Packing cartridge 96 also includes

Packing cartridge 96 also includes rod wipers 104 to protect and maintain the long life of the sealing elements by preventing contaminants in the region of the sealing elements.Bonnet stem threads 21 are designed so that no injury to the seals occurs when the stem is passed through packing cartridge 96.Dual bearings 18 suspend bonnet stem 20 to preferably prevent contact of any metal surface thereby eliminating wear and galling to either the bonnet stem 20 or the packing cartridge 96.To prevent rotation of bonnet ring 94 with respect to bonnet housing 98, screw 106 is tightened into the corresponding groove or inset disposed adjacent the end portion of bonnet housing 98.Rotation of bonnet ring 94 with respect to bonnet housing 98 may alter the stroke length adjustments as discussed hereinafter.Bonnet ring 94 retains packing cartridge 96 in position within bonnet housing 98.Bonnet ring 94 also preferably includes an additional seal 102 for safety purposes.To set the downward stroke length or drift 106 of bonnet stem 20, stem spacers 92 are removed or added as necessary to increase or decrease the combined spacer width 108 as indicated in FIG.3.In setting the bonnet stem drift, downstop 54 is first tightened to bonnet stem 20 with drive nut 110.Bonnet stem 20 is placed in its furthermost downward position.The position of the gate bore(not shown)through gate 22 is determined by running an appropriate drift tool(not shown)through valve body 60.The number of stem spacers 92 may then be removed or added as necessary to provide an accurate drift setting.Secondary metal-to-metal stem seal 112 provides sealing in the event of fire damage to the other seals and also acts as a stop for upward movement of gate 22.The adjustment of the up-stop drift is made in a manner dependent upon valve manufacture designs but may typically involve threadably engaging the gate stem with the bonnet stem and rotating until the correct adjustment is reached.Further rotation may be prevented by such means as a pin or other retainer means.FIG.4 discloses the relative ease with which various operators 114 may be changed out without altering the up-stop and down-stop drift as discussed hereinbefore.Thus the operator may be exchanged with the valve under pressure.No additional drift adjustments are necessary because the alignment is not altered and remains accurate for the particular valve.