# Tri-clamp regenerative displacer: Ø31.8, Ø44.5 and Ø69.9 with 12 slots, 1.5 mm gap

> What is a regenerative displacer and what size fits a tri-clamp spool?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: Spool bore minus a 1.5 mm radial gap (Senft annular-gap regenerator); 16 ga ASME BPE bores 34.8 / 47.5 / 72.9 mm
- Page: https://xemstudio.com/objects/tri-clamp-regenerative-displacer/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-regenerative-displacer · Plain text: https://xemstudio.com/objects/tri-clamp-regenerative-displacer/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 annular-gap regenerative displacer: the 1.5 mm radial gap between it and the spool is the regenerator path, so one spool with this displacer is a complete engine with no separate regenerator section.
- Sizes: 1.5 in Ø31.8 × 75, 2 in Ø44.5 × 90, 3 in Ø69.9 × 120 mm. Wall 1.5 mm, closed rounded end, open at the cap end.
- Twelve radial slots 1.2 mm wide run through the wall over the middle 70 % of the length (from 15 % to 85 % of L); they are the pockets for the regenerator matrix.
- Its cap has a spigot Ø(D − 3) × 3 into the shell, a Ø D × 1.5 flange and a Ø16 × 6 boss with the Ø3 rod hole; 10.5 mm overall.

## 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 |
|---|---|---|---|---|
| displacer OD in the spool bore | bore − 2 × 0.6 / 0.75 / 1.0 | tri-clamp-spool bore | designed | displacer-* |
| regenerative displacer OD in the spool bore | bore − 2 × 1.5 | tri-clamp-spool bore | designed | displacer-regenerative-* |
| regenerative cap spigot in the shell | shell bore (bore − 6) | regenerative displacer shell | slide | displacer-regenerative-cap-* |
| regenerative cap rod hole | Ø3 | Ø3 displacer rod | slide | displacer-regenerative-cap-* |

## Sizes

| spool_in | bore_mm | displacer_od_mm | length_mm | radial_gap_mm | slots |
|---|---|---|---|---|---|
| 1.5 | 34.8 | 31.8 | 75 | 1.5 | 12 |
| 2 | 47.5 | 44.5 | 90 | 1.5 | 12 |
| 3 | 72.9 | 69.9 | 120 | 1.5 | 12 |

## 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 (6 parts, CC BY 4.0, Xem Studio)

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

- displacer-regenerative-1.5in-75: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-1.5in-75.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-1.5in-75.stl) — 1.5 in annular-gap regenerative displacer Ø31.8 × 75: 12 radial slots for regenerator mesh, 1.5 mm radial gap
- displacer-regenerative-cap-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-cap-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-cap-1.5in.stl) — cap for the 1.5 in regenerative displacer: Ø28.8 × 3 spigot, Ø31.8 × 1.5 flange, Ø16 × 6 boss with the Ø3 rod bore and an M3 grub (Ø2.5 tapped) at 8 mm
- displacer-regenerative-2in-90: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-2in-90.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-2in-90.stl) — 2 in annular-gap regenerative displacer Ø44.5 × 90: 12 radial slots for regenerator mesh, 1.5 mm radial gap
- displacer-regenerative-cap-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-cap-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-cap-2in.stl) — cap for the 2 in regenerative displacer: Ø41.5 × 3 spigot, Ø44.5 × 1.5 flange, Ø16 × 6 boss with the Ø3 rod bore and an M3 grub (Ø2.5 tapped) at 8 mm
- displacer-regenerative-3in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-3in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-3in-120.stl) — 3 in annular-gap regenerative displacer Ø69.9 × 120: 12 radial slots for regenerator mesh, 1.5 mm radial gap
- displacer-regenerative-cap-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-cap-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/displacer-regenerative-cap-3in.stl) — cap for the 3 in regenerative displacer: Ø66.9 × 3 spigot, Ø69.9 × 1.5 flange, Ø16 × 6 boss with the Ø3 rod bore and an M3 grub (Ø2.5 tapped) at 8 mm

## 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/): Ø44.5 in the Ø47.5 bore, 1.5 mm radial gap

### Connects to
- [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/): Ø3 rod through the cold-end head

### Alternatives
- [Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacer/): plain displacer with a separate regenerator

### Also needed
- [Regenerator matrix disc Ø44 / Ø32 × 0.5 mm (mesh counts #40–#200)](https://xemstudio.com/objects/regenerator-mesh-disc/): matrix in the 12 slots

## Questions

**What is a regenerative displacer?**

A displacer whose gap to the cylinder is the regenerator: here a 1.5 mm radial gap with 12 slotted pockets in the wall, so the gas passes the matrix every stroke.

**What size regenerative displacer for a 2 inch spool?**

Ø44.5 × 90 mm in the Ø47.5 bore, 1.5 mm radial gap.

**How big are the slots?**

1.2 mm wide, through the 1.5 mm wall, 12 around, over the middle 70 % of the length: 63 mm on the 2 in displacer.

## 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 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 spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/)
- [Regenerator matrix disc Ø44 / Ø32 × 0.5 mm (mesh counts #40–#200)](https://xemstudio.com/objects/regenerator-mesh-disc/)
- [Tri-clamp power piston: ring-less full-bore pistons Ø34.8, Ø47.5 and Ø72.9](https://xemstudio.com/objects/tri-clamp-power-piston/)