Re-engineered pumps can also be an option to replace centrifugal pumps. When it is incorrectly applied or when the initial fluid and flow conditions have changed, the screw pump can be the right alternative for new conditions. In one case, a vertical centrifugal lube oil pump serving a large reduction gear had difficulties maintaining the required oil pressure when foam and air was present in the oil. A re-engineered pump was designed to match the dimensions and nozzle location of the original centrifugal pump and could be dropped in the original lube oil tank without any modifications. The original centrifugal pump did not require a pressure relief valve, so an external relief valve was added and installed on the pump mounting plate connecting back to the tank.
The pump design did not interfere with existing structures or expand outside the original pump dimensional envelope.
A recent development includes re-engineered pumps for nuclear power plants including the special certification required for such installations. In particular, lube oil pumps for emergency and stand-by diesel engines have been of interest, as the original lube oil pumps are no longer manufactured.
Re-engineered pumps can be tailored for a special service or duty that was not planned when the pump was initially purchased. The flexibility of the cartridge design allows for the pump to adapt and perform many new tasks. In one example, the original pump was designed for very low suction pressure and very viscous fluids similar to grease. But the suction line was a restriction, and the pump never worked as intended. The new re-engineered pump was modified to bolt right onto the suction box of the holding tank. The axial inlet was enlarged and a modification to the rotor liner allowed the pump screws to work like augers pulling the fluid into the pump suction.
The pump cartridge, which is a standard component, is kept in the manufacturer’s facilities. The rotors are hardened and finish ground in carbon steel, and the rotor liners are in cast or ductile iron. As standard, the pumps come equipped with mechanical seals.
The pump casing is designed and manufactured locally, and the final assembly, inspection and quality control take place at the manufacturer’s facility. If necessary, additional pipe spools with flanges and instrument tabs can be provided. Shims or a pump soleplate can be offered in order to maintain shaft height and allow coupling with an existing motor.