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Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 456
component is cured with heat and pressure.
press brake (production sheet-metal tool). A form of sheet-metal bending tool in which a long, straight
male die whose bottom edge has the correct bend radius is pressed down onto a sheet of metal placed over
a female die containing a long V-shaped groove. The male die is usually forced down by energy stored in a
large flywheel.
press fit. An interference fit between machine parts. The hole into which a part is to fit is slightly smaller
than the part itself, and the two can be assembled only by pushing the part into the hole with a press.
press-to-test light (indicator light). A type of indicator light used in an aircraft. The bulb may be tested by
pressing on the top of the light fixture to complete a circuit to ground. If the bulb is good, the light will
illuminate.
pressure. A measure of force applied uniformly over a given unit of surface area. Pressure is normally
expressed in such terms as pounds per square inch or grams per square centimeter.
pressure altimeter. Another name for a pneumatic altimeter. See pneumatic altimeter.
pressure altitude. The altitude in standard atmosphere at which the pressure is the same as the existing
pressure. Because a pneumatic altimeter operates solely on pressure, pressure altitude is the uncorrected
altitude indicated by an altimeter when its barometric scale is adjusted to standard sea-level pressure of
29.92 inches of mercury, or 1013.2 millibars.
pressure carburetor (reciprocating engine component). A fuel metering device that meters fuel to a
reciprocating engine on the basis of the mass of air flowing into the engine. The pressure forcing the fuel
through the metering jet is determined by the difference between two air-metering forces: the low pressure
produced at the throat of a venturi, and the high pressure of the air as it rams into the carburetor. These two
air pressures act on a diaphragm to control a fuel pressure regulating system that varies the pressure drop
across the fuel metering jet as a function of the mass of air flowing into the engine.
pressure casting. A method of casting metal parts in which molten or plastic metal is forced into
permanent molds under pressure.
pressure cooling (reciprocating engine cooling). A method of air-cooling an engine in which the
cylinders are enclosed in tight-fitting shrouds. The cowling is divided into two compartments by baffles
and seals, with half of each cylinder in each compartment. Ram air is directed into one compartment, and
the pressure in the other is decreased by air flowing over a flared exit or adjustable cowl flaps. The pressure
difference across the cylinders causes cooling air to be drawn through the fins to remove the unwanted
heat.
pressure-demand oxygen system. A type of oxygen system used by aircraft that fly at very high altitude.
This system functions as a diluter-demand system below about 40,000 feet. Above this altitude, the
regulator furnishes the mask with 100% oxygen under pressure to force the oxygen into the lungs, rather
than depending on the low pressure produced when the wearer of the mask inhales to pull in the oxygen.
See diluter-demand oxygen system.
pressure-fed spray gun (paint spraying device). A paint spray gun in which the material being sprayed is
fed to the gun under pressure from a pressure pot or pressure cup. Pressure-fed spray guns are used when a
large quantity of material is to be sprayed, or when the material is too heavy or too viscous to be picked up
by a suction-fed spray gun.
pressure fueling (aircraft fueling). The method of fueling used by almost all transport aircraft. The fuel is
put into the aircraft through a single underwing fueling port. The fuel tanks are filled to the desired quantity
and in the sequence selected by the person conducting the fueling operation.
Pressure fueling saves servicing time by using a single point to fuel the entire aircraft, and it
reduces the chances for fuel contamination.
pressure gradient (meteorology). The rate of decrease of pressure per unit distance at a fixed time.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 457
pressure-injection carburetor (reciprocating engine fuel metering device). A multibarrel pressure
carburetor used on large radial and V-engines. The fuel is metered on the basis of the mass of the air
flowing into the engine and is sprayed under pressure into the eye, or center, of the internal supercharger
impeller.
pressure jump (meteorology). A sudden significant increase in station pressure.
pressure manifold (fluid power system component). The portion of a fluid power system from which the
　
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