Espresso machine gaskets and seals

Espresso machine gaskets and seals

Espresso machine gaskets and seals

Each espresso machine uses gaskets and O-rings to seal the low-pressure hydraulics, espresso machines do not really work with high-pressure hydraulics. With incorrect use, incorrect selection of materials or lack of maintenance the chances for resulting leaks in an espresso machine are high.

The temperature range of an operational espresso machine varies. The temperature inside the boiler is 100 degrees (99.6 degrees) at 1 bar and up to 120 degrees at 2 bars.

The boiler pressure of an espresso machine can be from 0.8 bar to 2 bar. For the pump system, this pressure can be up to 12 bar. All materials discussed in the blog post are suitable for the pressure environment of an espresso machine, so the pressure is neglected here.

First, we will discuss the type of sealing materials and then the type of seals used in the machines.


The O-ring is one of the most important sealing components of an espresso machine. There are several materials commonly used for O-rings in espresso machines:

Chemical Term

ASTM designated abbreviation

Trade names






Chemigum®, Nipol®, Krynac®



Viton®, Fluorel®, Technoflon®



Silastic®, SILPLUS®, Elastosil, Wacker®

Ethylene Propylene


Nordel®, Royalene® Vistalon®, Buna EP®, Keltan®



Another important part next to the material is the Shore hardness of the material. For O-rings, the Shore A scale is used. This is a scale of 0 - 100 that defines the hardness from extra soft to extra hard. Each material has its own Shore range - the Shore number says nothing about the quality of the material, only about the hardness.1

Since an espresso machine is a multi-port hydraulic system, gaskets are required to make everything water- and airtight.

O-rings and their material

There are several materials commonly used for O-rings in espresso machines:






Hardness shore A

20 - 90

30 - 90

15 - 95

20 - 90

Temperature max





Temperature min










Compression set





Wear resistance










Water resistant

good - excellent




Steam resistant




poor - good

tear resistant

good - excellent


poor - good



Flange gaskets

In addition to the O-ringsflange gaskets are used to sealboilers,valvesheating elements, and brew groups. These are the crucial components to keep the hydraulic system tight.


Most commonly used is polytetrafluoroethylene (PTFE), usually under the trade name Teflon® by Chemours (formerly Du-Pont). This product covers a wide temperature range from -190 ° C to 260 ° C and is suitable for use in conjunction with food. The material itself is approved by the FDA (Food and Drug Administration). However, it is always convenient to have the declaration of conformity of the material manufacturer.

Fiber gaskets

There are many manufacturers of fiber gaskets in the world of seals. LikeKlinger,Frenzelit, and Victor-Reinz, just to name a few - so, it's difficult to discuss all the materials. That's why we keep it general for the specs. The products cover a wide temperature range from -50 ° C to 250 ° C on average.

Are all materials suitable for use in an espresso machine? Technically they are. But not all are classified as food-safe. If you want to know if the material you are using is food-safe read the product safety data sheet.

Copper gaskets

This type of gaskets and compression gaskets are primarily used to seal off connections between a male and female thread. Like with a safety valve on top of a boiler or a screw fitting and a threaded solenoid valve body.

Gasket type depending on component group

Each section of an espresso machine has different sealing methods and materials. The following parts of an espresso machine must be sealed:

Boiler flange:

Many boilers are basically a cylinder with a soldered end on one side and a bolt on the flange. To seal this flange, you need a flat boiler flange. These flanges are usually between 2 and 3 mm thick. Some have a bolt true configuration and others are just a thin ring. At present, significantly more O-rings are used.


Boiler fittings:

On top of the boiler, female connections are often soldered into the boiler. These are intended for parts such as pressure switch, safety valve, anti-vacuum valve, etc. To seal these components mainly shredded copper discs, fiber gaskets and PTFE gaskets are used.



