Split bearings eliminate the need for crane hire

United Utilities operates electricity, wastewater and water networks throughout North West England. Several of the company's wastewater sites incorporate orbital aeration tanks as part of the sewage treatment process. Each of these tanks has a number of horizontal rotors that agitate the sewage and introduce oxygen, thereby accelerating the treatment process. In the past, the rotors have always been supported by two solid bearings with internal seals. However, this arrangement has proved to have drawbacks over the long term. During periods of heavy rain it is possible for the sludge level in the aerator tanks to rise to the point where the bearings become temporarily submerged, compromising the bearing seals and leading to premature bearing failure.

Replacement then presents its own set of problems. In order to change the solid bearings, each rotor must be lifted clear of the tank. Furthermore, depending on the level of corrosion, the rotor may then have to be completely removed for workshop-based remedial work. In either case, the most substantial part of the cost is the hire of a crane with a 24m (80-foot) reach, which can be in excess of £2500 per day.

In an effort to eliminate these costs, Revolvo undertook a full evaluation of the existing application conditions and proposed an alternative based upon its SRB range of split roller bearings. The split bearing units were specified with housings and supports designed to be interchangeable with the existing bearing units wherever possible, or to incorporate adaptor plates if necessary.

Self-aligning split seals

In addition, the housings were equipped with high-performance split rubber lip seals with garter springs and retaining plates to guard against water ingress during intermittent submersion. As a result of the SRB split bearing units self-aligning properties, these seals are always concentric with the shaft, thereby maximising seal efficiency.

The use of SRB units also represents large future cost savings for United Utilities, as a result of the SRB's totally split design. Should the future need arise to change a SRB split bearing, it will only be necessary to support the rotor shaft, thereby eliminating the necessity and cost of crane hire. This in itself will easily recover the investment of using the SRB split bearing units.

An initial trial of four SRB units was undertaken at United Utilities' Hale Bank Works near Warrington. During the trial period, which was undertaken throughout the winter months and included several periods of heavy rainfall, the units were subjected to a number of short-term submersions. Despite this, the bearings have performed to expectations and continue to run smoothly.

Following the successful outcome of the Hale Bank trial, United Utilities is now in the process of evaluating the logistics and cost savings involved in replacing other existing solid bearing units on this type of application with the Revolvo design of SRB split roller bearings.