Abstract:
The invention seeks to provide a gasket for a quick connector that is inexpensive to fabricate, providing sealing over a wide range of fluid pressures, while presenting engagement forces that are small for flow diameters of large size. More precisely, the present invention provides a sealing gasket of elastically deformable material having a Y-shaped longitudinal axial section for use in a quick coupling for a fluid duct, the gasket ( 10 ) comprising an I-shaped stem ( 1 ) and a V-shaped portion ( 2 ), flash ( 3   p,    3   s ) of join plane (P 1 ) of the gasket being located between the I-shaped stem ( 1 ) and the V-shaped portion ( 2 ), preferably substantially perpendicularly to the longitudinal axis (P 2 ) of the gasket ( 10 ). The invention also provides the use of such a gasket, and a mold and a method for fabricating such a gasket.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from European patent application 07290296.8, filed Mar. 7, 2007. 
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a Y-shaped gasket, to a method of fabricating such a gasket, and to the use of such a gasket for reducing the engagement forces of a connector. 
     With the increasing use of quick connectors, in particular in the automobile industry, developing sealing techniques that have little influence on the engagement forces of such connectors is becoming a major preoccupation. These requirements relate to all fluids such as for example fuel (gasoline, diesel, biofuel), cooling liquid, brake liquid, urea, air, or oil. Certain applications are more critical because of the size of the connectors, such as air duct connectors used mainly for diesel engines, or water duct connectors used in heavy goods vehicles, for example. 
     The gasket most commonly used in such connectors is an O-ring, because it is inexpensive. Nevertheless, the forces required for engaging a connector fitted with such a gasket are high, in particular when the size of the gasket and/or its compression force increase. 
     Conventional shaped-section or lip gaskets are generally expensive to fabricate and require a housing that is complex. Furthermore, the fineness of their lips makes them more sensitive to thermal aging and to creep than the above-described solutions. 
     Finally, Y-gaskets are already known, but they are fabricated using three-matrix molds (one matrix for each branch of the Y-shape) that are difficult and expensive to implement. Furthermore, they lead to flash being formed in the join plane in zones that are functional in terms of mounting and/or sealing (in particular in the recess between the top lips of the Y-shape), thereby harming the intended operation of such zones. Those gaskets have therefore not been used in such couplings for the purpose of reducing engagement forces. 
     From the above, it can be seen that the greater the fluid flow diameter, the greater the size of the gasket and the greater the engagement forces. 
     SUMMARY OF THE INVENTION 
     The invention seeks to propose a gasket for a quick connector (snap-fastening or coupling) that is inexpensive to fabricate, that is suitable for being used instead of and replacing an O-ring or a four-lobe gasket, and that is capable of doing so without modifying the dimensions of the housings for such gaskets so as to avoid leading to costs associated with modifying existing parts, while providing sealing over a wide range of fluid pressures and presenting engagement forces that are small, preferably lying in the range 60 newtons (N) to 80 N for flow diameters of large size, e.g. about 50 millimeters (mm). 
     More precisely, the present invention provides a sealing gasket of elastically deformable material having a Y-shaped longitudinal axial section for use in a quick coupling for a fluid duct, the gasket comprising an I-shaped stem and a V-shaped portion, flash of join plane of the gasket being located between the I-shaped stem and the V-shaped portion, preferably substantially perpendicularly to the longitudinal axis of the gasket. 
