End-face mechanical seal
Since World War II, mechanical seals have replaced packing in many applications.
Even though these components are tightly pressed together, a small amount of leakage occurs through a clearance that is related to the surface roughness.
These two rings are machined using a process called lapping in order to obtain the necessary degree of surface finish and flatness.
The design of the mating ring must allow for minimizing distortion and maximizing heat transfer while considering ease of assembly and the static secondary sealing element.
Typical secondary sealing elements include O-rings, wedges or rubber diaphragms.
[1] In order to keep the primary sealing surfaces in intimate contact, an actuating force is required.
Another example of encasing is the drive mechanism which is necessary to prevent axial and rotational slippage of the seal on the shaft.
Classification by Design accounts for the details and features incorporated into a single seal ring/mating ring pair.
The most common seal face design is a plain, flat, smooth surface but there are many special treatments intended for specific applications.
In addition to torque, the drive mechanism must withstand the axial thrust produced by hydrostatic pressure acting on the components.
In such cases, a secondary sealing element might be manufactured from perfluoroelastomer and shaped in the form of a wedge, V or U.
Even though the scope of API 682 is somewhat limited, it may be extended to describe end-face mechanical seals in general.
Configuration refers to the number and orientation of the components in the end-face mechanical seal assembly.
[3][4] When the components are pre-assembled onto a sleeve and gland plate, the complete assembly is called a cartridge seal.
This complete assembly can be easily slid onto the shaft and bolted in place thus reducing the potential for installation errors.
An end-face mechanical seal generates heat from rubbing and viscous shear and must be cooled to assure good performance and reliable operation.
The flush may be heated, filtered or otherwise treated to improve the operating environment around the seal.
Piping plans for mechanical seals are defined by American Petroleum Institute specification 682 and are given a number.
Muskegon Piston Ring sold its Rotary Seal Division to EG&G Sealol who were later acquired by John Crane Incorporated.
The first commercially successful mechanical seal to be used on centrifugal pumps was probably made by the Cameron Division of the Ingersoll-Rand Company.
[6] Mechanical seals in the 1930s often used a face combination of hardened steel versus leaded bronze.
Carbon-graphite was not widely used as a seal face material until after World War II.
In the late 1930s, probably about 1938 or 1939, mechanical seals began to replace packing on automobile water pumps.
The famous Jeep of WWII used a rubber bellows seal in the water pump.
In the mid-1940s pump manufacturers such as Ingersoll-Rand, Worthington, Pacific, Byron Jackson, United, Union and others began to make their own mechanical seals.
Carbon-graphite was widely used as a seal face material; the mating seal face was often cast iron, Ni-resist, 400 series stainless steel, Stellite or aluminum oxide although tungsten carbide was coming into use.
In October, 1994, the American Petroleum Institute released API Standard 682, "A Shaft Sealing Systems for Centrifugal and Rotary Pumps”.
Among the major manufacturers: Today, in addition to face patterns such as spiral grooves and waves, materials have been developed that have special surfaces to promote hydrodynamic lift.
Lasers can be used to etch microscopic, performance enhancing textures on the surface of the seal face.
The application of specialized seal face patterns, surfaces, and controls is an emerging technology that is developing rapidly and holds great promise for the future.
