Gearbox drops in for engineering-free solution

After a 1975 gearbox seized at Harpenden sewerage works, Thames Water was faced with the choice of having to pay for the original gearboxes to be remanufactured or to replace a large part of the tank's peripheral equipment including the bridge and drive system to fit a modern replacement. For approximately half the cost of these two options, BSL and Brevini have teamed up to design and engineer a modern planetary solution that can be fitted as a direct replacement and meet Thames Water's aim of "no engineering" replacement. Jon Snaith Sales Manager of Brevini UK designed the solution.

He said: "We estimate there are over 100 of these particular 70s style gearboxes driving thickeners and scrapers at sewage works across the UK, many of which will be reaching the end of their operating life".

"We have seen several recently that require attention and the seizure at Harpenden gave us an opportunity to engineer a solution that could be fitted as a like-for-like replacement".

The order was placed on BSL Luton, which has a longstanding relationship with Thames Water and is used to providing maintenance solutions for the water industry.

Several companies were asked to quote for a direct replacement to the Sanderson Heliocentric gearbox but Brevini was the only company that was able to solve the engineering riddle of matching sizes, speed, power output and mounting requirements.

In order to match the fitting requirements Brevini designed and supplied a bespoke engineered flange and end cap for the new assembly.

The splined output pinion was then cut from the original gearbox and fitted to the output shaft of the new five-stage Brevini planetary unit to allow a seamless fit.

The solution means that the original mounting and bridgework, which is sound, can be retained and the new gearbox fitted without any alterations being made.

This was important for Thames Water as the company employs a "no engineering" policy where possible on replacement items in order to control costs.

Compared with the alternatives of having the original ageing gearbox remanufactured which would have involved replacing all worn parts with new parts made from scratch, or dismantling the scraper drive and bridge and adapting them to accommodate a new gearbox or indeed building new ones, the cost of the Brevini engineered solution is at least half that of estimates made for the alternatives.

Meeting strict cost criteria has become an increasingly important facet of most public service and utility engineering projects, making the Brevini solution ideal because it uses up-to-date technology that can be applied with a cost saving.

The savings are not just limited to the purchase and installation cost; Brevini planetary gear reduction stages are 98% efficient and a five-stage reduction can be powered by a very small electric motor.

Using a 0.25kW motor the package delivers an overall efficiency of 87.5%.

This high level of energy efficiency will provide substantial energy savings when compared to the original units.

A second thickener drive at Harpenden that uses the same heliocentric gearbox is also being replaced with a Brevini solution after the tank with the seized gearbox returned to operation.

Now the design solution has been approved and the first one fitted without a hitch, the overall project time for replacements has been reduced drastically compared with the alternatives.

The equipment is only out of action for a matter of days rather than weeks and the commissioning itself is straightforward and relatively simple to complete as no adjustment of the original mountings or drive are required.

Brevini gearboxes are available off the shelf and with engineering support via any one of over 120 BSL branches nationwide.

There are many other Brevini solutions already available for industry specific applications including slewing drives for the water industry, wheel and track drives for the mobile plant industry and for a wide range of general industrial mixing and conveying tasks.