     In preferred embodiments:
         the gasket may present an I-shaped stem and a V-shaped portion presenting maximum axial lengths (X/2) that are substantially equal, the flash of join plane being located between the I-shaped stem and the V-shaped portion, substantially in the middle of the gasket;   for the V-shaped portion determining a main lip and a secondary lip, the ratio of the nominal length of the secondary lip to the nominal length of the main lip may be selected to be greater than or equal to 1.2, and no greater than 2;   the ratio of the length of the main lip in the longitudinal axis direction to the length of the secondary lip in the longitudinal axial direction may be selected to be strictly less than 1, preferably to lie in the range 0.6 to 0.9, typically in the range 0.75 to 0.85;   the ratio of the distance between the recess in the V-shaped portion and the join plane to the nominal length of the main lip may lie in the range 0.4 to 0.45;   for the sealing gasket designed to be inserted in a groove of a first endpiece of the connector and for coming into leaktight contact with a wall of the other endpiece, the ratio of the height of the gasket section in the join plane to the distance between the bottom of the groove and the wall of the second endpiece may be selected to be strictly less than 1, typically to lie in the range 0.7 to 0.98, and preferably in the range 0.8 to 0.9;   for the gasket presenting a maximum radial height between the two lips, the amount of deformation of the main lip may lie in the range 18% to 22% of the maximum radial height;   the amount of deformation of the secondary lip may be less than the amount of deformation of the first lip;   the amount of deformation of the secondary lip may lie in the range 9% to 11% of the maximum radial height;   the I-shaped stem and the main lip may form respective angles with the longitudinal axis of the gasket, the angle of the I-shaped stem being smaller than the angle of the main lip;   the angle of the I-shaped stem may be greater than or equal to 2°, and the angle of the main lip may be less than or equal to 30°;   the secondary lip and the I-shaped stem may present respective lobes at their free ends for coming into contact with a groove bottom;   the I-shaped stem and the secondary lip may form between them an angle such that a concave side is provided between the free end of the I-shaped stem and the free end of the secondary lip;   the main lip may present a free end face that is substantially plane;   the secondary lip may present a free end face that is substantially plane;   the I-shaped stem may present a free end face that is substantially plane;   the I-shaped stem may present a wedging lobe for coming into contact with a groove edge by stressing the gasket in the groove; and   its material is selected from polymer materials, in particular from: FPM; HNBR; AEM; ACM; NBR; and EPDM.       

     The invention also relates to the use of a gasket as defined above in a fluid duct connector comprising a male endpiece and a female endpiece for the purpose of reducing the engagement forces of the male and female endpieces. 
     In preferred uses:
         the gasket may be placed in a groove in an endpiece such that the secondary lip bears against the bottom of the groove; and   the gasket may be placed in the groove of an endpiece such that the V-shaped portion is disposed in a direction opposite to the pressurized fluid flow direction, and when the fluid flows, the main lip and the secondary lip are pressed respectively against the groove and against the other endpiece so as to reinforce sealing.       

     The invention also provides a mold for fabricating the above gasket, the mold comprising a first matrix provided with a first cavity in the form of the I-shaped stem, and a second matrix provided with a second cavity in the form of the V-shaped portion, the depths of the two cavities being substantially such that the flash in the join plane is located between the I-shaped stem and the V-shaped portion. For example, the depths of the two cavities are substantially equal to as to form flash in the join plane substantially in the middle of the gasket. 
     Finally, the invention relates to a method of fabricating the above gasket implementing the above mold and comprising the steps consisting in:
         pressing the two matrices against each other so that the two cavities face each other;   injecting or placing non-cross-linked polymer material in the cavity;   causing said polymer material to cross-link, at least in part; and   unmolding the gasket by moving the matrices apart from each other, but not until the polymer material has cross-linked sufficiently for the main and secondary lips to be capable of deforming during unmolding and of returning to their molded shapes after unmolding.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics of the invention appear from the following detailed description made with reference to the accompanying drawings, which show, in particular: 
         FIGS. 1 to 3 : section views of a gasket of the invention that is “bore-mounted”; 
         FIG. 4 : a section view of a gasket of the invention that is “piston-mounted”; 
         FIGS. 5 and 6 : section views of variant gaskets of the invention; 
         FIGS. 7 to 9 : section views of a gasket of the invention that is “piston-mounted” prior to engagement, after engagement, and in use with a flowing fluid under a pressure of 3.5 bars; and 
         FIGS. 10 to 13 : section views showing the method of fabricating a gasket of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The gasket described below needs to be made of a material that is elastically deformable. The material of the gasket is preferably selected from polymer materials, in particular from fluorocarbon rubber (FPM), hydrogenated nitrile butadiene rubber (HNBR), ethylene-co-methyl acrylate (AEM), a copolymer of ethyl (or other) acrylate and a copolymer providing reactive sites for vulcanization (ACM), nitrile rubber (NBR), and ethylene propylene diene terpolymer (EPDM). 
     With reference to  FIGS. 1 to 3 , a gasket  10  of the invention presents a longitudinal axial section that is generally Y-shaped, with a longitudinal axial length X, the longitudinal axial length being defined as the length of the gasket in projection onto the longitudinal axis P 2  of the gasket  10 . 
