Top plug 206 also includes a POLYPA

Top plug 206 also includes a POLYPAK® seal 210, preferably formed of NITROX- ILE®.Hydraulic pressure moves piston 212 axially downwardly to move downstop 214 into engagement with stem spacers 216 as described hereinbefore.Piston 212 floats on preferably non-metallic wear bearings 218 and is further sealed with seals 220.Upper spring retainer 222 applies force from coil 224 to move downstop 214 upwardly.Base plate ring 226 is bolted to housing 228 and provides support for lower spring retainer 230 as described with respect to diaphragm-type actuator 10.The foregoing detailed disclosure and description of the invention is illustrative and explanatory thereof, and it will be appreciated by those skilled in the art, that various changes in the size, shape and materials as well as in the details of the illustrated construction, reliability configurations, or combinations of features of the various valve actuator elements of the present invention may be made without departing from the spirit of the invention.A valve actuator for moving a valve gate between open and closed valve positions within a valve body, the valve actuator comprising:an operator assembly comprising:an operator housing defining a pressure chamber therein and having a fluid entry port; andan operator member within the operator housing movable toward the valve body in response to pressurized fluid introduced into the operator housing pressure chamber through the fluid entry port; anda bonnet assembly comprising:a bonnet housing securable to the valve body, the bonnet housing having a bonnet housing bore therethrough;an elongated bonnet stem having first and second ends, the stem axially movable in the bonnet housing bore, unconnected at the first end to the operator member, and securable at the second end to the valve gate for moving the valve gate to the open and closed valve positions;a spring for producing a biasing force opposing axial movement of the operator member toward the valve body;a contact member, separate from the operator member, having an outer flange, and rotatably and axially affixed to the first end of the bonnet stem, and having a surface facing the operator member for drive contact with the operator member;an upper spring retainer having an inner flange for engagement with the outer flange to transmit the biasing force to the bonnet stem and to receive the movement of the operator member toward the valve body; anda base ring coaxially surrounding the bonnet housing, the base ring securing the operator housing to the bonnet housing by bolts disposed in apertures in the base ring and threaded into longitudinal openings in a base of the operator housing, wherein the bolts provide substantially the only securement between the operator assembly and the bonnet assembly.The actuator of claim 1, wherein the operator assembly further comprises a shaft extending from a shaft aperture in the operator housing, the shaft axially movable through the shaft aperture and unconnected to the bonnet stem.The actuator of claim 2, wherein the shaft is rotatable with respect to the bonnet stem.a seal cartridge disposed within a shaft aperture of the operator housing, the seal cartridge having a shaft bore therethrough with a seal therein for sealingly engaging a shaft and an outer surface with a seal thereon for sealingly engaging the shaft aperture; anda retainer ring disposed within the shaft aperture above the seal cartridge for retaining the seal cartridge within the shaft aperture, the retainer ring accessible from the exterior of the actuator to permit removal of the retainer ring and seal cartridge without removing the operator housing from the bonnet housing.a flexible diaphragm that applies pressure against the operator member, the flexible diaphragm having an engagement side that engages the operator member and a face side opposite the engagement side;