The neck rubber seals the charger neck, while the puncture pin pierces the seal. The neck rubber ensures that the gas can only flow towards the inside of the siphon. Both components are subject to high thermal shocks, as the gas flowing in the siphon when the charger is pierced, cools them to below freezing.
Over time, the material of the neck rubber will wear down and become inflexible. The gas then hisses out at the charger neck or, in extreme cases, can blow out and can cause frostbite. It is usually best to replace this part during maintenance.
There are two types of puncture pins and a neck rubbers available to buy. It is important that you pair them correctly. The longer blue rubber should be used for the longer pin. For short pins, use the shorter, black rubber.
The difference is because the fact that the redeemable chargers had a more inwardly positioned seal than the disposable chargers that have been on the market since 2018. The use of redeemable cartridges was made possible by the use of a long needle and all siphons were originally equipped with one. When changing to disposable chargers, the change in the sealing element would have caused the long needle to puncture the charger before it was sealed, so it was necessary to introduce a longer neck rubber to seal the charger’s neck sooner.
The blue neck rubber is widely available. It is marketed by Szász Kft. as “Szifon nyakgumi (A04)” and is listed in the LISS range as “9103 Neck-rubber”. It is also included in the Szász Siphon Repair Kits (unless it is an older kit), along with the long needle.
So again, the blue neck rubber is necessary because the old black neck rubber does not seal the charger neck when the seal is punctured, so the gas blows out. The black neck rubber is shorter than the blue one. However, another solution – used by LISS itself for its soda siphons manufactured after 2018 – is to use a shorter puncture pin. With the shorter pin, the black neck rubber also works properly. In other words, the key is to choose the matching pair of puncture pin and neck rubber. The longer blue coloured rubber should be used with the long puncture pin. For short pins, use the shorter, black rubber.