Glossary: Hydraulic Terminology Explained & Simplified
For those individuals who have little or no prior experience with the world of hydraulics, it can be very easy to become confused by the specialised vocabulary commonly used in this industry. To aid our clients in familiarising themselves with the terminology they will frequently encounter, we have assembled the following list of definitions. This is not a comprehensive list of hydraulic terminology, and for purposes of simplicity we have avoided explaining matters in detail.
AC – Stands for Alternating Current, a constantly changing current generated by a power source. Contrasted with Direct Current (DC).
Accumulator - A pressurised container used to store energy in hydraulic circuits or provide damping of actuator movement in hydraulic circutirs.
Aeration – The phenomenon of air becoming trapped in fluid, often causing hydraulic components to function erratically.
Attenuator – A device that reduces voltage or current.
Back pressure – The pressure required to overcome circuit resistance.
Baffle –Found in a fluid reservoir to reduce movement of fluid and encourage settlement of contaminants.
Bar - Metric pressure measurement equal to 1000 Pascals / 0.1 Megapascal or in imperial measurements 14.5psi an approximately one atmosphere / normal atmospheric pressure.
Bleed – The process of removing air from a hydraulic system.
Blister – In vulcanised (see below) material, a raised air-filled portion.
Breakout Pressure – The minimum amount of pressure needed to get an actuator moving.
Breather – Also known as a Vent, allows air to move in or out of a reservoir as the oil level changes within the reservoir, preventing unwanted pressurization or vacuum within vessels
By-Pass – A passage intended to provide alternative passage for the flow of fluids.
Cartridge – In the case of a filter the part that can be replaced when it is blocked or failing to function to its design specification. In the case of cartridge valves these are used to perform various functions
Check Valve – A type of valve that permits the flow of fluid in only one direction.
Chemical Resistance – The ability of a material to avoid sustaining alterations when exposed to certain chemicals.
Circuit – Interconnected components arranged to perform a specific function. A circuit is generally a part of a larger system.
Connector – A device that joins two sections of tubing, or joins a section of tubing to a specific component.
CPE – Stands for chlorinated polyethylene, a substance that has high impact- and weather-resistance.
Cracking Pressure – The amount of pressure needed to open a valve.
Cylinder – Also called an actuator, this is a device that in a hydraulic system converts the energy created by the activity of fluid into mechanical movement. Cylinders generally contain a piston (or similar device) whose motion provides the mechanical force required. There are a number of different kinds of cylinders: single-acting, double-acting, double-rod, rotary, vane-type, and others.
Date Code – Printed information on a product that expresses its time of manufacture. May take the form of letters, numbers, symbols, or anything else that the manufacturer finds proper.
Deburr – The process of removing rough edges.
DC – Stands for Direct Current, a steady current generated by a power source. Contrasted with Alternating Current (AC).
Directional Valve – This is a valve that either blocks or permits the flow of fluid through a specific channel.
Electro-Hydraulic Valve – A valve operated through the use of a solenoid.
EPDM – This stands for Ethylene Propylene Diene Monomer, a kind of synthetic rubber commonly used in seals operating in steam circuits.
Flow Divider – A device that splits the flow of fluid into two (sometimes more) separate streams.
Gasket – A type of seal, of no particular shape, size or material fitted between two faces.
Heat Energy – Energy generated by friction or flow resistance. One of the three types of energy found in a hydraulic system.
Horsepower – Imperial energy measurement that describes a system's normal power level, abbreviated to Hp (1.341Hp = 1kw)
Hydraulics – An engineering discipline that relates to the use of fluids in power transmission.
Hz – This stands for Hertz, which refers to the frequency of AC current (he number of cycles per second).
Inert Gas – A gas that will not explode when in contact with any other gases or substances. Nitrogen is one common type of inert gas.
Kilowatt - – Metric energy measurement that describes a system's normal power level, abbreviated to kW..
