Chinapromoter Blog

The correct way of installation will help the tube for a long life.and before the installation of tube fitting, we should get some Knowledge of the tube  installation and maintenance.

Installation and Maintenance of Tube

Tube Line making basic demand

1. Tube centerline basis for measurement: Always measure from the centerline except from the first bend which is measured from the end of the tube.
2. Tube Centerline Basis for Measurement
3. You Control Accuracy

Tube Bending

be caerful with the tube bending, and Follow this list to insure good results on each bend.

1. Measure and mark exactly. Insert tube in bender.
2. Always try to bend in the same direction! If you backbend, be sure to compensate for gain or pickup. Remember, gain always occurs to the right side of the tube radius block.
3. Clamp tubing securely in bender.
4. Check to make certain length mark is tangent to desired angle on radius block or in line with the desired degree on the link member.
5. Bend accurately to the desired angle plus springback allowance.
6. Open bender, remove tube.
7. Double check bend angle with triangle.
8. Check measurement length with tape or ruler.

Common Causes of Imperfect Bends

1. trying to bend too short a radius, or bending smaller diameter tube in larger radius block.
2. caused by the tube slipping in the bender, or by using non-annealed tubing. Tubes must be firmly clamped by clamp block to prevent slippage during bending process.
3. Bends with little or no flattening are produced when correct equipment and methods are employed; when proper consideration is given to co-relationship of the radius of the bend, material wall thickness and hardness of the tube.
    

Tube Clamping

Once you've taken the time to make good bends and installed them, it’s not enough to just let them lay suspended in mid-air. When tubing is left unsupported, shock and vibration will cause the tubing to shake, and in turn, cause the fitting to loosen and leak or even allow tube to fall through fatigue. Tube support and clamping is a necessary requirement in the fluid power industry. Tubing can be clamped individually, in sets, and can also be stacked. The most important part of any clamping system is having enough clamps to attain the final result. That being, a well supported, vibration and noise free system.

Also, most manufacturers specify SAE and JIC approved components on their equipment. The best way to meet these specs concerning clamps is to utilize a clamp that employs both an upper and lower unit made of metal and a rubber split bushing which surrounds the tube or pipe and fits on the inside of the clamping units.

Tubing end Preparation

Tube end preparation is essential in assuring leak-free systems. Some important points should be considered. special attention is It is necessary to prevent scratching and burring the O.D. of the tubing. This is especially important for gas service. Low-density gases such as helium and argon cannot be sealed with damaged tubing. Make certain not to drag tubing across any surfaces such as shelves, truck beds,  or storage racks, the floor and (or) ground of any plant/construction site.

Cutting the Tube End
To insure a good joint, tube must be cut off square. This can be accomplished with either a tube cutter or hacksaw. Cutting with a Hacksaw - When using a hacksaw to cut off tubing, it is essential to use a guide to assure square cutoffs.

Deburring the Tube End
The burrs formed by either the tube cutter or hacksaw must be removed prior to assembly to prevent those burrs from eventually damaging the system. O.D. burrs can prevent tubing from seating properly in a fitting body. I.D. burrs can restrict flow, as well as possibly break loose and damage fine filtration elements.

Cleaning the Tube End
After that it is essential to remove burrs from the tubing line. This can be accomplished by Flushing with solvent or low pressure compressed air.and swab with lint-free cloth.
 

The Installation of Types of Tube Fitting

After that care should be taken to insure that the port connection is properly prepared and installed so that it will accept the tubing. Different types of tube fitting should take different way.

Pipe thread port

1. Make sure pipe threads are free from nicks, burrs, dirt, etc. For use with tape.
2. Apply tape to threads starting with first thread. 1-1/2 to 2 turns of tape should be applied in the direction of the male pipe spiral.
3. Insert fitting into pipe port and turn it in finger tight. Tighten with wrench.
    

SAE Straight Thread O-ring Fitting (Non adjustable)

1. Make sure both threads and sealing surfaces are free of burrs, nicks & scratches, or any foreign material.
2. Lubricate O-ring with system compatible lubricant.
3. Tighten to torque level listed in the torque chart on page 32.

SAE straight thread O-ring fitting (Adjustable)

1. Inspect and correct both mating parts for burrs, nicks, scratches or any foreign particles.
2. Lubricate O-ring with system compatible lubricant.
3. Back off lock nut as far as possible toward fitting body make sure back-up washer and O-ring are pushed up as far as possible toward upper thread.
4. Screw fitting by hand into the port until back-up washer contacts face of the port and continue turning until snug. (Very slight wrenching maybe needed). Back-up washer is now in correct position for assembly.

Proper Tube Fitting Remake Instructions

A disassembled joint can be remade simply by retightening the nut to the position of the original make up. For maximum number of remakes, mark the fitting and nut before disassembly. Before retightening, make sure the assembly has been inserted into the fitting until the ferrule(s) seats in the fitting. Retighten the nut by hand. Rotate the nut with a wrench to the original position as indicated by the previous marks lining up. (A noticeable increase in mechanical resistance will be felt indicating the ferrule is being re-sprung into sealing position.) Then snug the nut 1/12 turn (1/2 hex flat) as shown from A to B, past the original position.

Tube Fitting Maintenance

Corrosion-Resistant Steel Tubbing

Corrosion-resistant  steel  tubing  (CRES)  is  used  in high-pressure  hydraulic  systems  (3,000  psi  and above) such as landing gear, wing flaps, and brakes. The tubing does not have to be annealed for flaring or forming. The flared section is strengthened by cold working and consequent strain hardening. Table 6-1 lists the most commonly used corrosion-resistant steel tubing  in  naval  aircraft  and  includes  some  of  the designations  by  which  the  corrosion  steel  tubing  is known.  Application  notes  are  intended  as  guidelines.

Aluminum Alloy Tubing

Aluminum alloy tubing is used for both high-pressure and general-purpose lines. Table 6-2 lists the most commonly used  aluminum alloy tubing and its applications. Use of aluminum alloy tubing is limited in certain areas of airborne hydraulic  systems by MIL-H-5440. Refer to the applicable drawing and the illustrated parts breakdown to determine the correct tubing  for a particular system. Aluminum alloy tube assemblies fabricated with aluminum alloy tubing 6061-T6 are authorized for repair or replacement for any aluminum line. MIL-T-6845 Cres tubing (304-1/8H) is a suitable substitute for all aluminum  alloy tubing when 6061-T6 is unavailable.

Special  Tubing

Corrosion-resistant steel 21-6-9 and titanium alloy 3AL-2.5V are presently being incorporated into new  model  aircraft. Repair and fabrication of assemblies using these materials may require special procedures. Refer to the applicable   maintenance directives for specific details.