GASKET FOR A BALL VALVE

Abstract

Disclosed is a gasket for a ball valve including: a valve body; a ball rotatable housed in the valve body; a first and a second seat positioned inside the valve body and housing the ball; and a seal of the type including a first and a second gasket interposed between the first and the second seat and the ball. Each gasket is a one-piece composite gasket and includes at least a first layer and a second layer made of thermoplastic materials, where the hardness, tensile strength and coefficient of friction values are different between the first and second layer, and where the first layer has lower values and coacts in a fluid-tight manner directly with the ball, while the second layer has higher values, normally acts as support for the first layer and coacts in a fluid-tight manner with the ball only upon reaching given operating conditions.

Claims

1) A gasket for a ball valve for connecting pipes in pressurized or low pressure fluid circuits, where said ball valve comprises: a valve body; a ball housed in the valve body so as to be able to rotate therein; a first and a second seat positioned inside said valve body and adapted to house said ball; sealing means of the type comprising a first and a second gasket interposed between said first and said second seat and said ball; where each gasket is a one-piece composite gasket and comprises at least a first layer and a second layer made of thermoplastic materials, where the hardness, tensile strength and coefficient of friction values between said first and second layer are different, and where said first layer has lower values and coacts in a fluid-tight manner directly with said ball, while said second layer has higher values, normally acts as support for said first layer and coacts in a fluid-tight manner with said ball only upon reaching given operating conditions.

2) The gasket according to claim 1, wherein said first layer is selected from thermoplastic materials having the following properties: hardness >55 Sh D tensile strength >25 MPa coefficient of friction between 0.06-0.1, per ASTM D 1894.

3) The gasket according to claim 2, wherein said first layer is selected from PTFE and its derivatives.

4) The gasket according to claim 3, wherein said first layer comprises a virgin or modified PTFE, strengthened by adding graphite.

5) The gasket according to claim 4, wherein said first layer comprises a virgin or modified PTFE, strengthened by adding carbon.

6) The gasket according to claim 1, wherein said second layer is selected from thermoplastic materials having the following properties: hardness >75 Sh D tensile strength >45 MPa coefficient of friction between 0.25-0.35, per ASTM D 1894.

7) The gasket according to claim 2, wherein said second layer is selected from PEEK or PCTFE.

8) The gasket according to claim 1, wherein said first layer and said second layer are structured respectively by means of a first and a second ring permanently joined to each other.

9) The gasket according to claim 8, wherein said first ring comprises a protrusion produced on its outer edge.

10) The gasket according to claim 8, wherein said first ring is alternatively facing the inside or the outside of said valve.

11) The gasket according to claim 8, wherein said second ring comprises a central annular recess and said first ring is inserted into said central annular recess.

12) The gasket according to claim 8, wherein said second ring comprises an annular cut-out and said first ring is inserted into said annular cut-out.

13) A ball valve comprising at least a gasket according to at least claim 1.

14) A ball valve comprising at least a gasket according to at least claim 2.

15) A ball valve comprising at least a gasket according to at least claim 3.

16) A ball valve comprising at least a gasket according to at least claim 4.

17) A ball valve comprising at least a gasket according to at least claim 5.

18) A ball valve comprising at least a gasket according to at least claim 6.

19) A ball valve comprising at least a gasket according to at least claim 7.

20) A ball valve comprising at least a gasket according to at least claim 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] These and other advantages will be more evident below, in the description of preferred embodiments of the invention provided by way of non-limiting example, and with the aid of the figures, wherein:

[0054] FIG. 1 represents a portion of a ball valve for pressurized fluid circuits, sectioned along a longitudinal plane, comprising two gaskets according to the invention;

[0055] FIGS. 2, 3 and 4 represent, in detail section views, a composite gasket according to three possible variants of the invention, housed in a seat of a ball valve for pressurized fluid circuits.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0056] With reference to FIG. 1 there is shown a portion of ball valve 2 for pressurized or low pressure fluid circuits substantially comprising

[0057] a valve body 3, adapted to couple with a first pipe upstream and a second pipe downstream (not illustrated) to which the valve 2 is to be fitted;

[0058] a ball 4 provided with a cylindrical cavity coaxial to the flow of the fluid, housed in the valve body 3 so as to be able to rotate therein;

[0059] a first and a second seat 5 positioned inside said valve body 3, coaxial to said pipes, and adapted to house said ball 4 with interposition of respective first and second gaskets 1.

[0060] With particular reference to the details of FIGS. 2-4, said gaskets 1 are illustrated according to possible variants of embodiment of the invention.

[0061] Said gaskets 1 are of composite type, produced by means of a first 10 and a second 20 layer of different materials, structured substantially in a ring.

[0062] The materials selected are all thermoplastic polymers, but have different physical-mechanical properties to one another.

[0063] A first layer 10 coacts in a fluid-tight manner with said ball 4, while a second layer 20 acts as support for said first layer 10 and coacts in a fluid-tight manner with said ball 4 upon reaching given operating conditions, for example a given high pressure value, i.e., when a predetermine pressure threshold is exceeded or upon reaching given conditions of wear of the gasket.

