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    Hydraulics Glossary – C

    A circular component of a hydraulic piston pump that is mounted off-centre and moves pistons when rotated.

    A hydraulic cylinder end closure that completely covers the bore area.

    The hydraulic cylinder end enclosure that covers the differential area between the bore area and the piston rod area.

    The replaceable element of a fluid filter. The pumping unit from a vane pump, composed of rotor, ring, vanes and one or both side plates.

    A valve that is inserted into a standard size cavity in a manifold block and is held in place with either self-contained screw threads or a cover secured with bolts. May be slip-in or screw-in types. Perform directional, pressure or flow control functions.

    The line or passage from the internal cavity of a pump or other component that will carry fluid leakage from the device to a low pressure reservoir or tank.

    A gaseous condition that occurs in hydraulic pumps when existing space is not filled by available fluid and the pressure is reduced to the vapour pressure. Cavitation will deteriorate the hydraulic oil and cause erosion of the inlet metal.

    A force directed outward and away from the centre of a rotating object.

    A certificate or document usually signed and dated

    A compartment within a hydraulic component / unit. May contain elements to aid in the operation or control of a unit, e.g. spring or drain chamber.

    Also known as “supercharge”. The process of replenishing a hydraulic system above atmospheric pressure or filling an accumulator with fluid under pressure. See also PRE-CHARGE PRESSURE.

    The pressure at which replenishing fluid is forced into the hydraulic system (above atmospheric pressure).

    A system of valves and passages allowing the addition or deletion of gas to the gas chamber of an accumulator without discharging any existing gas.

    A hydraulic control valve that allows fluid to flow in one direction, yet prevents back-flow in the opposite direction.

    A combination of components, devices and passages that form a working set of logic for a particular application.

    A hydraulic circuit in which return fluid is directed to the reservoir.

    Used to control a main circuit or component.

    Used to increase hydraulic cylinder speed by directing rod end discharge to the piston side of the hydraulic cylinder. Can be incorporated into directional control valve as fourth position.

    A “U” shaped mounting device that contains a common pin hole at right angle or normal to the axis of symmetry through each extension.

    A hydraulic system in which the hydraulic pump continually operates against a load, even in the neutral condition. A circuit in which flow through the system is blocked in neutral and pressure at the pump outlet is maintained at the maximum pressure control setting.

    This type of hydraulic valve is used in a hydraulic system where the hydraulic valve blocks the flow of hydraulic oil from the hydraulic pump into an accumulator. The accumulator is used to store the hydraulic oil under pressure. This hydraulic valve takes the pressure off the hydraulic pump and in neutral locks the hydraulic cylinder in place with no load on the hydraulic pump.

    A piping arrangement in which the hydraulic pump output, after passing through other hydraulic components, returns directly to the pump inlet.

    In a control system, a type of control that has an input signal and a feedback of the result of the input signal which is used to modulate the input signal automatically. See also OPEN LOOP.

    A relative measure of the surface lubricity, or reduction in friction of a lubricant.

    The portion of a fitting compressed by swaging or crimping to seal the hose onto the fitting to create a permanent attachment. Also known as a ferrule.

    A liquid having flash point at or above +100 degrees F (37.8 degrees C)

    An external signal to which the servo must respond. 

    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.

    Other nomenclature hydraulic “coupling”, “quick-action coupling”. The two separate quick-action coupling halves connected together.

    A single hydraulic or electrical unit.

    A visual indicator of pressure that is set for `zero’ psi at atmospheric pressure and includes a dial which will continue to indicate the level of pressure above or below atmospheric pressure.

    The change in volume of a unit of volume of a hydraulic fluid when subjected to a unit change of pressure.

    The name used to describe the change in pressure in a hydraulic system from low pressure to an elevated pressure. The change in pressure is usually made in a controlled amount of time to cause an even application of energy into the system. See also DECOMPRESSION.

    The exposure of a device or specimen under specified conditions, e.g. temperature, humidity for a specified period of time before testing.

    The ability to transfer to electrical potential.

    The hydraulic components such as pipes, tubes, and hoses that convey liquids throughout a hydraulic system.

    Ability to connect coupling halves with internal pressure applied to either or both coupling halves.

    A mechanical device used to attach two pieces of tubing together or to attach a piece of tubing to a connector.

    Any material or substance which is unwanted or adversely affects the fluid power system or hydraulic components, or both. Contaminants may be solid particles, liquids or gases.

