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Control Valves for Corrosive Applications
PLASTIC CONTROL VALVES
Collins Plastic Control Valves are highly responsive control valves designed for use with corrosive media and/or corrosive atmospheres.
Suitable for applications in numerous industries including chemical, petrochemical, pulp and paper, and municipal, Collins Control Valves are extremely corrosion-resistant, feature fast accurate positioning and are available with a wide selection of trim sizes.
These specialized control valves will stroke at the rate of approximately 1/2 inch per second. The differential area piston eliminates the necessity for auxiliary loading regulators. The actuator is molded of glass filled, UV inhibited polypropylene except for the integral positioner. Before shipment, the aluminum positioner and a portion of the cylinder are immersed in dipseal to provide atmospheric protection. The integral positioner eliminates the need for external linkages which are subject to corrosion and malfunctioning. Valves are available in Globe, Angle, or Corner configurations to fit your piping. Valves may be furnished without positioner for ON-OFF applications.
Collins initial objective to supply a chemically inert control valve package became a reality with the advent of its plastic, pneumatic actuator. When assembled with one of Collins plastic valve bodies, the resulting combination represents an effective way to handle both corrosive materials that flow through the valve as well as the harsh environments that can attack the outside of the valve and actuator.
These valves incorporate a unique closure between the cylinder and yoke, eliminating the previous threaded closure. The actuator is attached to the yoke with an internal locking ring which is inserted through a slot in the side of the actuator cylinder. This is accomplished by machining a half circle groove inside the lower edge of the cylinder and matching half circle groove in the yoke. When the yoke and cylinder are assembled, a 5/32” OD polypropylene rod is inserted through the slotted hole into the groove, locking the two together. See photo 1.
Collins plastic control valve package can therefore withstand the salty atmosphere of coastal areas as well as the industrial environments which are too corrosive for the metal actuators used with other control valves.
Along with its corrosion resistance the Collins control valve features a stem packing arrangement that virtually eliminates the problem of fugitive emissions (leakage), thereby protecting the environment. One Collins packing design is shown in Photo 2. This design consists of Kalrez* “O” Rings together with Kynar** guide spacers - which are held in compression by a spring loaded cap.
SPECIAL NOTE: In actual field tests lasting over one year, and after several thousand cycles of shop testing, the design in photo 2 yielded virtually no fugitive emissions (leakage).
*Kalrez® - Registered Trademark of DuPont Dow Elastomers **Kynar® - Registered Trademark of ELF Atochem North America Inc.
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