actual torque

The rotational force a motor generates. Actual torque ratings are measured for multiple pressure drops across a motor.

actuator

An active fluid system component that converts fluid power into linear or rotary motion to produce useful work. Actuators are at the end of a fluid circuit.

area

The amount of two-dimensional space in an object. Area is also used to measure the outermost surface of an object.

axial loads

Force applied parallel to the axis of the output shaft. Heavy axial loads can be accommodated by using heavy-duty bearings.

balanced vane motors

A hydraulic or pneumatic motor that contains a series of flat protrusions within a slotted rotor. A balanced vane motor produces torque when fluid pressure acts on the vanes and causes continuous rotation.

bearings

A device that minimizes friction between moving parts. Bearings allow for linear or rotational movement, and may also prevent movement by controlling forces that act on moving parts.

bent axis piston motor

A hydraulic or pneumatic motor that has pistons arranged in a circle within a cylinder block that is parallel to the driveshaft centerline. A bent axis piston motor has pistons that reciprocate against the output shaft flange.

blind end

A closure on one end of a cylinder actuator that covers the bore area to protect interior elements from damage. The blind end, or cap end, of a cylinder is opposite the rod end.

boom lifts

The lifting arm of a crane or derrick with an attached bucket. Boom lifts often use rotary actuators.

bore

The interior diameter of a cylindrical object. The bore of a cylinder actuator contains the movable elements within the cylinder barrel.

breakaway torque

The rotational force needed to initially move a stationary load. Breakaway torque is always higher than running torque.

cap end

A closure on one end of a cylinder actuator that covers the bore area to protect interior elements from damage. The cap end, or blind end, of a cylinder is opposite the rod end.

centerline lug

A type of fixed centerline mount that uses strong rectangular tabs to hold a cylinder in place. A centerline lug mount is best for cylinders used in lower pressure applications.

clevis

A type of pivot mount that allows a cylinder to travel in a fixed arc during extension and retraction. A clevis mount attaches to the cap end of a cylinder.

cushions

An impact-absorbing assembly containing a plunger, adjustable orifice, and a control valve on either end or both ends of a double-acting cylinder. Cushions decelerate the piston rod near the end of its stroke.

cylinder actuator

An actuator that directs force in a straight line. Cylinder actuators include a movable piston and rod that reciprocate in response to fluid pressure.

cylinder block

A solid unit that houses reciprocating pistons. The cylinder block in a piston motor rotates as the pistons reciprocate.

diameters

The distance from one edge of a circle to the opposite edge that passes through the center. The diameters of the piston and rod in a cylinder actuator affect its force output.

direct drive gerotor

A type of internal gear motor with an inner gear that drives the outer gear. A direct drive gerotor motor generates torque when there is a pressure drop across a gear tooth.

double rack and pinion actuator

A rack and pinion actuator that receives fluid pressure from two directions. A double rack and pinion actuator has one pinion and two racks.

double-acting cylinder

A linear actuator that exerts force in two directions as the piston and rod reciprocate. Double-acting cylinders use fluid pressure to extend and retract the piston.

double-vane actuator

A rotary actuator that produces rotary force in either direction when fluid pressure acts on two blades in a rotor. A double-vane actuator produces twice the torque of a single-vane actuator but occupies the same amount of space.

dynamic seals

A seal used between two connected components in a fluid system that move relative to one another during operation. Dynamic seals control leakage and prevent contamination from entering.

eccentric

Off center. The eccentric rotor in a radial piston motor rotates as the pistons reciprocate.

eccentricity

When two circular objects do not share a common center. Eccentricity in a direct drive gerotor motor results in pressure drops between the gear teeth.

effective piston area

The surface of the piston at the cap end or rod end of a cylinder actuator. The effective piston area depends on whether the cylinder exerts force during extension or retraction.

external gear motors

A fixed-displacement motor with a matching gear set. An external gear motor generates torque when fluid pressure pushing against a gear tooth results in a pressure drop.

fixed centerline mount

A mounting style that supports a stationary cylinder along its centerline. Fixed centerline mounts minimize side loading.

fixed displacement motor

A hydraulic or pneumatic motor that displaces a specific amount of fluid per cycle. A fixed displacement motor provides a constant speed when it receives a constant flow rate.

fixed side mount

A fixed cylinder mount that absorbs forces eccentric to a cylinder's centerline. Fixed side mounts attach on one side or edge of the cap and rod end.

flow rate

The total volume of fluid that moves through a fluid system or individual component in a given amount of time. Flow rate is measured in gallons per minute (gpm) or liters per minute (lpm).

fluid displacement

The volume of fluid a motor requires for one complete rotation of its output shaft. Fluid displacement, also known as motor displacement, is measured in cubic inches or cubic centimeters.

fluid power

Power produced by the flow of pressurized fluid. Fluid power is converted to mechanical power in a fluid system.