     The gasket  10  presents an I-shaped stem  1  and a V-shaped portion  2  determining a main lip  4  and a secondary lip  5 , the portions  1  and  2  being united via beads  3   p  and  3   s  situated in the join plane. The beads  3   p ,  3   s  are substantially triangular in shape, with flash  3   p   1  and  3   s   1  in the join plane at the tips of the beads. The beads  3   p ,  3   s , and thus the flash  3   p   1  and  3   s   1  are in alignment on a straight line P 1  perpendicular to the longitudinal axis P 2  of the gasket  10 . The straight line P 1  represents the join plane, i.e. the plane of contact between the two matrices of the mold (see the description below of  FIGS. 10 to 13 ). In the embodiment shown, the I-shaped portion  1  and the V-shaped portion  2  present maximum longitudinal axial lengths X/2 that are substantially equal, i.e. the beads, and thus the flash in the join-plane, are located between the I-shaped stem and the V-shaped portion, substantially halfway along the gasket  10 . 
     The fact of making a bead on the gasket reduces stresses in the join plane during unmolding, thereby avoiding damage to the gaskets. Consequently, the reject rate is decreased, which has a positive economic impact. 
     The beads  3   p  and  3   s  also serve to offset the flash away from the solid portion of the gasket, thereby making it easier to remove the flash, e.g. cryogenically. Flash is thus better controlled. 
     The flash in the join plane, an inevitable fabrication defect, is thus located in a portion of the gasket that does not perform any functional role. The main and secondary lips  4  and  5  can deform towards each other without being impeded by flash situated in the recess  6  between them. Similarly, the flash has no influence on sealing since it lies away from the contact zones of the gasket with the groove  20  and the endpiece  30 . 
     The gasket is “bore-mounted” in a groove  21  of a female endpiece  20 , i.e. since the gasket  10  is circular, the main lip  4  points towards the center of the gasket  10  while the secondary lip  5  and the I-shaped portion  1  are compressed against the bottom  22  of the groove  21 . 
     As shown in the figures taken together, the ends  1   a  and  5   a  respectively of the I-shaped stem  1  and of the secondary lip  5  are aligned parallel to the longitudinal axis P 2 . This characteristic enables the gasket to be optimally positioned as soon as it is installed in the groove, without imparting twisting to the gasket and thus without running any risk of the gasket escaping from the groove while being compressed. 
     The ratio of the longitudinal axial length Z of the main lip  4  to the longitudinal axial length X/2 of the secondary lip  5  is preferably selected to be strictly less than 1. This ratio X/2Z serves to reduce the risk of the main lip jamming in the groove  21  during engagement and deformation of the lip, thereby improving the quality and the effectiveness of the gasket. The best results are obtained for a ratio X/2Z that lies preferably in the range 0.6 to 0.9, and typically in the range 0.75 to 0.85. 
     Alternatively, or in combination, the ratio of the nominal length T ( FIG. 2 ) of the secondary lip  5  to the nominal lip S of the main lip  4  can be selected to be greater than or equal to 1.2. The nominal length of a lip is defined as being the length of the lip from the base of the lip  4 ,  5  to its distal end  4   a ,  5   a , where the base of the lip  4 ,  5  is defined by the straight line Dp-Ds passing through the recess  6  of the V-shaped portion  2  and the bead  3   p ,  3   s  adjacent to the lip  4 ,  5 . Since the main lip  4  is shorter than the secondary lip  5 , the risks of the main lip  4  jamming in the groove is reduced. Jamming of the main lip between the groove  20  and the endpiece  30  would completely prevent the connector from engaging. Sealing quality is also improved. After the engagement stage, contact between the main lip and the lip  22  would prevent the fluid for sealing from passing into the V-shaped zone and thus prevent proper operation of the gasket. 
     Furthermore, the ratio of the distance U between the recess  6  of the V-shaped portion  2  and the join plane P 1 , to the nominal length of the main lip preferably lies in the range 0.4 to 0.45. When less than 0.40, there is an increased risk of tearing or more generally of damaging the surface of the main lip  4  while unmolding during fabrication of the gasket  10  (see the description below of  FIGS. 10 to 13 ) and during repeated engagement and disengagement of the male and female endpieces of the connector. When greater than 0.45, the deformability of the main lip  4  is decreased and consequently engagement forces are increased. The increase in the stiffness of the main lip also influences the stability of the gasket during mounting by increasing the risk of capsizing. 
