Fittings for Fluid Systems 251

adapter

A pipe fitting that extends a run. An adapter joins two pipes of different types.

adjustable straight-thread O-ring fitting

A reusable fitting that is sealed by an O-ring located between the termination of a straight OD thread and a washer and locknut. The adjustable straight-thread O-ring fitting can be tightened and fixed in any orientation.

barbed fitting

A fitting characterized by the presence of angled barbs. A barbed fitting grabs and holds the ID of a hose.

barbs

An angled cylindrical feature on the OD of a fitting that grabs and holds the ID of a hose. Barbs allow hose to be easily mounted over the fitting but are difficult to remove.

bell reducer

A pipe fitting that extends a run by joining two pipes of different diameter. A bell reducer is often called a reducing coupling.

bite-type fitting

A fitting with a sharpened ferrule that grips into the tube when compressed. The bite-type fitting uses the sharpened ferrule to provide the seal.

cap

A pipe fitting that terminates a run by closing an end. A cap has female threads.

clamp

A mechanical device used to compress the flange against the O-ring in a split-flange O-ring fitting. Clamps are used when tightening the bolt.

compressed air

Air that has been squeezed into a small space, such as a tank. Compressed air can be used to move machine parts in a pneumatic system.

compressing

To tighten two components together or against one another. Compressing is the primary force behind many of the fluid power seals.

compression fittings

A type of tube fitting. Compression fittings are sealed by pressure caused by the interaction of threaded portions of the fitting.

conductor

A component that conveys fluid throughout a fluid system. Conductors can include pipe, tube, and hose.

contaminants

Damaging foreign material such as dirt or debris that causes wear to machine components. Contaminants may cause a loss of efficiency or a breakdown in a fluid system.

copper

A reddish metal that is very ductile, thermally and electrically conductive, and corrosive resistant. Copper is a commonly used material in fluid systems.

coupling

A component that connects two shafts in a mechanical system. A coupling transfers motion.

crest

The high point or peak of a thread. A crest is the surface of the thread which joins the flanks of the thread and is farthest from the cylinder or cone from which the thread projects.

crimping

The process of mechanically attaching a permanent fitting to the end of a hose. Crimping involves squeezing the metal fitting until it is bound to the hose.

cross

A pipe fitting that allows fluid to change directions. A cross joins pipe runs to anothers that run perpendicular and through the main run.

cylinder

A type of linear actuator that uses a piston to produce motion in a straight line. A cylinder is also known as a piston actuator.

deform

The forming of a metal into a distorted shape. Deformed metal has permanently lost its original shape.

double shutoff quick disconnect

A type of quick disconnect fitting. Double shutoff quick disconnect fittings feature one valve located in the stud connected to the hose and another valve located inside the fitting component that attaches closest to the air supply.

dry seal

A sealing condition caused by the crest of one thread contacting the root of another thread. Dry seals do not allow fluid to leak from a fluid system.

dynamic seal

A seal that is made between two objects that move relative to one another during operation. Dynamic seals wear faster than static seals.

ell

A pipe fitting that changes the direction of a pipe run. Ells are available in 22.5°, 45°, 60°, and 90° angles and have female threads on both ends.

external leakage

The unintentional movement of fluid from a fluid system into the environment. External leakage can be both dangerous and detrimental to the efficiency of the system.

failure

The faltering of a process or product. Failure can occur when seals are not installed properly.

female threads

A type of thread that appears on the inner diameter of a cylindrical part or round feature. A female thread meets with a male thread to make a seal.

ferrule

The portion of a flareless fitting that provides a seal by being compressed. The ferrule is also known as the sleeve.

fiber braid

Pneumatic tubing with fiber reinforcement that is woven over the tubing of the hose. Fiber braid is ideal for low to medium pressure operations.

field attachable hose fitting

A fitting that is not permanently attached to a hose. Field attachable hose fittings may be used on other hoses when the initial hose fails.

fitting

A component that connects, redirects, extends, or terminates the run of a fluid conductor. A fitting contains the fluid by providing a seal.

flange

A short cylindrical component used to seal and reinforce the connection between a fitting and a conductor. A flange fits around the conductor and is held in place by a clamp.

flank

The side of a thread between the root and crest. The flank surface intersection with an axial plane is theoretically a straight line.

flareless fittings

A fitting that achieves a seal through the compression of mating parts and a ferrule on the unflared end of a tube or hose. Flareless fittings consist of three components that contribute to the seal: the land, seal, and nut.

flareless fittings

A fitting that achieves a seal through the compression of mating parts and a ferrule on the unflared end of a tube or hose. Flare-less fittings resist vibration better than other fittings.

