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High pressure hydraulic fitting
This invention relates to a high pressure hydraulic fitting for use in a hydraulic system. In particular, it relates to a threaded plug-type fitting which includes an elastomeric "O"-ring.
Most prior art plug-type fittings are fabricated with a right angle flange which seats against a machined surface of a housing containing a threaded bore for mating engagement with the threads of the plug. These prior art systems often utilize elastomeric "O"-rings for sealing, and such rings are generally disposed within an annular groove or thread relief formed near the flange of the plug. When such threaded plugs having right angle flanges are tightened to standard torque values and are exposed to high pressure fluids within the system, such plugs tend to move axially with respect to the housing to an extent dependent upon the degree of tightening and upon the pressure applied. The gap created between the right angle flange of the plug and the housing presents an area into which the elastomeric "O"-ring tends to extrude due to passage of high pressure fluid around the threads. When this occurs, and when hydraulic pressure applied is subsequently reduced, the "O"ring is often severely damaged by the gradual pinching effect caused by the repetitive opening and closing of the gap.
Some examples of prior art couplings utilizing seals are shown in U.S. Pat. Nos. 2,443,187 to Hobbs; 3,147,984 to Benoit; 3,148,901 to Campbell; 3,160,426 to Faeser; and 3,255,916 to Rice.
SUMMARY AND OBJECTS OF THE INVENTION
The instant invention provides an improved fitting for high pressure hydraulic systems. The fitting includes a housing having a threaded bore therein and a first bevelled surface proximate the threaded bore. A threaded plug is provided for threadable engagement within said threaded bore and the plug has a second bevelled surface on the seal retaining flange thereof. The plug further includes an annular groove within which is mounted an elastomeric "O"-ring seal. Upon axial displacement of the plug with respect to the housing to a first predetermined extent under the influence of hydraulic fluid under pressure, the gap created between the first and second bevelled surfaces is a second predetermined value substantially less than the first predetermined value.
The main object of the present invention is to provide a fitting for a high pressure hydraulic system which substantially reduces the tendency for seal ring damage.
A more specific object of the present invention is to provide a threaded fitting for a high pressure hydraulic fluid system which substantially reduces the extent of "O"-ring extrusion for any given value pressure application to the fitting.
Other objects and advantages of the present invention will become apparent from the following description and drawing.
BRIEF DESCRIPTION OF THE DRAWING
a sectional elevation of a prior art high pressure hydraulic fitting;
a sectional elevation of the hydraulic fitting of the present invention; and
an enlarged cut-away view of a portion of the fitting and the threaded plug in displaced disposition.
DETAILED DESCRIPTION
A prior art fitting for a high pressure hydraulic system may be appreciated. A housing 2 is provided with a threaded aperture 3 within which is received the threaded shank portion of a plug 4. The plug member is equipped with a groove or relieved area 5 within which is disposed an elastomeric "O"-ring seal 6. As may be readily appreciated from the drawing, the housing has a first abutment surface 7 which mates with the second abutment surface or flange 8 of the plug when the plug is tightened with respect to the housing. The surfaces 7 and 8 are in engagement when there is little or moderate pressure within the system. However, upon the application of extremely high hydraulic fluid pressure upon an end surface 9 of the threaded plug, the plug moves axially with respect to the housing such that a gap (A) is created between the surfaces 7 and 8.
The size of this gap depends upon the pressure exerted upon the surface 9 and upon the torque which has been applied to tighten the plug 4 within the housing 2. For example, the plug having a thread size of 17/8inches when tightened to a torque rating of 120 ¡À 10 ft.-lb. will move axially a distance of 0.003 inch when 6500 psi is applied to the surface 9. For the sake of simplicity, the same set of values for pressure applied, thread size, and tightening torque will be used hereinafter to explain the advantages of the present invention. It should be understood, however, that various different tightening torque ranges are recommended for plugs of various sizes and pressure applications.
As is readily apparent , the size of the gap (A) is equal to the amount of axial movement of the plug and the elastomeric "O"-ring 6 tends to extrude into such gap to that same extent. Upon reduction of the application of a pressure (P) to the surface 9, the plug 4 tends to return axially toward the surface 7 and to pinch the extruded portion of the ring 6 between the surfaces 7 and 8 often causing severe damage to the seal.
