The mechanical seal is very much a product of the 20th Century. According to Mayer (1974), the concept of a mechanical seal was known as early as 1900. Schoenherr (1965) showed patents from 1913 and 1919 which have features of the modern mechanical seal. The first commercially successful mechanical seal to be used on centrifugal pumps was probably made by the Cameron Division of the Ingersoll-Rand Company about 1928 (Tetlow, 1951). Prior to this, mechanical seals had been used in small refrigeration machines but not in large pumps. The Cameron seal was first installed in a number of centrifugal pipeline pumps. Apparently, Cameron did not sell seals for general use and there was no multi-purpose seal available for centrifugal pumps until the 1930’s.
The mechanical seal appears to have been invented by George J. Cooke (Patent #1545080, “Seal for Rotating Shafts”) in 1923. His design was originally called a “Cooke Seal” and he founded the Cooke Seal Company. Cooke’s seal was first used in refrigeration compressors. The Cooke Seal Company was a sideline product for Cooke and he sold the company to Muskegon Piston Ring Company where it became the Rotary Seal Division. Muskegon Piston Ring sold its Rotary Seal Division to EG&G Sealol who were later acquired by John Crane Incorporated.
Wikipedia: End face mechanical seal
In 1929, J. M. Ryan of Crane Packing Company, developed a mechanical seal which became known as the “Ryan Seal”. The Ryan Seal used steel vs bronze faces, a single coiled spring and packing for the secondary sealing elements. The O-ring had not been invented at this time. The mating ring was made of steel and installed with an interference fit to the pump shaft. Sealing faces were machined, not lapped.
At least three Ryan Seals were sold. One was for pipeline service, one for refinery “bottoms” and another for boiler feed water.
In 1934, mechanical seals made by A. R. Tuck and J. H. Hohler were being used at the Standard Oil Refinery at Whiting, Indiana. C. C. Hall of Durametallic signed Tuck and Hohler to an exclusive agreement with Durametallic. Within 12 years, mechanical seals had become the primary product of Durametallic Corporation.
Those early pump seals often used a face combination of hardened steel versus leaded bronze. This face material combination was satisfactory in lubricating oils but required a lubricant, usually grease, for non-lubricating services. A better method for providing the lubrication, the double mechanical seal, was developed by Durametallic in 1937 (Miller, 1992). In addition, double seals were also used in corrosive, dirty and high pressure services. In some ways, double seals were similar to conventional packing that was separated by a lantern ring and fed by a gland oil system. Even though those first mechanical seals would be considered as excessive leakers today, leakage from a seal was still orders of magnitude less than leakage from packing. In fact, packing leakage and gland oil consumption was a measurable portion, in some cases nearly 10%, of the capacity of an oil refinery (Porges, 1950).
In the mechanical seals of the 1930’s, soft packing was used as secondary sealing elements. Soft packing was made from natural fibers, rubber, Neoprene or asbestos. The O-ring was developed in the 1930’s but not used in mechanical seals until after World War II. Neil Christensen discovered the optimum dimensions for the O-ring and its groove in 1933. He applied for a patent in 1937 and received patent #2,180,795 in 1939. Prior to World War II, rubber meant natural rubber although much work was being done to develop synthetics. During the war, natural rubber was difficult to obtain and manufacturing synthetic rubber became a wartime priority. Neoprene, Buna N, Buna S, and Butyl rubbers were the first synthetics. The synthetic rubbers were generally limited to temperatures less than 250 F.
In the mid 1930’s Crane Packing Company licensed a mechanical seal design from Chicago Rotary Seal. Through several Crane patents, this design evolved into the full convolution rubber bellows seal. By 1938, Crane Packing Ltd in England was making their own mechanical seals for pumps in oil refineries. These were multiple spring seals using gland packing for secondary sealing elements; face materials were carbon against Stellite. Later, Crane Packing Ltd also used rubber bellows seals. Some of their first rubber bellows seals were actually applied as stationary seals with the pressure applied from the ID; one interesting variation was used at 11,000 rpm!
Judging by patents filed, the mid-30s through the mid-40s was an active time for mechanical seal development. Patents included:
- 1936 (1939?) — First automobile seal, John Crane.