gear motors

A type of motor consisting of an idler gear and a drive gear connected to an output shaft. Gear motors have a fixed displacement and can rotate continuously.

gearboxes

An enclosed system of gears that transmits mechanical energy from a prime mover to an output device. A gearbox can also change the speed, direction, or torque of mechanical energy in a motor.

gerotor motors

A motor consisting of an internal gear that engages with one or more external gears. A gerotor motor, or internal gear motor, generates torque when fluid pressure acts on the surface area of the gears to cause rotation.

head end

The portion of a cylinder actuator containing the piston and piston rod that extends out of the barrel. The head end, or rod end, of a cylinder is opposite the cap end.

high-speed, low-torque

HSLT. A motor that operates at a constant speed and has a low torque output. High-speed, low-torque motors are often used with gearboxes to reduce starting speed and increase torque output.

HSLT

High-speed, low-torque. A motor that operates at a constant speed and has a low torque output. HSLT motors are often used with gearboxes to reduce starting speed and increase torque output.

hydraulic systems

A fluid power system that uses oil or another liquid under pressure to produce mechanical power. Hydraulic systems have a hydraulic pump as a power source.

idler gear

The driven gear in a gear motor. The idler gear in a gear motor maintains contact with the gear attached to the output shaft.

inlet port

The opening on the side of a component through which pressurized fluid enters. The inlet port on some rotary actuators can be switched with the outlet port to provide reverse rotation.

in-line piston motor

A hydraulic or pneumatic motor with an axial arrangement of pistons within a cylinder block that is parallel to the output shaft centerline. An in-line piston motor has pistons that reciprocate against an angled swashplate.

internal gear motors

A hydraulic motor consisting of an internal gear that engages with one or more external gears. An internal gear motor, or gerotor motor, generates torque when fluid pressure acts on the surface area of the gears to cause rotation.

kilopascals

kPa. An SI unit used to measure pressure. Kilopascal units may be used to express pressure ratings for a fluid system or fluid system component.

linear actuator

A fluid power actuator that directs force in a straight line. Linear actuators include double- and single-acting cylinders.

linear loading

Force concentric to an object's centerline. Linear loading is ideal for a cylinder actuator.

load

The force applied to an object or structure. The load in a fluid system must be able to be moved by the actuator.

low-speed, high-torque

LSHT. A motor that operates at low speed rates and consistently high torque. Low-speed, high-torque motors generally have large displacements.

LSHT

Low-speed, high-torque. A motor that operates at low speed rates and consistently high torque. LSHT motors generally have large displacements.

mechanical efficiency

The actual torque delivered to a motor compared to the motor's theoretical torque. Mechanical efficiency is expressed as a percentage.

motor displacement

The volume of fluid a motor requires for one complete rotation of its drive shaft. Motor displacement, also known as fluid displacement, is measured in cubic inches or cubic centimeters.

mounts

The way in which a cylinder actuator is attached to a fluid system component. Mounting hardware for a cylinder is manufactured separately from the cylinder.

National Fluid Power Association

NFPA. An organization consisting of manufacturers, distributors, customers, vendors, and educators who work together to administer and maintain fluid power industry standards. The National Fluid Power Association works to advance fluid power technology.

newton-meters

Nm. The metric unit used to measure torque. The newton-meter's English equivalent is the pound-foot.

orbiting gerotor

A type of internal gear motor with an inner gear containing one less tooth than the outer idler gear. An orbiting gerotor motor has concentric gears.

outlet port

The opening on a side of a component through which pressurized fluid exits. The outlet port on some rotary actuators can be adjusted to allow for reverse rotation.

output shaft

A shaft that rotates to transmit torque. An output shaft is mechanically linked to a motor or actuator.

pinion

A circular gear with a small number of teeth designed to mesh with a linear rack. A pinion gear rotates along a linear rack to produce torque in a rack and pinion actuator.

pintle

A cylindrical bar that serves as a stationary valve for a radial piston motor. A pintle directs fluid in and out of pistons.

piston

A cylindrical part connected to a rod within a cylinder actuator. A piston transmits or receives motion when fluid pressure acts on the connected rod.

piston rod

The movable part of a cylinder actuator that is attached to the piston. The piston rod reciprocates to exert force.

pivot mounts

A cylinder mounting style that absorbs forces along the cylinder centerline and allows the cylinder to move in an arc. A pivot mount allows a cylinder to achieve continuous rotation.

pneumatic systems

A fluid power system that uses pressurized air to produce mechanical power. A pneumatic system has a pneumatic compressor as a power source.

port

An opening on a valve or cylinder through which fluid can flow. A port allows fluid to enter or exit a device.

pound-feet

lb.-ft. The English unit used to measure torque. The pound-foot metric equivalent is newton-meters.

pounds per square inch

psi. An English unit used to measure the amount of pressure exerted per square inch. Pounds per square inch units may be used to express pressure ratings for a fluid system or fluid system component.