The structure and advantages of the present invention may be readily appreciated. Included is a housing 12 having a threaded bore 13 within which is received a threaded portion of a plug 14. The plug has a groove 15 for receiving an elastomeric "O"-ring seal 16, like the ring 6 in FIG. 1. However, unlike the prior art fitting, the instant housing has a bevelled surface machined thereon at a distal portion of the threaded bore 13. The plug 14 also has a bevelled surface 18 which precisely conforms for mating engagement with the bevelled surface 17. The bevel angle (¦Á) which the surfaces 17 and 18 make with respect to the bore axis of the fitting may be any acute angle but is preferably 30¡ã or less.
By recourse to the previously applied example and utilizing an angle (¦Á) of 30¡ã, the advantages of the present invention may be readily appreciated. When, as in the previous example, a pressure (P) of 6500 psi is applied to the surface 19 of the plug 14 which is tightened to the recommended torque, the plug displaces axially the amount (S), as shown. Concomitantly, a gap (A) is created between the bevelled surfaces 17 and 18. As is known from the previous example, the value for the axial displacement (S) is 0.003 inch. From the geometry of FIG. 3, it is apparent that the gap (A) may be readily determined by multiplying (S) by the sine of (¦Á). where ¦Á=30¡ã, therefore, the gap (A)=0.0015 inch. Thus, it is seen that by forming the bevelled surfaces at an angle of 30¡ã with respect to the axis of the fitting bore, the gap created between the mating surfaces of the components into which the seal ring tends to extrude is reduced by 50 percent. By choosing angles for the angle (¦Á) of less than 30¡ã, the reduction in gap size is even more dramatic.
It may be seen that the instant invention provides a high pressure fitting for a hydraulic system which utilizes a conventional elastomeric "O"-ring seal for sealing between the components but which substantially reduces the tendency for such seal to extrude between the components and to be damaged by pinching action upon reduction of pressure within the system.
While the invention has been described with particular reference to the preferred embodiments, it is apparent that variations and modifications are possible within the purview of the inventive concepts. No limitation with respect to such variations and modifications is intended, except by the scope of the appended claims.
Most prior art plug-type fittings are fabricated with a right angle flange which seats against a machined surface of a housing containing a threaded bore for mating engagement with the threads of the plug. These prior art systems often utilize elastomeric "O"-rings for sealing, and such rings are generally disposed within an annular groove or thread relief formed near the flange of the plug. When such threaded plugs having right angle flanges are tightened to standard torque values and are exposed to high pressure fluids within the system, such plugs tend to move axially with respect to the housing to an extent dependent upon the degree of tightening and upon the pressure applied. The gap created between the right angle flange of the plug and the housing presents an area into which the elastomeric "O"-ring tends to extrude due to passage of high pressure fluid around the threads. When this occurs, and when hydraulic pressure applied is subsequently reduced, the "O"ring is often severely damaged by the gradual pinching effect caused by the repetitive opening and closing of the gap.
Some examples of prior art couplings utilizing seals are shown in U.S. Pat. Nos. 2,443,187 to Hobbs; 3,147,984 to Benoit; 3,148,901 to Campbell; 3,160,426 to Faeser; and 3,255,916 to Rice.
SUMMARY AND OBJECTS OF THE INVENTION
The instant invention provides an improved fitting for high pressure hydraulic systems. The fitting includes a housing having a threaded bore therein and a first bevelled surface proximate the threaded bore. A threaded plug is provided for threadable engagement within said threaded bore and the plug has a second bevelled surface on the seal retaining flange thereof. The plug further includes an annular groove within which is mounted an elastomeric "O"-ring seal. Upon axial displacement of the plug with respect to the housing to a first predetermined extent under the influence of hydraulic fluid under pressure, the gap created between the first and second bevelled surfaces is a second predetermined value substantially less than the first predetermined value.
The main object of the present invention is to provide a fitting for a high pressure hydraulic system which substantially reduces the tendency for seal ring damage.
A more specific object of the present invention is to provide a threaded fitting for a high pressure hydraulic fluid system which substantially reduces the extent of "O"-ring extrusion for any given value pressure application to the fitting.
