VACUUM PUMPS AND GENERATORS Machinery's Handbook, 31st Edition
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p r 29.92 -------
p ´ min p atm = where p ′ min is the adjusted achievable vacuum (psi), p atm is atmospheric pressure (psi), and p r is the rated achievable vacuum (inHg). Most vacuum pumps are rated at sea level atmospheric pressure. Vacuum generators are sized according to the level of vacuum required and the required suction flow rate. Vacuum level generated is often expressed as a percentage of input pressure. Input tube diameter and air pressure must be known. A variety of options are available, including ejection, vacuum monitoring, and valving. Multi-stage generators are used to create deeper vacuum than single stage units. Some vacuum generators are optimized for high flow, while others for deep vacuum. Deep vacuum is desirable when picking up a heavy object with a leak-free seal. High suction flow is desirable when picking up objects where a leak-free seal is not possible. Vacuum Accessories: Many accessories are used with vacuum pumps and generators to filter, regulate, control, exploit, measure, and stabilize vacuum. It is important to note that vacuum rated greases must be used when grease is exposed to vacuum. Filters: Filters are critical when using vacuum, because contaminants can be sucked into the vacuum lines and damage the pump, generator, valve, or other components. Selection is based on body type, tube diameter, and maximum particle size that can pass through the filter. Fine filters are typically used with vacuum systems. They must be regularly replaced or cleaned to prevent clogging. Regulators: Like pressure regulators, these devices are essential for limiting and stabilizing vacuum pressure in a circuit. They may be manually or automatically con- trolled. These devices are outfitted with a gauge or digital readout. Vacuum regulators are sized with respect to range and accuracy of measurement, maximum flow rate, and port size. Valves: Many pressure valves can be used to control vacuum. However, if the valve uses air pressure to cause switching, an external pilot line with positive pressure must be provided. Grippers: There are a wide variety of grippers available for the purpose of picking up objects with vacuum. Their primary purpose is to provide a leak-free seal to maximize the effect of the vacuum system. Compliant grippers include suction cups, bellows, and vacuum pads of all shapes and sizes. Miniature valves are often used in applications with multiple grippers to restrict flow if no part is present. Measurement: Vacuum gauges and switches are used to measure the level of vacuum. They may be analog or digital, and measure in absolute or gauge pressure. Level Compensators: These compliant devices are used when multiple grippers are em- ployed in picking up a part. They provide some degree of shock and vibration dampening. Level compensators are available in a wide variety of sizes and stroke lengths.
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