The Port of Tilbury is London’s major and greenest port and at each high tide the water level inside the impounding dock is raised to meet shipping and operational requirements. This is performed by four 57.5” vertical A/F Vickers Armstrong pumps installed in the late 1960’s and over the years they have served the dock extremely well.
At any one time three pumps are used, pumping up to 6,000lt/sec of abrasive seawater for two hours either side of each high tide.
In early 2013 planned maintenance activities noted noise from the No.2 impounding pump which became a cause for concern. A thorough inspection revealed that in addition to this problem the pump was leaking from the bottom casing and therefore not running to its full capabilities. In order to resolve both problems the pump had to be shut down and pump distribution and repair specialist AxFlow Limited was called in to provide advice.
A decision was taken to completely remove the 40 ton pump, including the lower rising mains, from service. According to Mark Redgrove, Technical Support Manager at AxFlow, removing the pump did prove to be something of a challenge as the majority of the 144 1¼”bolts had rusted solid. “Once we had the pump in our Huddersfield workshop we undertook a full strip-down, “says Mark Redgrove. “This revealed considerable wear to several of the major components, with the lower rising main (LRM) and wear rings being the worst examples.
The LRM was very badly eroded so it was decided to make a new pattern and cast and machine a completely new component. The upper and lower bearings also needed replacing. The lower wear ring was missing altogether and the upper wear ring was also severely eroded/corroded, so both wear rings were replaced. Fortunately the shaft could be re-used and this was cleaned and dressed.
Other work involved replacing the cutless rubber bearings, skim-machining the muff coupling sleeves and making new couplings. The lower part of the Outlet Guide Vane casing at the upper wear ring was badly corroded making it necessary to machine it back and cast and refit a replacement piece. The spigot for the lower tunnel tube was also broken, so this was machined back by 10mm to reintroduce the spigot and a new 10mm longer tunnel tube was cast and machined.
In spite of the wear shown by many of the components and the aggressive nature of the seawater being pumped, the impeller was found to be in relatively good condition. Although the size and extent of wear to the pump was a challenge, it is now re-installed in the impounding station and running smoothly.
Picture: The impounding pump is now back and running smoothly. (Image: AxFlow)