Vacuum system horsepower requirements

A peculiarity of suction conveyors is that once the necessary degree of vacuum has been created in the system, it requires practically no more power to operate a long conveyor than it does a short one—within reasonable limits. With reasonably tight intakes, the formula for horsepower is given as Formula (30) and it will he noted that the power requirement is quite independent of the load carried, being simply that required to maintain the suction necessary to handle the capacity load. 

If the lines cannot be kept short or relatively free of bends, then pressure drops will exceed 12 in. Hg, requiring more horsepower. Where the pressure drop is greater than 12 in. Hg, which is the normal operating and limiting pressure for most vacuum systems, it is necessary to use a positive pressure system. All these factors must be considered initially to obtain the best delivery system most economically. 

If the system differential pressure requirements are low, sometimes a fan can be used. A fan is limited to a maximum of about 65 inches of water (just over 2psi) in vacuum service or 77 inches of water in pressure service (just under 3psi). To estimate fan horsepower use the equations found in Chapter 6 in the section entitled Horsepower Calculation. In lieu of manufacturer s data use an adiabatic efficiency of 50% for initial work. 

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See also in sourсe #XX -- [ ]

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