Three Piece Booster Pumps

The three-piece booster pump illustrated in Figures 10-11 and 10-12 is an example of the circulators used in small-to medium-size residential and light commercial hydronic heating systems since the 1930s.

A typical three-piece booster pump consists of the following three sections: (1) the pump body (also called the volute, body assembly, or waterway), (2) the coupling assembly, and (3) the motor assembly (also called the shaft-and-motor assembly).

The three-piece booster pump contains hermetically sealed sleeve bearings, a carbon/ceramic seal, and a coupler that uses springs in tension to provide quiet operation. The motor of a three-piece booster pump can be serviced by removing it from the pump body. Consequently, there is no need to drain the system or disconnect the pump from the piping for servicing.

The three-piece booster pump has an inline volute, which means the inlet and discharge ports are located along the same centerline. It has a strong starting torque, which enables it to free a stuck impeller without any difficulty.

The volute is just another term for the pump body. It contains the motor bracket, the impeller, the volute gasket, the inlet and discharge ports, and the pump mounting flanges.The shape of the volute will determine how the circulator is connected to the piping.

A three-piece booster pump requires periodic inspection. The mechanical seal will sometimes need replacement. After removing the old seal, clean the shaft and sleeve before installing a new one. The pump manufacturer will provide step-by-step instructions for servicing the pump mode.

This pump also requires periodic lubrication. A wool wicking is used to draw the lubricating oil into the bearing assembly (see Figure 10-13). Check the pump manufacturer’ s operating and maintenance instructions for the recommended lubricating schedule. As shown in Figure 10-13, the three-piece booster pump must always be installed with the oil ports facing upward and with the motor, motor shaft, and bearing assembly in a horizontal position.

Never plug or cover the weep hole, or you will trap the excess oil in the pump body.Any dirt or sediments in the oil may damage the bearings and shorten their service life.

Use only the lubricant specified by the pump manufacturer. An SAE 20 (nondetergent) or 10W-30–weight oil can be substituted if the pump manufacturer’s recommended oil is unknown.

The three-piece booster pump shown in Figures 10-11 and 10-12 can be installed to discharge in any direction (e.g., up, down, horizontally, etc.), but the motor shaft must always be in the horizontal position, the arrow on the pump body must always point in the direction of flow, and the conduit box must be positioned on top of the motor housing.