Sealed roller bearings keep plant running smoothly

Bucks County, Pa., located northeast of Philadelphia near the New Jersey border, has been growing constantly since just after World War II. In 1962, the Bucks County Water and Sewer Authority was created to handle the resulting expansion of the sewer system.

Recently, the authority completed its new Totem Road Pump Station to replace a smaller station built in 1972. While the previous pump station had one 21,000 gpm pump and two 12,000 gpm pumps, the new facility has two 36,000 gpm pumps and two 20,000 gpm pumps.

Large electric motors drive the four lift pumps located five stories below them. A combination of universal joints and spherical roller bearing pillow blocks keeps the long shafts in line through operating cycles that typically stretch to 24 hours at a time.

The shaft lengths required to reach from the motors to the pumps would exceed the maximum length of a single universal joint, so multiple joints are used to separate the span into sections.

Housed in a masonry building, the new 60 mgd lift station collects sewage from the systems of 11 municipalities in the county. The Neshaminy Interceptor transmits the sewage through a dual 42-inch diameter force main to Philadelphia’s Northeast Wastewater Treatment Plant.

Sewage arrives at the Totem Road station through a 17-mile long interceptor varying from 12 to 72 inches in diameter and goes through a shredder before entering a 27-foot wet well adjacent to the pump room. It is pumped from the well to the interceptor at the bottom level, five levels below grade where the pumps are located, but the expensive motors and controls are above ground level to protect them in case a mishap causes flooding.

All four pumps are Worthington-Dresser units, two rated at 20,000 gpm; the other two at 36,000 gpm. In normal operation, the two smaller pumps alternate 24-hour cycles. When the sewage level in the well exceeds 18 feet, one of the large pumps kicks in.

Drive motors for the two smallest pumps are 500 hp-rated units by U.S. Electrical Motors, a subsidiary of St Louis-based Emerson Electric Co., running on three-phase 460V power. The larger motors, by Canadian General Electric, are rated at 2,250 hp and run on three-phase 2,300V power.

Shaft diameters for the two 20,000 gpm pumps are 4.44 inches at the bearing and 11.22 inches diameter across the universal joint, with 9-inch tubing.

Shaft diameters for the two 36,000 gpm pumps are 7 inches at the bearing, and 17.126 inches diameter across the universal joint, with 10-inch tubing.

Overall, each shaft segment is approximately 15 feet long, and the shaft assembly passes through five levels from the motor to the pump below. At each level, the shaft segment is supported by a bearing and joined to the next segment by a universal joint coupling.

The bearings stabilize the shaft system, while the universal joints allow for misalignment and simplify shaft installation or replacement by allowing the removal of individual segments. Bearings are Series 6800 spherical roller bearing pillow blocks by Indianapolis-based Link-Belt.

Paul Lumbrezer of Johnson Power of North America, Broadview, Ill., who designed the shaft systems, says they were used here because they are self-aligning and have the capacity to transfer the shaft weight effectively.

The company supplied its standard industrial universal joint couplings as part of the shaft assembly. Widely used in a broad range of heavy-duty industrial applications, the joints can be repaired because they are designed as components.

Because they are used in a vertical application, the bearings are equipped with special contact seals to retain lubrication. Since installation, normal maintenance has consisted of lubricating the bearings once a month, according to plant personnel.