flare-type fittings

A fitting that achieves a seal through the compression of mating parts. Flare-type fittings connect on the flared end of a tube.

fluid engineer

A person who designs, builds, and maintains pneumatic systems. Fluid engineers make sure that components are properly configured during instillation.

fluid system

A power transmission system that uses the force of flowing liquids and gases to transmit power. Fluid systems include hydraulic systems and pneumatic systems.

hose

A type of hydraulic fluid conductor that joins other components usually in a nonlinear fashion. Hose bends and flexes and is the most versatile hydraulic conductor.

hose clamps

A circular clamp that fits around the OD of a hose where it meets the barbed fitting. A hose clamp provides pressure so that the hose does not slip off the barbed fitting.

hose fittings

A type of fitting used to connect a hose to another fluid component. Hose fittings can be either temporarily or permanently attached to a hose.

hydraulic fluid

The medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water.

inner diameter

ID. The size of a conductor, as measured along a line extending from opposite points on the inner surface and through the center of the conductor.

interference

The primary cause of pipe seals. Interference is caused by the interaction of inside diameter and outside diameter threads when tightened together.

internal leakage

The movement of fluid from one component to another within a fluid system. Internal leakage can both be helpful to the system by providing lubrication and detrimental to the system by hampering efficiency.

land

The portion of a flareless fitting into which the end of a tube is placed. The land is secured by the nut.

leakage

The movement of fluid either out of a fluid system or from one fluid component to another. Leakage causes a loss of efficiency and can lead to system failure.

locknut

A component of an adjustable straight-thread O-ring fitting that tightens an O-ring between a washer and the flat surface of a fluid component. Locknuts have their name because they lock down on the part.

lubrication

The act of applying lubricant to machines. Lubrication reduces friction and wear between mechanical components.

lubrication

The application of a substance to reduce friction between two surfaces in relative motion. Common lubricants are oil and grease.

male threads

A type of thread that appears on the outer diameter of a cylindrical part or round feature. A male thread meets with a female thread to make a seal.

metal-to-metal fittings

A fitting that achieves a seal through contact between two metal surfaces. Metal-to-metal fittings come in three types: pipe fittings, flare-type fittings, and flareless fittings.

multiple steel braid

Pneumatic tubing with metal reinforcement that is woven over the tubing of the hose. Multiple steel braid features more than one layer of steel braid reinforcement.

nipple

A small section of pipe of varying length. A nipple is used to connect fluid components.

nonadjustable straight-thread O-ring fitting

A reusable fitting that is sealed by an O-ring located between the termination of a straight OD thread and the wrench flats used to tighten the fitting inside a component. Non-adjustable straight-thread O-ring fittings do not point in any particular direction.

nonpositive seal

A seal that allows a small amount of fluid to pass through inside the fluid system. Leakage from a nonpositive seal can provide lubrication to hydraulic components.

nut

The portion of a flareless fitting that is tightened to provide compression on the ferrule. When the nut is tightened the bite-type fitting holds the tube.

O-ring

A flexible, rubberlike ring that is used to create a mechanical seal. O-rings are usually located in a groove and compressed between two or more fitting components.

O-ring fittings

Any fluid power fitting that uses an O-ring as the primary sealing mechanism. An O-ring is a flexible, rubberlike ring that is used to create a mechanical seal.

outer diameter

OD. The actual size of a conductor, as measured along a line extending from opposites points on the outer surface and through the center of the conductor.

permanent hose fitting

A fitting that is permanently attached to a hose. Permanent hose fittings are not replaceable.

pipe fittings

A type of fitting used to connect, redirect, extend, or terminate a pipe run. Pipe fittings come in a variety of shapes and are often named for the letters they resemble.

piston

A rod inside a cylinder that is moved by hydraulic or pneumatic pressure. Pistons are used at high pressure.

plug

A pipe fitting that terminates a run by closing an end. A plug has male threads.

pneumatic

Power created by the motion and control of gas, often air, under pressure. Pneumatic power is used to transmit motion to mechanical parts.

positive seal

A seal that does not allow any amount of fluid to pass through. A positive seal helps avoid leakage from the fluid system.

pressurized fluid

A fluid at a high pressure. Pressurized fluids perform the work in a fluid system.

preventive maintenance

Maintenance performed while a component is in working order to keep it from breaking down. Preventive maintenance includes lubricating, tightening, and replacing worn parts.

push-lock reusable fitting

A type of reusable fitting. Push-lock reusable fittings are forced onto the end of a hose and locked into place.

quick connect fittings

A fitting that is designed to attach to a line quickly and efficiently. A quick connect fitting is often a one-piece fitting that is forced onto the end of a hose and locked into place.