- 1938 — Hanns Hornschurch “Sealing Device” (perhaps the first balanced seal)
- 1939 — Robert Stevenson, “Seal Construction” (assigned to Sealol)
- 1941 — Olin Brummer, “Liquid Seal for Rotary Shafts” (assigned to John Crane)
In the late 1930’s, probably about 1938 or 1939, mechanical seals began to replace packing on automobile water pumps. At first only the more expensive automobiles used mechanical seals in the water pump. The famous Jeep of WWII used a Crane rubber bellows seal in the water pump. After WWII, all automobile water pumps used mechanical seals.
In 1938, F. B. Porges, an engineer at the Manchester Oil Refinery in England, built his own mechanical seals to solve some difficult sealing problems. Within a few years, Flexibox, Ltd. was established to market his mechanical seals. The first Flexibox products used a single ply formed metal bellows. Soon, Flexibox was making double and triple ply formed bellows.
The concept of balance ratio is mentioned in a seal patented in 1913 (Schoenherr, 1965); however, the balanced seal seems to have developed in the late 1930’s. Hanns Hornschurch obtained patent 2,128,744 for a “Sealing Device” that later became known as the double seal. In this design, the inner seal is balanced. This may have been the first application of balance ratio although that term was not used at the time. Later, Robert Stevenson of Stevenson Engineering (later to become Sealol) obtained patent 2,321,871 for a hydraulically balanced mechanical seal. In those early days, a balance ratio near 50% must have been typical judging by claims that face load resulted solely from springs and was not affected by pressure.
As rapidly as seals were developing during the late 1930’s, the pace accelerated after World War II.
Teflon became commercially available in 1944 but was not used in mechanical seals until after World War II. The inertness of Teflon allowed mechanical seals to be used in corrosive environments. Because of its rigidity, Teflon was usually made into wedges, U-cups, chevrons and bellows for use as secondary sealing elements. Teflon was considered usable up to 500 F.
After World War II, improvements made to carbon-graphite allowed this self-lubricating material to become more popular as a seal face material. The application of carbon-graphite really increased in the 1950’s.
In the mid-1940’s pump manufacturers began to make their own mechanical seals. Ingersoll-Rand had developed single, balanced seals that could be used up to 600 psig. This gave them an advantage over their competitors who were using double seals and lubricator systems. Worthington, Pacific, Byron Jackson, United, Union and others developed their own designs (Miller, 1992). Eventually the pump companies got out of the seal business except that the Byron Jackson seal became the Borg-Warner seal (now Flowserve) and the Worthington design was sold to Chempro (now John Crane – Sealol).
In 1945, Crane Packing developed and patented the full convolution rubber bellows seal in four variations: Types 1, 2, 3 and 4. Types 3 and 4 were the Jeep water pump seals and preceded Types 1 and 2 but were not numbered when they were introduced.
Also in 1945, Flexibox, Ltd. was established in Manchester, England to market mechanical seals that had been developed for use at the Manchester Oil Refinery beginning in 1938. The first Flexibox products used a formed metal bellows. Within a few years, Flexibox was making double and triple ply formed bellows.
In 1946, Jim Thayer at Crane Packing Company developed the Type 9 seal which used a Teflon wedge. The Teflon wedge was necessary in order to seal very corrosive or reactive fluids at DuPont chemical plants. About the same time, Crane Packing Company developed the Type 8B seal for pipeline services. The Type 8B used Buna O-rings and was balanced for pressures up to 1200 psig.
One reason that modern seals leak less is due to the improvements in manufacturing processes and quality controls. The first seal faces were not as flat and smooth as today. Although seal faces were lapped as early as 1938 (Porges, 1950, Crane Packing, 1938), precision lapping evolved along with the mechanical seal. In 1948, Crane established its Lapmaster division to market lapping machines and processes.
In the late 1940s, Olin Brummer left John Crane to found his own company, Brummer Manufacturing Company. He obtained a number of patents for mechanical seals and his advertising claims widespread use of Brummer water pump seals.
Cartridge seals were used on a regular basis by 1950; this convenient packaging of seal, sleeve and gland was probably developed by C. E. Wiessner of Durametallic about 1942 (Miller, 1992).
