Two francs that decide whether the pump draws water
The tank adapter is where the water tank connects to the machine's water line. That is exactly where this O-ring sits. As long as it seals, the pump draws water cleanly. As soon as it hardens, the pump intermittently draws air – and you hear it straight away: the pump gets louder and irregular, and the extraction collapses.
The ring is one of those parts that gets stressed every time you remove the tank and that nobody ever looks at. Two francs, one quick move, and many diagnoses resolve themselves. The part number is ST44997261.
When it is due
The pump gets irregularly loud even though the tank is full. The extraction collapses or the pressure fluctuates. There is water under the tank compartment. The tank slides in noticeably easily – it used to take a little resistance. Or the old ring feels hard and brittle rather than elastic when you take it out.
At a glance
| Type |
O-ring |
| Installation point |
Tank adapter |
| Fits |
Rocket machines with this tank adapter – the documentation gives no model list |
| Scope of delivery |
one O-ring |
| Part number |
ST44997261 |
| Specification |
Inner diameter, cross-section and material are not stated in the documentation |
| Installation |
Installation by a qualified technician recommended |
| Brand |
Rocket |
Important for installation
The ring sits in the water path. Unplug the machine and depressurise it first. Fit the new ring dry or with a little water at most – no oil and no grease, which have no place in the drinking water path. Check the groove for limescale first: a new ring on a scaled seat will not seal a single day longer than the old one. We deliberately do not give step-by-step instructions here.
Who it is for
For anyone whose pump is drawing air, and for anyone renewing all the seals in the tank path during a major service anyway. With O-rings, the part number decides, not the appearance – if you are not sure which ring is in your machine, send us a photo of the tank adapter.
The tank connectors in the Rocket catalogue
The block through which the water tank couples to the machine differs by model series – above all in the number of outlets. Around it sit the coupling, the connector and the sealing ring. We stock nine items for this, and they are not interchangeable.
Five connector blocks: R839906007, the 2-way connector for Typ R, Evoluzione and R58, R839905147, the 3-way connector for the Appartamento, R839906135, the 3-way connector for Type V, R439908722, the complete connector for the Appartamento TCA and A439910400, for which our documentation names no model series.
Three parts around it: A439905146, the coupling for the tank connector, C449900709, the elbow as a push-fit connector and ST44997261, the O-ring for the tank adapter – in other words, this product.
Plus the tank itself: R489910457, the fully assembled water tank. Also most often ordered together with a connector are the water tank for all models except the Cinquantotto, the water tank for the older version of the Giotto and Cellini, the tank lid with plastic insert and the filter in the water tank.
The connectors look alike. If in doubt, count the outlets on your old part, or send us your machine's serial number and we will check the fit.
What goes with it
In the same path you will find the tank connector A439910400, the coupling for the tank connector, the filter for the water tank and the valve ball for the tank venting. We carry the complete tank as the water tank, fully assembled. Everything else is in Rocket accessories and spare parts and in the spare parts.
From our workshop in Bern and Zürich
When someone comes to us saying “the pump has become loud”, we look at the seals in the tank path first and only then at the pump itself. Surprisingly often it is a hardened O-ring for two francs and not the pump for two hundred. That is our own order of checks, not a manufacturer requirement. To listen whether the pump is running smoothly again, we pull two or three shots with the Nutty Delight, the Cozy Chocolate or the Very Nutty. More in our coffee beans.
Returns excluded
Spare parts are excluded from exchange and from return. They are procured specifically for each order and cannot be resold after installation or a test fitting on the machine. So please check your machine's model, year of manufacture and serial number before ordering – or drop us a line and we will check the fit together. Your rights in the event of defective goods remain unaffected.
Frequently asked questions
What are the dimensions of the O-ring?
Inner diameter, cross-section and material are not documented for ST44997261. With O-rings, the part number is what decides anyway – if in doubt, measure the old ring and send us the dimensions.
Is this an electrical part?
No. It is purely a seal with no electrical function.
Can I use grease or oil?
We advise against it in the drinking water path. Fit the ring dry or with a little water at most.
Does it fit every Rocket?
The documentation gives no model list. Send us a photo of your tank adapter or the serial number and we will check the fit before you order.
Can I see the part in your showroom?
Yes. We are in Bern at Gerberngasse 44 and in Zürich at Hagenholzstrasse 50b. Let us know shortly before and we will have the part ready for you.
Questions about the fit? Write to us at [email protected]. We deliver across Switzerland and to Liechtenstein in 2-4 working days.