quick disconnect fittings

A fitting designed for use with components that are moved often and for preventing system air pressure failures. Quick disconnect fittings include single shutoff quick disconnect and straight through quick disconnect fittings.

reducing bushing

A pipe fitting with male and female threads. Reducing bushing extends a run by joining two pipes of different diameter.

reducing coupling

A pipe fitting that extends a run by joining two pipes of different diameter. Reducing coupling is often called a bell reducer.

root

The bottom of a thread valley. The root is the base where two flanks meet on a thread.

rotary seal

A dynamic seal achieved between a stationary cylinder and a rotating piston or shaft located inside the cylinder. A rotary seal minimizes fluid loss and guards against friction.

rotary unions

A fitting component designed to provide a dynamic seal while rotating continuously at high speeds. Rotary unions supply lubrication with oil or air.

rubber

An elastic material made from the latex sap of the rubber tree. A synthetic rubber is used to make O-rings for sealing systems.

run

The path followed by a piping system. A run is terminated by a fitting.

run-to-failure

A maintenance policy that allows a component to operate until it breaks down. When run-to-failure point is reached reactive maintenance may be performed.

seal

An intentional obstruction designed to keep fluids inside a fluid power system. A seal assures the working capability of the fluid system.

shaft

A long cylindrical device such as a rod or pole. A shaft is used to support rotating components or to transmit rotation in a mechanical system.

shock

The jarring impact caused by sudden acceleration, deceleration, or collision. Shock can cause leakage in a fluid system.

single shutoff quick disconnect

A type of quick disconnect fitting. Single shutoff quick disconnect fittings are located inside the fitting component that attaches closest to the air supply.

single steel braid

Pneumatic tubing with metal reinforcement that is woven over the tubing of the hose. Single steel braid features only one layer of steel braid reinforcement.

sleeve

A tubular part designed to fit over another part. The sleeve helps create a seal.

spiral clearance

The presence of space between the root of one thread and the crest of another along the entire length of the thread. Spiral clearance allows fluid to leak from a fluid system.

split-flange O-ring fitting

An O-ring fitting used for large OD tubing. Split-flange O-ring fittings form a seal when a flange is tightened over an O-ring with a clamp.

static seal

A seal that is made between two stable and immovable components. A static seal may move and flex during normal operation.

straight coupling

A pipe fitting that extends a run. Straight coupling joins two identical pipes on one end.

straight through quick disconnect

A quick disconnect fitting with no valves. Straight through quick disconnect fittings cannot be added or removed without first shutting off the air supply.

straight-thread O-ring boss

A reusable fitting that is sealed by an O-ring located between the termination of a straight OD thread and the wrench flats used to tighten the fitting into a component. A straight-thread O-ring boss is also called a straight-thread O-ring fitting.

straight-thread O-ring fitting

A reusable fitting that is sealed by an O-ring located between the termination of a straight OD thread and the wrench flats used to tighten the fitting into a component. A straight-thread O-ring fitting is also called an SAE straight-thread O-ring boss.

stress

A force that attempts to deform an object. Common forms of stress include compression, shear, and tensile.

stud

The component of a quick disconnect fitting that attaches to a hose. A stud is one of two valves in the double shutoff quick disconnect fitting.

swivel

A fitting component designed to provide a dynamic seal while rotating at low speeds, often less than 360° of rotation. A swivel often reciprocates back and forth.

synthetic

Something that is produced artificially. Synthetic materials include plastic and nylon and can be used to produce O-rings.

tapered

Gradually decreasing in size from one end of the object to the other. Tapered threads allow pipe fittings to achieve a positive seal.

tee

A pipe fitting that allows fluid to change directions. A tee joins three runs.

thermoplastic

A group of plastics that can be softened by heat, hardened by cooling, and then softened again by heat. This cycle can occur over and over again.

torque

A force that produces rotation. If torque guidelines are not followed, overtightening can cause fatigue and leakage.

tubing

A type of pneumatic fluid conductor that joins other components usually in a nonlinear fashion. Tubing is stronger than pipe, despite being easily bent.

union

A pipe fitting that extends a run. A union joins two conductors without turning the conductors to tighten the seal.

upstream

In a direction toward the source of power in a fluid system. Upstream is the direction from which the fluid is coming.

washer

A component of an adjustable straight-thread O-ring fitting that is squeezed by a locknut against the O-ring. A washer is a flat disc with a hole through the center that is often used with threaded fasteners to ensure joint tightness.

wrench flats

A flat surface beneath the fastener head. The wrench flats facilitates tightening with a wrench.

wye

A pipe fitting that allows fluid to change directions. Wye fittings run in one direction at 45° to the main run.