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check valve (fluid power system component). A valve that allows fluid to flow through it in one direction,
but prevents it flowing through in the opposite direction. See the illustration of ball check valve.
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cheek (reciprocating engine crankshaft). The offset portion of a crankshaft that forms the crankpin to
which the connecting rod big end is attached.
cheesecloth. A lightweight cotton gauze which has no sizing in it. Sizing is a substance, such as starch,
used to make a cloth stiff.
Cheesecloth is used as a straining element to remove lumps and contaminants from liquids.
chemical compound. A combination of two or more atoms of chemical elements which have joined
together to form molecules. A compound is different from a mixture in that the elements in a compound
unite in specific amounts to form a substance different from any of the original elements. In a mixture, the
elements keep their identity.
When two atoms of hydrogen join one atom of oxygen by sharing some of their electrons, the
chemical compound water (H2O) is formed.
chemical element. One of the fundamental building blocks of which all matter is made. There are just a
few more than 100 different chemical elements. Some elements exist in nature by themselves, and others
exist only in chemical compounds. Oxygen, carbon, gold, silver, and hydrogen are examples of chemical
elements.
chemical energy. Energy that exists in a chemical element or in a chemical compound. This energy may be
released when the element or compound joins (reacts with) other chemicals to produce new compounds.
For example, when gasoline (C8H18) burns, it reacts with oxygen (O2) in the air and forms
carbon dioxide (CO2) and water (H2O). It also releases a large amount of energy in the form of light and
heat.
chemical etching (metal processing). A process in which a chemical is used to microscopically roughen
the surface of a metal. Chemical etching is used to prepare a metal so primer will form a tight bond to its
surface.
chemical fire extinguisher. Any of three types of fire extinguishers: vaporizing liquid, carbon dioxide, or
dry powder. All three types of fire extinguishers expel the extinguishing agent and blanket the fire with an
inert gas to keep oxygen away from it. When a fire can no longer get oxygen, it will go out.
chemical milling. A method of machining large sheets of metal by chemically etching away part of the
surface. The inside of the skins of some high-performance aircraft are etched to remove metal not needed
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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for strength. Removing this metal by chemical milling reduces the weight of the aircraft.
Chemical milling produces a lightweight skin with all the needed strength and rigidity far more
economically than can be done with conventional machining or by building up a skin with riveted-on
stiffeners.
chemical oxygen candle system. An oxygen system used for emergency or backup use. Solid blocks of a
material that releases oxygen when burned are carried in special fireproof fixtures. When oxygen is needed,
the candles are ignited with a built in igniter, and oxygen flows into the tubing leading to the masks.
chemical reaction. A change in the chemical nature (the chemical characteristics) of elements when they
unite to form a chemical compound. Hydrogen is a lighter-than-air gas, and oxygen is also a gas. But when
two atoms of hydrogen unite with one atom of oxygen, one molecule of water (H2O), a liquid, is formed.
The compound water has different chemical characteristics from those of either of the elements oxygen or
hydrogen.
When hydrogen and oxygen combine to form water, a chemical reaction takes place.
chemical salt. A product that forms when an acid combines with a metal. For example, when hydrochloric
acid reacts with zinc, zinc chloride, a salt, forms.
Most chemical salts are porous and powdery and have no strength.
chemistry. The branch of science that deals with the composition, properties, and structure of matter.
Chemistry is primarily concerned with the materials of which matter is made, and with the energy
absorbed or released during changes in the characteristics of these materials.
cherry picker (maintenance equipment). A long, hydraulically operated boom with a man-carrying
bucket on its end. A person can be lifted in the bucket of the cherry picker so he can work at a high location.
They are used in aircraft maintenance for working on large airplanes. Cherry pickers are usually mounted
on a truck so that they can be moved from place to place where they are needed.
Cherry rivet. A patented blind rivet manufactured by the Cherry Rivet Division of Townsend, Inc. The
　
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