Hot Tub Pumps and Motors

Most impellers on hot tub pumps have a female-threaded hole on the centre backside (the side facing away from the water source) and screw onto the male-threaded end of the motor shaft. The rotation of the shaft is just like the action of a bolt being threaded into a nut. Therefore, as the shaft turns, it is always tightening the impeller on itself.

Impellers are rated by horsepower to match the motor horsepower that is used. These, in turn, determine the horsepower rating of the hot tub pump or pump/motor you have.

Seal Plate and Adapter Bracket

To remove the impeller or to access the seal, the volute is actually divided into two sections the actual curved housing for the impeller is actually the volute, while its other half is called the seal plate or adapter bracket.

The seal plate is joined to the volute with a clamp. An 0-ring or gasket between them makes this joint watertight. The motor is bolted directly onto this type of seal plate. In other designs, the seal plate is moulded together with an adapter bracket that supports the motor and bolts to the volute with a paper or rubber gasket between them to create a watertight joint.

Some pumps use a clamp that is made tight by a bolt and nut. Always assemble the clamp with the bolt on top to make future access easier. Moreover, if the pump leaks at all, the bolt gets wet, causing it to rust, making unscrewing it even tougher, or the bolt breaks altogether.

In all pump types, the shaft of the motor passes through a hole in the centre of the seal plate, and the impeller is attached, threaded onto the shaft.

Seal

If the shaft passed through the large hole of the seal plate without some kind of seal, the pump would leak water profusely. If the hole were made small and tight, the high speed of the shaft spinning would create friction heat and burn up the components in minutes, or the shaft would bind and not turn at all. Some clever engineer devised a solution to this problem, called a seal.

The seal allows the shaft to turn freely while keeping the water from leaking out of the pump. The seal has two parts. This assembly fits into a groove in the back of the impeller. The ceramic ring can withstand the heat created by friction. The left half of the seal fits into a groove in the seal plate and is composed of a metal bushing containing a spring. A heat-resistant graphite facing material is added to the end of the spring which will face the ceramic in the other half.

The tight fit of the seal halves prevents water from leaking out of the pump. The spring puts pressure against the two halves to prevent them from leaking. As the shaft turns, these two halves spin against each other but do not burn up because their materials are heat-resistant and the entire seal is cooled by the water around it. Therefore, if the pump is allowed to run dry, the seal will be the first component to overheat and fail.

Pump makers are always improving the heat dissipation (called heat sink) capabilities of their pumps, so that dry operation will result in little or no damage to the seal or pump components. Still, no matter what the maker claims, pumps are not designed to run without water for more than a few minutes while priming.

Motors, like the pumps they drive, are rated by horsepower, typically 1/2, 3/4, 1.0, 1.5, and 2.0 horsepower. The caps on each end of the motor housing are called end bells. A starting switch is mounted on one end with a small removable panel for connection and maintenance access.

In here you will also find the thermal overload protector. This heat-sensitive switch is like a small circuit breaker. If the internal temperature gets too hot, it shuts off the flow of electricity to the motor to prevent greater damage. As this protector cools, it will automatically restart; but if the unit overheats again, it will continue to cycle on and off until the problem is solved or the protector burns out altogether.

It takes a great deal of electricity to start a motor but far less to keep it going (in fact, about 5 to 6 times as much). The capacitor, as the name implies, has a capacity to store an electric charge. The capacitor is discharged to give the motor enough of a jolt to start; then the motor is able to run on the lower operating amount of electricity as designed. Without the capacitor, the motor would need to be served by very heavy wiring and high-amp circuit breakers to carry the starting amps. Capacitors are located in a separate little housing mounted atop the motor housing or inside the front end bell.

Some motors are designed to operate at two speeds. For example, some hot tubs operate at high speed for jet action, but lower speeds for circulation and heating. Normal rotation speed is 3450 revolutions per minute (rpm), and the low speed is 1750 revolutions per minute.

Most motors are designed to be connected to either a 110-volt or a 220-volt power source. By changing a wire or two internally, you determine which voltage is used. The instructions for this conversion are printed on the motor housing or on the inside of the access cover.

Finally, the housing of the motor is designed to adapt to various kinds of pump designs, called square flange, C-frame, the 48, the uni-seal flange, and others. When you replace a motor, be sure to buy the design that fits your pump.