Unit 15 Fluid ConductorsUnit 15 Fluid Conductors and and

ConnectorsConnectors

ConnectorsConnectors

Conductors are classified as eitherConductors are classified as either rigidrigid, , semi-rigidsemi-rigid, , oror flexibleflexible. . Conductors are referred to b type such asConductors are referred to b type such as pipepipe, , tubingtubing, , andand hosehose. . Pipe is considered rigid. Tubing is considered semi-rigid, andPipe is considered rigid. Tubing is considered semi-rigid, and hose is considered to be flexible.hose is considered to be flexible. The first conductor we will The first conductor we will discuss is pipe.discuss is pipe.

Up to this point we have discussed components of fluid power Up to this point we have discussed components of fluid power systems without attention to their connections. Conductors systems without attention to their connections. Conductors carry fluid from the power source to the system components and carry fluid from the power source to the system components and eventually the point of operation. To function properly, as well eventually the point of operation. To function properly, as well as safely, conductors must be able to withstand the highest as safely, conductors must be able to withstand the highest possible pressure of the system, deliver the fluid at required possible pressure of the system, deliver the fluid at required volumes, withstand high operating temperatures, and remain volumes, withstand high operating temperatures, and remain leak free during operation.leak free during operation.

Pipe and Materials and SealingPipe and Materials and SealingPipe is a rigid conductor which means it is not meant to be bent. Pipe is a rigid conductor which means it is not meant to be bent. Consequently, pipe must be connected using fittings and, as a rule, Consequently, pipe must be connected using fittings and, as a rule, everywhere there is a connection in a fluid power system there exists everywhere there is a connection in a fluid power system there exists the possibility of a leak. the possibility of a leak.

MaterialsMaterials

There are many materials that could be used for pipe There are many materials that could be used for pipe but only seamless steel is recommended for hydraulic but only seamless steel is recommended for hydraulic systems. Galvanized pipe is not recommended systems. Galvanized pipe is not recommended because of chips. because of chips.

Sealing Sealing

Pipe threads have to be tapered and usually use Pipe threads have to be tapered and usually use NPTFNPTF type thread. type thread.

ID, OD, and Wall Thickness and ID, OD, and Wall Thickness and Pipe SizePipe Size

Wall thickness determines the pressure rating of the pipe. Wall thickness determines the pressure rating of the pipe. Schedule 40, 80, and 160 are most common and are designated as Schedule 40, 80, and 160 are most common and are designated as low pressure, high pressure, and very high pressure respectively.low pressure, high pressure, and very high pressure respectively.

Pipe ThreadsPipe Threads

To form a leak proof seal, pipe threads are tapered on their outside To form a leak proof seal, pipe threads are tapered on their outside diameter about 1/16diameter about 1/16thth per inch. This taper causes an interference fit per inch. This taper causes an interference fit which is suppose to create a seal. In reality pipe threads don’t seal which is suppose to create a seal. In reality pipe threads don’t seal very well without the help of pipe tape or joint compounds. very well without the help of pipe tape or joint compounds.

Pipe ThreadsPipe Threads

NPTF type pipe thread is recommended for hydraulic systems. The NPTF type pipe thread is recommended for hydraulic systems. The major difference NPT and NPTF type thread is in the clearance left major difference NPT and NPTF type thread is in the clearance left between the crest and root of the thread. With the NPTF type, there between the crest and root of the thread. With the NPTF type, there is no clearance which aids in sealing.is no clearance which aids in sealing.

NPTNPT NPTFNPTF

Pipe FittingsPipe Fittings

Since pipe is heavy walled and not designed for bending into Since pipe is heavy walled and not designed for bending into shape, fittings must be used to make pipe connections. Fittings shape, fittings must be used to make pipe connections. Fittings are also used on tubing to connect sections.are also used on tubing to connect sections.

