Diaphragm crosshead hub and tapped backing disc: 2 in, with the displacer rod through the centre — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-diaphragm-crosshead/  (CC BY 4.0)
Basis: Design values from the sealed generator: Ø20 centre clamp as the stock 2 in diaphragm disc, M2 screws (ISO 4762) in ISO 273 medium clearance holes and Ø1.6 tap-drill holes, Ø3 guide bore; the pin height comes from the crank layout
Catalog version: 2026-10-20

Sizes: see table below
- The hub clamps the membrane from the crankcase side: a Ø20 × 3 disc with three Ø2.4 holes on Ø13 for M2 × 6 screws, heads up. Under the membrane the backing disc (Ø20 × 2, Ø5 centre hole) has three Ø1.6 holes tapped M2, so nothing stands below it into the working space.
- A Ø8 boss rises to 15 mm with a Ø3 bore straight through disc and boss: the displacer rod runs in it. This 15 mm close running fit is the only way for gas between the working space and the crankcase, the bleed that lets the crankcase follow the working space's mean pressure.
- A bar (z 5.5–9.5, 6 wide) runs out along +X to an arm at x 13.5–18.5 that carries the con-rod pin (Ø3 × 10, pressed) along X, 29.25 mm above the membrane face. The con-rod eye sits at x 8–13, beside the displacer's rod clevis (x ±6), so the two drives pass each other without touching.
- Fits: Ø3 bore run on the Ø3 rod (the bleed); pin hole press on the dowel; disc and backing clamp the membrane.

part  feature  value
hub  disc  Ø20 × 3, 3 × Ø2.4 on Ø13
hub  guide bore  Ø3 × 15 (run)
hub  con-rod pin  Ø3 along X at z 29.25, x 8.5–18.5
backing  disc  Ø20 × 2, Ø5 centre hole
backing  screw holes  3 × Ø1.6 (M2 tapped)

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- ISO: ISO 273 clearance holes for bolts and screws (fine / medium / coarse) — standard — dimensions are facts [verify license at link] — https://www.iso.org/standard/4196.html
- Wikipedia: Hagen–Poiseuille equation: plane Poiseuille flow between parallel plates (annular clearance leakage Q = π D δ³ Δp / 12 μ L) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation
- 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/tri-clamp-diaphragm-crosshead/index.json
API: https://xemstudio.com/api/geometry?object=tri-clamp-diaphragm-crosshead