Other objects and advantages of the present invention will become apparent from the following description and drawing.
BRIEF DESCRIPTION OF THE DRAWING
a sectional elevation of a prior art high pressure hydraulic fitting;
a sectional elevation of the hydraulic fitting of the present invention; and
an enlarged cut-away view of a portion of the fitting and the threaded plug in displaced disposition.
DETAILED DESCRIPTION
A prior art fitting for a high pressure hydraulic system may be appreciated. A housing 2 is provided with a threaded aperture 3 within which is received the threaded shank portion of a plug 4. The plug member is equipped with a groove or relieved area 5 within which is disposed an elastomeric "O"-ring seal 6. As may be readily appreciated from the drawing, the housing has a first abutment surface 7 which mates with the second abutment surface or flange 8 of the plug when the plug is tightened with respect to the housing. The surfaces 7 and 8 are in engagement when there is little or moderate pressure within the system. However, upon the application of extremely high hydraulic fluid pressure upon an end surface 9 of the threaded plug, the plug moves axially with respect to the housing such that a gap (A) is created between the surfaces 7 and 8.
The size of this gap depends upon the pressure exerted upon the surface 9 and upon the torque which has been applied to tighten the plug 4 within the housing 2. For example, the plug having a thread size of 17/8inches when tightened to a torque rating of 120 ¡À 10 ft.-lb. will move axially a distance of 0.003 inch when 6500 psi is applied to the surface 9. For the sake of simplicity, the same set of values for pressure applied, thread size, and tightening torque will be used hereinafter to explain the advantages of the present invention. It should be understood, however, that various different tightening torque ranges are recommended for plugs of various sizes and pressure applications.
As is readily apparent , the size of the gap (A) is equal to the amount of axial movement of the plug and the elastomeric "O"-ring 6 tends to extrude into such gap to that same extent. Upon reduction of the application of a pressure (P) to the surface 9, the plug 4 tends to return axially toward the surface 7 and to pinch the extruded portion of the ring 6 between the surfaces 7 and 8 often causing severe damage to the seal.
The structure and advantages of the present invention may be readily appreciated. Included is a housing 12 having a threaded bore 13 within which is received a threaded portion of a plug 14. The plug has a groove 15 for receiving an elastomeric "O"-ring seal 16, like the ring 6 in FIG. 1. However, unlike the prior art fitting, the instant housing has a bevelled surface machined thereon at a distal portion of the threaded bore 13. The plug 14 also has a bevelled surface 18 which precisely conforms for mating engagement with the bevelled surface 17. The bevel angle (¦Á) which the surfaces 17 and 18 make with respect to the bore axis of the fitting may be any acute angle but is preferably 30¡ã or less.
By recourse to the previously applied example and utilizing an angle (¦Á) of 30¡ã, the advantages of the present invention may be readily appreciated. When, as in the previous example, a pressure (P) of 6500 psi is applied to the surface 19 of the plug 14 which is tightened to the recommended torque, the plug displaces axially the amount (S), as shown. Concomitantly, a gap (A) is created between the bevelled surfaces 17 and 18. As is known from the previous example, the value for the axial displacement (S) is 0.003 inch. From the geometry of FIG. 3, it is apparent that the gap (A) may be readily determined by multiplying (S) by the sine of (¦Á). where ¦Á=30¡ã, therefore, the gap (A)=0.0015 inch. Thus, it is seen that by forming the bevelled surfaces at an angle of 30¡ã with respect to the axis of the fitting bore, the gap created between the mating surfaces of the components into which the seal ring tends to extrude is reduced by 50 percent. By choosing angles for the angle (¦Á) of less than 30¡ã, the reduction in gap size is even more dramatic.
It may be seen that the instant invention provides a high pressure fitting for a hydraulic system which utilizes a conventional elastomeric "O"-ring seal for sealing between the components but which substantially reduces the tendency for such seal to extrude between the components and to be damaged by pinching action upon reduction of pressure within the system.
While the invention has been described with particular reference to the preferred embodiments, it is apparent that variations and modifications are possible within the purview of the inventive concepts. No limitation with respect to such variations and modifications is intended, except by the scope of the appended claims.
Ningbo Belt Pneumatic Machinery Co.,Ltd
