PTFE

There are many factors to be considered when choosing the right type of hose for your application.  There are many different types of hose available on the market. They include metal, rubber, composite, PTFE and fabric. The decision of which hose type to buy depends on the application for which the hose is being used.

Metal hose is ideal for absorbing vibration, misalignment correction, thermal expansion or contraction of piping systems, and protecting equipment from excess motion.  Typically, metal hose is used when no other (non-metallic) constructed hose will work.  In other words, metal hose is used as a last resort.

Here are some of the factors that should alert you it's time to use metal hose:

In our latest video, Gallagher Fluid Seals Engineering Manager Craig Beil discusses the various PTFE fillers used in making seal materials. Fillers include carbon, glass, stainless steel and molybdenum disulfide. Watch the video to learn more about what PTFE fillers can do, and be sure to watch the other videos in our series.

Past videos have explored issues such as radial seal misalignment,  the use of spring energized seals and environmentally-designed static

Today we’ll continue our look at spring-energized seals by exploring some of the preliminary considerations to made when working with these seals.

A spring energized PTFE seal is selected to fit an exact set of service conditions found in your application.

Gallagher Fluid Seals recommends conducting a review of the entire sealing environment. You should use the Engineering Action Request (EAR) form before selecting a seal design.

Spring energized PTFE seals perform reliably in a variety of applications where conventional elastomeric seals fail due to chemical attack, extreme heat or cold, friction, extrusion or compression set.

PTFE seals have three basic design elements:

• A pressure-actuated U-shaped jacket
• A metal spring loading device
• High performance polymeric seal materials

So what is a spring energized PTFE seal? It’s a spring-energized U-cup that uses a variety of jacket profiles, spring types and materials in rod and piston, face and rotary seal configurations. They are used when elastomeric seals fail to meet temperature range, chemical resistance or friction requirements.

Jacket profiles are made from PTFE and other high performance polymers. Spring types are available in corrosion-resistant alloys, including stainless steel, Elgiloy and Hastelloy.

Today we’ll conclude our series of blog posts on PTFE by discussing some PTFE radial lip seal applications, as well as a brief look at wear sleeves.

PTFE has superior mechanical and physical properties and chemical resistance, which means the areas where PTFE radial lip seals are used is growing. These areas include:

Diesel Engine Applications

These consist of the front and rear crankshaft, accessory drive, and blower and thermostat seals. PTFE seals are used and tested in these areas because they can meet the performance and life requirements of modern engines.

Minimum wear, performance at high temperatures with limited lubrication, resistance to abrasive contaminants and fluid compatibility are the main factors for PTFE’s use in these applications.

Today we’ll continue our look at PTFE rotary seals by focusing on three areas: housing/bore considerations, pressure and shaft velocity and shaft misalignment and runout.

Housing/Bore Considerations

Typical PTFE rotary lip seals are pressed into the bore to assure proper OD sealing and seal retention in the housing. Most seal and housings are made from steel and cast iron. Take care when softer materials – aluminum, bronze, plastic – are used for the housing. Aluminum has a thermal expansion rate almost double that of steel. Metal case designs can lose the required press fit in an aluminum housing when they go through thermal cycles due to the higher rate of thermal expansion of aluminum.

A finish range of 32 to 63 μin Ra (0.8 to 1.6 μin Ra) is recommended for service pressures up to 3 psi (0.20 bar). For thicker fluids such as grease, a 125 μin Ra (3.17 μin Ra) finish would be acceptable with no system pressure.

A lead in chamfer is strongly recommended for all seal housings. The chamfer aligns the seal during installation and helps keep the seal from cocking. Both corners of the chamfer should be free of burrs or sharp edges. For pressurized rotary applications, take additional precautions to ensure the seal isn’t pushed from the housing.

As we continue this blog’s PTFE series, we’re going to take a closer look at PTFE rotary seal shaft considerations.

In rotating applications, proper surface finish is crucial for getting positive sealing and the longest seal life possible. Rotating surfaces that are too rough could create leak paths and can also be very abrasive. Unlike elastomer contact seals, PTFE lips can run on very smooth surfaces regardless of lubrication.

Over the past few weeks, we’ve gone into a lot of detail about how PTFE rotary lip seals work.

Today we’ll offer up a short glossary of some of the terms used when discussing these seals. We'll also break down some of the factors affecting PTFE rotary lip seal design.

Over the past few weeks, we’ve been discussing the basics of PTFE rotary seals. In today’s entry, we’ll take a look at PTFE radial lip seal design principles.

PTFE radial lip seals generally incorporate a uniformly thin element cross section, made to compensate for the high flexural modulus of PTFE, especially in cases of severe shaft run-out. The thin sections also minimize thermal expansion and compressive “creep” and their effects on maintaining a controlled contact pattern on the shaft surface.

Most PTFE seal constructions have the “body” portion of the element clamped between the two metal cases. To maintain proper retention pressure on the element, a thin element keeps compression set and “creep” at a minimum.