Hydraulic Lines and Fittings

Lecture 8

Purpose of Lines

All hydraulic lines are designed to transmit fluid from one place to another without leakingLines are built to withstand pressure, vacuum, and the hydraulic fluids used in the systemThere are two different types: Flexible and SteelAll lines have fittings on the end of them to connect to hydraulic devices

Steel Lines

Steel lines (tubing) is used when there is little vibration, limited space, no movement of the lines, and/or frequent replacement is neededSteel lines have two common type of connectors: JIC Flare and Flareless Compression

JIC Flare Fitting

Usually has a nut, backup sleeve, and a 37° flare of the lineThis type is often used on the outside of cylinders on construction or farm equipmentCan also be used for return lines

Flareless Compression Fitting

A special type of ferrule that replaces the flareBites into metal to provide a positive seal that won’t slipCan be used for return linesAlso used for pressure lines on the frame

Flexible Lines

Many different types and materials used to make flexible linesAll flex lines are measured by the inside diameter of the lineCan use fraction measurement or dash sizeAll lines rated in working pressure, vacuum, or burst pressure

Line Sizes

Lines can be from 3/16” to 4” in size (Inside Diameter or ID)Dash size is determined by taking the number and making it the numerator of the fraction 16– -3 hose size is 3/16” (3/16)– -12 hose size is 12/16” or ¾” (12/16)

Largest is –64 size (4”)

Hose Materials

Most hoses have an outer covering, a cloth or wire braid, and an inner material to prevent leakageCan be damaged by high temperaturesNeoprene or Buna-N used in most hydraulic hosesWire braids added to handle high pressures

SAE Hose Designations

SAE Number Braids Pressure

100R1 1 Wire 500 – 2500 PSI

100R2 2 Wire 1200 – 3500 PSI

100R3 2 Cloth 375 – 1250 PSI

100R4 1 Wire Spiral 50 – 300 PSI

100R6 1 Cloth 300 – 600 PSI

100R12 4 wire 2500 – 5000 PSI

Hose Maintenance - Replacement

Leaks at fitting or in hose. (Leaking fluid is a fire hazard.) Damaged, cut, or abraded cover. (Any reinforcement exposed.) Kinked, crushed, flattened, or twisted hose. Hard, stiff, heat cracked, or charred hose.

Hose Maintenance - Replacement

Blistered, soft, degraded, or loose cover.Cracked, damaged, or badly corroded fittings.Fitting slippage on hose.

Hose Routing

Make sure to install hoses so that they are as close as possible to the component – This keeps the line from being pulled off

Keep a little slack in all lines to allow movement

Hose Routing

Make sure the line flexes in and out rather than up and downMinimize movement if possible

Hydraulic Fittings

Several types of fittings used on hydraulic components– NPTF (National Pipe Tapered - Fuel)– JIC (37°)– O-Ring Boss– O-Ring Flange– Flat Faced O-Ring (Forseal)

NPTF Fittings

The most commonly used on older equipmentSeals by a tapered threadThe farther you turn it, the better it sealsStandard pipe thread can leak without the use of pipe sealant

JIC Fittings

The next most common fitting usedSeals by seating an angled flared area against another angled areaCan leak if the seating area is scratchedHose end can be easily disassembled and repositioned

O-Ring Boss

Uses an O-Ring to seal the fittingOften has a jam nut that is used to compress the o-ring Permits turning an angled fitting to a desired position without leaking

O-Ring Flange Fittings

Primarily used on hose endsHas a round flat surface that uses an o-ring to seal it against the componentIs compressed by a separate backup flange that usually has 4 boltsCan leak if the flange is bent or the surface is scratched

Flat Faced O-Ring Fittings

Also called Forseal fittingsSimilar to JIC except the seating area is flat and the fitting has an o-ring in itCan leak if the face is deeply scratched or o-ring is badNewest type used on hydraulic equipment

Fitting Installation - NPTF

Inspect port components to ensure that male and female threads are free of nicks, burrs, dirt, etc. Apply sealant/lubricant to male pipe threads. With any sealant, the first few threads should be left uncovered to avoid system contamination. If Teflon tape is used, it should be wrapped 1-1/2 turns in a clockwise direction when viewed from the end.

Fitting Installation - NPTF

Screw Fitting into female pipe port to finger tight position. Wrench tighten fitting to the appropriate Turns From Finger Tight in the next chart, making sure the tube end of the shaped fitting is aligned to receive incoming tube or hose assembly.

Turns From Finger Tight Chart

Pipe Thread Size Turns From Finger Tight

2 2.0 - 3.04 2.0 - 3.06 1.5 - 3.08 2.0 - 3.012 2.0 - 3.016 1.5 - 2.520 1.5 - 2.524 1.5 - 2.532 1.5 - 2.5

Fitting Torque – O-Ring BossThread Size Assemly Torque

(in-lb)Assemly Torque(ft-lb)

2 85 - 95 7 - 83 160 - 180 13 - 154 205 - 235 17 - 195 245 - 275 21 - 236 300 - 340 25 - 298 545 - 595 46 - 5010 1010 - 1100 85 - 9512 1250 - 1350 105 - 11514 1675 - 1825 139 - 151