When considering polymer jacketed seals — especially PTFE-based products — some form of energizer is typically required. These types of seals are usually specified to operate both in very high pressures, low pressures, or even in a vacuum.  

At certain pressures (typically above 100psi), the system pressure will energize the seal and prevent leakage. But at low pressures, additional energy is required to force the jacket material to mate with the hardware.  

The solution to this is to add a spring to the seal. The spring provides the needed sealing-energy to prevent leakage at low media pressures.

When considering a high pressure-application, there are start/stop conditions where the system is at low pressure. If the seal allows some amount of leakage at low pressure, it becomes possible for that leakage level to increase once as the pressure builds.  

This phenomenon is called “blow-by.” Once it occurs in a system, it’s difficult to get the seal to seat and seal correctly.

Canted Coil Spring Energizer

There are several types of energizers to consider when specifying a seal. These can be as simple as an O-Ring or some other elastomer. 

Springs are an integral part of all sealing systems. A simple air cylinder has O-rings to seal in the air, and the O-ring exhibits spring-like qualities to ensure a good seal over a broad temperature range.

But what are the different types of springs and materials in sealing systems? And how do you choose the best for your application?

Being commodity items, U-Cups are readily available in a number of materials and can be found on-the-shelf from multiple distributors and manufacturers in many standard sizes.

Named for the shape of their cross-section, a U-Cup’s design will be pressure energized increasing sealing effectiveness when compared to a standard O-Ring.

This means as pressure increases, the sealing lips are continually forced into the mating hardware surface, ensuring good contact at all times.

The simple and easily moldable design is an effective sealing solution to many systems in both hydraulic and pneumatic applications. Modifications in lip thickness and inclusion of an O-Ring Energizer can tailor sealing loads and wear life to specific situations.

A key advantage to an elastomeric U-Cup is the relatively small and simple hardware space needed. Because of their flexible compounds, most U-Cups can be installed in a solid gland configuration.

A basic ID or OD groove is all you need for proper seal retention. Plus, no special tools or considerations need to be taken for correct installation.

U-Cups are available in many of the same compounds as standard O-Rings such as Nitrile, Fluorocarbon, and EPDM, but polyurethanes may be the most common material.

Urethane provides a good combination of elasticity/pliability and toughness. Therefore, it exhibits good sealing characteristics as well as, durability and wear resistance.

These desirable qualities make U-Cups an optimal solution for many sealing systems across multiple industries and they can be found in countless standard products. But Eclipse is approached many times a year with customers pushing the limits of standard U-Cups and in need of better solutions.

The Client's Issue

Eclipse was approached by a leading pneumatic cylinder manufacturing seeking a sealing solution for a unique application.

While U-Cups typically provide optimal sealing performance in pneumatic cylinders, this application presented a difficult challenge.

The air cylinder was to be used as an actuator for a latch on a large industrial oven. While pressures, speeds, and cycle times were nothing out of the ordinary, the temperature at which it had to operate at was — a continuous 500°F.