181:, giving rise to coolant leakage, where the block and liner expanded at different rates: specifically when the liners contracted more rapidly as engine load was reduced. The solution to this was to redesign the liner so that they were located at the top instead, reducing the distance susceptible to expansion. The high compliance of the Wills Ring, thanks to their internal pressurisation, allowed reliable sealing, even though the short clamping distance now had little elasticity and so the applied clamping force from the head bolts could vary substantially.
114:. The thin tube walls are sensitive to damage from rough handling, point tools and crimping during assembly. The pressure-actuated form is considered to be slightly more resistant to point damage, but more at risk of folding and crimping, as they are not supported by internal pressurisation during assembly.
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Rings are pressurised by either a static gas fill during manufacture, or may be pressure-actuated by the applied pressure on the joint in service. These pressure-actuated rings have vents on the pressure side to allow gas ingress. The 4 MPa pressure limit of the unpressurised ring is exceeded by
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Rings are installed in machined grooves in, usually one of, the mating faces. The correct perpendicular depth of these grooves (rather than their width or cross-sectional area) is an important factor that controls seal performance. Unlike the grooves for elastomer O-rings, the width and shape of the
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A Wills Ring is an O-ring in the form of a hollow metallic tube. They are pressurised internally by gas pressure The advantages of this construction are that the rings can seal against a wide range of conditions. Metallic construction makes them robust against high or low temperatures and chemical
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attack. Softer coatings may be applied to provide even better compatibility, or to seal against roughly machined surfaces. Internal pressurisation makes them compliant, both for the range of movement required and with their speed of response being faster than
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Wills Rings are expensive in comparison to other seals, such as elastomer O-rings or metallic foil head gaskets. A typical comparison is one ring costing approx. $ 50 each, around the price of a high-performance head gasket for a four-cylinder engine.
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The vented and slotted forms are usually vented to the inside, for carrying an internal pressure, but are also available with external vents, for use in high external pressures, such as in undersea use.
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groove is unimportant, just the depth. It is even possible for this 'groove' to become an open-sided groove or aperture, provided that this free height is maintained.
158:. These are not widely used, owing to their high cost and the good performance of other modern gaskets, but they have a place for high-performance engines.
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racing engines. Coventry Climax's more mundane utility engines did not require these seals, but they were adopted to production car engines such as the
169:, and when these were re-tuned for racing, it was a regular practice to add this type of supplementary seal. Some Coventry Climax designs, such as the
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177:. These were located in place at the base of the liner, rather than near the cylinder head. They were thus susceptible to problems from differential
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As vacuum systems will develop a maximum of 1 Bar pressure differential, they use the internally pressurised or solid forms instead.
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One of the best-known applications for pressurised Wills Rings, or Cooper Rings as they were originally known, is for sealing the
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the 40 MPa of the internally pressurised ring and 200 MPa or 1,000 MPa for the externally pressurised forms.
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A high performance seal suitable for extreme pressures and still sealing when pressure is released.
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Hollow, metallic Wills Rings are used as they have better springback than
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Limited springback and pressure capacity, these are mostly used as a non-
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was an accident caused by the poor dynamic response of cold elastomers.
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soft metal seals and higher temperature limits than elastomer O rings.
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seal. They are used for extremely arduous service, such as sealing the
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or varying thicknesses of silver plating are also available.
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O-rings. Their flexure is also unaffected by temperature.
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Suitable for even higher pressures than the slotted form.
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One of the first applications in this case was for the
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They are only used for static face sealing, not moving
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Wills Rings are manufactured in five overall types:
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240:Motor-racing quality, rather than aerospace.
121:Wills Rings are constructed in a variety of
366:. Busak & Shamban. 2004. Archived from
338:"A Hillman Imp Wills Ringed cylinder Head"
413:. Veloce Publishing. pp. 113–115.
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315:. Busak & Shamban. Archived from
284:. Busak & Shamban. Archived from
88:Lower cost and higher clamping forces
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435:"Wills ring for SOHC Pinto engine"
388:. Veloce Publishing. p. 299.
67:Hollow, internally gas pressurised
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336:Roy Mc Bride (23 November 2010).
208:Space Shuttle Challenger disaster
73:Hollow, slotted pressure-actuated
173:, used an open-deck block with
411:Coventry Climax Racing Engines
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222:is approximately 0.1 MPa
260:Trelleborg Sealing Solutions
76:Best springback performance.
310:"Wills Rings: Installation"
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386:1½-litre GP Racing 1961–65
24:is a form of all-metallic
98:metallic seal for use in
384:Whitelock, Mark (2006).
361:"Wills Rings: Catalogue"
279:"Wills Rings: Overview"
409:Hammill, Des (2004).
146:Cylinder head gaskets
85:Hollow, unpressurised
220:Atmospheric pressure
32:of high performance
152:combustion chamber
420:978-1-903706-83-1
179:thermal expansion
123:refractory metals
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133:. Coatings of
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256:"Wills Rings"
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368:the original
340:. CKD Boats.
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141:Applications
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47:Construction
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167:Hillman Imp
54:elastomeric
30:head gasket
22:Cooper Ring
454:Seal rings
395:184584016X
194:References
175:wet liners
125:including
96:outgassing
18:Wills Ring
448:Category
41:yielding
171:FWMV V8
131:Inconel
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112:glands
26:O-ring
371:(PDF)
364:(PDF)
320:(PDF)
313:(PDF)
289:(PDF)
282:(PDF)
91:Solid
415:ISBN
390:ISBN
206:The
185:Cost
135:PTFE
129:and
154:of
20:or
450::
346:^
328:^
297:^
268:^
258:.
36:.
16:A
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102:.
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