CDD5000 – Dosing and Material
Dosing Pumps
Dosing pumps can be either solenoid-operated or motor-driven, depending on the dosing rate and back pressure in the system. Additionally, recommended manufacturers are EMEC, Prominent, LMI, Pulsafeeder, and Walchem.
Moreover, all wetted parts of the pump head shall be Kynar™, PVC, CPVC, or ceramic. Seals and o-rings shall be Viton™, Kalrez™, or Teflon™. Select the electronic controls on the pump based on the control scheme that maintains stable levels of chlorine dioxide in the water stream. Typically, a flow-metering device on the main water stream will control dosing. Alternatively, periodic injections at regular time intervals may control dosing. The pump should come with some type of automatic bleed system to expel gases that may evolve from the solution “air bind” the pump head, and return them to the solution container. Finally, consult the pump manufacturer for proper selection. SVS AQUA can assist you in pump selection.
Transfer Pumps
Transfer pumps should be motor-driven centrifugal, magnetic drive style. In addition, the maximum recommended developed head is 20 psig or 45 ft. hd. All wetted parts of the pump head shall be Kynar™, PVC, or CPVC. Seals and o-rings shall be Viton™, Kalrez™, or Teflon™.
Piping
Use PVC or CPVC rigid pipes to conduct the solution. Specifically, use schedule 40 pipes for pressures ranging from 5” Hg vacuum to 25 psig. For full vacuum to 25 psig, use schedule 80 pipes. Cemented joints should be used wherever possible. Avoid using flanged joints, and minimize the use of threaded joints. Seal all threaded joints with Teflon™ tape, and do not use liquid Teflon™. Additionally, install double-walled piping for long-distance runs or when the piping passes through walls or floors.
Tubing
Tubing used in dosing systems shall be flexible Kynar™. In addition, fittings shall be Kynar™ compression type. Tubing runs shall be kept to a minimum. Furthermore, to ensure protection against UV radiation from sunlight or indoor lighting, wrap the tubing with tape or enclose it within a larger tube made of opaque material, such as colored polypropylene, preferably black.
Hoses
Transfer hose shall be PVC. Moreover, construction can be reinforced or non-reinforced and shall be vacuum-rated. Material can be clear or colored. In addition, the minimum size shall be 3⁄4”.Manufacture hose connections in multibarb style using PVC, CPVC, Kynar™, or glass-reinforced polypropylene. Seal all threaded joints with Teflon™ tape. Do not use liquid Teflon™.
Material Compatibility of Chlorine Dioxide
Undiluted chlorine dioxide solutions are corrosive to most metals. In particular, it is incompatible with aluminum, brass, bronze, carbon and stainless steel, copper, iron, and zinc. However, it is generally compatible with titanium and Hastelloy C. Undiluted, it is also incompatible with many plastics and elastomers. For example, in many instances, chlorine dioxide will diffuse into and through polymers. As a result, in some cases, it will denature plastic material, causing embrittlement, discoloration, or softening. Such materials as PVC, CPVC, HDPE, and polyethylene are in this category. When you use such materials with concentrated chlorine dioxide solutions, inspect them fully every month and replace them if any stress cracking is visible.
On the other hand, generally, an undiluted chlorine dioxide solution is most compatible with fluoropolymers, such as Kynar™ and Halar™, and with fluorinated elastomers, such as Viton™, Teflon™, and Kalrez™. It also is compatible with vinyl ester-FRP materials. Exposure to concentrated chlorine dioxide solutions may embrittle even the highly resistant fluoropolymers listed as acceptable. You should inspect them monthly and replace them if any stress cracking is visible. Furthermore, in a diluted form of less than 50 ppm concentration, the solution is compatible with most common piping and seal materials for durations of up to one week. At the same time, at less than 10 ppm concentration, it is generally safe for these materials.