Silicone instead of rubber – the ring for the hot side of the R9
Silicone withstands higher continuous temperatures than many other elastomers and stays soft for a long time. That is exactly why this ring sits where an ordinary rubber ring would harden after a short time. The designation 4250 is a size code from the standard; the part number M449905837 is what counts when you order.
The R9 family has several sealing rings that are hard to tell apart in your hand. The material is the reason why you shouldn't swap them for one another: what stays tight for years in a cold spot turns porous within weeks in a hot one.
When it's due
A ring that no longer returns to its round shape when removed, but stays lying there as a flat strip, has lost its resilience and no longer seals reliably.
You can spot hardening with a squeeze test: an intact silicone ring can be pressed together between your fingers and springs back. A worn one feels like a piece of coated wire.
Moisture, escaping steam or a fine limescale edge at the joint are the signs you can see from the outside – usually only once it has been going on for a while.
At a glance
| Type |
O-ring, sealing ring |
| Installation point |
Steam and water circuit of the R9 |
| Fits |
Rocket R9, for which the manufacturer lists the number M449905837 |
| Scope of delivery |
one O-ring |
| Part number |
M449905837 |
| Version |
Silicone, size designation 4250 |
| Installation |
Fitting by a specialist recommended |
| Brand |
Rocket |
Important for installation
The installation point carries hot water or steam. The machine must be disconnected from the power supply, depressurised and cooled down before it is opened. Place the ring cleanly in the groove, do not twist it and do not pull it over threads.
Who it's for
For businesses with an R9 and for technicians who carry out an overhaul and replace all the sealing rings.
We don't have a dedicated machine category or a permitted model tag for the R9 – the item can be found via the part number and the spare parts category.
The O-rings and sealing rings in the Rocket catalogue
Rocket fits a whole range of O-rings in the steam circuit, water circuit and boiler that look very similar from the outside. For most of them, the documentation states neither the inner diameter nor the cross-section – they can only be reliably told apart by their part number. That's why we list them individually, with the number in the title or in the table:
-
O-ring steam and water tap – A449904334
-
O-ring for the cap of the steam and water tap – A449904672
-
O-ring rotary knob steam and water, Cellini and Giotto – C400002786
-
O-ring water nozzle, Appartamento to Mozzafiato – C400003008
-
O-ring 3-way valve – M449907403
-
O-ring S2 valve – M449907143
-
O-ring 4250 silicone, R9 – M449905837
-
O-ring 3187 Viton, R9 – R499907384
-
O-ring drain elbow, Boxer, RE A and R9 – M449905463
-
Copper sealing ring heat exchanger – C479900673
-
O-ring boiler top, Porta Via – A449906261
-
O-ring boiler bottom, Porta Via – A449906262
-
O-ring heating element, Porta Via – A449910266
-
O-ring 18 × 5 mm machine foot, R Cinquantotto – A449906954
If you measure your removed part and don't know the number, send us the model and serial number – we'll check it against the exploded diagram.
What goes with it
For the R9 we also stock the valve seal kit, the lever seal kit and the O-ring 3187 Viton.
Mechanically, the spindle R229905344 and the steam and water valve also match.
Everything else can be found in Original spare parts and Rocket accessories and spare parts.
How we handle it in Bern and Zurich: during an overhaul, we replace all the silicone rings of an assembly together, even if only one was leaking. Replacing them one by one means opening the machine again in three months – and the rings cost less than the labour. That's our experience, not a manufacturer requirement. Afterwards, we run a full cycle with Cozy Chocolate until temperature and pressure are stable again.
No returns
Original spare parts are excluded from exchange and return. They are procured specifically for each order and cannot be resold after installation or a test fit on the machine. So before ordering, please check the model, year of manufacture and serial number of your machine – or drop us a quick message and we'll clarify the fit together. Your rights in the case of defective goods remain unaffected.
Frequently asked questions
What does the number 4250 mean?
It's a size designation from an O-ring standard. What matters for ordering is the part number M449905837.
Can I use a normal NBR ring of the same size?
We advise against it. The material is the point here: silicone withstands the temperature, many standard rings don't.
Does it also fit the R9 One?
The documentation lists the number for the R9. We're happy to check whether your series uses the same position based on the serial number.
Are several rings needed?
That depends on the assembly. One ring per position is supplied.
Can I see the part in your showroom?
Yes. You'll find us in Bern at Gerberngasse 44 and in Zurich at Hagenholzstrasse 50b. Bring the removed part with you, we'll 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.
