Valve materials, pumps

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. 

AH columns, distributors, and ancHlary hardware such as piping, valves, and pumps must be constmcted of corrosion-resistant materials, or coated with an appropriate substance. AH streams that contact the hardware during each step of the cycHc operation need to be considered in this selection. 

The products for these appHcations are fabricated from materials from brass mills (manufacturers of copper and alloy mill products), wire mills, and foundries (manufacturers of castings). Brass mill products consist of sheet, strip, plate, rod, bar, tube, pipe, forgings, extmsions, and mechanical wire. Wire mills make electrical wire. Foundry castings consist primarily of plumbing products and industrial valves and pumps. 

Process flow diagrams are more complex and show all main flow streams including valves to enhance the understanding of the process as well as pressures and temperatures on all feed and product lines within all major vessels and in and out of headers and heat exchangers, and points of pressure and temperature control. Also, information on construction materials, pump capacities and pressure heads, compressor horsepower, and vessel design pressures and temperatures are shown when necessary for clarity. In addition, process flow diagrams usually show major components of control loops along with key utilities. 

Positive pumps are normally fitted with relief valves. These are not usually fitted to centrifugal pumps unless the process material is likely to explode if it gets too hot. As an alternative to a relief valve, such pumps may be fitted with a high-temperature trip. This isolates the power supply. Or a kick-back, a small-diameter line (or a line with a restrietion orifice plate) leading from the delivery line baek to the suction vessel, may be used. The line or orifice plate is sized so that it will pass just enough liquid to prevent the pump from overheating. Small-diameter tines are better than restriction orifice plates as they are less easily removed. 

The corrosive and mechanical effects of flow are observed in pipes, especially at bends and downstream of flow disturbances, tube and shell heat exchangers, valves and pumps. More corrosion and/or harder materials are used in such areas. Austenitic stainless steels work harden and hence are superior in flowing conditions to ferritic stainless steels of otherwise similar corrosion resistance. Hard... 

Storage vessels can be made in a large variety of shapes and sizes. Absorption and distillation towers are available in several different forms and many sizes. Reaction vessels such as coppers, stills and Cellarius receivers can be supplied in the special materials to withstand thermal shock. Valves and pumps of many types are available to suit all conditions. Piping can be... 

Subcutaneous in vivo testing of these polymers (13,14) has shown minimal tissue response—similar, in fact, to the response to poly-(tetrafluoroethylene). These materials are candidates for use in heart valves, heart pumps, blood vessel prostheses, or as coating materials for pacemakers or other implantable devices. 

In preliminary process design, the primary consideration is contact by inhalation. This happens either through accidental release of toxic material to the atmosphere or the fugitive emissions caused by slow leakage from pipe flanges, valve glands, pump and compressor seals. Tank filling also causes emissions when the rise in liquid level causes vapor in the tank to be released to atmosphere, as discussed in Chapter 25. 

Limited aperture releases are conceptualized in Figure 4-2. For these releases material is ejected from holes and cracks in tanks and pipes, leaks in flanges, valves, and pumps, and severed or ruptured pipes. Relief systems, designed to prevent the overpressuring of tanks and process vessels, are also potential sources of released material. 

The coefficient of hnear expansion of this alloy in the temperature range of 21 to 100°C (70 to 212°F) is 12.2 x l(r /°C (6.8 x 10- /°F), which is slightly above that of cast iron (National Bureau of Standards). Since this material has practically no elasticity, the need for expansion joints should be considered. Connections for flanged pipe, fittings, valves, and pumps are made to ASME B16.1, Class 125. 

Poly (3,3-Bis(Chloromethyl)Oxetane) This is marketed by Hercules as Penton chlorinated polyether. Its thermal, flame, and chemical resistance are used primarily for corrosion-resistant equipment in the process industries, such as valves, fittings, pumps, meters, and linings for steel pipe and tanks, for service in many corrosive atmospheres up to 250°F. or higher. At 4.50/pound, growth possibilities appear limited by increasing competition from lower-cost materials. 

Vitrified clayware is sintered stoneware which is hardly porous and can withstand chemical and mechanical outside influences. For those reasons vitrified clayware is used for sewers, as a coating for vessels, reactor inlets, pipes, valves and pumps. Plastic clay with a relatively high content of aluminium and alkali metals and a low lime content is used as raw material... 

The use of synthetic polymers in medicine and biotechnology is a subject of wide interest. Polymers are used in replacement blood vessels, heart valves, blood pumps, dialysis membranes, intraocular lenses, tissue regeneration platforms, surgical sutures, and in a variety of targeted, controlled drug delivery devices. Poly(organosiloxanes) have been used for many years as inert prostheses and heart valves. Biomedical materials based on polyphosphazenes are being considered for nearly all the uses mentioned above. 

The polymeric materials are used in (i) barrier applications (ii) self-supporting structures (tanks, piping, valves and pumps) (ii) column internals, seals, gaskets, adhesives and caulkings. An overview of polymeric materials used in corrosion control applications is given in Figure 4.8. 

Because of its elastic recovery properties, PTFE, a self-lubricating compound, is used in sealing and flexing applications such as sanitary seals, valve diaphragms, o-rings in mechanical seals, and seals and seats of stem and rotary valves such as ball valves. It is also commonly used as a liner or coating material for valves and pumps for the pharmaceutical industry. 

Eluent entering the pump should not contain any dust or other particulate matter. Particulates can interfere with pumping action and damage the seal or valves. Material can also collect on the inlet frits or on the inlet of the column, causing pressure buildup. Eluents or the water and salt solutions used to prepare the eluents are normally filtered with a 0.2 or 0.45 pm nylon filter. 

A dynamic model of a distillation column can be assembled from simpler units, as trays, heat exchangers (condenser, reboiler), reflux drum, valves and pumps (Fig. 4.5). Tray modelling has to answer two issues (1) accurate description of material and energy holdup, and (2) accurate pressure drop calculation. 

The differences in objective and principle between HPLC and FI separations bring major dissimilarities in the related equipments. The FI flow systems produce much less flow impedance during operation, even when packed columns are implemented. Columns are much shorter, and packing materials are much coarser when they are used to serve FI separation purposes. This in turn substantially lowers the requirement to withstand high pressures for the valves and pumps of a FI system, so that high pressure pumps such as those used in HPLC are not necessaiy. On the other hand, the high versatility of FI often demands multi-functional valves, and multi-channel pumps. These differences may be better understood after comparing the related instrumentation described in Chapter 2 to standard HPLC equipment. 

The storage tank should be clearly and boldly marked indicating the flash point of the solvent stored. This can either state the category of material, such as Highly Flammable or Flammable , or more specifically Flash Point Below 32°C . All pipes, valves and pumps should be clearly marked to indicate their purpose. 

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