Hydraulic Lines and Fittings

1
Hydraulic Lines and Fittings

• Lecture 8

2
Purpose of Lines

• All hydraulic lines are designed to transmit
  fluid from one place to another without leaking
• Lines are built to withstand pressure, vacuum,
  and the hydraulic fluids used in the system
• There are two different types Flexible and Steel
• All lines have fittings on the end of them to
  connect to hydraulic devices

3
Steel Lines

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

4
JIC Flare Fitting

• Usually has a nut, backup sleeve, and a 37 flare
  of the line
• This type is often used on the outside of
  cylinders on construction
  or farm equipment
• Can also be used for
  return lines

5
Flareless Compression Fitting

• A special type of ferrule that replaces the flare
• Bites into metal to provide a positive seal that
  wont slip
• Can be used for return lines
• Also used for pressure lines on the frame

6
Flexible Lines

• Many different types and materials used to make
  flexible lines
• All flex lines are measured by the inside
  diameter of the line
• Can use fraction measurement or dash size
• All lines rated in working pressure, vacuum, or
  burst pressure

7
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)

8
Hose Materials

• Most hoses have an outer covering, a cloth or
  wire braid, and an inner material to prevent
  leakage
• Can be
  damaged by
  high temperatures
• Neoprene or Buna-N used in most hydraulic hoses
• Wire braids added to handle high pressures

9
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
10
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.    

11
Hose Maintenance - Replacement

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

12
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

13
Hose Routing

• Make sure the line flexes in and out rather than
  up and down
• Minimize movement if possible

14
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)

15
NPTF Fittings

• The most commonly used on older equipment
• Seals by a tapered thread
• The farther you turn it, the better it seals
• Standard pipe thread can leak without the use of
  pipe sealant

16
JIC Fittings

• The next most common fitting used
• Seals by seating an angled flared area against
  another angled area
• Can leak if the seating area
  is scratched
• Hose end can be easily
  disassembled and repositioned

17
O-Ring Boss

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

18
O-Ring Flange Fittings

• Primarily used on hose ends
• Has a round flat surface that uses an o-ring to
  seal it against the component
• Is compressed by a separate backup flange that
  usually has 4 bolts
• Can leak if the flange is bent or
  the surface is scratched

19
Flat Faced O-Ring Fittings

• Also called Forseal fittings
• Similar to JIC except the seating area is flat
  and the fitting has an o-ring in it
• Can leak if the face is deeply scratched or
  o-ring is bad
• Newest type used on hydraulic equipment

20
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.

21
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.

22
Turns From Finger Tight Chart
Pipe Thread Size Turns From Finger Tight
2 2.0 - 3.0
4 2.0 - 3.0
6 1.5 - 3.0
8 2.0 - 3.0
12 2.0 - 3.0
16 1.5 - 2.5
20 1.5 - 2.5
24 1.5 - 2.5
32 1.5 - 2.5
23
Fitting Torque O-Ring Boss
Thread Size Assemly Torque(in-lb) Assemly Torque(ft-lb)
2 85 - 95 7 - 8
3 160 - 180 13 - 15
4 205 - 235 17 - 19
5 245 - 275 21 - 23
6 300 - 340 25 - 29
8 545 - 595 46 - 50
10 1010 - 1100 85 - 95
12 1250 - 1350 105 - 115
14 1675 - 1825 139 - 151