Pumping rings, used to promote circulation in seal systems, were developed in the early 1950s.
By 1954, mechanical seals were used with such regularity in the refining and process industries that the American Petroleum Institute included seal specifications in the first edition of its Standard 610, Centrifugal Pumps for General Refinery Services. Because of problems when converting from packing to seals, the seal specifications (just over one page in length!) were mostly concerned with stresses, bolting and gasketing. Glands were required to use a minimum of 4 bolts of at least 2 inch diameter and to have a nonferrous close clearance throttle bushing. In 1955, the American Standards Association attempted to standardize some pump dimensions and nomenclature. This work led to the American Voluntary Standard (AVS) pump which eventually became the ANSI pump.
By 1956, many of the conceptual designs and application guidelines that are in use today had been developed (Elonka, 1956). Commercially available designs included both rotating and stationary flexible elements, balanced and unbalanced hydraulic loading, rubber and metal bellows, and a wide variety of spring designs and types. Secondary sealing elements included O-rings, wedges, U‑cups and various packings. Carbon-graphite was widely used as a seal face material but the mating seal face was often cast iron, Ni-resist, 400 series stainless steel, Stellite or aluminum oxide ceramic although tungsten carbide was coming into use. Hard facings, especially Stellite, were often applied to stainless steel and used in process pump seals. When two hard faces were used, the carbon-graphite face was usually replaced with cast iron, bronze or sometimes tungsten carbide. Then, as now, stainless steel was widely used for springs, retainers, sleeves and glands. Temperature ratings for these seals were in the ranges of 200 to 800 F depending on design and materials. Pressure ratings were up to 1000 psig depending on design and materials. Single and multiple (called “double” and “tandem”) seal arrangements were used as necessary to accomplish the required performance. It is doubtless fair to say that the allowable leakage for mechanical seals in the 1950’s was significantly more than today. After all, in those days, leakage from seals was compared to leakage from packing and the mechanical seal was a definite improvement!
In 1956, the Japanese NOK Corporation developed its first general purpose mechanical seal.
Karl Schoenherr, himself a major contributor to mechanical seal technology, credits Herbert B. Hummer, chief engineer of Durametallic, with the developing the pressure-velocity product (PV) as a guideline for design and application of mechanical seals (Schoenheer, 1995). Hummer’s work on PV began in the early 1950’s. In addition to PV, Hummer demonstrated the effects of shaft deflection on seal performance and developed guidelines for limits. Schoenherr, then Chief Engineer of John Crane, promoted the PV concept as well as published many articles on the basics of mechanical seals.
Metal bellows have been used as sealing elements in mechanical seals, valve stems and other equipment since 1950. In 1957, Sealol introduced the edge welded metal bellows seal. Previously, metal bellows seals had used a formed bellows which was much thicker and stiffer than the edge welded metal bellows. The early focus was on high temperature applications.
DuPont commercialized the first fluoroelastomer, Viton A.
In the early 1960s, Crane Packing Company developed the Type 8B-1 seal which was an O-ring version of their Type 9B product.
In the 1960’s theoretical studies and testing of mechanical seals began to focus on surface effects and hydrodynamics. Researchers began to look into and write about asperities@ as a means of mechanical load support as well as developing hydrodynamic operation. At Burgmann, Mayer placed circulation grooves on the seal face to promote cooling. At Crane, Trytek developed hydropadded seal faces.
Rayleigh pads had been used for some time in thrust bearings but were not considered stiff enough to prevent face contact over the wide range of operating conditions of a mechanical seal. Muijderman improved on the Rayleigh pad by using spiral grooves. In the late 1960’s, working at Crane Packing Company, James F. Gardner developed and patented a non‑contacting mechanical seal for compressors which used spiral grooves on the seal faces. In 1989, A. O. Lebeck was granted Patent 4,836,561 for his Wavy-Tilt-Dam Seal Ring approach to non-contact sealing. Today, most new compressors are furnished with non-contacting dry gas seals and many older compressors have been retrofitted to use them.
