Calculate spear length
From the keg's H3 dimension you get the overall length of the spear and the length to the seal. For DIN, Euro and Slim kegs, or with your own dimension.
The right spear length
The H3 dimension runs from the sealing surface in the keg neck down to the sump in the keg. From it follow the overall length of the spear, which is used for ordering, and the length to the seal.
The overall length runs from the top of the spear to the end of the down tube. Spears are ordered by this length. In AOBAOSI drawings it is called TL (total length), the length to the seal SL (length till sealing edge). H3 values for DIN and Euro kegs are based on catalogue data from a European manufacturer. Depending on manufacturer and year of manufacture they differ by a few millimetres. To be sure, measure H3 on an empty, upright keg with a measuring rod through the keg neck.
The down tube moves down when the spear opens
On the S, D and M systems the down tube is movable by design. As soon as the spear is opened, it moves down by the valve stroke. This happens at the keg coupler just as it does at the cleaning and filling head in the brewery, so every time the keg is filled. That is why the set bottom clearance is larger on these systems than on A and G.
If the spear is clearly too long, the end of the tube touches down on the sump when the spear opens and is pressed against it. The consequences:
- Pressure marks and scoring in the sump. Deposits and microorganisms adhere more easily there, and cleaning reaches them less well.
- Mechanical damage to the sump itself.
- Burrs and sharp edges at the end of the spear tube.
We have seen very clear marks of this kind on sumps. So order the spear length based on the measured inner height H3 and with the bottom clearance of the respective system. In the keg cross-section you can reproduce the effect with the “too long” setting.
H3 and bottom clearance
How a down tube of the wrong length affects cleaning and dispensing is shown by the keg cross-section.
What is the H3 dimension of a keg?
H3 is the distance from the sealing surface in the keg neck down to the sump in the keg. It is the basis for the spear length.
How do I calculate the spear length up to the seal?
H3 minus the bottom clearance of the valve system. Example: 50 l DIN keg with H3 541 mm and a type A spear: 541 mm − 9 mm = 532 mm.
What is the overall length of a spear?
The length from the top of the spear to the end of the down tube, TL in AOBAOSI drawings. Spears are ordered by this length. It is H3 plus a fixed allowance per system: A 27 mm, G 27 mm, S 15 mm, D 15 mm, M 21 mm. Example: DIN keg 50 l with H3 541 mm and type A: 568 mm.
What bottom clearance do the systems have?
A and G: 9 mm. S and D: 14 mm. M: 15 mm. On S, D and M the down tube moves down by the valve stroke when the dispensing, filling or cleaning head opens it; the set clearance remains 14 and 15 mm respectively.
Why is the right length so important?
A tube that is too long touches the bottom or, during cleaning, stops the jet from spreading, and when dispensing the beer foams. A tube that is too short leaves more beer in the sump with every keg.
How do I measure H3 myself?
On an empty, upright keg, with a measuring rod through the keg neck down to the sump. H3 values vary by a few millimetres depending on manufacturer and year of manufacture.