# Tri-clamp diaphragm head: 1.5 and 2 in, membrane in place of the gasket

> How do I make a diaphragm power piston on a tri-clamp fitting?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: ISO 2852 clamp face and 20° back cone from the ferrule on this site (rim 2.85, recess 1.6, back cone continued down to the tube OD at the ferrule's own hub height), ASME BPE tube bores; membrane cavity sized from the diaphragm stroke
- Page: https://xemstudio.com/objects/tri-clamp-diaphragm-head/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-diaphragm-head · Plain text: https://xemstudio.com/objects/tri-clamp-diaphragm-head/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- The head is a cap-style part that clamps onto any standard ferrule with the standard clamp. The membrane goes where the gasket would: its bead sits in the 1.6 mm recesses of the ferrule and the head, its web between the two lands, so the clamp closes exactly as on a Type B gasket.
- The back of the clamp face is the ferrule's 20° cone, continued down to the tube OD (Ø38.1 / Ø50.8) at 5.25 / 5.25 mm from the face, so the clamp groove meets the head just as it meets a ferrule (0.4 mm take-up, 0.6 mm squeeze). Behind that the head is a neck at the tube OD.
- Behind the membrane: a cavity at the bore (Ø34.8 / Ø47.5) deep enough for the centre disc and its nuts at full outward travel (1.5 in ±5, 2 in ±7.5 mm), a pocket for the rod boss, a Ø3 rod guide straight through a Ø16 boss, and four Ø4 vents so the space behind the membrane stays at air pressure.
- Fit: the Ø3 guide is a running fit on the Ø3 rod; the face is a clamp face. Everything else is drawn at size.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| clamp face | ISO 2852 (land Ø43.5–Ø50.5 / Ø56.5–Ø64, rim 2.85, 20° back to the tube OD) | standard clamp + membrane bead | clamp | diaphragm-head-* |
| bead recess | Ø43.5 / Ø56.5 × 1.6 | membrane bead | clamp | diaphragm-head-* |
| rod guide | Ø3 | Ø3 diaphragm rod (slides through it) | run | diaphragm-head-* |
| membrane cavity | Ø34.8 × 10.65 / Ø47.5 × 13.15 from the face | centre disc and nuts at full travel | designed | diaphragm-head-* |
| boss pocket | Ø12 × 16.65 / Ø12 × 19.15 from the face | rod boss at full travel | designed | diaphragm-head-* |
| vents | 4 × Ø4 | air behind the membrane | designed | diaphragm-head-* |

## Sizes

| size_in | flange_mm | groove_mm | neck_od_mm | cavity_dia_mm | cavity_depth_mm | back_mm | guide_top_mm | design_stroke_mm |
|---|---|---|---|---|---|---|---|---|
| 2 | 64.0 | 56.5 | 50.8 | 47.5 | 13.15 | 17.0 | 30.0 | 15.0 |
| 1.5 | 50.5 | 43.5 | 38.1 | 34.8 | 10.65 | 14.5 | 27.5 | 10.0 |

## Where the files are

- ISO (via iTeh sample): [ISO 2852 clamp liners: face profile and flange / groove diameters](https://cdn.standards.iteh.ai/samples/7850/eb49c396488d408c8ced3e2961d76cf3/ISO-2852-1974.pdf) — PDF — standard excerpt; dimensions are facts
- ASME: [BPE Bioprocessing Equipment (clamp fitting dimensions, tube OD and wall)](https://www.asme.org/codes-standards/find-codes-standards/bpe-bioprocessing-equipment) — standard — ASME; dimensions are facts (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-diaphragm-head/index.json

- diaphragm-head-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-diaphragm-head/diaphragm-head-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-diaphragm-head/diaphragm-head-2in.stl) — 2 in diaphragm head: ISO 2852 face (land Ø56.5–Ø64, rim 2.85, recess 1.6 inside Ø56.5), 20° back cone to the tube OD Ø50.8 at 5.25, membrane cavity Ø47.5 × 13.15, boss pocket Ø12 × 19.15, Ø3 rod guide to 30.00, 4 × Ø4 vents
- diaphragm-head-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-diaphragm-head/diaphragm-head-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-diaphragm-head/diaphragm-head-1.5in.stl) — 1.5 in diaphragm head: ISO 2852 face (land Ø43.5–Ø50.5, rim 2.85, recess 1.6 inside Ø43.5), 20° back cone to the tube OD Ø38.1 at 5.11, membrane cavity Ø34.8 × 10.65, boss pocket Ø12 × 16.65, Ø3 rod guide to 27.50, 4 × Ø4 vents

## Questions

**Does the diaphragm head fit a standard tri-clamp ferrule?**

Yes: the face and the 20° back are the ISO 2852 profile, so the standard clamp closes on it and the membrane bead sits where the gasket bead would.

**How far can the rod move?**

2 in: ±7.5 mm (15 mm stroke); 1.5 in: ±5 mm (10 mm stroke). The cavity is drawn for that travel with 1.4 mm to spare behind the nuts.

**Why the vents?**

So the air behind the membrane does not act as a spring against the engine; the working gas is only on the ferrule side.

## Fits with

- [Tri-clamp diaphragm membrane: flat, 1.5 and 2 in clamped size](https://xemstudio.com/objects/tri-clamp-diaphragm-membrane/)
- [Tri-clamp diaphragm centre disc and backing disc: 1.5 and 2 in](https://xemstudio.com/objects/tri-clamp-diaphragm-disc/)
- [Tri-clamp (Tri-Clover) sanitary ferrule, 1/2 to 4 inch](https://xemstudio.com/objects/tri-clamp-ferrule/)
- [Tri-clamp clamp, two-bolt: every flange size ½ to 4 in](https://xemstudio.com/objects/tri-clamp-clamps/)
- [Sanitary clamp tees and short-outlet tees (7MP, 7MPS): ½ to 4 in](https://xemstudio.com/objects/sanitary-clamp-tees/)
- [Build list: Tri-clamp tee diaphragm gamma, 2 in](https://xemstudio.com/objects/list-tri-clamp-tee-diaphragm-gamma/)
- [Build list: Tri-clamp elbow diaphragm alpha, 2 in](https://xemstudio.com/objects/list-tri-clamp-elbow-diaphragm-alpha/)