Fluid power with applications 7th edition book answers
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Some advantages of this arrangement are: greatly reduced noise levels at the machine, the availability of backup pumps to take over if a working pump fails, less total horsepower and flow, and increased uptime of all machines.Īnother advantage hydraulic-powered machines have over pneumatic ones is that they operate at higher pressure - typically 1500 to 2500 psi. These hydraulic systems operate more like a compressed-air installation because the power source is in one location.Ī few other manufacturers are setting up central power units when the plant has numerous machines that use hydraulics. Because these presses require no flow during their long closing times, a single large pump can operate several of them. They usually have a central power unit with pipes running to and from the presses out in the plant. Rubber-molding plants depart from this scheme. Hydraulic systems usually have a dedicated power unit for each machine. Most hydraulic systems use mineral oil for the operating media but other fluids such as water, ethylene glycol, or synthetic types are not uncommon. The fluid is an almost non-compressible liquid, so the actuators it drives can be controlled to very accurate positions, speeds, or forces. Such charts give an idea of the energy losses due to leaks or bypassing.Ī hydraulic system circulates the same fluid repeatedly from a fixed reservoir that is part of the prime mover. Several data books have charts showing cfm loss through different size orifices at varying pressures. It takes approximately 5 compressor horsepower to supply air to a standard hand-held blow-off nozzle and maintain 100 psi. Leaks in an air circuit do not cause housekeeping problems, but they are very expensive. ( Chapter 17 has information on air-oil circuits.)Īir-operated systems are always cleaner than hydraulic systems because atmospheric air is the force transmitter. An air-driven device can use a combination of air for power and oil as the driving medium to overcome this problem, but the combination adds cost to the circuit. This is mainly because the power source (the air compressor) is installed remotely from the machine in an enclosure that helps contain its noise.īecause air is compressible, an air-driven actuator cannot hold a load rigidly in place like a hydraulic actuator does. Fortunately, an air motor does not have to run continuously but can be cycled as often as needed.Īir-driven machines are usually quieter than their hydraulic counterparts. A 1-hp air motor can take up to 60 cfm to operate, so the 1-hp air motor requires (60/4) or 15 compressor horsepower when it runs. It takes approximately one horsepower to compress 4 cfm of atmospheric air to 100 psi. Air motors are one of the most costly components to operate. Compressing atmospheric air to a nominal working pressure requires a lot of horsepower. Either process cuts secondary machining operations and cost.įirst cost of an air circuit may be less than a hydraulic circuit but operating cost can be five to ten times higher. Because air systems operate at relatively low pressure, the components can be made of relatively inexpensive material - often by mass production processes such as plastic injection molding, or zinc or aluminum die-casting. Two main advantages of air-operated circuits are their low initial cost and design simplicity.
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Most pneumatic circuits run at low power - usually around 2 to 3 horsepower. Again the fluid is different but the operating characteristics change little. Hydraulic systems may use a variety of fluids - ranging from water (with or without additives) to high-temperature fire-resistant types. The gas may be different but the system's operating characteristics are the same. Because nitrogen is usually supplied in gas cylinders at high pressure, it has a very low dew point at normal system pressure. Readily available nitrogen gas is not hazardous to the atmosphere or humans.
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While these systems are the same in many aspects, they can have very different characteristics in certain ways.įor example: remote outdoor applications may use dry nitrogen gas in place of compressed air to eliminate freezing problems. Most fluid power circuits use compressed air or hydraulic fluid as their operating media.