Repairs made to reservoir pumps

The pumps were originally commissioned in 1924 for the Metropolitan Water Board and were driven by uniflow steam engines. Since the reservoir was officially opened in 1925 by King George V and Queen Mary, the machinery has been upgraded several times and the pumps are now driven by electric motors.

After years of frequent use, certain areas of the pumping equipment were suffering from cavitation damage, which in turn was seriously hindering the efficiency of the pumping system. This needed to be promptly addressed and so a thorough inspection including a hydraulic profile was arranged. 

Due to the physical size and weight of the top half of the pump casing, it was not practical to turn the casing over, therefore, the casing was mounted on blocks (supported by the crane for safety) and scanned from underneath. During this inspection, each casing was identified as having 'Substrate corrosion to rust Grade D'. This is the highest level of corrosion grade on the scale, indicating severe rusting of the cast iron and pitting. (ISO-8501-1)

Once the hydraulic profile was completed and all the equipment had been scanned, it was decided that several refurbishment applications should be carried out on three of the pump volutes, totalling a surface area of 282m². Due to the extent of the damage (some areas of each volute exhibited up to 50% corrosion) complete metal repairs were prescribed followed by a protective coating. Rebuilding and protection were required to restore the heavily corroded cast iron substrate so the pump could continue to perform at its maximum efficiency. After inspecting the impellers, each of them consisting of a surface area of 44.5m², it was decided that once each had undergone a thorough cleaning, they could be put back into service.

Application method

Firstly, all machined faces were protected from the blasting process before Sponge Blasting equipment was used on the upper and lower casings. This was used to remove the previous coating, create a substrate cleanliness of at least SA 2 ½ and produce a surface profile of no less than 75µm. The application area was then vacuumed and examined to make sure it was dust free and all the blast media was removed. 

Once the substrate had been tested for salt contamination, the application areas were masked out ready for the application of Belzona 1111 (Super Metal). Applied using a Belzona applicator, this material was used to rebuild the areas of undulation and pitting damage. A solvent free epoxy resin reinforced with silicon steel alloy, this repair composite provides robust corrosion resistance and will ensure the substrate will remain protected when it comes into contact with abrasive material. 

After Belzona 1111 had cured and within the two-hour coating window, the first coat of Belzona 1341 (Supermetalglide) in a grey colour was brush applied. This was followed by the second coat in blue to achieve a total dry film thickness of 400 microns. This coating was specified as it will provide long-term erosion and corrosion protection to the equipment and improve the efficiency of the pump. Belzona says its 1341 has been proven to increase efficiency by up to 7% on new equipment and up to 20% on refurbished equipment. It does this by using hydrophobic technology which repels process fluids and reduces the turbulent flow. Once cured, the coated surfaces were thoroughly checked for any misses or pin holes. 

By using modern polymer technology, Belzona was able to restore the centrifugal pumping equipment and ensure the historic Queen Mary Reservoir was back to running as smoothly and efficiently as possible.