ASA American Standards Association
axial piston pump A pump in which the pistons stroke in the same direction on the cylinder block's centerline; these pumps are either an in-line or angle design.
capacity Same as volumetric output.
cavitation A condition that occurs in pumping when available fluid does not fill the existing space; cavitation causes erosion of the metal in the inlet and speeds deterioration of the hydraulic oil.
centrifugal pump A nonpositive-displacement pump that is used in a hydraulic system where a large volume of flow is required at relatively low pressures; a centrifugal pump is either a volute or diffuser type.
cfs cubic foot (feet) per second
chassis ground The difference of potential between a point in the circuit and a ground point that is measured by the voltmeter. Also called common ground. See also earth ground; ground; zero reference point.
common ground Same as chassis ground.
cylinder A hydraulic actuator that is constructed of a piston or plunger which operates in a cylindrical housing by the action of liquid under pressure; a cylinder can be one of several types: single acting, double acting, differential, nondifferential, ram type, piston type, cushioned, or lockout.
delivery rate Same as volumetric output.
directional-control valves Valves that control the flow direction; they can be a poppet, a sliding-spool, a check, a two-way, or a four-way valve. See also flow-control valves, pressure-control valves; valves.
displacement The amount of liquid that is transferred from the pump's inlet to its outlet in one revolution or cycle; displacement is either fixed or variable. See also fixed-displacement pump; variable-displacement pump.
displacement principle Principle which explains how fluid is taken in at one point and is displaced to another point; displacement is either nonpositive or positive. See also nonpositive-displacement pump; positive-displacement pump.
energy The ability to do work, expressed in ft lb. See also friction; heat energy; kinetic energy; potential energy.
flow The movement of the hydraulic fluid caused by a difference in the pressure at two points; velocity and flow rate are the two ways to measure flow. See also flow rate; velocity.
flow rate The measure of how much volume of a liquid passes a gpoint in a given time, measure in GPM. See also flow; velocity.
flow-control valves Valves that are used to control the actuator speed by metering the flow; they can be a gate, a globe, a needle, a restrictor, an orifice-check, or a flow-equlizer valve. See also directional-control valves;
pressure-control valves; valves.
force Anything that tends to produce or modify motion, expressed in pounds.
FPT flow, pressure, and temperature
friction The resistance to relative motion between two bodies. See also energy; heat energy; kinetic energy; potential energy.
ground A point of reference in an electrical circuit to which all circuit voltages are compared; circuit voltages are either positive or negative with respect to ground. See also chassis ground; earth ground; zero reference point.
head The vertical distance between two levels in a fluid.
heat energy The energy a body possesses because of its heat; considered a dynamic factor. See also energy; friction kinetic energy; potential energy.
hp horsepower; standard unit of power; one HP is equal to 550 ft lb of work every second.
hydraulic motors A piece of equipment that converts hydraulic energy into mechanical energy; hydraulic motors can be gear, vane, or piston types.
hydraulic testers lightweight units used to check or troubleshoot a hydraulic-powered system.
hydraulics The science of transmitting force and/or motion through the medium of a confined liquid.
nonpositive-displacement pump This type of pump discharges liquid in a continuous flow. See also displacement principle; positive-
open-center system A pump system where the pump's output has a free flow path back to the reservoir in the circuit's neutral condition.
positive-displacement pump This type of pump discharges volumes of liquid that are separated by periods of no discharge. See also displacement principle; nonpositive-displacement pump.
potential energy Energy due to position; in hydraulics, potential energy is a static factor. See also energy; friction; heat energy; kinetic energy.
pressure The force exerted against a specific area, expressed in psi.
pressure-control valves Valves that may limit or regulate pressure, create a particular pressure condition required for control, or cause actuators to operate in a specific order. Pressure-control valves can be a relief, a pressure-reducing, a sequence, or a counterbalance valve. See also directional-control valves; flow-control valves; valves.
reciprocating pump A type of pump that depends on a reciprocating motion to transmit liquid from its inlet side to its outlet side.
resistance A condition in a hydraulic system that is usually caused by a restriction or obstruction in the path or flow.
rotary pump A positive-displacement pump in which rotary motion carries the liquid from the pump's inlet to its oulet.
SPDT single pole-double throw switch
SPST single pole-single throw switch
STOP system Troubleshooting system in hydraulics in which a person should Study the cirucit diagrams, Test by using a reliable tester, Organize the knowledge gained from the circuit-test results, and Perform repairs, taking time to do the job well.
torque Circular force on an object.
turbulent flow Flow that develops when flow speed increases beyond a given point. See also laminar flow.
two-stage pump A pump that consists of two separate pump assemblies that are contained in one housing.
typical mobile circuits Hydraulic-lift, power-steering, and road-patrol-truck circuits.
USAES United States Army Engineer School
USASI United States of American Standards Institute
vane-type pump A pump in which a slotted rotor splined to a drive shaft rotates between closely fitted side plates that are inside of an elliptical- or circular-shaped ring; vane pumps can be couble, unbalanced, or balanced.
variable-displacement pump A pump in which the pumping-chamber sizes can be changed; the GPM delivery can be changed by moving the displacement control, changing the drive speed, or doing both. See also displacement; fixed-
velocity The average speed of a fluid's particles past a given point, measured in fps. See also flow; flow rate.
velocity pressure Pressure caused by kinetic energy. See also kinetic energy.
volumetric output The amount of liquid a pump can deliver at its outlet port per unit of time at a given drive speed, usually expressed in GPM or cubic inches per minute. Also called delivery rate or capacity.
work The measure of force multiplied by distance.