For most espresso machines, the tubes are made of copper and the nut and brackets are made of brass. These soldered fittings are bolted to a male or a female fitting (using the fitting). This creates a small indentation that seals watertight. It's the same principle as a compression fitting in your home heating or cooling system.

The disadvantage of this system is that, in contrast to the heating or cooling system in your house, the soldering compression fitting is fixed. the sealing probabilities will never be the same as the first time installed. The advantage of the central heating and drinking water systems used in homes. Is that the compression ring can be removed and easily replaced with a new one.

Solenoid valves

There are 2 types of solenoid valves

The flanged solenoid valve normally has 2 bottom O-rings for the input and output. When the 4 screws are tightened, the O-ring is slightly compressed and seals.

The threaded solenoid valves work a little differently. In most cases, an external thread is screwed into the solenoid valve. Between the housing of the solenoid valve and the fitting is a small copper gasket.

Steam and water valves

Most steam and water valves operate on the principle of turning a switch clockwise to close a valve and open the valve counterclockwise.

The other principle works with a lever. When lowering or pushing a lever, a valve guide pushes or pulls a valve stem. This valve stem has at the end a gasket holder which normally presses against a valve seat. When lowering or pressing, so a gap between the valve seat and the seal opens, which opens the valve.

So, what type of gaskets are used for these valves?

For the valve gasket, these seals are used to seal the boiler to the outside:

To seal the shafts, the following gasket materials are common:

In most cases, a valve consists of a valve body and a valve fitting. To seal these, the following gasket types are used:

Water filling valve

The water filling valve is the most complex valve assembly in an espresso machine. It is often a combination where the pump pressure gauge, the overpressure valve (OPV), the attachment for a solenoid valve, attachments for brew groups, and in some situations also a manual filling valve are attached. This situation varies for the different brands and may even be different for each model.

Brew group

The brew group is the component with the most seals.  

The portafilter gaskets

These gaskets are installed in the brew group to seal the portafilter during the brewing process. Due to the wear of the metal of the brew group or the portafilter, they can be supplied in different height sizes. If the highest gasket is not high enough, there are always packing rings. These are often available in a 0.5mm and a 0.8mm configuration.

These portafilter gaskets are the gaskets that need to be replaced most often, due to the sliding motion over the portafilter gasket.

Traditionally, these gaskets are made of NBR rubber, but in recent years there have also been silicone gaskets.

Group locking gasket

This gasket is used in 2 different cases.

The gaskets that secure the brew group to the frame need not withstand water or pressure.

  • Cellulose gasket;
  • Fiber gasket.

For the case, where the brew group needs to be secured to the boiler, it is more likely to use other materials because they have to withstand pressure, temperature, and water.

Valve gaskets

In older pump machines that are not operated with a solenoid, valve gaskets are always required. These gaskets are normally forced under spring pressure against a valve seat to seal the valve in the brew group.

These gaskets are often made from the following materials:

  • EPDM;
  • FKM.

HX systems

Some brands such as La Cimbali and San Remo use a system in which the HX is directly connected to the brew group. To seal the heat exchanger, a seal is placed between the HX and the brew groups. Flat gaskets or O-rings are used for this purpose.

Heating elements

There are different types of heating elements. This also means that there are a variety of heater gaskets.

Heating element types:

Both the thread and flange heaters can use the same types of gaskets:

Sealing of groups or valve parts

The sealing of larger parts is mainly done with flat gaskets or O-rings. This depends mainly on the manufacturers, as they use different design methods.

Best material

So, can you say that 1 material is the best? No, not really, every material has its pro’s and con’s.

For static seals, I prefer silicone or FKM O-rings - pricewise silicone is more interesting. In cases where O-rings cannot be used, I prefer a food-safe fiber material gasket because it is more compressible and malleable than PTFE.

For dynamic seals, I would not recommend silicone because it has low tear resistance. But sealing materials like NBR, EPDM, and FKM are all suitable for this application. It is likely that the NBR and EPDM will have to be replaced faster due to aging under temperature stress.