Inputs
Flat spear (A-type) · allowance 27 mm · base clearance 9 mm
From the sealing edge in the neck down to the sump. Spears are ordered by this dimension – it is neither the external height nor the tube length.
Deduction from the external height: 65 mm. That is an approximation – curvature and neck differ by manufacturer and year of manufacture.
For this keg H3 is stored directly, without approximation. On the 20 l slim keg it varies by manufacturer: 501, 504 or 508 mm.
The three dimensions on the keg
Keg contour from our CAD model of a DIN 50 keg, converted to your H3 and diameter. The spear is drawn in simplified form.
Three dimensions not to be confused
H3
A keg dimension: from the sealing edge in the neck, where the housing seal sits, down to the sump. It is measured on the empty keg standing upright. H3 is the figure a spear is ordered by.
Total length
A spear dimension: from the top edge of the spear to the end of the down tube. It is H3 plus an allowance that is fixed for each design.
Tube below the sealing edge
The part that actually reaches into the keg: from the sealing edge to the end of the tube. That is H3 minus the base clearance. Tubes are cut to this dimension.
Where the figures come from
| Type | Total length | Tube below sealing edge | Base clearance |
|---|---|---|---|
| A Flat | H3 + 27 mm | H3 − 9 mm | 9 mm |
| S EU Sankey (S-type) | H3 + 15 mm | H3 − 14 mm | 14 mm |
| D US Sankey (D-type) | H3 + 15 mm | H3 − 14 mm | 14 mm |
| G Three-lobe | H3 + 27 mm | H3 − 9 mm | 9 mm |
| M Combi | H3 + 21 mm | H3 − 15 mm | 15 mm |
Weight for all five types: (H3 − 9) × 0.315 g + 300 g, ± 5 %.
The length allowances and the weight formula appear in exactly this form on the assembly drawings of the manufacturer whose spears we sell – including the tolerance figure of five per cent. On the flat (A-type) and the triangular spear (G-type) the allowance is considerably larger at 27 mm, because the housing sits on top of the neck with its flange. The base clearances are set per valve system.
Why the base clearance is not a safety margin plucked from the air
During cleaning and filling the valve opens wider than when dispensing. On the EU Sankey spear (S-type) that is around 6.5 to 8 mm on the beer path against 4 mm in the dispensing position. The 14 mm of base clearance are the space this larger cleaning lift needs.
On top of that comes the design, and that explains the jump in the table. With the flat spear (A-type) and the triangular spear (G-type) the down tube stays where it is: coupler, cleaning head and filling head only push the valve open, the tube does not travel downwards. With the EU Sankey spear (S-type), the US Sankey (D-type) and the combi spear (M-type) it is different by design. There the whole down tube pushes a few millimetres deeper into the keg as the head is coupled on. That is exactly why the column shows 14 and 15 mm there and not 9 mm – the travel the tube makes when coupling has to stay clear at the bottom.
What happens when the length is wrong
Too long
During cleaning the medium cannot spread out at the end of the tube – the jets stay flat, and the shoulder and edge areas lie in the spray shadow.
When dispensing, the end of the tube practically bottoms out: no beer comes at all, or only foam, because flow velocities at the sump differ widely.
Too short
During cleaning the jet breaks up over the long path and falls back as a fountain in the middle instead of spreading over the walls – the same fault, a different reason.
When dispensing, a considerably larger amount of beer stays in the keg, with every single container. That is a direct loss and one of the most frequent grounds for complaints from the trade.
What that looks like in section is shown by the animation of spear length in six cases.
Limits of this calculator
- H3 is the critical input. Anyone deriving it from the external height is working with an approximation for curvature and neck. That differs by several millimetres between manufacturers and years of manufacture.
- The base clearance depends on the type, not on the keg. With special designs it can differ.
- The weight is a manufacturer formula with ± 5 % and applies to the spears we supply. Other makes deviate.
- Measuring beats calculating. Before ordering a production run, a sample belongs in the keg, not in the table.