Hose, Tubing, and Fitting Selection and Fabrication
Objective. Students will fabricate two hydraulic hose assemblies to specified length, end-fitting type, and pressure rating, achieving a leak-free assembly verified at rated working pressure.
This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.
VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.
Why Hose and Fitting Selection Matters
A wind turbine's hydraulic system controls the pitch of rotor blades, engages the brakes, and operates yaw drives — functions that keep the machine running safely and efficiently. A poorly selected or badly fabricated hose assembly can burst, weep, or pull apart at a coupling, causing injury, fire risk, environmental contamination, and unplanned downtime. Your job as a technician is to choose the right hose, the right fitting, and the right crimp — every time.
Reading a Hydraulic Hose Catalog
Manufacturers publish detailed specification sheets for every hose product. The key values you must match to the application are:
- Inside diameter (I.D.): Governs flow rate and velocity. Sized in fractions of an inch or metric equivalents; also expressed as a "dash size" (e.g., -8 means 8/16 = ½ inch I.D.).
- Working pressure rating: The maximum continuous operating pressure the hose is rated to carry, expressed in PSI or bar. Always select a hose whose working pressure rating equals or exceeds the system's maximum operating pressure.
- Minimum burst pressure: Typically four times the working pressure rating per industry convention, though always confirm against the specific product data sheet.
- Bend radius: The tightest curve the hose can make without kinking or damaging internal reinforcement layers.
- Temperature range: Confirm compatibility with the hydraulic fluid type and expected ambient temperatures inside the nacelle.
- End-fitting compatibility: The catalog will specify which fitting series (JIC, NPT, ORFS, BSP, etc.) and dash sizes are approved for each hose series.
Service bulletins from wind-turbine manufacturers specify the hose series, pressure rating, and fitting type required for each repair. Never substitute a lower-rated hose or an unapproved fitting type — document all selections on a parts worksheet so the repair is traceable.
Hose and Fitting Types
SAE J516 JIC (37° flare) fittings are common in high-pressure hydraulic circuits. The 37-degree flare on the fitting mates with a matching flare surface to create a metal-to-metal seal. Thread-seal tape is not used on JIC threads; the seal is at the flare, not the threads.
NPT (National Pipe Taper) fittings use tapered threads that wedge together to form a seal. Thread-seal tape or anaerobic thread sealant is applied to the male threads before assembly. NPT is common on lower-pressure porting and instrumentation connections.
ORFS (O-Ring Face Seal) fittings provide a positive seal through an O-ring captured in a face groove. They are preferred in high-vibration, high-pressure environments and are increasingly specified in modern wind-turbine hydraulic circuits.
Cutting and Preparing Hose
Use only a hose-cutting saw — a dedicated abrasive or circular blade tool designed for hydraulic hose. Utility knives produce uneven cuts that prevent proper fitting insertion. After cutting:
1. Measure the cut-off length against the job specification, accounting for the amount of hose that slides into each coupling shell (the "cut-off allowance" listed in the catalog).
2. Blow out the bore with dry, filtered compressed air to remove any rubber particles or wire strands from the reinforcement layers.
3. Insert the fitting stem into the hose bore by hand until the hose end is flush with the skirt of the coupling shell.
Crimping
A bench-mounted hydraulic crimping machine compresses a segmented die set around the coupling shell, permanently locking the fitting to the hose. The critical output is the crimp diameter — the outside diameter of the shell after crimping, measured with a crimp-diameter gauge (a precision caliper tool). Every fitting/hose combination has a target crimp diameter and a tolerance (e.g., ± 0.010 inch) published in the manufacturer's crimp specification chart. Record the measured crimp diameter on the lab log. Assemblies outside tolerance must be cut off and re-fabricated; a shell that is over-crimped can damage the hose internally, while an under-crimped shell will pull off under pressure.
Pressure Testing
After fabrication, every assembly is pressure-tested before installation. On the lab test stand:
1. Connect the assembly to the test stand fittings. Ensure all connections are hand-tight, then wrench-tight.
2. Bleed air from the circuit per the stand's procedure.
3. Raise pressure slowly to the rated working pressure of the hose.
4. Hold pressure for the duration specified in the test procedure (often one to two minutes).
5. Visually inspect all joints. Any weeping, seeping, or dripping constitutes a failure. Tag the assembly, relieve pressure, and set it aside for analysis.
6. Record the test pressure, hold time, and pass/fail result in the test log.
Never stand directly in line with a pressurized fitting during testing. Hydraulic fluid ejected under pressure is an injection hazard that can cause severe injury requiring immediate medical attention.
Safety Requirements for This Lab
- PPE: Safety glasses and nitrile gloves at all times. A face shield is required during pressure testing.
- Lockout/tagout (LOTO): The test stand must be fully de-energized and pressure relieved before you connect or disconnect any hose.
- Inspection before use: Inspect the hose stock for cuts, abrasions, or bulges before cutting. Damaged stock is rejected.
- Fluid handling: Hydraulic fluid is a skin and eye irritant. Report any spill immediately and clean up per the lab's spill procedure.
- Housekeeping: Cut hose ends and metal filings from the saw are a puncture hazard; dispose of them in the designated container.
Key terms8
Worked examples4
- Identify total cut-off allowance: 2 ends × 1.75 in = 3.50 in
- Subtract from overall assembly length: 36.00 in − 3.50 in = 32.50 in
- Calculate the lower acceptance limit: 1.062 − 0.010 = 1.052 in
- Calculate the upper acceptance limit: 1.062 + 0.010 = 1.072 in
- Compare the measured value (1.048 in) to the range (1.052 in to 1.072 in): 1.048 is below 1.052
- Compare each hose's working pressure rating to the system maximum: Hose A (2,500 PSI) is less than 2,800 PSI — inadequate.
- Hose B (3,000 PSI) is greater than or equal to 2,800 PSI — meets the requirement.
- Select Hose B and confirm its I.D., temperature range, and fitting compatibility with the service bulletin before ordering.
- Test pressure equals the rated working pressure: 3,000 PSI.
- Round to the nearest readable increment: 3,000 PSI falls exactly on a 50-PSI increment, so target the 3,000 PSI mark.
- Hold duration: 90 seconds (1 minute 30 seconds) as specified by the test procedure.
- During the hold, visually inspect all joints for leaks; record pressure, hold time, and result in the test log.
Materials: Hydraulic hose stock (multiple I.D. sizes), NPT and JIC fittings assortment, bench crimping machine, crimp-diameter gauge, hose-cutting saw, hydraulic test stand, pressure gauge, thread-seal tape, hose-manufacturer catalog, safety glasses, nitrile gloves, NCCER workbook
Check: Both completed assemblies must pass a leak-free pressure test at rated working pressure; instructor confirms crimp diameter is within manufacturer tolerance; lab log entry completed with all measurements recorded.
Practice check8
Answer each question, then check it. Nothing is recorded; this is your own practice.
