In the first phase, the piston moves from left to right:

Creates pressure in right chamber → forces water out right discharge valve

Creates suction in left chamber → draws water in through left suction valve

When the piston reverses direction, the operations are reversed.

Working Head Pump

A second type of reciprocating pump, designed primarily for deep wells, involves a plunger and cylinder located below the water level in the well.

The vertical action of the plunger forces water up through the cylinder and drop pipe to the surface.

Power is provided by an electric motor or gasoline engine at the surface.

Rotation is transformed into up-and-down motion by:

Gear box

Lever or walking beam

Also called "sucker rod pumps" or "stroke pumps."

Vertical Turbines

Superficially similar in design to the submersible, the vertical turbine differs in details of the stage configuration.

Turbines are easily recognized by their distinctive bowl units.

These contain long tapered passages which facilitate water flow and permit maximum impeller size within a given pump diameter.

This configuration enables vertical turbines to pump large volumes of water.

Primary applications:

Farm irrigation

Community water supply

High-volume industrial work

Normally powered by an electric motor at the surface and connected to the pump by a long shaft.