Gas barrier seal
Eliminates product contamination

Pharmaceutical companies sought a gas barrier seal to eliminate product contamination. For safety and purity reasons, pharmaceutical manufacturers must maintain sterile conditions while producing medicinal products. ML-200 seals eliminate seal face wear debris and barrier liquid leakage by utilizing non-contacting seal faces and an inert barrier gas.

Before development work began on the M-Series mixer seals, they gathered input from mixer seal users - pharmaceutical, mining, and chemical processing companies that use low-rpm vertical mixers and the mixer manufacturers themselves. According to Bill Dentler, Mixer OEM Manager who chaired the product development task force, the information provided by mixer seal users proved invaluable during the design of the new seals.
Flowserve designers learned that:
Mixer manufacturers and end users both wanted to be able to convert from a wet seal to a dry seal. This capability makes it easier to convert equipment from one process to another, thus maximizing equipment versatility. The ability to convert from a wet seal to a dry seal, within the same dimensions, also simplifies the design process for original equipment manufacturers (OEMS) because they can incorporate the mixer seal dimensions into a new product and decide later what type of seal is required. The cartridge design of the M-Series seals permits end users and OEMs to convert among wet contacting, dry contacting, and dry non-contacting sealing by changing out the seal faces or replacing the seal cartridge as necessary.
Mixing companies use vertical mixers to mix metal slurries in autoclaves. These companies were often forced to use titanium or other hardened alloy mixer seals because of the abrasive, corrosive environment in the autoclaves. Due to the cost of these seals, the mining companies requested a more affordable material option for corrosive environments. The corrosion-resistant option for the M-Series has been engineered to minimize the volume of high alloy required for the wetted surfaces. Minimizing the high alloy volume lowers the material and fabrication costs for this option.
Many of the companies surveyed have a plant nitrogen supply, and they wanted a seal that can use nitrogen as a barrier. This would allow them to eliminate expensive liquid circulation and lubrication systems. The MD-200 and ML-200 can both use a nitrogen barrier.
Users requested less expensive mixer seals containing fewer parts. Previous mixer seal designs often contained a large number of parts, and the fabrication costs for these parts contributed to the high overall cost of the seal. M-Series seals utilize a cartridge design, and the seals are constructed from fewer components because the entire seal package is an integral unit. Because they have fewer parts, M-Series seals are inherently less expensive. Flowserve designers used the information gathered from mixer seal users to create a brand new seal concept incorporating as many of the requested features as possible. As a result of the close cooperation between the design team and users, the new seals are finding enthusiastic acceptance in the marketplace.
The engineers worked closely with OEMs during the development of the new mixer seals. As a result of this cooperation, M-Series seals are being developed for major mixer OEMs and glass-lined vessel manufacturers.
The new M-Series cartridge canister double seals are designed for low-rpm vertical applications in the pharmaceutical, chemical processing, mining, and petrochemical industries. These zero emissions seals have been specifically designed for the high pressures and increased temperatures of current mixer, dryer, and low-speed agitating equipment. M-Series mixer seals are available in three different configurations: a back-to-back canister arrangement for ease of installation.
- The MW-200 is a liquid lubricated seal.
- The MD-200 is a contacting dry running seal that uses inert a humidified gas barrier.
- The ML-200 is a non-contacting, dry running seal that uses an inert gas barrier. This version incorporates the Advanced Pattern Gas Seal (APGS) technology.
All three models feature interchangeable components. M-Series seals can be easily converted between the wet and dry running versions by changing out the stator and rotor seal faces.
M-Series mixer seals were designed to cover a wide range of applications. Depending on the model, they have an operating temperature range from –40 to 500 °F (-40 to 260°C), can handle pressures up to 500 psig (35 bar) with a minimum pressure differential of 25 psi, and can operate at shaft speeds from 0 to 500 rpm.
Because mixer applications typically require a high degree of radial deflection, M-Series seals will tolerate runout to 0.125 in. (3 mm) full indicator movement (FIM) and shaft end play up to 0.024 inch (0.6 mm). The seals are available in shaft sizes ranging from 2.000 in. to 6.500 in., in 0.250 in. increments. Metric/DIN versions will also be available.

Seal face geometry reduces leakage
The MW-200 liquid lubricated and MD-200 dry running versions both include balanced seal faces capable of handling pressure reversals. The ML-200 incorporates the proven APGS face technology and utilizes an inert barrier gas to develop seal face separation at zero rpm. And the ML-200’s non-contacting seal face design does not produce wear debris. The non-contacting seal faces make the ML-200 particularly suitable for pharmaceutical applications and any other applications where product contamination must be eliminated or minimized. The ML-200 uses a gas barrier auxiliary system consisting of a filter, flow regulator, needle valve, flow meter, and pressure gauge. The seal face pattern provides both hydrostatic and hydrodynamic lift, or eating seal face separation under static pressure regardless of peripheral speed.
Field and laboratory testing has shown leakage rates of less than10 cc/day for the liquid lubricated version and less than 1 standard cubic foot per hour (scfh) per inch of shaft size at the minimum differential pressure for the contacting and non-contacting dry running versions.

Advanced design features
The hydraulically balanced stator design of the M-Series mixer seals reduces the hydraulic loading on the stators. This reduced loading lowers the hydraulically induced waviness, extending seal life and reducing leakage throughout the operating pressure range. The seals also maintain equal seal face spring loading with axial shaft movement. The through collar springs help to eliminate seal face overloading due to high spring forces.
These seals incorporate a patented low-drag o-ring secondary seal that reduces dynamic O-ring drag. The low-drag O-ring is held in place by an extension spring that permits the O-ring to expand to allow for thermal and chemical swell. All three mixer seal models in the M-Series use carbon rotors. The M W-200 and ML-200 utilize direct sintered silicon carbide stators, while the MD-200 uses high-purity ceramic stators. Food grade and corrosion resistant materials are also available.

Installation made easy
The M-Series is a shaft centered seal design: the seal cartridge is centered on the equipment shaft instead of the housing. The shaft centered design reduces the shaft-to-vessel concentricity requirements and provides increased tolerances. Jack bolts and eye bolts are also provided for easier installation and removal. Optional features are available
M-Series seals are available with several user-specified optional features.
These include:
- A pre-engineered, optional cooling coil that is available for high temperature applications using liquid lubricated seals.
- A pre-engineered sanitary gland that can be used for debris catching and steam cleaning for dry running seals. The gland sits at the bottom of the seal, and it can be flushed out by attaching a steam line to the seal port.
- A pre-engineered, corrosion-resistant high alloy option that is available for harsh environments. The reduced volume of high alloy required makes this an economical option.