Applied Product Catalog 2016 2017 Page i45 Technical Reference

Fluid Power Glossary All Things Industrial SM i45 ABSOLUTE - A measure having as its zero point or base the complete absence of the entity being measured. ABSOLUTE PRESSURE (psia) - The pressure above absolute zero, the sum of atmospheric and gauge pressure. ACCUMULATOR - A container in which fluid is stored under pressure as a source of fluid power. It also absorbs shocks and surges and smoothes out operation. ACTUATOR - A device for converting hydraulic energy into mechanical energy. A motor or cylinder. AERATION - Air in the hydraulic fluid. Excessive aeration causes the fluid to appear milky and components to operate erratically because of the compressibility of the air trapped in the fluid. AMPLITUDE OF SOUND - The loudness of a sound. ANNULAR AREA - A ring shaped area - often refers to the net effective area of the rod side of a cylinder piston, i.e., the piston area minus the rod area. ASTM - American Society for Testing Materials. ATMOSPHERE (ONE) - A pressure measure equal to 14.7 psi. ATMOSPHERIC PRESSURE - Pressure on all objects in the atmosphere because of the weight of the surrounding air. At sea level, about 14.7 psi absolute. BACK CONNECTED - A condition where port connections are on normally unexposed surfaces of hydraulic equipment. (Gasket mounted units are back connected.) BACK PRESSURE - A pressure in series. Usually refers to pressure existing on the discharge side of a load. It adds to the pressure required to move the load. BAFFLE - A device, usually a plate, installed in a reservoir to separate the pump inlet from return lines. The baffle also aids fluid cooling. BAR - A unit of pressure based on 105 Newtons per square meter, equal to 100 kPa (kilopascals), approx. equal to 14.5 psig. BERNOULLI PRINCIPLE - An increase in velocity causes a decrease in pressure. BLEED-OFF - To divert a specific controllable portion of pump flow directly to a reservoir. BREATHER - A device which permits air to move in and out of a container or component to maintain atmospheric pressure. BSPP - British Standard Parallel Pipe. BSPT - British Standard Pipe Thread. BY-PASS - A secondary passage for fluid flow. CARTRIDGE - The replaceable element of a fluid filter. The pumping unit from a vane pump, composed of the rotor, ring, vanes and one or both side plates. A removable valve element that fits into a cavity in a hydraulic component, e.g. manifold. CASE DRAIN LINE - A line conducting fluid from a component housing to the reservoir. CAVITATION - A localized gaseous condition within a liquid stream which occurs where the pressure is reduced to the vapor pressure. CELSIUS - A temperature scale. 0 Celsius is the freezing point of water. CENTISTOKES (cSt) - A unit of kinematic viscosity. 1 cSt = 10-2 square centimeters per second (cm 2 /s). CHAMBER - A compartment within a hydraulic unit. May contain elements to aid in operation or control of a unit. Examples: spring chamber, drain chamber, etc. CHANNEL - A fluid passage, the length of which is large with respect to its cross- sectional dimension. CHARGE (supercharge) - To replenish a hydraulic system above atmospheric pressure. To fill an accumulator with fluid under pressure (see pre-charge pressure). CHARGE PRESSURE - The pressure at which replenishing fluid is forced into the hydraulic system (above atmospheric pressure). CHECK VALVE - A valve which permits flow of fluid in one direction only. CIRCUIT - The complete path of flow in a hydraulic system including the flow- generating device. CLOSED CENTER - The condition where pump output is not unloaded to tank in the center or neutral operating condition. CLOSED CIRCUIT - A piping arrangement in which pump delivery, after passing through other hydraulic components, bypasses the reservoir and returns directly to pump inlet. COMPENSATOR CONTROL - A displacement control for variable pumps and motors which alters displacement in response to pressure changes in the system as related to its adjusted pressure setting. COMPONENT - A single pneumatic or hydraulic unit. COMPRESSIBILITY - The change in volume of a unit volume of a fluid when it is subjected to a unit change in pressure. CONTROL - A device used to regulate the function of a unit (see Hydraulic Control, Manual Control, Mechanical Control and Compensator Control). COOLER - A heat exchanger used to remove heat from the hydraulic fluid. COUNTERBALANCE VALVE - A valve which maintains resistance to flow in one direction but permits free flow in the other. Usually connected to the outlet of a vertical double-acting cylinder to prevent uncontrolled falling, dropping or cavitation. CRACKING PRESSURE - The pressure at which a pressure actuated valve begins to pass fluid. CUSHION - A device sometimes built into the ends of a cylinder which restricts the flow of fluid at the outlet port, thereby slowing the motion of the piston rod. CYLINDER - A device which converts fluid power into linear mechanical force and motion. It usually consists of a movable element such as a piston and piston rod, plunger rod, plunger or ram, operating within a cylindrical bore. DELIVERY - The volume of fluid discharged by a pump in a given time, usually expressed in gallons per minute (gpm). DELTA P ( P) - The change in pressure between two points in a system, such as in a passageway or between the inlet and outlet of a component. DEMULSIFY - To separate water from oil. DE-VENT - To close the vent connection of a pressure control valve permitting the valve to function at its adjusted pressure setting.

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