This unique design allows the pump to be installed inside a storage tank in a vertical pump column with a suction (foot) valve located at the bottom. Because the pump is installed through the top of the tank, all connections below the maximum liquid level of the tank can be eliminated. This design also eliminates the possibility of major tank leakage because of a pipe or connection problem and permits the storage vessel to be located below ground level.
The submerged pump and motor unit is designed to fit into the smallest practical column diameter by using an axial diffuser design. The column acts as a guide to seat the pump during installation and also performs as the discharge pipe from the pump to the top of the tank. Each pump is fitted with an inducer, which is an axial flow impeller located at the lowest possible level of the tank to improve the net positive suction head required (NPSHR), allowing operators to lower tank liquid levels to extremely low levels. To isolate the tank contents from the pump column, a suction valve is used that incorporates a dual pressure sensitive seal. The suction valve is flanged to the lower end of the pump column and is closed by coil springs as well as by the hydrostatic pressure of the liquid in the tank.
To open the valve, the inlet feet of the pump press down against the bottom plate during insertion, forcing it to open using just the weight of the pump. It can be closed at any time by simply hoisting the lifting eye, located at the top of the column, without disassembly of any other components. Once the valve is closed, the column can be inerted with nitrogen gas to allow the safe removal of the pump even with liquid in the tank. The power cables used in the retraction system are made of a high-quality armored cable. These cables are Underwriter’s Laboratory (UL) listed and were developed specifically for use in cryogenic liquids. The lifting cables used are an anti-twist, stainless steel cable, that can provide many years of use without replacement.