PTFE valves

The structures of three monomers are shown. In each case, show the structure of the polymer that would result from polymerization of the monomer. Vinyl chloride is polymerized to vinyl plastics and PVC pipe. Tetrafluoroethylene polymerizes to Teflon , used as non-stick coatings and PTFE valves and gaskets. Acrylonitrile is polymerized to Orion , used in sweaters and carpets. 

Apparatus for preparations. All reactions were performed with a stainless steel vacuum line. Preparations were carried out in Teflon reactors assembled especially for each. The reactors were joined to the metal line via flexible fluorinated ethylene propylene (FEP) tubes and a polytetrafluoroethy-lene (PTFE) valve. FEP-tube reactors were prepared by first cutting lengths to —25 cm. These tubes were softened at one end by heating in a flame, then squeezed with broad-nose pliers to seal the end. One-armed reactors consisted of one of these tubes connected directly to a PTFE valve. T-shaped reactors had two of these tubes connected to a PTFE T-joint, which itself was connected via FEP tubing to a PTFE valve. All reactors were made vacuum-tight with PTFE swage connections. 

Figure 2 Diagram of a U-shaped mercury manometer for reliably introducing 1 atm of gas into a reaction vessel attached to a high vacuum line. Initially, both sides of the U-shaped column are evacuated along with the rest of the high vacuum manifold. Once a high vacuum has been obtained, the PTFE valve on the manometer is closed, and the high vacuum line is isolated from the vacuum source. Then the gas of choice is introduced into the main manifold until the mercury level advances 760 mm. The manifold is now charged with 1 atm of gas.

Figure 7 A commercially available Schlenk tube containing a PTFE valve. The valve, tube, and ground-glass joint sizes may vary.

Aqueous hydrogen fluoride of greater than 60% maybe handled in steel up to 38°C, provided velocities are kept low (<0.3 m/s) and iron pickup in the process stream is acceptable. Otherwise, mbber or polytetrafluoroethylene (PTFE) linings are used. For all appHcations, PTFE or PTEE-lined materials are suitable up to the maximum use temperature of 200°C. PTEE is also the material of choice for gasketing. AHoy 20 or Monel is typically used for valve and pump appHcations. Materials unacceptable for use in HE include cast iron, type 400 stainless steel, hardened steels, titanium, glass, and siHcate ceramics. 

The PTFE micropowders are commonly used in plastics, inks, lubricants, and finishes such as lacquer. Lubricants containing micropowders are used for bearings, valve components, and other moving parts where sliding friction must be minimized or eliminated. Nonstick finishes that require good release properties, for example, in the food and packaging industry, commonly use PTFE micropowders. 

New materials also emerged. Nylon, developed brilliantly by W. H. Carothers and his team of research workers for Du Pont as a fibre in the mid-1930s, was first used as a moulding material in 1941. Also in 1941 a patent taken out by Kinetic Chemical Inc. described how R. J. Plunkett had first discovered polytetrafluoroethylene. This happened when, on one occasion, it was found that on opening the valve of a supposedly full cylinder of the gas tetrafluoroethylene no gas issued out. On subsequently cutting up the cylinder it was found that a white solid, polytetrafluoroethylene (PTFE), had been deposited on the inner walls of the cylinder. The process was developed by Du Pont and, in 1943, a pilot plant to produce their product Teflon came on stream. 

Industrial equipment is a continuing area of development for plastics. Pipes, pumps, valves and sight glasses, made from such materials as PVC, PTFE and poly-4-methylpent-l-ene, have become well established on account of their corrosion resistance. The nylons are used for such diverse applications as mine conveyor belts and main drive gears for knitting machines and paper-making equipment. These and other materials are widely used where such features as toughness, abrasion resistance, corrosion resistance, non-stick properties, electrical insulation capability and transparency are of importance. 

Uses of the polyamide-imides include pumps, valves, gear wheels, accessories for refrigeration plant and electronic components. Interesting materials may be made by blending the polymer with graphite and PTFE. This reduces the coefficient of friction from the already low figure of 0.2 (to steel) to as little as 0.02-0.08. 

Service stop valves on small compressors may also carry a connection for a pressure cut-out or gauge, or for the temporary fitting of guages or charging lines when servicing. The valve backseats to close off this port while gauges are being fitted. Valve seats are commonly of soft metal or of a resistant plastic such as PTFE. 

Fluoroplastic FPs have superior heat and chemical resistance, excellent electrical properties, but only moderate strength. Variations include PTFE, FEP, PFA, CTFE, ECTFE, ETFE, and PVDF. Used for bearings, valves, pumps handling concentrated corrosive chemicals, skillet linings, and as a film over textile webs for inflatables such as pneumatic sheds. Excellent human-tissue compatibility allows its use for medical implants. 

The critical part of the valve consists of a synthetic sapphire ball resting on a seat. The seat may be of stainless steel, PTFE or, more usually, also of sapphire. When the flow is directed against the ball the ball moves forward allowing the liquid to flow past it. When the direction of pressure changes resulting in potential flow-back through the valve, the ball falls back on its seat and arrests the flow. 

It exploded spontaneously in a glass bomb closed with a PTFE-lined valve. No previous indications of instability had been noted dining distillation, pyrolysis or irradiation. 

Sampling for gas phase chromatographic analysis can be readily achieved by a grease-free, rotatable, multiple-ported gas sampling valve. Various commercial units of this sort are available. However, the author s laboratory preferred to fabricate to its own design (Y. Shimoyama, 1970) the result is a valve containing only stainless steel and PTFE and specifications... 

Agent same as anolyte circuit. Energetics piping to be PFA-lined carbon steel pumps to be titanium valves to be PFA-lined ductile cast iron agitators to be PTFE-coated stainless steel seals and gaskets to be Kalrez, PTFE, or PTFE-clad. Heat exchangers to be 304L stainless steel. Catholyte evaporator to be Inconel 690/625 hydrocyclones to be titanium. 

Inert material of the sampling device (bags, tubes, valves), no losses by diffusion Preflushing Prediction equipment Volume of the sample Sampling time.pump speed Storage time(<24h) Inert tube material (PTFE. stainless steel, glass) Preflushing Predilution equipment Heated probe jf Dust filters required... 

Various fluoropolymer equipment, for example, connectors and valves, is available from laboratory suppliers (at a high price). The principle of a simple, quick, and inexpensive method for connections of electrochemical cells using PTFE tubes is shown in Fig. 4. 

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