The ring that stops the steam tap from blowing out at the knob
A steam or water tap seals in two places: at the front on the valve seat, so nothing passes through when it is closed, and all the way around the spindle, so nothing escapes past the knob. This O-ring takes care of the second job.
It works under movement: every time you open and close the tap, the spindle turns inside it. Add heat and limescale to that. Of all the seals in the tap, it is the one that needs replacing most regularly – and also the cheapest.
When it needs replacing
Steam or water escapes at the knob when you open the tap, not at the steam wand. That is the clear sign, and not something to wait on: whatever comes out there is hot.
A knob that suddenly turns noticeably more easily or jerkily also points to a worn-out ring.
If a damp film remains on the spindle after closing, or limescale builds up there, the seal is already no longer complete.
At a glance
| Type |
O-ring, spindle seal |
| Fitting location |
Steam and water tap, on the spindle |
| Fits |
Rocket machines for which the manufacturer lists part number A449904334 |
| Scope of delivery |
one O-ring |
| Part number |
A449904334 |
| Version |
Elastomer |
| Installation |
Installation by a specialist recommended |
| Brand |
Rocket |
Important for installation
The tap carries steam and hot water. Before opening it, disconnect the machine from the power supply, release the residual pressure through the tap and let it cool down. Remove limescale from the spindle and groove before fitting; a new ring on a rough, scaled spindle will not last any longer than the old one.
Who it is for
For anyone who has noticed leakage at the knob of their steam tap, and for workshops overhauling a tap.
The ring is often part of a chain: spindle, spring, ball plate and cap belong to the same tap and are available individually from us.
The O-rings and sealing rings in the Rocket catalogue
Rocket fits a whole range of O-rings in the steam path, water path and boiler that look very similar from the outside. For most of them, the documentation states neither inner diameter nor cross-section – they can only be told apart reliably by the part number. That is why we list them individually, with the number in the title or in the table:
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O-ring steam and water tap – A449904334
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O-ring for the cap of the steam and water tap – A449904672
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O-ring rotary knob steam and water, Cellini and Giotto – C400002786
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O-ring water nozzle, Appartamento to Mozzafiato – C400003008
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O-ring 3-way valve – M449907403
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O-ring S2 valve – M449907143
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O-ring 4250 silicone, R9 – M449905837
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O-ring 3187 Viton, R9 – R499907384
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O-ring drain elbow, Boxer, RE A and R9 – M449905463
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Copper sealing ring heat exchanger – C479900673
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O-ring boiler top, Porta Via – A449906261
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O-ring boiler bottom, Porta Via – A449906262
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O-ring heating element, Porta Via – A449910266
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O-ring 18 × 5 mm machine foot, R Cinquantotto – A449906954
If you measure the part you removed and don't know the number, send us the model and serial number – we will check it against the exploded view.
What goes with it
Directly next to it sit the ball plate and the spring for the steam and water tap.
Depending on the series, the matching spindle goes with it: Premium Plus and Evoluzione, R58 and Bicocca or Appartamento.
The O-ring for the cap belongs to the same tap. All items are listed in Rocket accessories and spare parts.
Our workshop habit: when a tap is open because of the spindle ring, we check the spring and the ball plate at the same time and descale the spindle in a warm descaling bath instead of sanding it down. Sanded spindles become rough and wear through the new ring within months. That is our experience from Bern and Zurich, not a manufacturer's specification. For the function test, we froth milk for a cappuccino made with Cozy Chocolate.
No returns
Original spare parts are excluded from exchange and return. They are procured specifically for each order and cannot be resold once they have been installed or test-fitted on the machine. So before ordering, check the model, year of manufacture and serial number of your machine – or drop us a line and we will clarify the fit together. Your rights in the event of defective goods remain unaffected.
Frequently asked questions
How can I tell that it is this ring and not the valve seat?
If steam escapes at the knob while the tap is open, it is the spindle seal. If it drips from the steam wand while the tap is closed, it is the valve seat.
What are the ring's dimensions?
The manufacturer does not state any dimensions for this item. The decisive reference is the number A449904334.
Does the ring fit every Rocket tap?
No. Rocket uses several tap designs. Send us the model and serial number and we will check the fit.
Can I just turn the tap tighter until a replacement arrives?
Please don't. That will damage the valve seat, and a one-franc part turns into an expensive repair.
Can I see the part in your showroom?
Yes. We are in Bern at Gerberngasse 44 and in Zurich at Hagenholzstrasse 50b. Bring the part you removed, we will compare it with the replacement on site and you only take home what really fits.
Questions about the fit or the serial number of your machine? Write to us at [email protected]. We deliver across Switzerland and to Liechtenstein in 2-4 working days.