power source

A device that generates the energy needed to power a tool or system. The power source in a hydraulic system is a hydraulic pump, while the power source in a pneumatic system is a pneumatic compressor.

pressure drop

The difference in pressure measurements between any two points of a system or a component. A pressure drop occurs when force acts on a fluid as it flows through a hydraulic system component.

pressure rating

The range of pressure a cylinder actuator can withstand during normal operation. Pressure ratings are considered when selecting a cylinder actuator for a fluid system application.

preventive maintenance

Regularly scheduled service and upkeep performed while a machine is still in working order. Preventive maintenance can prolong equipment life and increase production.

prime mover

The component in a fluid power system that provides mechanical energy for the power source. Prime movers for fluid power systems include electric motors and internal combustion engines.

rack

A flat bar with teeth that is designed to mesh with a round pinion gear. A rack in a rack and pinion actuator moves linearly while the pinion rotates.

rack and pinion actuators

A rotary actuator with a round pinion gear that rotates against a linear toothed rack. A rack and pinion actuator can rotate up to 360 degrees in either direction.

radial

Having parts arranged in straight lines coming from the center of a circle. A radial arrangement of components is used in vane motors and some piston motors.

radial loads

Force applied perpendicular to an object's axis of rotation. Radial loads on a cylinder actuator can result in premature wear.

radial piston motor

A type of hydraulic or pneumatic motor with a radial arrangement of pistons within a cylinder block. In a radial piston motor, the pistons are perpendicular to the output shaft centerline.

reciprocates

To move back and forth repeatedly. The reciprocating movement of a piston rod in a cylinder actuator produces linear motion or force.

reservoir

The main storage container for fluid in a hydraulic system. The reservoir supplies fluid to the pump.

rod end

The portion of a cylinder actuator containing the piston and piston rod that extends out of the barrel. The rod end, or head end, of a cylinder is opposite the cap end.

rotary actuator

An actuator in a fluid system that directs force in a circular motion. Rotary actuators contain movable components that rotate when fluid pressure acts on them.

rotor

A rotating part of an electrical or mechanical device. A rotor is the driven component of most rotary actuators.

running torque

A rating that may refer to a load or a motor. Running torque is a percentage of a motor's theoretical torque.

side loading

Force eccentric to an object's centerline. Side loading on a cylinder causes increased stress on the bearings and seals and may eventually bend the piston rod.

single-acting cylinder

A linear actuator that exerts force in one direction as the piston rod extends or retracts. Single-acting cylinders use an external force to return the piston to its unactuated position.

single-vane actuator

A rotary actuator that produces rotary mechanical force when fluid pressure acts on blades in a rotor. A single-vane actuator can rotate up to 280° in either direction.

starting torque

A motor rating that indicates the maximum amount of torque a motor can generate from a standstill. More starting torque is required than running torque.

stroke

The length of travel of a piston when it moves in or out of a cylinder. Stroke length is adjustable in some fluid system devices.

swashplate

A flat, angled component of an in-line piston motor that maintains contact with the piston shoes to cause the pistons to reciprocate. The swashplate angle determines the in-line piston motor's displacement.

tapered roller bearings

A type of roller bearing featuring tapered inner and outer ring raceways and rollers. The tapered roller bearing can withstand high radial and thrust loads.

theoretical force

The rated push or pull an object exerts. Theoretical force of a cylinder actuator depends on the effective piston area and the supplied fluid pressure.

theoretical torque

A motor rating that indicates the total amount of torque available at the motor output shaft. Theoretical torque figures are based on zero mechanical losses.

tie rod extended

A type of fixed centerline cylinder mount that uses metal or steel rods to attach a cylinder to a machine. A tie rod extended mount attaches at the cap or rod end of a cylinder.

torque

A twisting or turning force that produces rotation. Torque is produced in a rotary actuator because of the pressure drop across the motor.

trunnion

A type of pivot cylinder mount that attaches to the cap end, rod end, or intermediate points along a cylinder. A trunnion mount allows the cylinder to travel in an arc during extension or retraction.

valve plate

A thin disc that covers the ports on a component. A valve plate directs fluid in and out of a component.

vane actuators

A rotary actuator that consists of one or more blades in a rotor. A vane actuator may rotate up to 360 degrees.

vanes

A mechanism positioned radially from the center of a rotor in a vane actuator. Vanes rotate when fluid pressure acts on them.

variable displacement motor

A hydraulic or pneumatic motor that displaces an adjustable amount of fluid per each rotating or reciprocating cycle of the motor. A variable displacement motor has adjustable speed and torque.

vent

An air breather cap. A vent in a cylinder actuator exhausts fluid to the outside air or drains it to the reservoir.

flange

A type of fixed centerline mount that attaches to the cap or rod end of a cylinder. A flange mount's location depends on the cylinder's primary direction of force.

flange

A type of fixed centerline mount that attaches to the cap or rod end of a cylinder. A flange mount's location depends on the cylinder's primary direction of force.