End Face Mechanical Seal

End Face Mechanical Seal

When a pump operates, the liquid could leak out of the pump between the rotating shaft and the stationary pump casing. Since the shaft rotates, preventing this leakage can be difficult. Earlier pump models used mechanical packing (otherwise known as Gland Packing) to seal the shaft. Since World War II, mechanical seals have replaced packing in many applications.An end face mechanical seal uses both rigid and flexible elements that maintain contact at a sealing interface and slide on each other, allowing a rotating element to pass through a sealed case.

A "cartridge seal" is a prepackaged seal that is common in more complex applications and were originally designed for installation in equipment where a component type seal was difficult due to the equipment design. Examples of this are horizontally split and vertical pumps. In 1975 the A W Chesterton Company designed the first cartridge seal that fit pumps with varying stuffing box bore sizes and gland bolt patterns.
The secondary sealing surfaces are the other aspects in the seal that require a fluid barrier but are not rotating relative to one another. Usually the secondary sealing elements are rubber diaphragms, O-rings, or PTFE wedges.

Some Basic Features of End Face Mechanical Seal:

• A gap seal is an important feature that is used with bearings or other parts susceptible to wear and tear. A good example is an O-ring.
• A clearance seal is designed to fill or close the space between two parts, such as machine housing.
• The seal allows the parts to vibrate without causing damage.One example of this particular type of seal is called a floating seal.
• It is designed to be easily replaceable.
• These types of seals are normally made out of rubber or flexible synthetic materials.

WHY DO PUMPS NEED TO BE SEALED?

Fluid enters a centrifugal pump through the suction nozzle at the center of a rotating impeller. As the impeller rotates, its vanes fill with fluid, then force it out to the pump casing where it exits the pump through the discharge nozzle.
Unfortunately, the discharge pressure will force fluid back behind the impeller, where it attempts to exit by way of the rotating drive shaft. Attempts have been made by pump manufacturers to minimize this leakage through design, but the leakage won't be stopped entirely.