open-assembly time (adhesive consideration). The amount of time allowed to elapse between the spreading of an adhesive on the surfaces to be joined and the time the surfaces are clamped together.
open-center hydraulic system. A fluid power system in which the selector valves are arranged in series with each other. Fluid flows from the pump through the center of all of the selector valves, back into the reservoir when no unit is being actuated.
open-center selector valve (hydraulic system component). A type of selector valve that functions as an unloading valve as well as a selector valve. All open-center selector valves are installed in series, and when no unit is being actuated, fluid from the pump flows through the centers of all of the valves and returns to the reservoir.
When a unit is selected for actuation, the center of the selector valve is shut off and the fluid from the pump goes through the selector valve into one side of the actuator. Fluid from the other side of the actuator returns to the valve and goes back to the reservoir through the other selector valves. When the actuation is completed, the selector valve is placed in its neutral position. Its center opens, and fluid from the pump flows straight through the valve, unloading the pump.
open circuit (electrical circuit condition). A condition in which there is no complete path for electrons to flow from one terminal of the source of electrical energy to the other terminal.
open-circuit voltage. The voltage of a battery measured when it is supplying no current to the circuit. Open-circuit voltage is higher than closed-circuit voltage because there is no voltage drop across internal resistance of the battery.
open-end wrench (mechanic’s hand tool). A hand tool used by mechanics to turn nuts and bolts. The jaws of the wrench are in the form of a slot with parallel sides that fit the nut or the bolt head. These jaws are usually offset from the axis of the handle by about 15°.
open-hearth furnace. A furnace used for melting metals. Pig iron and scrap metal are placed in a shallow hearth within the furnace and are melted by heat supplied by a direct flame and from radiation from the walls and ceiling of the furnace.
open wiring (aircraft electrical system installation). Electrical wiring installation in which the wires are tied together in bundles and clamped to the aircraft structure rather than being enclosed in conduit.
operate. 14 CFR Part 1: “Use, cause to use or authorize to use aircraft, for the purpose (except as provided in § 91.13 of this chapter) of air navigation including the piloting of aircraft, with or without the right of legal control (as owner, lessee, or otherwise).”