Dart valve assembly for a bypass plunger

1. A dart valve assembly for a bypass plunger wherein a dart valve including a valve stem having an outside surface diameter is disposed within a clutch bobbin having an inside surface diameter in contact with the outside surface diameter of the valve stem, comprising:

a clutch bobbin formed of synthetic material disposed around the valve stem; and

a surface profile formed axially along the inside surface diameter of the clutch bobbin and along the outside surface diameter of the valve stem; wherein

the surface profile formed in the clutch bobbin is substantially the same as formed on the valve stem and includes a series of uniform arc segments forming periodically alternating crests and valleys in the region of contact.

2. The assembly of claim 1 , wherein the uniform arc segments comprise:

circular arc segments disposed end-to-end along the respective surfaces; and

the circular arc segments face alternately inward and outward of the respective surfaces of the bobbin and the dart valve stem thereby forming the alternating crests and valleys.

3. The assembly of claim 2 , wherein the arc segments are defined by:

a radius R relative to a center disposed either side of the respective surfaces by a distance L such that R−L=H, where H is the peak excursion of each crest and valley from the respective surface;

a spacing S equal to the length of the chord of an arc segment; wherein

0.001≦H≦0.004 inch.

4. The assembly of claim 3 , wherein the values of R, S, and H respectively comprise:

R=0.050 inch;

S=0.060 inch; and

H=0.0025 inch.

5. The assembly of claim 1 , wherein the surface profile comprises a sinusoid having:

a peak amplitude value H=+/−(R−L) relative to the nominal surface diameters where L defines a center of a radius R relative to the nominal surfaces of the valve stem OD and the bobbin ID; and

a period 2×S where S=base dimension of each crest and valley.

6. The dart valve assembly of claim 1 , wherein the synthetic material comprises:

a thermoplastic material selected from the group consisting of oil filled nylon, unfilled nylon, filled and unfilled polyetheretherketone, polyaryletherketone, polyetherimide, polyphenylene sulfides, polyamides and variations thereof.

7. The dart valve assembly of claim 1 , wherein the bobbin comprises:

at least first and second arcuate bodies, having at least one circumferential groove formed in the outer diameter of each arcuate body, that together substantially encircle the valve stem.

8. The dart valve assembly of claim 1 , wherein the clutch comprises:

at least first and second arcuate bodies that together substantially encircle the valve stem; and

a garter spring disposed in at least one circumferential groove disposed around the outside of the first and second arcuate bodies and securing the at least first and second arcuate bodies against the valve stem.

9. The dart valve assembly of claim 8 , wherein the first and second arcuate bodies comprise:

first and second substantially hemispherical bodies having at least one circumferential groove formed in the outer diameter of each hemispherical body, that together substantially encircle the valve stem.

10. A dart valve assembly for a bypass plunger, comprising:

a dart valve formed of metal, having a valve head attached to a first end of a cylindrical valve stem, the valve stem having an outside diameter (O.D.) surface defined by a first longitudinal surface profile;

a clutch disposed around the dart valve stem, the clutch including a split bobbin surrounded by at least one garter spring, the split bobbin formed of a synthetic material and having an inside diameter (I.D.) surface defined by a second longitudinal profile; wherein

the first and second longitudinal profiles of adjacent cylindrical surfaces of the dart valve stem O.D. and the split bobbin I.D. each comprise a uniform sequence of equal amplitude ridges alternating with equal amplitude grooves around the dart valve stem O.D. and the split bobbin I.D. such that the grooves are defined by the nominal diameter of the stem or bobbin less an amplitude dimension H and the ridges are defined by the nominal diameter of the stem or bobbin plus an amplitude dimension H; and wherein

the first and second surface longitudinal profiles are substantially the same and the amplitude dimension H is defined by 0.001 inch≦H≦0.0045 inch.

11. The assembly of claim 10 , wherein the synthetic material from which the bobbin is formed comprises:

a thermoplastic material selected from the group consisting of oil filled nylon, unfilled nylon filled and until led polyetheretherketone, polyaryletherketone, polyetherimide, polyphenylene sulfides, polyamides and variations thereof.

12. The dart valve assembly of claim 10 , wherein the clutch comprises:

at least first and second substantially hemispherical bodies that together substantially encircle the valve stem, the first and second bodies having at least one circumferential groove formed in the outer diameter of each hemispherical body; and

a garter spring disposed in at the least one circumferential groove disposed around the outside of the first and second substantially hemispherical bodies and securing the at least first and second substantially hemispherical bodies against the valve stem.

13. A dart valve assembly for a bypass plunger wherein the dart valve assembly comprises:

a dart valve having a valve head and a cylindrical valve stem formed of metal, the valve stem having an outside diameter surface profile defined by a first sequence of rings oriented in an axial direction; and

a clutch disposed on the dart valve, the clutch including a split bobbin formed of a synthetic material and having an inside diameter surface profile defined by a second sequence of rings oriented in an axial direction; wherein

the first and second sequences of rings form substantially the same profile.

14. The assembly of claim 13 , wherein the first and second sequences of rings are in slidable contact.

15. The assembly of claim 13 , wherein the first and second sequences of rings are formed to substantially the same dimensions in cross section.

16. The assembly of claim 13 , wherein the first and second sequences of rings comprise:

an alternate sequence of ridges and grooves along a portion of the length of the stem and the bobbin on their respective outside and inside diameters.

17. The assembly of claim 13 , wherein the first and second sequences of rings comprise:

ridges defined by the nominal diameter of the stem or bobbin plus an amplitude dimension H alternating periodically with grooves defined by the nominal diameter of the stem or bobbin less an amplitude dimension H; wherein

the amplitude dimension H is defined by 0.001 inch≦H≦0.0045 inch.

18. The assembly of claim 13 , wherein the synthetic material from which the bobbin is formed comprises:

a thermoplastic material selected from the group consisting of oil filled nylon, unfilled nylon filled and unfilled polyetheretherketone, polyaryletherketone, polyetherimide, polyphenylene sulfides, polyamides and variations thereof.

19. The assembly of claim 13 , wherein the clutch comprises:

at least first and second substantially hemispherical bodies that together substantially encircle the valve stem, the first and second bodies having at least one circumferential groove formed in the outer diameter of each hemispherical body; and

a garter disposed in each at least one circumferential groove disposed around the outside of the first and second substantially hemispherical bodies and securing the at least first and second substantially hemispherical bodies against the valve stem.

20. The assembly of claim 19 , wherein the garter comprises:

a coil spring formed of metal having coils oriented normal to the longitudinal axis of the spring or canted at an angle to the longitudinal axis of the spring.