one of the main elements of pneumatic automatic control; impedes the free flow of air or a gas to produce a pressure gradient.
The total pressure gradient in a pneumatic resistance is made up of the gradients in the individual areas of the flow (at the input, the output, and inside the element). A distinction is made between constant resistances, which are nonadjustable or manually adjustable, and variable resistances, which are automatically controlled. Nonadjustable constant resistances are usually made in the form of a very constricted channel of constant cross section and a certain fixed length. Adjustable constant resistances are made in the form of a “fixed seat-movable part” combination, such as cone-cone or cone-cylinder; the relative position of the parts, which is selected during adjustment, controls the cross section of the resistance’s passage and hence the pressure drop. The cross section is unchanged during operation in all constant pneumatic resistances.
Variable pneumatic resistances are made mainly with nozzle-baffle, sphere-cone, and sphere-cylinder combinations; their passage cross section varies during operation. The parameters of a pneumatic resistance depend to a great extent on the nature of the gas flow (laminar or turbulent).
T. K. BERENDS