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A gate valve comprises a valve body, a stem bore which extends through the valve body, a stem which is disposed in the stem bore and which includes a first stem portion that is sealed to the stem bore, a second, smaller diameter stem portion that is sealed to the stem bore, and a gate pocket that is

A gate valve comprises a valve body, a stem bore which extends through the valve body, a stem which is disposed in the stem bore and which includes a first stem portion that is sealed to the stem bore, a second, smaller diameter stem portion that is sealed to the stem bore, and a gate pocket that is located between the first and second stem portions, and gate which is disposed within the gate pocket between the first and second seats.

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1. A gate valve which comprises:a valve body which includes a stem bore that extends therethrough and a seat bore that extends therethrough and intersects the stem bore generally transversely; a stem which is disposed in the stem bore and which includes a first stem portion that is sealed to the ste

1. A gate valve which comprises:a valve body which includes a stem bore that extends therethrough and a seat bore that extends therethrough and intersects the stem bore generally transversely; a stem which is disposed in the stem bore and which includes a first stem portion that is sealed to the stem bore and a second stem portion that is sealed to the stem bore; first and second seats which are each positioned at least partially within the seat bore and which each include a flow bore that extends therethrough; a gate which is operatively connected to the first and second stem portions and is disposed between the first and second seats; first actuating means for moving the gate from a first position to a second position; second actuating means for moving the gate from the second position to the first position; wherein one of the first and second positions corresponds to an open position in which a through bore in the gate is aligned with the flow bores in the first and second seats, and the other position corresponds to a closed position in which the through bore is offset from the flow bores; a first seat retaining flange which is secured to the valve body over a first end of the seat bore; wherein the first seat is retained in the seat bore between the gate and the first seat retaining flange; and wherein the first seat retaining flange comprises an integral metal seal which seals against the seat bore. 2. The gate valve of claim 1, further comprising:a second seat retaining flange which is secured to the valve body over a second end of the seat bore; wherein the second seat is retained in the seat bore between the gate and the second seat retaining flange. 3. The gate valve of claim 2, wherein the second seat retaining flange comprises an integral metal seal which seals against the seat bore.4. The gate valve of claim 1, wherein the first actuating means comprises a hydraulic chamber which is connected to a source of hydraulic control fluid and which is in communication with a first end of the stem proximate the first stem portion.5. The gate valve of claim 4, further comprising:a cylinder housing which is connected to the valve body over a first end of the stem bore proximate the first end of the stem; wherein the hydraulic chamber is defined between the cylinder housing and the first stem portion. 6. The gate valve of claim 1, wherein the second actuating means comprises a spring which is functionally disposed between the stem and the valve body.7. The gate valve of claim 6, further comprising:a spring housing which is connected to the valve body over a second end of the stem bore proximate the second stem portion; and a spring retaining flange which is connected to a second end of the stem proximate the second stem portion; wherein the spring is positioned between the spring housing and the spring retaining flange. 8. The gate valve of claim 7, further comprising:a stem extension which is connected to the second end of the stem; wherein the spring retaining flange is integral with the stem extension. 9. The gate valve of claim 7, further comprising means for limiting the compression of the spring.10. The gate valve of claim 9, wherein the limiting means comprises a support sleeve which is positioned between the spring housing and the spring retaining flange.11. The gate valve of claim 7, further comprising means for manually moving the gate between the first and second positions.12. A gate valve which comprises:a valve body which includes a stem bore that extends therethrough and a seat bore that extends therethrough and intersects the stem bore generally transversely; a stem which is disposed in the stem bore and which includes a first stem portion that is sealed to the stem bore, a second stem portion that is sealed to the stem bore, and a gate pocket that is located between the first and second stem portions; first and second seats which are each positioned at least partially within the seat bore proximate the gate pocket and which each include a flow bore that extends therethrough; a gate which is disposed within the gate pocket between the first and second seats; first actuating means for moving the gate from a first position to a second position; second actuating means for moving the gate from the second position to the first position; wherein one of the first and second positions corresponds to an open position in which a through bore in the gate is aligned with the flow bores in the first and second seats, and the other position corresponds to a closed position in which the through bore is offset from the flow bores; wherein the diameter of the first stem portion is larger than the diameter of the second stem portion; wherein the second actuating means comprises a spring which is functionally disposed between the stem and the valve body; a spring housing which is connected to the valve body over a second end of the stem bore proximate the second stem portion; a spring retaining flange which is connected to a second end of the stem proximate the second stem portion; wherein the spring is positioned between the spring housing and the spring retaining flange; and means for manually moving the gate between the first and second positions; wherein the manual moving means comprises a toggle lever which is connected to the second end of the stem. 13. A gate valve which comprises:a valve body which includes a stem bore and a seat bore that intersects the stem bore generally transversely; a stem which is disposed in the stem bore and which includes first and second stem portions that are each sealed to the stem bore; first and second seats which are each positioned at least partially within the seat bore; a gate which is operatively connected to the first and second stem portions and is positioned between the first and second seats; first actuating means for moving the gate from a first position to a second position; second actuating means for moving the gate from the second position to the first position; wherein one of the first and second positions corresponds to an open position in which a through bore in the gate is aligned with a flow bore in each of the first and second seats, and the other position corresponds to a closed position in which the through bore is offset from the flow bores; wherein the first actuating means comprises a hydraulic chamber which is connected to a source of hydraulic control fluid and which is in communication with a first end of the stem proximate the first stem portion; a cylinder housing which is connected to the valve body over a first end of the stem bore and which comprises a receptacle that is adapted to receive a corresponding portion of the valve body; wherein the hydraulic chamber is defined between the cylinder housing and the first stem portion. 14. A gate valve which comprises:a valve body which includes a stem bore and a seat bore that intersects the stem bore generally transversely; a stem which is disposed in the stem bore and which includes first and second stem portions that are each sealed to the stem bore; first and second seats which are each positioned at least partially within the seat bore; a gate which is operatively connected to the first and second stem portions and is positioned between the first and second seats; first actuating means for moving the gate from a first position to a second position; second actuating means for moving the gate from the second position to the first position; wherein one of the first and second positions corresponds to an open position in which a through bore in the gate is aligned with a flow bore in each of the first and second seats, and the other position corresponds to a closed position in which the through bore is offset from the flow bores; a spring housing which is connected to the valve body over a second end of the stem bore and which comprises a receptacle that is adapted to receive a corresponding portion of the valve body; and a spring retaining flange which is connected to a second end of the stem proximate the second stem portion; wherein the spring is positioned between the spring housing and the spring retaining flange.