     In addition, the ratio of the height A of the section of the gasket  10  in the join plane P 1  to the distance H between the bottom  22  of the groove  21  and the wall  31  of the second endpiece  30  of the connector can be selected to be strictly less than 1. By means of this ratio, the gasket is not compressed radially, i.e. in the direction P 1 , by the other endpiece of the connector, thereby further reducing engagement forces. For greater safety, the ratio H/A is preferably selected to lie in the range 0.7 to 0.98, and typically in the range 0.8 to 0.9. 
     Thus, a gasket as described above enables the main lip  4  to deform during mutual engagement of the two endpieces  20  and  30 . 
     In a preferred embodiment, the gasket  10  presents a maximum radial height B between the two lips  4 ,  5  and the amount of deformation of the main lip  4  lies in the range 18% to 22% of the maximum radial height B. This amount enables deformation to be sufficient to reduce the engagement forces while ensuring the main lip  4  is pressed against the other endpiece  30  of the connector in a manner that is appropriate for ensuring sealing (see  FIGS. 7 to 9 ). 
     Preferably, the amount of deformation of the secondary lip  5  is less than the amount of deformation of the main lip  4 . Thus, by deforming, the secondary lip  5  contributes to the general resilience of the gasket  10 , but because the amount it deforms is less than that of the main lip  4 , the engagement force is exerted mainly against the main lip  4  with little being transmitted to the secondary lip. The thickness and the stiffness of the main lip  4  generates a reaction force pressing the main lip  4  against the endpiece  30  and ensuring sealing against the wall  31 . On the other side, against the bottom  22  of the groove  21 , sealing is provided by compressing the bore-mounted gasket  10 . The amount of deformation of the secondary lip  5  can preferably be selected to lie in the range 9% to 11% of the maximum radial height B. 
     The engagement forces can also be reduced by reducing friction between the gasket  10  of a first endpiece  20  and the contact face of the second endpiece  30 . 
     Each of the faces  1   f  of the I-shaped stem  1  and of the main lip  4  preferably forms an angle with the longitudinal axis P 2  of the gasket  10 , the angle α 1  of the I-shaped stem  1  being less than the angle α 2  of the main lip  4 . The angle α 1  of the I-shaped stem  1  may be greater than or equal to 2°. In addition, adapting this angle α 1  makes it possible to obtain a greater or smaller volume of material for the gasket  10 . Thus, the larger this angle, the less material there is in the gasket. The more the diameter of the connector increases, the greater the risk of the gasket  10  twisting in the groove  21  in a bore-mounted configuration. An increase in the quantity of material thus decreases the risk of twisting, thereby improving the stability of the gasket during mounting. A large angle α 1  is therefore preferred for a gasket that is intended for a small-diameter connector, and a smaller angle α1, down to 2°, is preferred for a gasket intended for a larger-diameter connector. The angle α 1  also represents an economic adjustment variable. When the cost of the material is high, a large α 1  can have a non-negligible economic impact. 
     The angle of the main lip may be less than or equal to 30°. This angle α 2  is determined by constraints of the fabrication method. When greater than 30°, it becomes difficult to unmold the gasket from a two-matrix mold and there is an increased risk of the lip tearing during unmolding (see the description below of  FIGS. 10 to 13 ). This phenomenon, and thus the limiting values, depends on the material used. 
     Beside the bottom of the gasket  21 , the I-shaped stem  1  and the secondary lip  5  preferably form between them an angle α 3  such that a concave side  7  is formed between the free ends la and  5 a of the I-shaped stem  1  and the secondary lip  5 . This concave side serves firstly to allow the gasket  10  to be flattened against the bottom  22  of the groove  21 , and secondly enables the functional contact zones of the gasket  10  against the endpiece  20  on which it is mounted to avoid coinciding with the position of the join plane and the bead  3   s  carrying the flash  3   s   1 . When using a bore-mounting, this concave side enables the outside diameter of the gasket to be compressed against the bottom of the groove. 
     The angle α 3  is substantially symmetrical about the join plane, i.e. the secondary lip and the I-shaped stem forms substantially the same angle relative to the join plane for forming the concave side  7 . This makes it possible to distribute stresses symmetrically in the join plane when it is positioned on the grooved bottom  22  or  22 ′ ( FIG. 4 ). 
