# Tri-clamp displacer head: ISO 2852 cap with Ø3 rod bore and 4 mm barb, 1.5, 2 and 3 in

> What end cap guides the displacer rod out of a tri-clamp Stirling cylinder?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: ISO 2852 cap face (Ø50.5 / 64.0 / 91.0 flange, 6 mm cap) with a Ø3 run bore on centre and a 4 mm hose barb
- Page: https://xemstudio.com/objects/tri-clamp-displacer-head/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-displacer-head · Plain text: https://xemstudio.com/objects/tri-clamp-displacer-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

- An ISO 2852 end cap with the displacer-rod guide and a transfer port on its back, so a stock clamp and Type B gasket seal it to any ferrule of its size.
- On centre: a Ø3 bore straight through cap and boss for the Ø3 displacer rod (run fit). The bore is the rod guide and the clearance seal; nothing is pressed into it.
- Off centre: an integral 4 mm hose barb (Ø6.4 base, Ø3.2 bore) for the transfer tube to the power cylinder, at 13.75 / 20.25 / 33.75 mm from the axis on the 1.5 / 2 / 3 in head.
- Flange Ø50.5 (1.5 in, also fits 1 in ferrules), Ø64.0 (2 in), Ø91.0 (3 in).

## 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 |
|---|---|---|---|---|
| head faces | ISO 2852 | ferrule face + Type B gasket | clamp | head-* |
| transfer-port barb | Ø6.4 barb, Ø3.2 bore | 4 mm ID tube | designed | head-displacer-* |
| rod-guide bore | Ø3 × 16.4 (through cap and Ø10 boss) | Ø3 displacer rod | run | head-displacer-* |

## Sizes

| size_in | flange_od_mm | rod_bore_mm | barb | barb_offset_mm |
|---|---|---|---|---|
| 1.5 | 50.5 | 3 | 4 mm (Ø6.4, Ø3.2 bore) | 13.75 |
| 2 | 64.0 | 3 | 4 mm (Ø6.4, Ø3.2 bore) | 20.25 |
| 3 | 91.0 | 3 | 4 mm (Ø6.4, Ø3.2 bore) | 33.75 |

## Where the files are

- Long Earth Society: [Tri-clamp Stirling engine builds](https://longearthsociety.com/engineering/) — web, video — LES site
- James R. Senft: [An Introduction to Low Temperature Differential Stirling Engines (displacer and gap design)](https://www.stirlingengine.com/) — book — Moriya Press (verify at link)
- Wikipedia: [Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine) — web — CC BY-SA 4.0 (text)

## Free STEP/STL (3 parts, CC BY 4.0, Xem Studio)

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

- head-displacer-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-1.5in.stl) — 1.5 in ISO 2852 cap: Ø3 rod-guide bore straight through the cap and its Ø10 × 12 boss for the Ø3 displacer rod (running fit, see Mating features); 4 mm transfer-port barb
- head-displacer-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-2in.stl) — 2 in ISO 2852 cap: Ø3 rod-guide bore straight through the cap and its Ø10 × 12 boss for the Ø3 displacer rod (running fit, see Mating features); 4 mm transfer-port barb
- head-displacer-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-3in.stl) — 3 in ISO 2852 cap: Ø3 rod-guide bore straight through the cap and its Ø10 × 12 boss for the Ø3 displacer rod (running fit, see Mating features); 4 mm transfer-port barb

## How it fits

### Goes in or on
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/): ISO 2852 face on the spool ferrule

### Connects to
- [Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacer/): Ø3 rod from the displacer cap through the Ø3 bore
- [Silicone tube 1 × 3 to 10 × 14 mm (ID × OD)](https://xemstudio.com/objects/silicone-tube/): 4 mm ID tube on the transfer barb
- [Tri-clamp power head: ISO 2852 cap with a Ø15.9 socket for a 10 mL syringe, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-syringe-head/): transfer tube to the power cylinder

### Alternatives
- [Tri-clamp crank head: ISO 2852 cap with Ø3 rod bore and two 623 towers, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-crank-head/): rod bore plus crank towers in one head

### Also needed
- [Tri-clamp clamp, two-bolt: every flange size ½ to 4 in](https://xemstudio.com/objects/tri-clamp-clamps/): clamp and gasket on the face

## Questions

**How does the displacer rod get out of a tri-clamp cylinder?**

Through the Ø3 bore on the centre of this head: the Ø3 rod runs in it, and the bore length is the clearance seal.

**What is the barb on the displacer head for?**

The transfer port: a 4 mm barb (Ø6.4 base, Ø3.2 bore) for the tube to the power cylinder.

**Does it need a special clamp?**

No: the face is ISO 2852, so a stock clamp and Type B gasket for the flange size seal it.

## Fits with

- [Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacer/)
- [Tri-clamp power head: ISO 2852 cap with a Ø15.9 socket for a 10 mL syringe, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-syringe-head/)
- [Tri-clamp crank head: ISO 2852 cap with Ø3 rod bore and two 623 towers, 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-crank-head/)
- [Tri-clamp clamp, two-bolt: every flange size ½ to 4 in](https://xemstudio.com/objects/tri-clamp-clamps/)
- [Silicone tube 1 × 3 to 10 × 14 mm (ID × OD)](https://xemstudio.com/objects/silicone-tube/)
- [Tri-clamp end cap, 6 mm flat: 1.5 and 2 in](https://xemstudio.com/objects/tri-clamp-end-cap/)