Keg spear troubleshooting: causes and remedies

Seal damaged by cleaning

The limits for steam, caustic and acid are set not by the stainless steel but by the EPDM. Cleaning beyond them destroys precisely the two parts that are meant to seal. The spear then looks perfect from the outside and still leaks.

Check and fix: check the cleaning programme against the limits: steam no more than 135 °C and no more than two minutes; caustic and acid no more than 80 °C, no more than ten minutes, no more than 3 %.

Body seal reused

The body seal is a single-use seal. If it is refitted after the spear has been removed, it often no longer seals reliably between keg and spear body. On the flat spear Type A, the leak shows up below the flange at the edge of the keg neck. Beer or CO₂ escapes, and the beer spoils.

Check and fix: remove the spear from the depressurised keg and refit it with a new body seal. As a rule, use a new body seal every time the spear is removed.

Seal aged or worn

The CO₂ valve and body seal are the wear parts. They age even when everything has been done correctly.

Check and fix: remove the spear from the depressurised keg and replace the seal kit. Part numbers are on the Spare parts page.

Deposits or foreign matter on the valve seat

A particle or beerstone on the sealing surface holds the valve slightly open.

Check and fix: inspect and clean the valve seat. If the leak returns after cleaning, replace the seal.

Wrong seal on a Sankey spear

The locking variants of the Sankey spear need different seals.

Check and fix: read the marking on the lug and order the matching kit.

Keg got too warm

In a documented case from 2017, 20-litre slim kegs with flat spears from another manufacturer came back from summer export with their seals pushed out. The Weihenstephan Research Centre of TU München measured in a water bath: at 30 °C the keg was at 3.5 bar, above the permissible operating pressure of 3.0 bar. At 35 °C the pressure exceeded 6 bar and the seal was pushed out. The carbonation level was normal. This is intended: a flat spear gives way under overpressure before the keg is damaged. Between roughly 6 and 10 bar the seal is pushed out or the spear opens to one side and releases the pressure. A type S EU Sankey spear withstands higher pressure.

Check and fix: maintain the cold chain during transport and storage. Slim kegs have less gas headspace above the beer and reach the critical limit sooner than wider kegs of the same volume.

Too much beer in the keg

The gas cushion in the headspace is small. The less room is left, the more steeply the pressure rises as the keg warms up.

Check and fix: check the fill volume and do not reduce the gas cushion.

Filling or cleaning head pushes the valve in too far

On the flat spear A and the identically machined G, the valve stroke is between 9 and 12 mm; plants are usually set to the middle. No head may push the valve in further than that, whether the keg coupler or the filling or cleaning head of an automatic keg plant. If the stroke is set too long, the seal and, in the worst case, the whole spear are damaged. This then shows up as a leak or as a seal that no longer holds, and looks like a fault in the spear.

Check and fix: measure the stroke on the cleaning and filling heads and set it to the middle of the range, around 10.5 mm for A and G. Check the setting regularly, for example during plant maintenance or after a head change. If leaks pile up after filling, look at the stroke first: a quick check on the plant saves many complaints.

Beer too warm

Saturation pressure rises steeply with temperature. If the pressure is too low, the beer releases gas in the line.

Check and fix: measure the temperature in the glass, not on the cooler’s display.

Dispense pressure too low

The most common setting error. Its effect is delayed: first the beer goes flat, then it foams. Lowering the pressure further makes things worse.

Check and fix: recalculate the target pressure for the actual keg temperature and compare it with the pressure gauge.

Keg coupler draws in air

A common case that is easily overlooked.

Check and fix: check the keg coupler, seals and connections for leaks.

Keg almost empty

Once the beer level drops below the opening of the down tube, gas comes through with the beer. No adjustment will fix that.

Check and fix: weigh the keg. If it only foams at the end of the keg, the fill level is the cause.

Spear length does not match the keg

If the spear is too short for the inner height H3, the down tube ends too far above the sump. Whatever lies below it cannot be drawn off.

Check and fix: determine H3 and the system and check the length with the calculator.

Down tube presses on the sump

On the S, D and M systems the down tube moves down when the spear is opened, by the keg coupler or by the cleaning and filling head. If the spear is clearly too long, it presses on the sump. The consequences: sharp edges and scoring where microorganisms can survive, and mechanical damage to the sump and the tube edge. We have seen such marks in practice.

Check and fix: re-measure the spear length and check it with the calculator against H3 and bottom clearance.

Keg coupler and spear belong to different systems

Each system has its own keg coupler. A and G are identical inside, but not outside: the type A keg coupler does not fit G.

Check and fix: identify the spear on the keg, see Compatibility. The keg neck does not help here, as it is the same on all threaded systems.

Keg neck not parallel to the keg

If the keg neck is crooked, i.e. not parallel to the top and bottom chime of the keg, the spear cannot be screwed in cleanly and sits at an angle. The sealing surfaces of the filling plant then no longer seal properly. It looks like a spear fault, but the cause lies deeper in the keg.

Check and fix: check the geometry of the keg neck: is it parallel to the top and bottom chime? Also check the thread and sealing seat for damage and inspect the seals. A recognised keg service company can straighten a crooked neck, after which the keg is fit for use again.

Wrong tightening torque or alignment

On A and G, after installation one point of the black safety triangle points to the line on the body.

Check and fix: tighten to 80 ± 5 Nm and check the alignment. The manual for A and G shows every step.