     In order to maintain sealing during compression of the gasket  10  against the bottom  22  of the groove  21 , the secondary lip  5  and the I-shaped stem  1  both present at their respective free ends  5   a  and  1   a , respective lobes  5   b  and  1   b  for coming into contact with the bottom of a groove. Limiting the contact zone to two contact zones makes it possible locally to achieve greater contact pressures in each of these zones. The lobes  1   b  and  5   b  at the ends  1   a  and  5   a  are in alignment parallel to the longitudinal axis P 2 . This characteristic enables the positioning of the gasket to be optimized on being installed in the groove, without inducing twisting of the gasket and thus avoiding any risk of the gasket escaping from the groove while being compressed. 
     When the gasket of the invention is used in a connector for reducing the engagement forces required on the male and female endpieces, the gasket may either be “bore-mounted” as described above, or else it may be “piston-mounted”, as shown in  FIG. 4 , i.e. since the gasket  10  is circular, the main lip  4  extends away from the center and is directed towards the outside of the gasket  10 , with the secondary lip  5  and the I-shaped portion  1  being pressed against the bottom  22 ′ of the groove  21 ′ disposed in the outer periphery of the endpiece  20 ′. 
     The main lip  4  and the secondary lip  5  are preferably terminated by respective rounded lobes  4   b  and  5   b . This facilitates unmolding during fabrication. In addition, the lobe  4   b  serves to provide sealing while limiting the contact area with the endpiece  30 ′, thereby reducing engagement forces. 
     In preferred manner, the maximum width of the groove is slightly greater than the axial length X of the gasket  10  so as to ensure the gasket is properly positioned in the groove. 
     However, during engagement, stress is exerted against the main lip  4  of the gasket  10  and transmitted to the entire gasket. Although flexible, the gasket does not absorb all of this stress and its intrinsic stiffness tends to cause the gasket to capsize. In order to limit this phenomenon, the secondary lip  5  and/or the I-shaped stem I may present a respective face  5   c ,  1   c  at the respective free end  5   a ,  1   a  that is substantially plane. 
     Alternatively, and as shown in  FIG. 5 , the face  1   c  of the I-shaped stem  1  may present a wedging lobe  1   d  for coming into contact with an edge  23  of the groove  21  by stressing the gasket in this groove, thus making it possible to avoid the gasket  10  capsizing during a stage of connector engagement, but requiring the gasket to be stressed in the groove. This lobe needs to be defined in such a manner that axial compression of the gasket is possible while conserving the capacity for the gasket to be tightened radially. For this purpose, the lobe  1   d  projects beyond the lobe  1   b , so that an offset D is sufficient to ensure prestressing on the gasket to hold it in the groove and thus prevent it from capsizing. A part having this design is particularly suitable for bore-mounting. 
     The main lip may also present a face  4   c  at its free end  4   a  that is substantially plane, thereby making it possible to reduce the risks of liquid passing between the main lip and the wall of the endpiece against which it is pressed. 
     With reference to  FIGS. 5 and 6 , the lobe  1   d  ( FIG. 5 ) or the rounded edge  1   e  ( FIG. 6 ) connects the face  1   c  to the face  1   f  that is inclined at an angle α 1 . This lobe improves unmolding, makes it easier to prepare the mold, and reduces mold wear since there is no sharp threshold. 
     With reference to  FIGS. 7 to 9 , the gasket  10  is “piston-mounted” and is placed in the groove  21 ′ of an endpiece  20 ′ in such a manner that the V-shaped portion  2  is disposed in a direction F 1  opposite to the direction F 2  in which the fluid under pressure flows. When the fluid flows ( FIG. 9 ), the secondary lip  5  and the main lip  4  are pressed respectively against the groove  21 ′ and the other endpiece  30  so as to reinforce sealing; pressurization thus takes place in the V-shaped portion of the gasket. 
     The Y-type gasket provides a large deformation potential for the main lip  4 . During connector engagement ( FIG. 8 ), this lip deforms, thereby generating low engagement forces. 
     Pressurization can take place in one direction only. This is the direction opposite to the engagement direction. In other words, the pressure is applied to the V-shaped portion of the gasket. 
     The gasket is suitable for sealing fluid (cooling liquid, fuel, etc.) and gas (air, blow-by, etc.). 
