40 Questions
What is the maximum allowed wrinkle or kink in tubes for fluid systems with working pressures of 500 psi or greater?
1% of the tube OD
Why is it essential to determine the cause of a tube failure?
To prevent similar failures from occurring in the future
What is the purpose of pressure-testing tubing prior to installation?
To ensure the tubing can withstand several times the normal operating pressure
What should be used at points where the tubing passes through bulkheads?
Flexible grommets or hose
What is the minimum clearance required between tubing and structure or rigid members, unless otherwise specified?
1/16 in.
What is the primary reason for replacing damaged aircraft fluid lines?
To ensure safe operation of the aircraft
Why may replacement tubing need to be fabricated?
Because replacement parts are not available
What is the maximum allowable distance between supports for tubing, according to the table?
Specified in the table, but not provided in the text
What is the purpose of using the Bend Allowance Chart?
To calculate the bend allowance
What is the formula for calculating bend allowance?
2πR / 360°
How do you calculate the flat dimension?
Subtract the setback for each bend from the overall dimension
What is the purpose of dividing the bent object into flats and bend allowances?
To calculate the overall length of the bent object
What is the minimum bend radius for tube bending?
2.5 to 3 times the OD
What is the acceptable method for bending soft, non-heat-treated aluminium tubing in an emergency?
Bending by hand to form the desired radius
What is the objective of tube bending?
To obtain a smooth bend without flattening
What is the purpose of the stick diagram of tubing development?
To demonstrate the layout of the calculations
What is the primary concern when cutting tubing?
Producing a square end, free of burrs
What tool is used to remove both inside and outside burrs from tubing?
De-burring tool
What is the consequence of slight damage to the tubing wall during deburring?
Fractured flares or defective flares may occur
Why should the cut end of the tube be polished before flaring?
To remove any sharp edges that could cause the tubing to crack
What are the two major types of tube joints?
Flared and flareless fittings
What is the purpose of the tube flaring tool?
To prepare tube ends for flaring
What can happen to the tube if it is not properly cleaned and deburred?
Draw marks can spread and split the tube when it is flared
What should be checked on the tube ends before flaring?
The roundness, square cut, and cleanliness of the tube end, and the absence of draw marks or scratches
What is the purpose of the swivel nut or flange?
To secure the nipple to the mating connection in the fluid system
What is unique to each manufacturer's hose fittings?
The characteristics and tolerances
Why should nipples and sockets from different manufacturers not be intermixed?
Due to differences in characteristics and tolerances
What is the purpose of colour-coding on hose fittings and nuts?
To show the material used
What is the recommended pressure for testing fabricated hoses?
1.5 times system pressure
What is the alternative to pressure testing a new purchased hose from an approved vendor?
Operational check using system pressure
What is the consequence of a hose assembly failing the pressure test?
It can be very dangerous to personnel and property
What is the importance of following safety procedures during pressure testing?
To protect personnel and property from potential hazards
When installing hose or hose assemblies, what should be ensured regarding identification markings?
They are visible
What can happen to the length of the hose when pressure is applied?
It changes in length from +2% to -4%
Why should swivel connector nuts be finger-tightened initially?
To avoid stripping threaded areas of fittings
How should the final torque be applied to end fittings?
Using a torque wrench and holding the fitting stationary
Why should the hose be held manually when applying final torque?
To prevent rotation and scoring of the fitting's sealing surface
What should be used to prevent chafing when routing and clamping the flexible hose?
Cushion-type clamps
What should be ensured when supporting the flexible hose or hose assemblies?
That they are not restricted
When flexing is required in an installation, how should the hose be bent?
In the same plane of movement
Study Notes
Calculating Bend Allowances
- Use the Bend Allowance Chart or formula to calculate bend allowances
- Formula: angle of bend / (2πR) × 360°
Calculating Flats
- Calculate flats by subtracting setback for each bend from overall dimension
- This leaves the flat dimension
Calculating Overall Length
- Divide bent object into flats and bend allowances
- Number them progressively (e.g., 1-2, 2-3, 3-4, etc.)
- Calculate each length independently, then lay out calculations
- Development length equals the total of all lengths
Tube Bending
- Objective: obtain smooth bend without flattening tube
- Use mechanical or hand-operated tube bender
- Minimum bend radius: 2.5 to 3 times the OD
Tube Cutting
- Produce square end, free of burrs
- Remove burrs from inside and outside the tube using a de-burring tool
- Avoid reducing or fracturing the wall thickness of the tubing
Tube Flaring
- Preparation: use tube flaring tool to prepare tube ends
- Check tube ends for roundness, square cut, and cleanliness
- Remove draw marks and scratches
Tube Joint Preparation
- Two major tube joints: flared fitting and flareless fitting
- Flared fitting: single-flared joint and double-flared joint
Wrinkle or Kink Limitations
- Wrinkles or kinks in tubes: limit to 1% of tube OD for working pressures ≥ 500 psi
- Limit to 2% of tube OD for working pressures < 500 psi
Typical Repairs
- Repair or replace damaged aircraft fluid lines
- Use replacement tubing of the same size and material as original
- Pressure-test tubing prior to initial installation
Clamps
- Maintain minimum clearance of 1/16 in. or 1/4 in. between supports
- Use flexible grommets or hose at points where tubing passes through bulkheads
Pressure Test Stands
- Hydraulic or pneumatic pressure test fabricated hoses prior to installation
- Test to 1.5 times system pressure
- New purchased hoses can be operationally checked after installation
Installation Procedures
- Remove protective closures from hydraulic lines, hose, or hose assemblies
- Install hose or hose assemblies without twisting, chafing, or over bending
- Observe bend radius and allow for component movement and possible changes in length
This quiz covers the calculation of bend allowances in aviation maintenance, using the Bend Allowance Chart or the bend allowance formula.
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