Pipe Installation ConsiderationsPipe Installation Considerations

Since metal is removed when threading, it is critical that metal Since metal is removed when threading, it is critical that metal shavings not be allowed to get in the system. When applying shavings not be allowed to get in the system. When applying sealing compounds, make sure not to allow any of the compound to sealing compounds, make sure not to allow any of the compound to overlap the end of the pipe. Never start sealant tape any closer to overlap the end of the pipe. Never start sealant tape any closer to the edge than two threads. When tightening pipe threads, be the edge than two threads. When tightening pipe threads, be aware that the wedging action generates radial force on the outer aware that the wedging action generates radial force on the outer pipe and that over tightening pipe threads can result in a rupture.pipe and that over tightening pipe threads can result in a rupture.

TubingTubing

The main advantage of tubing is that it can be bent into shape The main advantage of tubing is that it can be bent into shape and thus requires fewer fittings. Fewer connections generally and thus requires fewer fittings. Fewer connections generally means there will be less possibility of leaks. Tubing is also means there will be less possibility of leaks. Tubing is also known for its ability to absorb vibration and has a smooth known for its ability to absorb vibration and has a smooth inside finish which is good for fluid movement.inside finish which is good for fluid movement.

Tubing MaterialsTubing Materials

SteelSteel CopperCopper BrassBrass AluminumAluminum Stainless SteelStainless Steel PlasticPlastic

Although tubing may be made of many different Although tubing may be made of many different materials, fluid power systems only use one or more materials, fluid power systems only use one or more of them. Generally, carbon steel tubing is the choice of them. Generally, carbon steel tubing is the choice of hydraulic systems and either steel or plastic of hydraulic systems and either steel or plastic tubing for pneumatic systems. Aluminum, copper, tubing for pneumatic systems. Aluminum, copper, and brass have the tendency to fracture. Stainless and brass have the tendency to fracture. Stainless steel is expensive. steel is expensive.

Tubing SizeTubing Size

Tubing size is determined by outside diameter. As tubing wall Tubing size is determined by outside diameter. As tubing wall thickness increases, its internal diameter decreases. As wall thickness increases, its internal diameter decreases. As wall thickness increases, the burst pressure of the tubing also increases.thickness increases, the burst pressure of the tubing also increases.

Tubing Size and Pressure RatingTubing Size and Pressure Rating

Three very important terms Three very important terms associated with tubing are: associated with tubing are: burstburst pressure, pressure, workingworking pressure, and pressure, and safetysafety factor. factor.

Burst pressure is the point at Burst pressure is the point at which a tube will rupture at a which a tube will rupture at a given pressure value. Working given pressure value. Working pressure is the value considered pressure is the value considered safe to operate the system at safe to operate the system at under normal circumstances. under normal circumstances. Safety factor is the ratio Safety factor is the ratio between working pressure and between working pressure and burst pressure. As a general burst pressure. As a general rule, a good safety factor is at rule, a good safety factor is at least 4 to 1.least 4 to 1.

Tube FittingsTube Fittings

Tube fittings generally fall into one of two categories: flared Tube fittings generally fall into one of two categories: flared and flare-less. A flared tube fitting, shown above at left, and flare-less. A flared tube fitting, shown above at left, consists of a body, sleeve, and a nut. A seal is generated consists of a body, sleeve, and a nut. A seal is generated between the tube flare and the body when the nut is tightened between the tube flare and the body when the nut is tightened against the sleeve and tube. The main reason of the sleeve is to against the sleeve and tube. The main reason of the sleeve is to keep the nut from twisting the tube flared end when the nut is keep the nut from twisting the tube flared end when the nut is tightened. It is important to note that some flare assemblies, tightened. It is important to note that some flare assemblies, such as low pressure 45 degree flares, do not use a sleeve. such as low pressure 45 degree flares, do not use a sleeve. Flare-less tube fittings use basically the same components Flare-less tube fittings use basically the same components except that the seal is created by a donut shaped piece that is except that the seal is created by a donut shaped piece that is sometimes referred to as a “ferrule” rather than a sleeve.sometimes referred to as a “ferrule” rather than a sleeve.

