Low torque back seating stem for gate valve

A gate valve adapted for stem back seating has a stem and bonnet assembly with a rotatable bearing ring to which the stem is releasably fixed during normal gate opening and closing operations. During back seating, the stem is released from the bearing ring and the bearing ring is fixed to the bonnet cap, enabling low torque back seating by rotation of the stem relative to the bearing ring and bonnet cap.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates generally to gate valves and, more 
particularly, to gate valves adapted for stem back seating. Gate valves 
are commonly used to control fluid flow during drilling, completion and 
production phases of well operations. Typically, gate valves are operated 
by turning a hand wheel or other handle to actuate the gate to and from an 
open and closed position. 
Gate valve back seating surfaces on the stem and the bonnet body serve to 
form a pressure seal between the stem packing chamber and the valve body 
chamber when replacement of the stem packing is needed. The back seating 
shoulder on the stem is back seated against a surface on the bonnet body. 
In normal gate opening and closing operations, the stem is axially fixed 
and raises and lowers the gate by rotation since the stem and lift nut are 
matingly threaded. Therefore, in order to effect back seating, the bonnet 
cap must usually be unscrewed to allow the stem to be moved axially upward 
until the backseat shoulder on the stem contacts the bonnet body. A large 
amount of torque is often required to loosen the bonnet cap. In many 
instances torque-assisting tools such as chain tongs are needed to loosen 
the bonnet cap. Employing such torque-assisting devices presents potential 
hazards and adds to costs and operational time. 
It is, therefore, an object of the present invention to provide effective 
and practical means for low torque back seating of gate valves. The 
present invention achieves this objective by implementing a stem and 
bonnet assembly having a rotatable bearing ring to which the stem is fixed 
during normal gate opening and closing operations, and the bearing is then 
fixed to the bonnet cap and the stem is released therefrom during back 
seating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A low torque valve stem and bonnet assembly (10) is shown in FIG. 1. The 
assembly includes a bonnet body (12) having a central bore (14) 
therethrough. The lower end (16) of the bonnet body (12) is adapted to fit 
onto a gate valve body (not shown). The upper end (18) of the bonnet body 
(12) is adapted to be received in the lower end (20) of a bonnet cap (22). 
The lower end of the central bore (14) forms a back seating surface (24). 
A valve stem (26) is received through the central bore (14) of the bonnet 
body (12). The lower end (28) of the stem (26) is threaded and adapted to 
mate with internal threads of a gate lifting nut (not shown). Upon 
rotation of the stem (26) the gate valve lifting nut is raised or lowered 
between open and closed positions. Adjacent the lower end (28) of the stem 
(26) is a back seating shoulder (30) adapted to form a pressure seal with 
the back seating surface (24) of the bonnet body (12) when the stem (26) 
is moved axially upward into a back seating position. When the stem (26) 
is in the back seating position the back seating shoulder (30) and surface 
(24) form a seal that seals off the stem packing chamber (32) from the 
valve body chamber (34) formed by the bonnet body (12) and the gate valve 
body. Stem packing (36) is received in the stem packing chamber (32) and 
contained by a retainer nut (38) and packing nut follower (40). 
The bonnet cap (22) having a closed end (42) opposite the open lower end 
(20) is secured to the upper end (18) of the bonnet body (12) by threads 
or other suitable means, including set screws (50). A bearing ring (44) is 
rotatably received within the bonnet cap (22). The bearing ring (44) 
includes bearing assemblies (46). Grease fitting (52) are provided to 
lubricate the bearing assemblies (46). The bearing ring (44) has an 
internal bore (48) that is at least partially threaded to receive the stem 
(26). 
During normal gate opening and closing operations the stem (26) is fixed 
relative to the bearing ring (44) by at least one or a plurality of small 
screws (54) each received in a generally radial hole (56) in the bearing 
ring (44) such that the small screws (54) extend into the stem (26). 
Whereby, turning the stem (26) causes the stem (26) and bearing ring (44) 
to rotate relative to the bonnet assembly and the gate lifting nut (not 
shown) so that the threaded engagement of the stem lower end (28) and gate 
lifting nut will cause axial displacement of the gate lifting nut and 
gate. 
During backseating, the small screws (54) are removed by first removing 
large screws (58) which are radially received in the bonnet cap (22). 
Washers (60) are provided to prevent the large screws (58) from extending 
into the holes (56) in the bearing ring (44) during normal gate opening 
and closing operations. After the large screws (58) are removed, the small 
screws (54) are removed. The large screws (58) are then replaced without 
washers (60) so that the large screws (58) will extend into the holes (56) 
in the bearing ring (44). With the bearing ring (44) fixed with respect to 
the bonnet cap (22), the stem (26) is rotated and caused to move axially 
relative to the bonnet assembly, bearing ring (44) and gate lifting nut 
until the back seating shoulder (30) contacts the back seating surface 
(24). Once the stem (26) is back seated, a seal is formed by the back 
seating shoulder (30) and surface (24) to seal off the stem packing 
chamber (32) from the valve chamber (34) so that the stem packing (36) can 
be removed and replaced. 
Although the best mode contemplated for carrying out the present invention 
has been herein shown and described, it will be apparent that modification 
and variation may be made without departing from what is regarded to be 
the subject matter of the invention.