Case Study: Vehicle Refrigeration Capillary Tube — Flow-Rate Acceptance Testing at 700 kPa
Industry: Automotive | Hardware: LF Series Mass-Flow Tester + LT-KZ02 Claw-Type External-Clamp Quick Connector
| Specification | Value |
|---|---|
| Test Pressure (Nominal) | 700 kPa (range: 650–750 kPa) |
| Accept Flow Window | 3.42–3.58 L·min⁻¹ |
| Cycle Breakdown | Charge 5 s / Measure 10 s / Exhaust 2 s |
| Total Cycle Time | 17 s |
| Detection Method | Mass flow rate |
| Connector Pressure Rating | 50 bar (5,000 kPa) |
Problem
Automotive refrigerant capillary tubes operate at high pressure (650–750 kPa) with bore diameters under 3 mm. The inherent dimensional variation in drawn-tube manufacturing means that tube-to-tube bore diameter differences of ±0.05 mm produce flow-rate differences far larger than any seal leak — making pressure-decay testing unreliable as a go/no-go criterion for this geometry. Pressure-based testing at 700 kPa also demands connectors rated well above the test pressure to survive production cycles without deforming the thin-wall tube ends.
Solution
The LF Series mass-flow tester measures actual volumetric flow rate through the tube under steady-state pressurization, rather than pressure decay. This method is inherently insensitive to the minor bore-diameter variation in production tubing — the accept window (3.42–3.58 L·min⁻¹) reflects the correct flow characteristic of a properly manufactured tube, not an arbitrary pressure threshold. The LT-KZ02 stainless-steel claw-type connector is rated to 50 bar (5,000 kPa) — 7× the test pressure — with a grip range of 6–52 mm OD.
Result
- 17-second cycle — faster than prior pressure-decay test with higher discrimination accuracy
- Accept window 3.42–3.58 L·min⁻¹ provides positive tube-integrity confirmation, not just leak detection
- LT-KZ02 connector sustains full test pressure with zero tube-end deformation over 500,000+ production cycles
- Method directly correlates to refrigerant flow performance in vehicle thermal management system