diaphragm(redirected from aperture-stop)
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diaphragm (dīˈəfrămˌ), term used to describe any of several large muscles, found in humans and other mammals, which separate two adjacent regions of the body. The most commonly known muscle of this class is the thoraco-abdominal diaphragm. In humans, the thoraco-abdominal diaphragm acts as a partition between the cavity of the chest and that of the abdomen. The chief muscle used in respiration, it is relaxed and dome-shaped during exhalation. During inhalation it contracts, pulling downward, and with the combined contraction of the chest muscles allows the chest cavity to expand. Any interference with its free movement, as in the paralysis of poliomyelitis, seriously impedes the function of the lungs and therefore endangers life. In its downward movement the thoraco-abdominal diaphragm also stimulates the stomach and liver and thus aids in the digestive processes. Spasmodic contraction results in hiccups. The thoraco-abdominal diaphragm is also subject to developmental defects, hernia, injury, displacement, and infection. Other diaphragms in the human body include the pelvic diaphragm and the urogenital diaphragm, which use similar muscular contractions and expansions in their respective functions.
diaphragm(dÿ -ă-fram) See stop.
the musculotendinous partition that (in mammals and man) divides the thoracic cavity from the abdominal cavity.
The diaphragm provides for diaphragmatic respiration and equalization of pressure in the thoracic and abdominal cavities; it also regulates the outflow of blood from the inferior and superior venae cavae into the right atrium of the heart and the distribution of gases in the cardiac part of the stomach and intestine (cardiac opening). During exhalation the diaphragm protrudes cupola-like into the thoracic cavity: with inhalation it flattens by contracting and thereby increases the volume of the thoracic cavity. The diaphragm has a peripheral muscular part and a central tendinous part. In many insectivorous and predatory mammals the tendinous part of the diaphragm is not well developed. In all mammals the diaphragm has openings through which pass the inferior vena cava; the azygos and hemiazygos veins: the vagus (two branches), phrenic, splanchnic, and sympathetic nerves: and the periaortic plexus. The muscular part of the diaphragm consists of lumbar, costal, and sternal sections. The aorta and esophagus usually pass through openings (in sloths through a single opening) between the internal muscle bundles in the lumbar section of the diaphragm. The muscle bundles, in contracting, prevent the backing up of food from the stomach. In the anthropoid apes and man the pericardium fuses with the upper surface of the diaphragm.
(in Russian, diafragma, also stiffener—see  below). In engineering, a part of instruments, machines, mechanisms, and structures; it is usually a plate or partition (with or without an aperture).
(1) A measuring diaphragm most often is a disk with an aperture. Along with the venturi and the common nozzle, it serves as one of the standard constricting devices used in industry for measuring the rate of flow of liquids, gases, and vapors passing through a pipe, on the basis of the principle of variable pressure drop. The axis of the diaphragm aperture should coincide with the axis of the pipe. As the substance to be measured passes through the diaphragm, the average rate of flow in the constricted section increases as a result of the conversion of part of the potential energy of pressure into kinetic energy. The static pressure of the flow is lower behind a diaphragm than in front of it. The pressure difference (drop), which is measured by a differential manometer, is proportional to the square of the rate of flow of the flowing substance and serves as a measure of the flow rate.
Measuring diaphragms are divided into standard (normal) and nonstandard types. The use of standard diaphragms is governed by special rules. When the flow rate is to be measured under conditions that differ from the conditions established by these rules, nonstandard diaphragms (such as eccentric, segmented, and paired types), which require individual calibration under conditions similar to operating conditions, are used. Depending on the methods of pressure selection, normal diaphragms are divided into the disk type (in the form of a flat disk), with reading of pressure by means of separate pipes, and the chamber type (with ring chambers), for reading pressures in the planes of the diaphragm disk. Normal diaphragms are used in pipes larger than 50 mm in diameter; chamber diaphragms, for pipes up to 500 mm in diameter and for a working pressure of up to 10 meganewtons per sq M (MN/m2), or 100 kilograms-force per sq cm (kgf/cm2); and disk diaphragms, for pipes 450–1,600 mm in diameter and pressures of up to 1.6 MN/m2 (16 kgf/cm2). The relative error of measurement of the flow rate when diaphragms are under favorable conditions (in the absence of additional corrections for viscosity and the roughness of the pipe) ranges from ±0.5 percent to 1.5 percent, and under more severe conditions from ±3 percent to 3.5 percent.
REFERENCESKremlevskii, P. P. Raskhodomery, 2nd ed. Moscow-Leningrad, 1963.
Pravila 28–64 izmereniia raskhoda zhidkostei, gazov i parov standartnymi diafragmami i soplami. Moscow, 1964.
Avtomatizatsiia, pribory kontrolia i regulirovaniia proizvodstvennykh protsessov v neftianoi i neftekhimicheskoi promyshlennoist, Spravochnik, book 2. Moscow, 1964.
G. G. MIRZABEKOV
(2) For optical instruments seeIRIS.
(3) In turbines, a diaphragm is a ring partition to which the vanes of the guiding unit are secured. The diaphragms are removable along the horizontal. Diaphragms that operate at temperatures up to 250° C are made from SCh 18–36, SCh 21–40, and SCh 24–44 cast iron; diaphragms operating at high temperatures are made of 15KhM, 20KhM, and 35KhM chromium-molybdenum steel.
(4) In hydraulic-engineering structures, a stiffener is a device within the body of earth dams and rock-filled dams; it is made in the form of a vertical wall of concrete, reinforced concrete, metal, or less frequently, wood. It ensures the rigidity of the movable part of the stop gate.
V. N. POSPELOV
ii. In accumulators, the portion that divides its two portions—one filled with gas and the other fluid.