Xem Studiomeasured geometryLibrary › Stirling engines › Free-piston ·
Gas-spring piston Ø14.9 × 15 and Ø19.9 × 20
What size is the gas-spring piston in a free-piston Stirling engine? · Hardware · basis: Gas spring k = γ·p·A² / V; piston drawn at bounce-space bore − 0.1 (0.05 mm radial gap as drawn)
Long Earth Society build part. The LES free-piston test bed: Ø40 core on flexures in a 2 in tri-clamp vessel. The engines
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. Mating features
- sizes
- 2 in table
Notes
- The small piston on the rod that compresses a sealed bounce space and makes a gas spring: Ø14.9 × 15 for a Ø15 bore, Ø19.9 × 20 for a Ø20 bore.
- Solid, with a Ø5 bore (fit: slide) for the rod and 0.5 mm chamfers. As drawn it is 0.1 mm under its bore, a 0.05 mm radial gap.
- Stiffness k = γ·p·A²/V: the Ø20 piston at 1 bar with 20 cm³ of bounce space gives about 690 N/m; a smaller volume is stiffer.
Sizes
| file | diameter | length | bore it runs in | rod bore | k at 1 bar, 20 cm³ |
|---|---|---|---|---|---|
| gas-spring-piston-15x15 | 14.9 | 15 | 15 | 5 | ≈ 220 N/m |
| gas-spring-piston-20x20 | 19.9 | 20 | 20 | 5 | ≈ 690 N/m |
Mating features
Drawn at the exact size. Open press, slide, run and socket features by your process's clearance; leave designed gaps and clamp fits as drawn.
| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| rod bores | Ø5 | Ø5 rod | slide | all |
| gas-spring piston in its bore | Ø15 / Ø20 (= bore) | Ø15 / Ø20 bounce-space bore | run | gas-spring-piston-* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| NASA (NTRS, public domain) | Free-piston Stirling engine design and analysis (RE-1000 test results) (1984) | US Government work, public domain | |
| NASA (NTRS, public domain) | Dynamics of free-piston Stirling engines (1987) | US Government work, public domain | |
| Wikipedia | Free-piston engine | web | CC BY-SA 4.0 (text) |
| Wikipedia | Beale number | web | CC BY-SA 4.0 (text) |
| Ohio University | Stirling cycle machine analysis (Urieli), free online | web | Author's site |
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 2 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| gas-spring-piston-15x15 | gas-spring piston Ø15 (= the Ø15 bounce-space bore; clearance-seal running fit) × 15, Ø5 rod bore | STEP · STL |
| gas-spring-piston-20x20 | gas-spring piston Ø20 (= the Ø20 bounce-space bore; clearance-seal running fit) × 20, Ø5 rod bore | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=gas-spring-piston
How it fits
Connects to
Ø5 rods with E-clip grooves, 120 and 150 mmon the Ø5 rod
Free-piston Stirling displacer Ø29 × 75 and Ø39 ×…spring for the displacer rodAlternatives
Planar spiral flexure bearing leavesflexure stiffness instead of gasYou might also need
Questions
How stiff is a gas spring?
K = γ·p·A²/V; Ø20 at 1 bar with 20 cm³ gives about 690 N/m.
What keeps a gas spring's mean position from drifting?
Centring ports: two 0.5 mm holes the piston uncovers at mid-stroke.