Short answer: Reading a PTFE gasket drawing before ordering means checking five things: the ID/OD against your flange standard (not just the numbers), thickness with tolerance, whether the torque/bolt-load note matches your bolting plan, surface finish callouts on sealing faces, and marking requirements. Two minutes with this checklist prevents the classic failure: a gasket that fits perfectly and still leaks because the flange was never what the drawing assumed.
Drawings travel between engineering and purchasing intact — but assumptions don’t. This reading order catches the gaps.
Check 1: Dimensions Against the Real Flange
Confirm ID/OD against your actual flange standard (ANSI B16.21, DIN 2690, EN 12560, etc.) — not just plausibility. A DN80 gasket for DIN PN10 differs from DN80 for ANSI 150#. If the drawing says “per DIN,” verify which DIN. Bolt-hole gaskets: hole count and pitch circle get forgotten most often.
Check 2: Thickness and Tolerance
Nominal thickness without tolerance is an invitation. Look for a band (±5% or ±0.1 mm) and check the thickness is consistent with the flange condition discussed earlier — 3 mm on a 0.2 mm gap flange is overkill that will creep.
Check 3: Load and Torque Notes
| Drawing note | What to confirm |
|---|---|
| “Torque to XX Nm” | Matches your bolt spec and gasket thickness (thinner gaskets need controlled torque, not max torque) |
| “Do not exceed XX MPa stress” | Virgin PTFE crushes above ~40–50 MPa gasket stress — note must exist for thin sections |
Check 4: Surface and Edge Callouts
Sealing-face finish requirements (Ra values) and edge condition (chamfer, deburr) — these are where quotes diverge, because they drive process steps.
Check 5: Marking and Revision
Revision number current, lot-marking requirement stated if you need traceability. Chunhuan produces gaskets to customer drawings with a DFM check before quoting — drawings with the five checks above quote fastest and cleanest.
Frequently Asked Questions
What should I check first on a PTFE gasket drawing?
Dimensions against your actual flange standard (ANSI/DIN/EN) — including bolt-hole count and pitch circle, which are the most commonly forgotten features.
Why does gasket thickness need a tolerance on the drawing?
Without a band, thickness is unverifiable and creep behavior is unpredictable. Look for ±5% or tighter, consistent with the flange gap.
What gasket stress limit applies to virgin PTFE?
Roughly 40–50 MPa maximum sustained gasket stress before crushing risk — thin sections should carry an explicit stress/torque limit note.
How do surface finish callouts affect gasket quotes?
Ra requirements and edge treatment drive process steps; undefined finishes make quotes diverge and lead to rework at delivery.
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