Connect SodaStream CO2 cylinder to TR21-4 soda cylinder valve

How to join TR21-4 (often pin-valve) and TR21x4 (soda / SodaStream-style), and what stops it leaking.

End ASodaStream CO2 cylinder (TR21-4 (often pin-valve))Seals directlyEnd BTR21-4 soda cylinder valve (TR21x4 (soda / SodaStream-style))

These connect directly. SodaStream CO2 cylinder mates with TR21-4 soda cylinder valve without an adapter.

The two ends

End A: SodaStream CO2 cylinder (TR21-4 (often pin-valve))
End B: TR21-4 soda cylinder valve (TR21x4 (soda / SodaStream-style))
A seals on: O-ring on the valve stem
B seals on: O-ring on the valve stem
Part needed: none, direct fit

A SodaStream cylinder is a TR21-4 trapezoidal thread underneath, so a plain TR21-4 adapter fits the older bottles directly. What changes is the newer proprietary quick-connect valve some bottles add on top of that thread.

Older SodaStream bottles take a plain TR21-4 adapter; newer pin-valve bottles need a pin-adjustable adapter to reach the thread. Check which valve your bottle has before assuming a plain TR21-4 fitting will seat.

Related connections

SodaStream CO2 cylinderTR21-4 (often pin-valve)TR21-4 soda cylinder valveTR21x4 (soda / SodaStream-style)TR21-4 soda cylinder valve to CGA-320 CO2 cylinder valveadapter TR21-4 soda cylinder valve to W21.8 CO2 cylinder valveadapter SodaStream CO2 cylinder to CGA-320 CO2 cylinder valveadapter SodaStream CO2 cylinder to W21.8 CO2 cylinder valveadapter

Sources: MoreWinePro / KegLand deluxe SodaStream cylinder adapter (CGA320 male x TR21-4 female, pin adjustment KL24662) · CO2Art guide to cylinder connections: disposable/small cylinder threads (M10x1, 3/8-24 UNF 16g, 5/8-24 UNF 74g, M16x1.5 95g) · CO2Art guide to cylinder connections (CGA320, W21.8, DIN477, BS341, G5/8, TR21-4)