Deep discharging puts all the cells in a battery in the same condition, ready to receive a new charge.
deepening (meteorology). A decrease in the central pressure of a pressure system. This term is usually applied to a low rather than to a high, but technically it is acceptable in either case.
deep-vacuum pump. A vacuum pump capable of removing almost all the air from an air conditioning system. A deep-vacuum pump can reduce the pressure inside the system to a few microns.
defect. A flaw, damage, or imperfection in a component or a piece of material that requires a repair or replacement of the part.
defective. Faulty, or not operating as it should.
deflation (pneumatic component procedure). The release of air from a pneumatic component.
deflator cap. A cap for a tire, strut, or accumulator air valve that, when screwed onto the valve, depresses the valve stem and allows the air to safely escape through a hole in the side of the cap.
deflecting-beam torque wrench (precision hand tool).
A calibrated wrench which indicates the amount of torque being applied to a nut or bolt. This is done by measuring the amount the beam of the wrench deflects when the torque is being applied.
According to Hooke’s law of elasticity, the beam will deflect the same amount each time a given amount of torque is applied by the wrench.
The indication of the amount of torque is read by the position of a pointer attached to the drive of the wrench, over a fixed scale fastened to the beam of the wrench.
defense visual flight rules. See DVFR.
degauss. To demagnetize an object, or to neutralize a magnetic field. Magnetic recording tape is erased by degaussing it.
degeneration (negative electrical feedback). Feedback of an electrical signal from the circuit output to the circuit input, with a phase opposite the phase of the signal on the input. Degeneration stabilizes the output of a circuit, decreases circuit distortion, and improves the frequency response of the circuit.
degreaser. A chemical solution used to remove oil and grease from a part. Stoddard solvent and naphtha are two popular degreasers used in aircraft maintenance shops.
dehumidify. To decrease the amount of moisture (water vapor) in the air. Dehumidifying is often done by installing a small cooling system in the room to cause moisture to condense on its coils. Water vapor is removed from the air and changed into liquid water.
dehydrator. A material that removes some of the moisture from the air inside a component. Some dehydrators use silica gel to absorb the moisture. The silica gel crystals may be colored with an indicator dye that changes its color from blue to pink when the crystals absorb moisture.
dehydrator plug (reciprocating engine preservative device). A transparent plastic tube filled with a desiccant agent, such as silica gel, and an indicator, such as cobalt chloride.
One end of the tube is sealed, and the other end is fitted with a perforated plug and threaded so that it can be screwed into a spark plug hole.
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