Free-piston displacer: Ø39.4 sealed shell and cap for a 2 in tri-clamp engine — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/fpse-displacer/  (CC BY 4.0)
Basis: Design values of the free-piston generator; collapse margin from the thin-tube buckling relation p = 2E/(1 − ν²)·(t/D)³ at E 200 GPa (assumed)
Catalog version: 2026-10-20

Sizes: see table below
- Ø39.4 shell, 0.8 wall, 209.9 long with its cap: it reaches from the bottom of the hot spool (the expansion space under it) through joint A into the 3 in cooler spool, where its cold face meets the compression space under leaf B.
- It runs with a designed 0.30 radial gap in the liner and the cooler insert, never touching: leaf B at joint B holds its cold end on the axis and the rod's gland holds the other end of the rod.
- Sealed with the gas it was assembled in. Thin-tube collapse pressure of the shell: about 37 bar for a wall of modulus 200 GPa, against 16 bar absolute at the relief setting; the cap's flange takes the end load on the shell's rim.
- Moving mass with its rod, plug, stinger and gas-spring piston: 365 g (at 7.9 g/cm³).

part  size
shell  Ø39.4 × 206.9, wall 0.8
cap  spigot Ø37.8, flange Ø39.4 × 3, boss Ø16 × 8
gap  0.30 radial (designed)
travel  ±6 room, ±4.47 at the design point

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Ohio University (Urieli): Stirling cycle machine analysis: ideal adiabatic and simple analysis (after Urieli & Berchowitz, Stirling Cycle Engine Analysis, 1984) — web — author's site — https://www.ohio.edu/mechanical/stirling/
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/fpse-displacer/index.json
API: https://xemstudio.com/api/geometry?object=fpse-displacer