Design for maintainability

Equipment design will focus on maintainability and rehabUity and not primarily on performance. Design for maintainability wfil become an accepted philosophy that fully rec-... 

Design for Maintainability allows access to, space for maintenance and does not exceed human performance capab iIi t i es ... 

Figure 3. ANP-Design and manufacturing fold Assessing potential errors inherent within maintenance tasks as a part of design for maintainability.

Too often designers think of normal use and operation of equipment and they forget the tasks related to maintenance and repair. Designs that incorporate maintainability concepts will reduce errors during maintenance activities. Designing for maintainability will help prevent unnecessary damage to components because workers cannot see or reach into areas where they need to do work. They will reduce accidents and injuries resulting from maintenance and repair work. 

Fig. 3. Diagram of a static pool for interface slices designed for maintaining a pool of constant volume and tonicity. A separate media reservoir is connected to the bath by a capillary. See text for discussion. (From Taylor, 1980.)...

An optimal combination between aerodynamic and weight requirements was achieved for the Transrapid by modular hybrid (mixed) construction methods. For example, the glass-fibre-reinforced plastic (GRP) front module is designed for maintaining aerodynamic pressure as well as for stability under cross wind forces of 500 km/h, and is bonded to the front of the aluminium structure of the rail cars with Sikaflex products (Fig. 5). 

Feldman, Edwin B. Building Design for Maintainability, McGraw-Hill, New York, 1975. 

Mason, S., Ferguson, C.A. and Pethiek, A.J. (1986), Ergonomic Principles in Designing for Maintainability. Luxembourg ECSC Community Ergonomics Action Report 8, Series 3. 

Flexible Impeller Pumps. Flexible impeller pumps are designed for general-use service. They can be utilized for pumping in either direction, have low pulsations, and are easy to service and maintain. These pumps are typically limited to low capacities and pressures. 

CSPE. Chlorosulfonated polyethylene (CSPE), a synthetic mbber manufactured by DuPont, is marketed under the name Hypalon. It can be produced as a self-curing elastomer designed to cure on the roof. The membrane is typically reinforced with polyester and is available in finished thicknesses of 0.75 to 1.5 mm. Because CSPE exhibits thermoplastic characteristics before it cures, it offers heat-weldable seams. After exposure on the roof, the membrane cures offering the toughness and mechanical set of a thermoset. The normal shelf life of the membrane for maintaining this thermoplastic characteristic is approximately six months. After the membrane is fully cured in the field, conventional adhesives are needed to make repairs. 

Crystallization batches range from 30,000 to 60,000 Hters for each pan. Continuous centrifugals are typically used for second, third, and affination steps continuous vacuum pans are less common but are used in the U.S. for intermediate strikes. Most horizontal batch crystallizers have been replaced by continuous units, and all are designed for controlled cooling of the massecuite to maintain supersaturation. 

The batch-suspension process does not compensate for composition drift, whereas constant-composition processes have been designed for emulsion or suspension reactions. It is more difficult to design controUed-composition processes by suspension methods. In one approach (155), the less reactive component is removed continuously from the reaction to keep the unreacted monomer composition constant. This method has been used effectively in VT)C-VC copolymerization, where the slower reacting component is a volatile and can be released during the reaction to maintain constant pressure. In many other cases, no practical way is known for removing the slower reacting component. 

At processing temperatures, most polymers emit fumes and vapors that may be irritating to the respiratory tract. This is also tme for PVC and its additives. Such irritation may extend to the skin and eyes of sensitive people. Processing emissions exposure can also be greatly reduced or eliminated by the use of properly designed and maintained exhaust ventilation. 

No-wax tile has long been important ia the resideatial market. Such products have a high gloss surface coatiag that resists abrasioa and soiling. When properly designed and maintained, no-wax tile retains its shiny appearance for an extended period of time without appHcation of floor poHsh. 

The best known use of the hairpin is its operation in true counter-current flow which yields the most efficient design for processes that have a close temperature approach or temperature cross. However, maintaining countercurrent flow in a tubular heat exchanger usually implies one tube pass for each shell pass. As recently as 30 years ago, the lack of inexpensive, multiple-tube pass capability often diluted me advantages gained from countercurrent flow. 

Continuous Cake Filters Continuous cake filters are apphcable when cake formation is fairly rapid, as in situations in which slurry flow is greater than about 5 L/min (1 to 2 gal/min), shiny concentration is greater than 1 percent, and particles are greater than 0.5 [Lm in diameter. Liquid viscosity below 0.1 Pa s (100 cP) is usually required for maintaining rapid liquid flow through the cake. Some designs of continuous filters can compromise some of these guidelines by sacrificial use of filter aid when the cake is not the desired product. 

Dyna Whirlpool A unique vessel design for capacities up to 100 t/h has been developed by the American Zinc Co. The separation occurs in a cyhndrical-shaped separatory vessel maintained in an in-chned position from horizontal. This system, known as the Dyna Whirlpool (DWT) process, provides for separate entiy of the medium and the feed sohds, as illustrated in Fig. 19-37. A distinct feature of this separator is that the feed enters the separator via gravity flow. Feed size may range from 0.05 to 0.0002 m (2 in to 65 mesh). Magnetite or ferrosilicon is generally used. 

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