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Fluid Power

HANDBOOK

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PNEUMATIC

hose & tubing THE

basic function of pneumatic hose and tubing is to convey pressurized air to actuators, valves, tools and other devices. But there are countless types and sizes of tubing and hose on the market, so engineers should consider a number of important factors to select the right one for a given task. Start with construction. Tubing for air applications may be extruded of a single material or reinforced internally, typically with textile fibers, for higher strength. Pneumatic hose generally consists of an inner tube, one or more layers of reinforcing braided or spiral-wound fiber, and an outer protective cover. In broad terms, hose is more rugged than tubing but costs more. The air supply and application set a baseline for the necessary product performance. Flow requirements help determine hose or tubing size. Tubing is generally specified by OD and wall thickness, while hose is specified by ID. Regardless, choosing too small an inner diameter “chokes” flow and results in pressure losses, inefficiency and excessive fluid velocity that can shorten service life. Too large a diameter, on the other hand, results in higher than necessary weight, size and cost. Also ensure that products operate below the stated maximum working pressure. Manufacturers generally rate tubing by measuring the burst pressure at 75° F, and then divide it by an appropriate safety factor (typically 3:1 or 4:1) to determine the maximum working pressure. Keep in mind that published burst-pressure ratings are only for manufacturing test purposes, and in no way indicate that a product can safely handle pressure spikes or otherwise operate above maximum working pressure. Also note that some products handle vacuum to approximately 28 in.-Hg without collapse. IMAGE COURTESY OF AUTOMATION DIRECT

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