Pressure filtered air

Figure 2.2. Positive pressure filtered air clean laboratory...

Soviet Ground Forces have even more significant compensations. All their modern tanks and armoured personnel carriers have protective seal-out liners and positive-pressure filtered air systems. These features enable their crews to operate in a shirt sleeve environment at periods when NATO forces would require full individual protection. Soviet armour is fully capable of riding over and across contaminated ground and, after rapid decontamination, is able to resume the advance. Other fighting vehicles, including support vehicles, missile transporters, and command vehicles possess either air filtration systems (in the more modern models) or individual protective equipment for their crews. Collective protection facilities, like the PP-2, are also a prominent part of the Soviet inventory. Once erected in the field, these centres enable work to be undertaken without protective clothing or allow soldiers to eat, rest, and complete other bodily functions. They may serve various purposes, for example, as centres for command and communication and as medical aid posts. ... 

Lunchrooms, (i) The employer shall provide for employees working in regulated areas, lunchroom facilities which have a temperature controlled, positive pressure, filtered air supply, and which are readily accessible to employees working in regulated areas. 

Lunchroom facilities For those employees who must have a positive pressure, filtered air supply readily accessible to employees. Employees must wash their hands and face prior to eating, drinking or smoking. The employer must ensure that employees do not enter lunchroom lacihties with protective work clothing or equipment unless surface fibers have been removed from the clothing or equipment. Employees may not smoke in work areas where they are occupationally exposed to asbestos. 

This reduction in permeabiUty due to cake consoHdation or coUapse may be so large that it may nullify or even overtake the advantage of using high pressures in the first place and there is then no reason for using the generally more expensive pressure filtration hardware. While a simple Hquid pump may be cheaper than the vacuum pump needed with vacuum filters, if air displacement dewatering is to foUow filtration in pressure filters, an air compressor has to be used and is expensive. 

A variation of the same principle is the DDS-vacuum pressure filter which has a number of small disks mounted on a shaft which rotates discontinuously. The cake is formed on both sides of the disks when they are at the bottom position, dipped into the slurry. When the disks come out of the slurry and reach the top position, hydrauhcaHy driven pistons squee2e the cake and the extra Hquid then drains from both sides of the cake. The cake is removed by blowback with compressed air. 

The vertical recessed plate automatic press, shown schematically in Figure 15 and described previously, is another example of a horizontal belt pressure filter. Cycle times ate short, typically between 10 and 30 minutes, and the operation is fully automated. The maximum cake thickness is about 35 mm washing and dewatering (by air displacement) of cakes is possible. Apphcations include treatment of mineral slurries, sugar, sewage sludge, and fillers like talc, clay, and whiting. 

Air Permeability. Air permeabiUty is an important parameter for certain fabric end uses, eg, parachute fabrics, boat sails, warm clothing, rainwear, and industrial air filters. Air permeabiUty of a fabric is related to its cover, or opacity. Both of these properties are related to the amount of space between yams (or fibers in the case of nonwovens). The most common method for specifying air permeabiUty of a fabric involves measuring the air flow per unit area at a constant pressure differential between the two surfaces of the fabric. This method, suitable for measuring permeabiUty of woven, knitted, and nonwoven fabrics, is described in ASTM D737. Units for air permeabiUty measured by this method are generally abbreviated as CFM, or cubic feet per square foot per minute. 

Air Backflush A configuration unique to microfiltration feeds the process stream on the shell side of a capillaiw module with the permeate exiting the tube side. The device is rim as an intermittent deadend filter. Eveiw few minutes, the permeate side is pressurized with air. First displacing the liquid permeate, a blast of air pushed back-... 

It should be noted that the total loss of head of a filter bed is in inverse ratio to the depth of penetration of the matter in suspension. In a normal wastewater treatment plant, the water is brought onto a series of rapid sand filters and the impurities are removed by coagulation-flocculation-filtration. Backwashing is typically performed in the counterfiow mode, using air and water. One type of common filter is illustrated in Figure 6, consisting of closed horizontal pressurized filters. 

J. Pressure ventilated large induction or synchronous motors A Pressure Ventilated motor requires a closed pressure system to force filtered air or nitrogen into the motor casing (housing) to avoid corrosive or explosive conditions internally. Constance reference 56 describes some of the details of such a system also see Ecker et al. [69]. 

Filter back washing normally needs low-pressure compressed air and a flow of filtered water about ten times the... 

Such units may use chilled water or direct-expansion refrigerant, and will have the air filter at the top. It may not be possible to introduce outside air through it, so the room will have a pressurized fresh air supply, which will be filtered to remove fine dusts which may affect the computers. Computer room units work with a very high sensible heat ratio of 0.95 or more, so they have large coils to keep the ADP up near the dew point of the room air. Most will have an inbuilt steam humidifier to replace any moisture which is removed on the coil. 

All laboratory operations are carried out in laminar flow cabinets in rooms in which filtered air is maintained at a slight positive pressure relative to their outer environment. Operators wear sterilized clothing and work aseptically. Antibiotic fermentations are, of strict necessity, pure culture aseptic processes, without con-tamirrating orgarrisms. 

Filtered air may be used to purge a complete room, or it m be confined to a specific area and incorporate the principle of laminar flow, which permits operations to be carried out in a gentle current of sterile air. The direction of the airflow may be horizontal or vertical, depending upon the type of equipment being nsed, the type of operation and the material being handled. It is important that there is no obstruction between the air supply and the exposed product, since this may resnlt in the deflection of microorganisms or particulate matter fiom a non-sterile surface and canse contamination. Airflow gauges are essential to monitor that the correct flow rate is obtained in laminar flow units and in complete suites to ensure that a positive pressure fiom clean to less clean areas is always maintained. 

Drying or cooling. Dressings packs and other porons loads may become dampened during the sterilization process and mnst be dried before removal fiom the chamber. This is achieved by steam exhanst and application of a vacnum, often assisted by heat from the steam-filled jacket if fitted. After drying, atmospheric pressure within the chamber is restored by admission of sterile filtered air. 

Filtered air (Chapter 17) is used to achieve the necessary standards this should be maintained at positive pressure throughout a clean or aseptic area, with the highest... 

The clean laboratory for trace metals was divided into three areas entrance laboratory (with clothes changing annex), instrument laboratory, and ultraclean sample preparation laboratory, all under positive pressure with active charcoal filtered air. Personnel using the clean rooms were required to wear hair caps, polyethylene gloves, laboratory coats, and designated shoes. These items are worn only in the clean rooms. 

A filtered air supply should maintain a positive pressure relative to surrounding areas under all operational conditions and flush the area effectively. Final filtration should be at or as close as possible to the point of input to the area. A warning system should be included to indicate failure in the air supply and an indicator... 

---