75 psig, T1 is 800, P1 is 237.8 psig, and T2 is300°F:Solution:Substituting:PNEUMATIC GASESIn chapter 1, you learned that many factorsare considered in determining whether to usehydraulics or pneumatics as a power source in afluid power system. Once it is determined thatpneumatics will be used as the source of power,some of the same factors are considered inselecting the pneumatic gas.QUALITIESThe ideal fluid medium for a pneumaticsystem is a readily available gas that isnonpoisonous (nontoxic), chemically stable, freefrom any acids that cause corrosion of systemcomponents, and nonflammable. It also will notsupport combustion of other elements.Gases that have these desired qualities may nothave the required lubricating power. Therefore,lubrication of the components of some pneumaticsystems must be arranged by other means. Forexample, some air compressors are provided witha lubricating system, some components arelubricated upon installation or, in some cases,lubrication is introduced into the air supply line.Two gases meeting these qualities and mostcommonly used in pneumatic systems are com-pressed air and nitrogen.COMPRESSED AIRCompressed air is a mixture of all gasescontained in the atmosphere. In this manual,compressed air is referred to as a gas when it isused as a fluid medium.The unlimited supply of air and the ease ofcompression make compressed air the most widelyused fluid for pneumatic systems. Althoughmoisture and solid particles must be removedfrom the air, it does not require the extensivedistillation or separation process required in theproduction of other gases.Compressed air has most of the desiredproperties and characteristics of a gas forpneumatic systems. It is nonpoisonous andnonflammable but does contain oxygen, whichsupports combustion. One of the most undesirablequalities of compressed air as a fluid medium forpneumatic systems is moisture content. Theatmosphere contains varying amounts of moisturein vapor form. Changes in the temperature ofcompressed air will cause condensation ofmoisture in the pneumatic system. This condensedmoisture can be very harmful to the system, asit increases corrosion, dilutes lubricants, and mayfreeze in lines and components during coldweather. Moisture separators and air driers(dehydrators) are installed in the compressed airlines to minimize or eliminate moisture insystems where moisture would deteriorate systemperformance.The supply of compressed air at the requiredvolume and pressure is provided by an aircompressor. (For information on air compressors,refer to Naval Ships’ Technical Manual, chapter551.) In most systems the compressor is part ofthe system with distribution lines leading from thecompressor to the devices to be operated. In thesesystems a receiver is installed in-line between thecompressor and the device to be operated to helpeliminate pulsations in the compressor dischargeline, to act as a storage tank during intervals whenthe demand for air exceeds the compressor’scapacity, and to enable the compressor to shutdown during periods of light load. Other systemsreceive their supply from cylinders which must befilled at a centrally located air compressor andthen connected to the system.Compressed air systems are categorized bytheir operating pressures as follows: high-pressure(HP) air, medium-pressure (MP) air, and low-pressure (LP) air.High-Pressure Air SystemsHP air systems provide compressed air at anominal operating pressure of 3000 psi or 5000psi and are installed whenever pressure in excess11-7
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