Tube Fitting Installation Guide: A Practical Handbook for Single-Cell End Plates

Materials

• Swagelok Tube Fitting: Stainless Steel Swagelok Tube Fitting, Male Connector, 1/4 in. Tube OD × 1/8 in. Male NPT (Part No. SS-400-1-2)
• PTFE Tape (polytetrafluoroethylene tape)
• Open-end Wrench
• 1/4 in. Tube

Figure: (a) Complete fitting before installation — Swagelok SS-400-1-2, full view. (b) Installed on the end plate. (c) Swagelok tube fitting disassembled — nut, back ferrule, front ferrule, body (left side: Swagelok fitting; right side: Male NPT).

Part 1: NPT Thread Installation

The end plate is pre-tapped with 1/2 in. Female NPT threads. The Male NPT fitting requires PTFE tape to ensure a gas-tight seal.

PTFE Tape Wrapping

The wrapping direction and number of turns directly affect sealing performance. Swagelok’s official recommendations:

1. Wrap in the direction of the threads (clockwise), ensuring the tape does not unwind during tightening
2. Begin wrapping from the second thread, leaving the first thread exposed to aid alignment
3. Apply 2–3 wraps; excessive thickness may cause insertion difficulty or introduce tape debris into the line

For a detailed video demonstration, see: Swagelok PTFE Tape Application.

Tightening the Male NPT

Align the PTFE-wrapped Male NPT end with the end plate’s threaded port. Hand-tighten 2–3 turns to confirm thread alignment, then tighten with a wrench.
Judge tightening torque by feel: snug, then add an additional 1/4–1/2 turn.
NPT threads are tapered by design; over-tightening will deform the end plate threads.

Part 2: Swagelok Tube Fitting Installation — Tube Side

The Swagelok two-ferrule fitting achieves its seal through progressive compression of the front and rear ferrules against the tube during the tightening process.
The installation procedure must be followed rigorously; otherwise, the fitting will not achieve its rated pressure class.

Installation Procedure

1. Disassemble the fitting: Unscrew the nut and remove the front ferrule and back ferrule. Verify the orientation of all three components — the front ferrule’s tapered face points toward the body; the back ferrule’s tapered face points toward the nut.
2. Insert the tube: Insert the 1/8 in. stainless steel tube into the fitting body, all the way to the bottom (the tube must contact the internal shoulder stop). Rotate the tube slightly during insertion to confirm it is fully seated. If the tube is not bottomed out, the ferrules will compress at the wrong position, causing the fitting to leak.
3. Hand-tighten: While holding the tube fully seated, finger-tighten the nut into the body until the ferrules begin to grip the tube surface and the nut can no longer be turned by hand.
4. Tighten 1-1/4 turns: Use one wrench to hold the fitting body stationary and another to tighten the nut by 1-1/4 turns (i.e., 450°).
   This is the critical step in Swagelok installation — tightening 1-1/4 turns correctly compresses the front and back ferrules onto the tube, forming a gas-tight seal.
   Fewer than 1 turn results in an incomplete seal; more than 1-1/2 turns over-compresses the tube, reducing fitting service life.

For the complete installation procedure, refer to the official Swagelok video: Swagelok Tube Fitting Installation and the installation guide page.

Common Mistakes

References

• Swagelok Tube Fitting Installation Video — YouTube
• Swagelok Tube Fitting Installation — Michigan Swagelok
• PTFE Tape Application — Michigan Swagelok