Hydraulics Jargon Buster: D

DEAD TIME: A real, definite delay between two related actions, measured in units of  time.

DEAD-WEIGHT ACCUMULATOR: A hydraulic component used to store hydraulic fluid. The dead-weight accumulator increases and relieves pressure through the use of a weighted vertical piston. See hydraulic accumulators.

DEBURR: The removal of ragged edges from the inside diameter of a fitting or hose end. An essential task to ensure a good seal.

DECOMPRESSION: The change in pressure in a hydraulic system from elevated pressure to a lower pressure. Such a change in pressure is normally made in a controlled amount of time to cause an even release of energy in the system.

DELIVERY: the volume of fluid discharged by a pump in a given time, usually expressed in gallons per minute (gpm).

DEMULSIBILITY: Ability of an oil to separate from water. The resistance of a hydraulic fluid to emulsification, or how well a hydraulic fluid resists mixing with water.

DETENT: A spring device which maintains the spool of a hydraulic directional control valve in position.

DETENT RELEASE: A mechanical, hydraulic or electrical device for releasing the detent.

DE-VENT: To close the vent connection of a pressure control valve, allowing the valve to operate at its adjusted pressure setting.

DE-WAXING: Removal of paraffin wax from lubricating oils to improve low temperature properties.

DIFFERENTIAL CYLINDER: Any hydraulic cylinder in which the two opposed pistons are not equal.

DIFFERENTIAL PRESSURE: The value of pressure measured as the absolute difference between the inlet pressure and outlet pressure.

DIRECT CURRENT: A steady level of electrical current that only flows in one direction in a circuit.

DIRECTIONAL VALVE: A hydraulic valve whose main function is to prevent or direct flow through particular channels.

DIRT CAPACITY: The volume or weight of particles that a strainer or filter will hold at the limit of its operation.

DIRT TOLERANCE: An indication of the internal clearance of a hydraulic pump. Hydraulic pumps with high dirt tolerance have the most clearance, are the least efficient, and allow the most backflow. Hydraulic pumps with low dirt tolerance have the least amount of clearance, are the most efficient, and allow little to no back-flow.

DISPLACEMENT: The amount of liquid transferred from the inlet of the hydraulic pump to the outlet in a single revolution. Displacement can be fixed or variable.

DOG-LEG ASSEMBLY: Two hose assemblies joined by a common elbow.

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

DOUBLE-ACTING SLEEVE: Other nomenclature “two-way sleeve”. Allows one hand push-to-connect or pull-to-disconnect convenience when the quick-action coupling female half is clamp or bulkhead mounted and connected to a hose.

DOWNSTREAM: The passage beyond a device, normally at the outlet of direction of flow.

DRAIN: A passage in, or line from, a hydraulic component which returns leaked fluid to the reservoir or a vented manifold.    

DRIFT: The amount of movement of a device after a pre-set condition has been applied. Normally drift is measured with varying temperature, although drift may also be plotted against any variable, such as humidity, etc.

DRIVE GEAR: The gear in a hydraulic gear pump that is attached to the driving mechanism. The drive gear turns the driven gear.

DRIVEN GEAR: The gear in a hydraulic gear pump that is rotated by the drive gear.

DRIVING MECHANISM: A component of a hydraulic gear pump that rotates the driving gear.

DUROMETER HARDNESS: A measure of elastomer hardness by use of a durometer.

DUST CAP: A removable device that protects the male tip half when disconnected from the female coupling half. Excludes contamination.

DUST PLUG: A removable device that protects the female body half when disconnected from the male tip half. Excludes contamination.

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