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Actuator – A mechanical device powered by electricity, air, or hydraulic fluid that is used for operating a control component such as a valve.

Actuator, Rack and Pinion – An actuator that uses a linear (rack) and circular (pinion) gear for transmitting force from a pair of pneumatically or hydraulically powered pistons to control a valve.

Accumulator, Bladder – A cylindrical pressure vessel that is used to store hydraulic fluid for future release of potential energy by a compressible gas in the bladder.

Accumulator, Piston – A cylindrical pressure vessel that is used to store hydraulic fluid at one end for future release of potential energy by a compressible gas on the other end of the piston.


Back Pressure – The level of pressure on the return or downstream side of a device or system.

Bladder – An elastic diaphragm used for separating fluids.

BOP (Blowout Preventer) – Equipment installed on the wellhead or wellhead assemblies to contain wellbore fluids either in the annular space between the casing and tubulars, or in an open hole during well drilling, completion, and testing operations.

Bypass – A secondary passage for fluid flow.


Cavitation – The formation and collapse of gaseous bubbles as a result of high vacuum on rotational equipment, such as a pump vane.

Check Valve – A valve that controls fluid flow in one direction but prevents flow in the opposite direction. Also known as a retention or reflux valve.

Conventional Oil and Gas – A petroleum resource that is extracted using standard methods to economically remove fuel from an oil well.

Control Panel

Cracking Pressure – The amount of pressure at which a pressure operated valve (i.e. relief valve) begins to allow a small flow rate of fluid to pass.

Cv – Valve sizing flow coefficient that is determined experimentally for each size and style of a valve with water at standard operating conditions. Thus, a valve’s Cv can be expressed as the number of gallons of water per minute (GPM) at 60°F that can flow through the valve in one minute with a difference in pressure across the valve as one pound per square inch (psi). Cv is directly proportional to the valve’s flow rate (Q) and specific gravity (SG) of the fluid but inversely proportional to the pressure drop (DP), which can further be expressed by the following equation:


Deadband – A numeric range in pressure regulators that is specified by the difference between the set pressure and the outlet pressure that triggers the regulator to open and reset itself to maintain system pressure.

Detent – A mechanical stop or catch in a device (e.g. valve) that prevents motion until an external force is applied.

Directional Control Valve – A valve that is used in hydraulic and pneumatic systems for allowing fluid flow into various paths from one or more sources.


Exhaust Line – A passage that is open to atmosphere to allow venting of pressurized fluid from a device or system.


Flow Plate – A static component in a Pressure Regulator that is used in conjunction with (linearly traveling) Seal Rings to direct and seal high pressure fluid for regulating downstream hydraulic pressure.

Flow Rate, Volume – The velocity of a fluid through a flow area expressed in units of gallons per minute in the US. This value is directly proportional to the pressure differential across an orifice (or valve opening) and flow coefficient (Cv) but inversely proportional to the specific gravity of the fluid.

Fluid Power Control – The term used to describe a means of controlling the energy of pressurized fluid.

Four Way Valve – A valve that has four ports for pressure (inlet), return (tank/reservoir), and two working (e.g. hydraulic cylinder) ports. Typically used for changing the direction of a cylinder or other output device.


Gasket – A synthetic or rubber flap used for sealing a gap between two surfaces.


Heat Treated – A process that is used for increasing the hardness of metals.

Hydraulic Circuit – A network or system of interconnected components and piping for controlling the direction and pressure of high-pressure fluid.

Hysteresis – The delay between the input and output in a system upon a change in direction. Regarding pressure regulators, it is the difference between the original set pressure before full flow and the pressure that it resets to when flow is shut off.




Koomey Unit – Industry specific terminology for a legacy hydraulic power unit with a control valve manifold assembly for the purpose of operating a BOP stack.


Linear Actuator – An actuator (see Actuator) that transfers power linearly as a means of operating a control device (e.g. valve).


Manifold – A hollow block with porting machined throughout the length to interconnect various control components for the advantage of reducing the footprint, materials, and leak points.

Manual Override – A means of manually actuating a device that is primarily remotely operated.



Offshore Drilling and Production – A means of drilling and producing oil and gas away from land, over the ocean.

Onshore Drilling and Production – A means of drilling and producing oil and gas on land.


Pilot Operation – A means of remotely operating a device using hydraulic or pneumatic pressure.

Pipe Nipple – A short externally threaded pipe used for connecting two internally threaded components.

Precharge Pressure – The pressure of compressed gas in an accumulator before the fluid is released to the system.

Pressure Regulator – A pressure operated valve that can reduce and regulate a hydraulic system’s pressure to a value that was set by the user. A complex device that uses spring energy acting on a piston to control the inlet pressure inside the cavity or body of the regulator, which is then outputted to the circuit.



Receiver Gauge – A measuring device that displays the indication of changes in a parameter (e.g. pressure, flow, etc.).

Relief Valve – A pressure operated valve that is used for exhausting high-pressure fluid when it has reached its maximum pressure that was set by the manufacturer. This valve does not regulate pressure but rather is used to limit a hydraulic system’s pressure.

Rotor – A rotating component that works in conjunction with seal rings in a valve to direct high-pressure fluid between various ports, as operated by the user.

ROV – Remotely Operated Vehicle that is used in subsea applications for intervening with equipment in water depths unattainable by a diver.


SAE ORB (O-ring Boss) – A means of connecting a hydraulic hose or pipe to a control component with an O-ring at the base of the straight external threads and a groove or boss at the fore face of the straight internal threads, thus producing leak control in medium to high pressure applications with less effort in comparison to tapered threads.

Seal Ring – A ShearFlo sealing component that is used for sealing high pressure fluid and directing flow through a port.

Shuttle Valve – A valve with three ports and a central ball or spool check valve that is used for connecting two intermittent sources to one outlet.

Splash Zone – The area on a marine vessel or structure that is subject to saltwater exposure by spray or temporary emersion.


Three Way Valve – A valve that has three ports for pressure (inlet), one open and one closed port. Typically used for blocking or opening a common flow passage.

Topside – The above waterline deck area of an offshore oil rig.

Transmitter – An analog device that produces a signal level (e.g. gauge) during state changes (e.g. convert hydraulic pressure to a proportional air pressure reading).

Two Way Valve – A valve that has two ports for pressure (inlet) and an outlet. Typically used for opening or closing a flow passage.


Unconventional Oil and Gas – A petroleum resource that is extracted using more complex and sophisticated methods to economically remove fuel from non-traditional reserves, such as oil shale and oil sands.


Vent Port – The port that allows excess pressure to exhaust to ambient pressure or the tank/reservoir.


Water Glycol – A hydraulic fluid alternative (to mineral oil) that is composed of 35-60% water to provide fire resistance, combined with a glycol antifreeze (e.g. ethylene, diethylene, or propylene) that is nontoxic and biodegradable plus a thickener (e.g. polyglycol) to provide lubricity. Although it is becoming the standard hydraulic fluid in some countries and industries, it does need to warrant concern due to its relatively low lubricity which can cause galling and other damage to hydraulic equipment.





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