From the Fothergill brochure, page 14

Wills rings

Will Rings ® have been continuously developed since WW II. Pressure filled 'O' rings in particular have gained a very good reputation for providing reliable seals in fluid or vacuum service. Rings are nitrogen-filled to create internal pressure so the resilience of the ring increased over a wide range of temperatures. The apparent yield strength of the ring material increases in direct proportion to the nitrogen expansion curve to offset the loss of strength of the metal due to the increase in temperature.

For most applications an internal ring pressure of 4137KPa (600 lbf/in²) is found to be sufficient.

The operating temperature (and the system pressure) determines the ring pressure. This means that there will be enough pressure inside the ring to maintain the seal in case of a sudden temperature drop. At the same time a sudden rise in the temperature the heat can be transferred to the gas inside the ring is rapid enough to ensure the maintenance of the seal against possible increased system pressure, or against lower viscosity of system material.

All Wills 'O' rings are formed from close tolerance material, produced to the highest metallurgical standards and are inspected before despatch.
Weld quality is of paramount importance and rigorous quality control is exerted to ensure that joints are indistinguishable from the main body of the ring. X-raying is carried out as standard procedure with thin wall rings (0.254mm = 0.010 in.).

Most applications require a ring to be made from mild steel type EN2. Many rings are also plated or coated, enabling them to accomodate a coarser finish on flange faces. A plated or coated ring reduces the need for the flange surface to be very smooth. Without a coat, spiral or radial machining marks will form a leak path across the face of the seal.

Wills Rings should not be re-used on joints of a critical nature.

The text from the Fothergill brochure, next to the illustration:

Mild steel pressure-filled 'O' rings are used by the Competitions Department of Chrysler (U.K.) Ltd., as cylinder-head seals for high-compression Imp engines.

Located in grooves in the cylinder-head around the combustion chambers, the rings are pulled down on to the wet cylinder liners, where torque flattens the base of the ring to form a fully-effective seal, capable of withstanding ratios above 9:1.

Use of Wills 'O' rings, pressure-filled to 6894KPa (1000 lbf/in²) eliminates the use of metal cylinderhead gaskets and provides improved reliability in rallying and racing.

The illustration shows the rings in position on the head, and the paper gasket which completes the head/block seal.

Mild steel (standard material) has a temperature limit of 550 °C

According to the installation instructions, you had better be right careful not to damaged the ring nor the flange !

Installation instructions

Preparation
In the installation of a Wills metal 'O' ring, it must be appreciated that the seal is only one of a number of interdependent elements that are necessary to achieve a satisfactory barrier against leakage. If an effective and reliable joint seal is to be made, then careful consideration much be give to the following elements:

1. Ring accomodation grooves
   It is essential that the Wills Ring is located in a groove machined to the dimensions and surface finish recommended in the product catalogue.

2. Flanges
   All flanges in contact with the Wills Ring seal must be of rigid design in order to prevent any distortion occurring. Also, it is important that the flange seating surfaces are machined concentric with the line of the seal. Spiral or radial machining marks can form a leak path across the seal face.
   The bolts or other devices used to clamp the joint must be capable of transmitting the correct force required to achieve a sound joint. Good quality clean thread surfaces are essential in attaining consisyent bolt torque control.

Procedure
To ensure a permanent seal, the following method of installing Wills Rings should be carried out.

1. Carefully clean the flange groove
   to remove any contaminant that can become trapped between the seal and the mating surfaces and cause leakage

2. Inspects the cleaned surfaces
   to ensure that they are free of nicks, dents or scratches which can create a leak path

3. Just prior to fitting, remove the Wills Ring from its protective wrappings.
   It is important to remember that metal seals can be damaged by sqeezing, twisting or scratching.

4. Fit the Wills Ring into the flange cavity, taking care not to damage it, and then position the upper flange.

5. Tighten the claming bolts, partially torquing and alternating from one side of the flange to the other

6. When replacing Wills Rings, it is important that the flange seating surfaces are not damaged by careless removal of the old ring. It is recommended that the old ring is prised out with a tool made from a softer material than the flange, or alternatively by puncturing the seal on its top surface and lifting it out with a sharp pointed tool.

© Fothergill & Harvey, 1982; Publ.# FEP 2007

Literature

Will Rings : metallic 'O' rings for fluid and vacuum service in severe environments. - 1980. - © Fothergill & Harvey. - 18 p. - [Publ. No. TY96A]

Wills Rings ®. - Busak + Shamban Group, 1995. - 14p. - [99 GB/M11/005/0195/7.0]