Kinetic Energy –Kinetic energy is defined as the energy a mass possesses due to its motion. In hydraulics kinetic energy is defined as the energy possessed by the moving oil measured by the energy consumed by an actuator. .
Lag – A delay in an expected response in a system.
Line – Any hose, pipe, or tube used to convey fluid through a hydraulic system.
Linear Actuator – This is a device that turns hydraulic (fluid) energy into a linear movement.
Lubricator – A device that inserts oil into an air line or grease or other lubricant into components that require lubrication to operate and prevent wear.
Micron – Frequently used to measure the size of particles present in fluid, a micron is 1/1000th of a millimeter or one-millionth of a meter. The micron rating of a filter refers to the average minimum size of the particles that it is capable of removing from a system.
Needle Valve – This is a valve that uses a tapered point to enable very precise control of fluid flow.
Operating Pressure – This is the typical pressure level of a hydraulic circuit. Sometimes called system pressure. Measured in bar (metric) or psi (imperial).
Pascal - Metric unit of pressure equal to 1 Newton / square metre
Pilot Valve – This is a valve that controls another valve (which is therefore often called a pilot-controlled valve).
Piston – The moveable part that fits inside a cylinder.
Potential Energy – There are two types of potential energy a hydraulic system may possess. The first is gravitational potential energy and this is defined as the potential energy that can be released if the mass was to travel from its elevated height to a lower height. This will occur in hydraulics if the reservoir is higher that the component it is feeding.
The second is pressure potential energy and this can be defined as the potential energy that exists over a pressure differential. This energy can be released by allowing the higher pressure to decrease across the differential. In hydraulics this can be seen when pressure is built behind a component such as a ram or actuator and is then released to generate work. Accumulators work on this principle as they store pressure in order to release it when needed.
Pour Point – The temperature at which a particular fluid becomes semi solid and cannot flow.
PTFE – This stands for polytetrafluoroethylene, a synthetic fluoropolymer used in a wide variety of applications, including hydraulic systems.
Pump - The device at the core of all hydraulic systems that energises the fluid in a circuit.
Ram - A hydraulic ram is another term used for a hydraulic cylinder - see cylinders above.
Rated Pressure – The amount of pressure recommended by the manufacturer for a specific system or component of a system. Measured in bar (metric) or psi (imperial).
Reciprocation – Repetitive motion.
Rectifier – A device that converts alternating current (AC) into direct current (DC).
Relief Valve – A valve that reduces pressure in a hydraulic system. A thermal relief valve reduces pressure generated by heat expansion.
Reservoir – The part of the system in which fluid can be stored. Sometimes called a sump or a tank.
Return Line – This is the line through which fluid flows back to the reservoir.
Seal - An item made of rubber or some other substance that prevents leakage from a high pressure area to a low pressure one.
Silt – Small debris particles sometimes found in a reservoir.
Solenoid – An electromagnetic coil made into a helix shape, sometimes used with hydraulic equipment to move a spool or other type of electro hydraulic valve.
Static Pressure – The amount of pressure generated by fluid in a resting state.
Strainer – A type of filter used to remove course particles from a hydraulic system normally on the suction side of a pump.
Surge – A temporary increase in system pressure.
Thermal Expansion – The phenomenon where heat causes hydraulic fluid to expand.
Valve – A device in a hydraulic system that regulates fluid by controlling its pressure, its direction, or its flow rate.
Velocity – The speed in which fluid flows through a line (meters per second, m/s or feet per second, ft/s).Alternatively, it is the speed at which a component rotates, expressed in revolutions per minute (rpm).
Vent Valve – A type of valve that allows air in a hydraulic system to be released into the space outside or into a specified chamber.
Viscosity – The measure of fluidity of a liquid.
Vulcanisation – A chemical process that enhances the durability of rubber and similar materials.
Weathering – Damage sustained to the surface of a hose due to contact with outside elements, such as sun rays and rain.
If you have any questions or concerns, we are always willing to field feedback from our clients. Please contact us at your convenience.