Over the long term pumps inevitably display signs of wear because it is almost impossible to design a pump that is free from operational deterioration. Wear has an adverse influence on the performance of the pump, causing mechanical failure, leakage and energy (hydraulic) losses. Components most likely to be affected are bearings, mechanical seals, wear rings, rotating elements and the shaft. Then there is the matter of the internal surfaces which can be subjected to corrosion and erosion by the pumped fluid.
Turning old into new
Pump servicing, repair and refurbishment is a mainstream activity for AxFlow GB and at its Service Base in Huddersfield the Company provides pump users with a wide range of facilities, including supplying and fitting mechanical seals and the specialist Belzona coating service. When called in to provide both on-site or off-site maintenance and repair, it is standard procedure to examine the pump in detail and to discuss with the customer the application and operating conditions. In this way the Company's engineers are able to provide a wholly effective solution to the problem regardless of the age of the pump and to give a guarantee on its repair work. Where feasible, remedial work is carried out at the customer's premises and typically this will involve identifying the problem if there has been a pump failure.
The main objective is to get the customer's plant and production back up and running as quickly as possible, but not at the expense of creating further problems that might arise in the future. Pump replacement may at first seem the easiest option, but this can be costly for the customer and may not always be the best long term solution. Two of the latest restoration projects have involved a 42-year-old Allen Gwynnes 1meter diameter intake cooling water make-up pump for a power station in the East Midlands and a 46-year-old Vickers impounding pump in Hull docks.
Weighing in at around 5 tonnes, including the 600kg 75cm diameter impeller, the Allen Gwynnes DESC pump was installed when the power station was first constructed in the 1960's and is one of three pumps extracting water from the adjacent River Trent. The scope of the service work included stripping the pump down and performing a complete dimensional check. Remedial work involved replacing the impeller wear rings and rebalancing the whole rotating assembly. The contract also provided the opportunity to convert the upper stuffing box to a split semi-cartridge mechanical seal in order to allow easy replacement without there being a need to remove the motor, bearing and coupling. The lower stuffing box was also converted to a standard cartridge seal.
"Historically, the gland leakage led to bottom bearing failure and required constant maintenance to keep the bearing in a usable condition," reports Mark Redgrove, AxFlow Technical Support Manager. "We reassembled the pump with new bearings, casing wear rings, fasteners and gaskets before filling it with (a lot of) water to check the integrity of the seals. Once all the tests were complete we painted the pump and organised a fast delivery to site."
At Hull docks, the Vickers pump is employed at periods around high tide to maintain the dock water level. Having removed the pump from service for inspection, it was clear that a full overhaul would be required. This required the replacement of the cutlass bearing and shaft sleeve, refurbishing the mechanical seal, reconditioning the Michell bearings and installing a new GRP bell mouth because the original one had suffered severe damage from cavitation. In addition, the impeller was re-tipped, machined and balanced and all the internal surfaces coated with Belzona to stop corrosion.
According to AxFlow Managing Director Tony Peters, these two significant restoration projects demonstrated the Company's ability to proved completely new engineered sealing arrangements and apply Belzona coatings which give it a considerable advantage when faced with a challenging pump refurbishment. These coatings not only give excellent protection against corrosion, erosion and cavitation, but enhance the hydraulic performance of the pump which in turns leads to higher levels of operating efficiency. As a result, our coatings service is now becoming an integral part of the AxFlow proposition. Read more about our service offering.