In 1962 Burgmann in Germany started to develop and produce mechanical seals. Dr. Ehrhard Mayer investigated and improved thermo-hydrodynamic seals with circulation grooves for high pressure applications.
Tungsten carbide began to be used as a seal face material about 1963.
Elastomer bellows, previously available only in natural rubber, Neoprene or Buna, began to be made out of fluoroelastomer in 1965.
In 1971, DuPont again revolutionized elastomers with its high temperature and corrosion resistant perfluoroelastomer, Kalrez.
In 1972, solid reaction bonded silicon carbide began to be used as a mechanical seal face.
Standard cartridge seals were introduced for ANSI pumps by Chesterton. Previously, the small seal chambers (really stuffing boxes) on ANSI pumps dictated that component seals be used.
Stationary metal bellows seals as we know them today were developed as part of a seal reliability/development program at Exxon’s Baton Rouge refinery. The Exxon Pump Team was not satisfied with reliability and performance of seals in hot services. Beginning in January, 1976 stationary metal bellows seals were designed, manufactured and assembled by the Exxon team using parts from various seal manufacturers. The Exxon team tested 19 seals in many variations before deciding to give the designs to seal manufacturers for commercial development.
Until the late 1980’s, the popular ANSI (“chemical duty”) pumps had stuffing boxes that were designed for packing. It was difficult to fit mechanical seals, especially multiple seals, into this small space. Independent tests by several pump and seal manufacturers confirmed the obvious: seals performed better with more radial clearance. The result was enlarged seal chamber designs. Other seal chamber variations, such as tapers and flow directing vanes, soon followed.
The Clean Air Act of 1990 placed limits on fugitive emissions from pumps. Seal manufacturers responded with improved designs – often derived from computer modeling – and better materials. Emphasis was placed on cartridge assemblies and multiple sealing arrangements. As a result, the requirements of the Clean Air Act were met.
Non-contacting dry gas seals proved so reliable and popular for compressors that variations were soon applied to pumps. In the late 1980’s, “Upstream Pumping” (Buck and Volden, 1990) used spiral grooved seal faces to create a self-pressurizing double seal from a low pressure liquid buffer fluid. But within a few years, the liquid buffer had been replaced by a gas barrier to make the double dry gas seals that are increasing in popularity daily.
In October, 1994, the American Petroleum Institute released the first edition of API Standard 682, “Shaft Sealing Systems for Centrifugal and Rotary Pumps”. This standard, the first to address the requirements of the oil refining industry, has had a major effect on the sealing industry. In addition to providing guidelines for seal selection, API 682 requires qualification testing by the seal manufacturers. API 682 also sets a goal for reliability: three years of continuous service. API 682 is now in its 4th Edition and work has begun on 5th Edition.
Even though those first mechanical seals would be considered as excessive leakers today, leakage from a seal was orders of magnitude less than leakage from packing. In fact, packing leakage and gland oil consumption was a measurable portion, in some cases nearly 10%, of the capacity of an oil refinery. (Reference 11)
There should be little doubt that the reliability of mechanical seals has improved dramatically since its commercial introduction. The life of those first seals must have been on the order of a few months or less. In the late 1940’s one user’s goal for mechanical seal life was nine months – about the same as some refinery operating units were expected to remain on stream (Reference 10). By the early 1960’s, seal manufacturers were using the PV value to design for a wear life of two years. In the early 1970’s, most pumps were using mechanical seals and a reasonably good gross average mean time between pump repairs in an oil refinery was 15 to 30 months. Studies (Reference 12) showed that very few seals failed by wearing out. With improvements in pump design (API 610 editions 6, 7, and 8), improvements in seal design and application techniques (API 682) and careful attention to details, some users have achieved mean time between repairs of more than six years.
There has been much consolidation in the mechanical seal industry. Among the major manufacturers:
- John Crane (Smiths Group of Great Britain) includes Sealol (Rotary), Flexibox, Safematic, Ropac;
- Flowserve includes BW/IP (Borg-Warner), Durametallic, Five Star, Pacific Wietz;
- EagleBurgmann includes Eagle, Burgmann.
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. Piezoelectric materials and electronic controls are being investigated for creating truly controllable seals. 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.