Flared Tube FittingFlared Tube Fitting

37 degree Flare Fitting SAE “B”37 degree Flare Fitting SAE “B” Ferrule Compression FittingFerrule Compression Fitting

JIC 37 degree flares are recommended for high pressures above JIC 37 degree flares are recommended for high pressures above 1000PSI. SAE 45 degree flares are primarily used in pneumatic 1000PSI. SAE 45 degree flares are primarily used in pneumatic systems and are for pressures below 1000PSI. The flare-less tube systems and are for pressures below 1000PSI. The flare-less tube fitting can be used in both hydraulic and pneumatic systems and has fitting can be used in both hydraulic and pneumatic systems and has pressure ranges up to 3000PSI. Flare-less tube fittings should be pressure ranges up to 3000PSI. Flare-less tube fittings should be used on medium and heavy wall tubing. The most critical step in used on medium and heavy wall tubing. The most critical step in making a single flare tube fitting is forming the flare. The tube must making a single flare tube fitting is forming the flare. The tube must be cut square, cleaned free of burrs, measured exactly, and flared be cut square, cleaned free of burrs, measured exactly, and flared without galling, over-thinning, or splitting the end of the tube. without galling, over-thinning, or splitting the end of the tube.

Flare Less Tube FittingFlare Less Tube Fitting

Sleeve Type Compression FittingSleeve Type Compression Fitting O-Ring Type Compression FittingO-Ring Type Compression Fitting

The types above are used when tubing cannot be flared The types above are used when tubing cannot be flared or to avoid flaring. In both cases the sleeve holds the or to avoid flaring. In both cases the sleeve holds the tube in place.tube in place.

Tubing InstallationTubing Installation

As a rule, tubing runs should be kept as short as possible with As a rule, tubing runs should be kept as short as possible with as few bends or turns as possible but not completely straight. as few bends or turns as possible but not completely straight. Bends do help absorb vibration and allow for expansion and Bends do help absorb vibration and allow for expansion and contraction. contraction.

Tube Bending RadiusTube Bending Radius

Hydraulic tubing is bent with a special tool. Each tube has a Hydraulic tubing is bent with a special tool. Each tube has a standard bend radius to which the tube may be bent without standard bend radius to which the tube may be bent without flattening, kinking, or wrinkling. The rule of thumb for flattening, kinking, or wrinkling. The rule of thumb for calculating the bend radius is given by the following formula: calculating the bend radius is given by the following formula: Bend Radius + 3 X Outside Diameter of Tube. Bend Radius + 3 X Outside Diameter of Tube. The bend The bend radius is measured from the inside center of the radius to the radius is measured from the inside center of the radius to the centerline of the tube, not the outside as done with a hose.centerline of the tube, not the outside as done with a hose.

Hose Hose

Outer CoverOuter Cover

ReinforcementReinforcement

Inner TubeInner Tube

The standard components of a three piece hose assembly are the The standard components of a three piece hose assembly are the inner tube, reinforcement layer, and the outer cover. The inner inner tube, reinforcement layer, and the outer cover. The inner tube comes into direct contact with the fluid and must be tube comes into direct contact with the fluid and must be compatible with it. The reinforcement layers provide strength compatible with it. The reinforcement layers provide strength for the hose and must be able to withstand the system pressure. for the hose and must be able to withstand the system pressure. The outer cover protects the other two by providing a contact The outer cover protects the other two by providing a contact surface for the hose. The outer cover should not be allowed to surface for the hose. The outer cover should not be allowed to rub against anything during normal operation.rub against anything during normal operation.

Hose ConstructionHose Construction

Although basic hose construction includes three pieces, hoses Although basic hose construction includes three pieces, hoses can be constructed with multiple reinforcement layers made can be constructed with multiple reinforcement layers made from many materials including steel that give the hose three from many materials including steel that give the hose three possible ratings: possible ratings: suction, medium pressure, high pressure, and suction, medium pressure, high pressure, and very high pressure.very high pressure.