[0064] Said first layer 10, the softer and more flexible of the two, is selected from thermoplastic materials having the following properties:

[0065] hardness >55 Sh D

[0066] tensile strength >25 MPa

[0067] coefficient of friction between 0.06-0.1 (ASTM D 1894).

[0068] A thermoplastic material having these properties is polytetrafluoroethylene (PTFE), better known by its trade names: Teflon, Fluon, Algoflon, Hostaflon, Inoflon.

[0069] This polymer can be used virgin or with the addition of other stabilizing and fluidifying components to improve its application possibilities or fillers based on silica, carbon, graphite, bronze, stainless steel, exd, to increase the mechanical, pneumatic or chemical performances.

[0070] For the application of the present invention, excellent results were obtained with a virgin PTFE having the following properties:

TABLE-US-00001 VIRGIN PTFE Unit of measurement Test Value Tolerance Physical properties Specific weight g/cm.sup.3 ISO 1183 2.3 — Water absorption % ISO 62 0.01 — (23° C./73° F.) Equilibrium water % ISO 62 — — absorption (23° C./73° F.) Mechanical properties Hardness ShD ASTM >55 +/−3   D1894 Ultimate tensile strength Mpa ASTM 24.82 +/−0.03 D638 tV Tensile elongation at % ASTM 248 — break D638 tV Coefficient of friction Mpa ASTM 0.06 — D1894 Coefficient of wear 10E−8 — — — (Mpa)(m/min)h Charpy pendulum impact J/m ASTM 145 test (23° C./73° F.) D256 Thermal properties Operating temperature ° C. — −200/200 — (220 short term) Thermal conductivity W m−.sup.1 ° C..sup.−1 ASTM — — C177 Heat deflection ° C. ISO 75 at 49 — temperature 1.8 Mpa AVG coeff. of linear 10E.sup.−5 ° C..sup.−1 ASTM 1.2 — expansion below TG D696 Flammability ° C. UL 94 V-0 — Melting point ° C. DSC 327 — Glass transition (TG) ° C. DSC −75 — Other properties Tensile modulus Mpa DIN 560 — 53457

[0071] Even better results are obtained with a PTFE modified with the addition of 25% carbon, having the following properties:

TABLE-US-00002 RPTFE (25% Carbon) Unit of measurement Test Value Tolerance Physical properties Specific weight g/cm.sup.3 ISO 1183 2.1 — Water absorption % ISO 62 0.03 — (23° C./73° F.) Equilibrium water % ISO 62 — — absorption (23° C./73° F.) Mechanical properties Hardness ShD ASTM >62 +/−3   D1894 Ultimate tensile strength Mpa ASTM 13 +/−0.03 D638 tV Tensile elongation at % ASTM 70 — break D638 tV Coefficient of friction Mpa ASTM 0.12 — D1894 Coefficient of wear 10E−8 — — — (Mpa)(m/min)h Charpy pendulum impact J/m ASTM 140 test (23° C./73° F.) D256 Thermal properties Operating temperature ° C. — −200/200 — (250 short term) Thermal conductivity W m−.sup.1 ° C..sup.−1 ASTM 0.59 — C177 Heat deflection ° C. ISO 75 at — — temperature 1.8 Mpa AVG coeff. of linear 10E.sup.−5 ° C..sup.−1 ASTM 1.15 — expansion below TG D696 Flammability ° C. UL 94 V-0 — Melting point ° C. DSC 320 — Glass transition (TG) ° C. DSC — — Other properties Tensile modulus Mpa ASTM 1000 — D412 Compression stress Mpa ASTM 8 — D695

[0072] Said second harder layer 20 having the function of support, is selected from thermoplastic materials having the following properties:

[0073] hardness >75 Sh D

[0074] tensile strength >45 MPa

[0075] coefficient of friction between 0.25-0.35 (ASTM D 1894).

[0076] Thermoplastic materials with these properties are polyether ether ketone (PEEK) and the polychlorotrifluoroethylene (PCTFE), to be selected based on the different needs and applications.

[0077] In detail, PEEK has the following mechanical properties:

[0078] hardness >85 Sh D

[0079] tensile strength >100 MPa

[0080] coefficient of friction between 0.25-0.30 (ASTM D 1894).

