Mechanical seals are used to prevent leakage from rotating equipment such as pumps or compressors. There is always a risk of a liquid, such as oil, leaking out of a pump and contaminating the environment. Seals reduce the probability of leaking by wrapping around a pump and providing a tight enclosure. There are several types of seals available to protect mechanical pumps.
Single-shaft seals are the most common pump seals. Single-shaft seals consist of a rotating unit with a mating face that connects to a stationary unit. The seal body is sprung using a series of small spring or by a single coil spring. The springs are used to keep the seal shut when the pump is inactive. The spring may also be used to drive the rotating head of the seal.
Double seals are available in two different configurations: back-to-back seals and tandem seals. Back-to-back seals are two seals connected by their backs. The internal seal is placed so it faces the impeller, while the external seal is facing the gland plate. In tandem seals, the face of the internal seal is connected to the back of the external seal. Back-to-back seals operate in reverse mode, while tandem seals work normally.
External seals are used to convert a packed pump into a seal. External seals are used if a stuffing box cannot accommodate a normal sized seal. They operate in reverse mode and use spring pressure to keep the seal faces closed. The seal can only be used in limited ways because the differential pressure across the seal is limited.
Cartridge seals are self-contained units that consist of a shaft sleeve, a seal and a gland plate. The seal is fitted onto a pump shaft and requires no further service. The cartridge seals are available in single and double forms. The gland plate is often fitted with various tappings to support flushing, disaster control and cooling water injection.
Article Sources : Pump Seal Types