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Horizontal Slurry Pump Shaft Sealing

Centrifugal horizontal slurry pumps have a rotating shaft passing through a stationary casing, so leakage must be prevented by using shaft sealing system. There are three basic shaft seal types, gland packing seal, centrifugal expeller seal and mechanical seal, the correct type of seal must be carefully selected to suit each individual application.

Gland packing seal

Gland packing seal is the first choice when some slurry dilution is acceptable.

The most critical requirement for achieving satisfactory gland life is the supply of gland flush water at the correct pressure. For normal operation, gland flush water pressure should always be 70 to 110 kPa higher than the stuffing box pressure. In practice the flush water pressure is often set at 35 to 70 kPa above the pump discharge pressure.

Gland packing seal pumps do not absorb more power than centrifugal expeller seal pumps, and normally the power expended by flush water is lower than the power expended by expeller, so gland packing seal provides substantial operating cost savings.

Centrifugal expeller seal

Centrifugal expeller seal is most widely used for single stage pumps when flush water is not available.

Expeller is designed to reduce bypass pressure from the pump into the shaft seal area, it is mounted in a separate chamber (expeller ring) behind the main impeller.

Expeller seal does not require flush water, but the expeller absorbs an additional 5% power and are effective with suction pressure to a maximum of 10% of the discharge pressure.

Mechanical seal

The mechanical seal consists of a stationary and a rotating face pressed together to prevent leakage.

Mechanical seal is not widely used in slurry pumping applications, because mechanical seals are more expensive, and the seal faces often are damaged by solids.