[0081] For the application of the present invention, excellent results were obtained with a virgin PEEK having the following properties:

TABLE-US-00003 VIRGIN PEEK Unit of measurement Test Value Tolerance Physical properties Specific weight g/cm.sup.3 ISO 1183 1.3 — Water absorption % ISO 62 0.05 — (23° C./73° F.) Equilibrium water % ISO 62 0.5 — absorption (23° C./73° F.) Mechanical properties Hardness ShD ASTM >84.5 +/−3   D1894 Ultimate tensile strength Mpa ASTM 100 +/−0.03 D638 tV Tensile elongation at % ASTM 34 — break D638 tV Coefficient of friction Mpa ASTM 0.34 — D1894 Coefficient of wear 10E−8 — 1.44 — (Mpa)(m/min)h Charpy pendulum impact KJ m.sup.−2 ASTM 7 test (23° C./73° F.) D6110/ ISO 179-1 Thermal properties Operating temperature ° C. — −100/250 — (310 short term) Thermal conductivity W m−.sup.1 ° C..sup.−1 ASTM 0.25 — C177 Heat deflection ° C. ISO 75 at 152 — temperature 1.8 Mpa AVG coeff. of linear 10E.sup.−5 ° C..sup.−1 ASTM 4.7 — expansion below TG D696 Flammability ° C. UL 94 V-0 — Melting point ° C. DSC 343 — Glass transition (TG) ° C. DSC 143 — Other properties Electrical conductivity ohm om ASTM 1E.sup.−17 — D257 Tensile modulus Gpa ASTM 3.5 — D638 tV Compression stress Mpa ASTM 119 — D695 Izod impact strength test J m.sup.−1 ASTM 94 — (0.25 mm 23° C./73° F.) D256

[0082] Instead, PCTFE has the following mechanical properties:

[0083] hardness >75 Sh D

[0084] tensile strength >45 MPa

[0085] coefficient of friction between 0.3-0.35 (ASTM D 1894).

[0086] Excellent results were obtained with a PCTFE having the following properties:

TABLE-US-00004 PCTFE Unit of measurement Test Value Tolerance Physical properties Specific weight g/cm.sup.3 ISO 1183 2.1 — Water absorption % ISO 62 0 — (23° C./73° F.) Equilibrium water % ISO 62 0 — absorption (23° C./73° F.) Mechanical properties Hardness ShD ASTM >75 +/−3   D1894 Ultimate tensile strength Mpa ASTM 40 +/−0.03 D638 tV Tensile elongation at % ASTM 150 — break D638 tV Coefficient of friction Mpa ASTM — — D1894 Coefficient of wear 10E−8 — — — (Mpa)(m/min)h Charpy pendulum impact KJ m.sup.−2 ASTM — test (23° C./73° F.) D6110/ ISO 179-1 Thermal properties Operating temperature ° C. — −2507150 — Thermal conductivity W m−.sup.1 ° C..sup.−1 ASTM — — C177 Heat deflection ° C. ISO 75 at — — temperature 1.8 Mpa AVG coeff. of linear 10E.sup.−5 ° C..sup.−1 ASTM — — expansion below TG D696 Flammability ° C. UL 94 V-0 — Melting point ° C. DSC 210 — Glass transition (TG) ° C. DSC — —

[0087] As already stated above, with the correct combination of the materials selected for the two layers, the gasket 1 is also suitable to operate in a wide temperature range (from cryogenic to high temperatures) and with maximum chemical inertia.

[0088] Purely by way of example, the tests showed that:

[0089] the combination PTFE-PEEK is optimal for high pressure applications up to 420 bar with temperatures from −100° C. to 220° C.;

[0090] the combination PTFE-PCTFE is optimal for medium/high pressure applications up to 250 bar with temperatures from −196° C. to 150° C.

[0091] With particular reference to the geometry of said gasket 1, in all the possible variants of embodiment said first layer 10 and said second layer 20 are structured respectively by means of a first and a second ring permanently joined to each other to form a single piece.

[0092] As said soft and flexible first layer 10 made of PTFE is adapted to coact in a fluid-tight manner first with said ball 4, said first ring comprises a protrusion 11 produced on its outer edge.

[0093] The greater the elastic springback of the PTFE used is, the more this protrusion 11 protrudes: this protrusion 11 must be sufficient to offset the deformation compression sustained by said first ring subjected to the pressure of the ball 4.

[0094] With reference to FIG. 2, said first and said second ring are permanently joined to each other by co-moulding and said first layer 10 made of softer and more flexible material is facing the inside of the ball valve 2.

[0095] With reference to FIG. 3, said second ring of the layer 20 made of harder material substantially occupies the whole of the seat 5 and has a central annular recess 21, open along its outer edge, into which said first layer 10 made of PTFE is inserted by interference, with mechanical bonding.

[0096] With reference to FIG. 4, said second layer 20 made of harder material produced by said second ring also substantially occupies the whole of the seat 5, but has an annular cut-out 22 arranged along its free edge at its corner more external to the valve 2. Said ring-shaped first layer 10 made of PTFE is provided in this annular cut-out 22, fixed by means of chemical bonding.

[0097] Operation of the composite gasket 1 is described below.

[0098] When the valve 2 is in closed position, the seal is obtained through contact between the ball 4 and the gasket 1.

[0099] This is a progressive seal, which uses the capacity to adapt and slide of said first layer 10 made of PTFE as soft and flexible material, and the mechanical physical support of said second layer 20 made of PEEK or PCTFE as harder material.

[0100] It is clear that in conditions of low pressure in the first instance the first layer 10 made of softer material that deforms and also absorbs the construction “defects” of the valve resists, while at high pressures and in conditions of wear of the gasket, said second layer 20 also provides a seal.