Hose SizeHose Size

Hose size is given by a “dash” number which relates to Hose size is given by a “dash” number which relates to the inside diameter of the hose. The dash numbers the inside diameter of the hose. The dash numbers graduate in 1/16graduate in 1/16thth inch increments. A hose with a –16 inch increments. A hose with a –16 imprinted on the side would have an inside diameter imprinted on the side would have an inside diameter of 1 inch. A hose could have a very large outside of 1 inch. A hose could have a very large outside diameter but a very small inside diameter so trying to diameter but a very small inside diameter so trying to judge inside diameter by examining the outside judge inside diameter by examining the outside diameter is not practical.diameter is not practical.

Hose Pressure ClassificationsHose Pressure Classifications

The pressure rating of a hose is determined by its construction. The The pressure rating of a hose is determined by its construction. The more reinforcement layers a hose has, the more pressure it can more reinforcement layers a hose has, the more pressure it can stand. In addition to layers, the type of reinforcement also pays a stand. In addition to layers, the type of reinforcement also pays a role in determining the pressure rating of a hose.role in determining the pressure rating of a hose.

Hose FittingsHose Fittings

Hose fittings can be classified as either permanent or reusable. Hose fittings can be classified as either permanent or reusable. Permanent hose fittings are installed on the hose by “crimping” Permanent hose fittings are installed on the hose by “crimping” and cannot be disassembled. Reusable hose fittings are screwed and cannot be disassembled. Reusable hose fittings are screwed or clamped on the hose end. The big difference between skive or clamped on the hose end. The big difference between skive and no-skive hose is in the thickness of the outer cover. The and no-skive hose is in the thickness of the outer cover. The thicker cover requires a different fitting shell.thicker cover requires a different fitting shell.

Quick CouplingsQuick Couplings

Quick couplings are used for convenience because they can Quick couplings are used for convenience because they can installed and removed by hand and in situations where there will installed and removed by hand and in situations where there will be repeated connecting and disconnecting of lines. There are be repeated connecting and disconnecting of lines. There are three kinds of couplings: single shutoff, double shutoff, and three kinds of couplings: single shutoff, double shutoff, and straight through. Single shutoffs are used with compressed air. straight through. Single shutoffs are used with compressed air. Double shutoffs are used with liquids, and straight through are Double shutoffs are used with liquids, and straight through are used where flow must be unrestricted.used where flow must be unrestricted.

Hose Installation ConsiderationsHose Installation Considerations

Avoid twisting hose. Small twists in a hydraulic hose can Avoid twisting hose. Small twists in a hydraulic hose can have devastating results. Do not install hose tight as in have devastating results. Do not install hose tight as in the illustration on the right. Hose needs room to expand the illustration on the right. Hose needs room to expand and contract.and contract.

Hose Installation ConsiderationsHose Installation Considerations

Hose movement needs to be considered on equipment Hose movement needs to be considered on equipment using pivoting actuators. The cover should not be using pivoting actuators. The cover should not be allowed to come into contact with any other machine allowed to come into contact with any other machine part as the machine operates.part as the machine operates.

Hose Installation ConsiderationsHose Installation Considerations

Hydraulic hose will expand with pressure and at the same Hydraulic hose will expand with pressure and at the same time shorten in length. Secure all hoses firmly being time shorten in length. Secure all hoses firmly being careful to allow for some movement.careful to allow for some movement.

Hose Bend RadiusHose Bend Radius

Two conditions that contribute to shortened service life are installing Two conditions that contribute to shortened service life are installing the hose twisted or over bent. A small twist in a hose, as little as 10 the hose twisted or over bent. A small twist in a hose, as little as 10 degrees, can shorten the life of the hose by 90 percent. Examine the degrees, can shorten the life of the hose by 90 percent. Examine the “lay line” during installation to ensure there are no twists in the “lay line” during installation to ensure there are no twists in the hose. The minimum recommended bend radius of a hose is hose. The minimum recommended bend radius of a hose is determined by manufacturers who specify limits on charts.determined by manufacturers who specify limits on charts.