    Used to harness the power of a hydraulic system. The three basic types of hydraulic control valves are tandem centre, open centre (motoring spool), and closed centre. Both the tandem centre and the closed centre types are available in a three-way or four-way valve. By opening or closing valves, you can control how much or in what direction a hydraulic piston moves. Valves can also control many pistons working with each other at the same time.

    Occurring when a hose is being flexed regularly e.g. in the case of connections to moving components.

    A mechanical device used to transfer heat from a fluid to air or another fluid. Normally constructed of finned tubes with one fluid on the inside and the other fluid or air on the outside of the tubes. See also HEAT EXCHANGER.

    The process by which material degrades by chemical or electrochemical means.

    Additive for protection of wetted metal surfaces from chemical attack by water or other contaminants.

    The ability of a hydraulic fluid to resist rust and deterioration within the hydraulic components of a hydraulic system.

    A valve used to balance the weight of a machine or a “dead load” by creating a a back pressure in the system cylinders that is big enough to hold or “counter” the weight. A counterbalance valve is normally closed and is opened by internal pressure in the counterbalance valve or from a separate source of fluid, that is connected to the opposite end of the balanced cylinder.

    A frequently used alternative to the term “fitting”. A mechanical device used to attach the shaft of an electric motor or other motive power device to a hydraulic pump.

    Other nomenclature “body half”, “coupler”, “socket”.

    Other nomenclature “male tip”, “nipple”, “plug”.

    The pressure at which a pressure operated valve begins to leak fluid.

    A gear-within-gear pump that consists of an inner gear that is separated from the outer gear by a crescent-shaped component that provides both support and a seal.

    A fitting attachment method that uses a number of fingers or dies mounted in a radial configuration. The dies close perpendicular to the hose and fitting axis; compressing the collar, ferrule, or sleeve around the hose.

    A cushion built into the hydraulic cylinder to restrict flow at the outlet port thereby stopping motion of the piston rod through a smooth deceleration and stop of the cylinder at the end of the stroke.

    The directed flow of electrical charges from one point to another around a closed electrical circuit. Current is measures in units called amperes or amps.

    A device which provides controlled resistance to motion.

    A single, complete operation consisting of progressive phases starting and ending at the neutral position.

    Movement from normal to extreme position and return.

    A hydraulic actuator constructed of a plunger or piston inside a cylindrical housing. The piston or plunger operates because of pressurized liquid and converts fluid power into linear mechanical force and motion.

    A hydraulic cylinder equipped with adjustable stops at one end to limit piston travel.

    A hydraulic cylinder end closure which completely covers the bore area.

    Volume required for one full extension of the hydraulic cylinder.

    Volume required by one full retraction of the hydraulic cylinder. (Generally, less than extending)

    A mechanical or hydraulic device, adjustable, for limiting hydraulic cylinder stroke.

    A hydraulic cylinder which can apply force and motion to the moveable element in either direction. See also under DOUBLE-ACTING CYLINDER.

    A hydraulic cylinder in which the relative rotation of the cylinder housing and the piston and piston rod, plunger, or ram, is fixed.

    A hydraulic cylinder design which permits the use of two or more hydrulic cylinders in series, automatically synchronizing hydraulic cylinder position at the end of each stroke.

    A hydraulic cylinder which can apply force to the moveable element in only one direction.

    Two or more hydraulic cylinders with interconnected piston assemblies.

    A hydraulic cylinder with one closed end and a telescoping movable shaft at the other end. When fluid flow is applied to a port in the closed end, the telescoping shaft extends until all collars or pistons reach their limit. When fluid is applied to the shaft end port, the shaft will retract into the chamber until all the pistons or collars reach their closed end limits. The cylinder will produce an output force at the shaft end in proportion to its internal area multiplied times the pressure potential of the fluid power system.

    When fluid flow is applied to a port in the closed end, the telescoping shaft extends until all collars or pistons reach their limit. When an external weight is applied to the shaft end, the shaft will retract into the chamber until all the pistons or collars reach their closed end limits. The cylinder will produce an output force at the shaft end in proportion to its internal closed end area multiplied times the pressure potential of the fluid power system. 

    The push of a hydraulic cylinder in pounds: Thrust = Piston Area (in.) x Pump Pressure (PSI) or Thrust = bore diameter squared x .78 x PSI