     The gasket may be designed for low pressures (1 bar to 3 bars) or medium pressures (up to 10 bars or 15 bars). The ability to withstand pressure depends to a great extent on the material selected for the gasket. For low pressures, the material may be selected to present hardness of about 60 on the Shore scale, whereas for medium pressures, the hardness of the material may be selected to about 70 on the Shore scale. In particular applications, it is possible to make use of materials presenting hardness of 80 or even 90 on the Shore scale. These values can then be reduced in appropriate manner so that the engagement forces are compatible with the desired values. 
     Pressurization can also take place in both directions F 1  and F 2 . The gasket of the invention can then perform a membrane function when the fluid flows in the same direction F 1  as the orientation of the V-shaped portion  2 , and a sealing function when the fluid flows in the direction F 2  opposite to the direction F 1  in which the V-shaped portion  2  is oriented. 
     It is also possible to envisage utilization for dynamic sealing with low friction requirements when pressure is applied in one direction only, with lower abrasion and friction requirements. 
     Finally, after the male and female portions have been mutually engaged, suction is often established in the circuit in the direction of arrow F 1  prior to placing it under normal pressure in the direction of arrow F 2 . The gasket is thus subjected to reverse pressure which would tend to separate the main lip  4  from the endpiece  30 ,  30 ′, urging it towards the secondary lip  5 , and thus preventing suction from being established in the circuit. Surprisingly, because of its special shape, the Y-type gasket of the invention with hardness of about 60 on the Shore scale and presenting a radio U/S lying in the range 0.4 to 0.45 can withstand suction of 1 bar before separating from the endpiece  30 ,  30 ′, thereby enabling the circuit to be emptied before it is pressurized. 
     With reference to  FIGS. 10 to 13 , the gasket of the invention is fabricated in a mold  40  comprising two matrices  41  and  42 . 
     The first matrix  41  is provided with a first cavity  41   a  having the shape of the I-shaped stem  1 , and the second matrix  42  is provided with a second cavity  42   a  having the same shape of the V-shaped portion  2 . At the interface between the two matrices  41  and  42  there is the join plane P 1 . Because of the shape of this mold  40 , the beads  3   p ,  3   s  of the join plane are located between the I-shaped stem and the V-shaped portion, substantially perpendicularly to the longitudinal axis P 2  of the gasket. In this way, the flash  3   p   1 ,  3   s   1  situated at the tips of the beads  3   p ,  3   s  is not located on a functional portion of the gasket  10 , i.e. not on the lips nor between them in the recesses separating them. 
     Preferably, the depths of the two cavities  41   a  and  42   a  are substantially equal so as to form beads  3   p ,  3   s  carrying join-plane flash  3   p   1 ,  3   s   1  substantially in the middle of the gasket. 
     The first step in fabricating the gasket  10  with the mold  40  consists in pressing the two matrices  41  and  42  against each other so that the two cavities  41   a  and  42   a  face each other ( FIG. 1 ). Then non-cross-linked polymer material  11  is injected into the cavities  41   a  and  42   a  of the mold ( FIG. 11 ) via injection gates (not shown) disposed in the join plane and not away from the join plane. Finally, the gasket can be unmolded by moving the matrices apart from each other along arrow F 3  once the polymer material  11  has cross-linked sufficiently to enable the main and secondary lips  4  and  5  to deform during unmolding and return to their molded shapes after unmolding. During an additional step, the flash situated at the tips of the beads is removed cryogenically. The gasket is thus taken to a temperature lower than its glass transition temperature, and then fine particles, e.g. of plastics material or of metal, are projected against the gasket. The flash, which is tiny in thickness compared with the gasket, is broken by such particles and eliminated. The gasket is then returned to ambient temperature. 
     The invention is not limited to the embodiments described and shown:
         geometrical modifications can be implemented so as to make the gasket suitable for use in rolled grooves.       

     With a piston-mount, the inside diameter of the gasket is stretched. The minimum amount of stretch (tolerance calculation) is preferably 3%. The maximum amount of stretch must be less than 10%. With a bore-mount, the outside diameter of the gasket needs to be compressed, and it is this compression that ensures the gasket is stable in the groove. This compression cannot be quantified since it depends on the material and the ratio of the inside diameter of the gasket divided by the section of the gasket. It is appropriate to seek a ratio of less than 10 or as close as possible to that value. 
     The maximum acceptable compression for the Y-type gasket is about 30%.