Split roller bearings reduce maintenance costs

The split-to-the-shaft design and advanced sealing of Revolvo's SRB bearings has resulted in their application on aerators at a water treatment plant for Wessex Water. The SRB split bearings allow easy maintenance, without having to remove the shafts of long horizontal rotors that agitate sewage and introduce oxygen to the treatment process. Previously a crane was required to completely remove the solid support bearings, at a cost running to thousands of pounds per day. In addition, the sealed SRB bearings are designed to withstand full submersion in sewage sludge, which can occur due to raised levels in the aerator tanks during periods of heavy rainfall.

Wessex Water operates wastewater and water networks throughout South 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 which 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 not proved ideal 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 bearing units 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 out 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 crane hire, which can be in excess of 2500 per day.

In an effort to reduce maintenance, Revolvo was asked to find a solution. The company undertook a full evaluation of the existing application conditions and proposed a solution 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 incorporate adaptor plates if necessary. The housings were also equipped with high-performance split rubber lip seals with garter springs and retaining plates, to guard against water ingress during intermittent submersion. Finally, and importantly, the bearings were equipped with remote grease points that allow maintenance without engineers ever having to come into contact with the sludge waste.

Effective sealing system

Commenting upon the design of the bearings, Revolvo's Sales and Marketing Director, Adrian Menzies, says: "Revolvo has a very successful history of installing bearings in applications where they will be submerged in sludge or effluent. Thanks to a very effective sealing system our bearings are capable of surviving far longer than traditional bearings - eight years, or more - with no more basic maintenance than standard regreasing required. Another advantage of SRB split roller bearings is that, when they do reach the end of their life, they are very easy to replace."

The use of SRB bearings promises large future cost savings for Wessex Water, because of the SRB's totally split design. Should the need arise in future to change a SRB split bearing, then it will only be necessary to support the rotor shaft, 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 the treatment works. The trial period was undertaken throughout the winter months and contained several periods of heavy rainfall, subjecting the SRB to a number of high water level situations. Despite this, the bearings have performed to expectations and continue to run smoothly and reliably.

About SRB bearings

Unlike solid bearings, SRB split bearings are totally split to the shaft, a design that both simplifies and expedites installation and cuts downtime to approximately 10 per cent of that required to replace solid bearings of a similar size. In addition, Revolvo SRB bearings can have a longer life span because they cannot be cross-located. They also provide superior sealing arrangements, which means longer bearing life with reduced levels of maintenance.

In addition, the design of Revolvo's SRB split bearing allows the upper half of the housing and outer bearing raceway to be removed, whilst the shaft is still supported by the lower section of the housing and bearing; this feature enables inspection of the bearing raceways, cage and rollers to be undertaken with the bearing and shaft in situ, which would be impossible with a conventional solid roller bearing.

This is a valuable feature generally, but especially regarding large machines, where sheer weight and size can be a barrier to fast and effective servicing. It also allows for faster bearing replacement, which can save continuous-type businesses a lot of money in costly downtime.

For more information about Revolvo's split-shaft SRB bearings, visit the website at www.revolvo.com.