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[Art Montemayor]

Fina:

Normally, what is understood as a "double-suction pump" is a horizontal, split-casing, centrifugal pump that receives suction liquid in both sides of the rotating impeller. This is a much desired type of mechanical design because it effectively balances the thrust effect of the rotating impeller and reduces the thrust bearing need and wear.

A small capacity centrifugal pump is usually of a single-suction design: it receives liquid through the out-board side of the rotating impeller. This type of design imposes an unbalanced thrust of the shaft thrust bearing that has to be taken into account. It also, through inherent configuration, imposes unbalanced forces on the pump and may cause vibrations.

A double-suction centrifugal pump is what everyone should have in their applications. However, that statement is easier said than done. This design is among the most expensive and can only be justified on an engineering application when rather large capacities (or critical applications) are involved. Because of the design and configuration, two shaft seals are required - as opposed to only one used on the single-suction models. Also, an outboard support bearing is also employed which keeps the pump shaft aligned and true. This is still another important mechanical feature that gives this type of design a dependable and long-term successful pumping reputation. Its poorer cousin, the single-suction model has to suffer with a cantilever design for its shaft.

The design can be seen in most pump text books and in Perry's Chemical Engineering Handbook.