Espresso machine safety valves
  • By Thijs Brooks
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    • Espresso machine safety valves

    One of the most important safety features on a espresso machine is a boiler safety valve. This is the last resort of your espresso machine

    Why do you need a safety valve? One of the most recent incident of a pressure valve not working correctly is with Sainsbury’s in 2009. Where the boiler of a Elektra espresso machine exploded. There was a new type of safety valve installed which didn’t function properly

    A typical espresso machine boiler is filled with water and heated with a heating element. Seen it is a closed boiler there will be an increase of pressure inside the boiler, as well as temperature. Normally the element is controlled with a pressure switch, when the pressure inside the boiler reaches a certain pressure the pressure switch will shut off the power to the heating element. Once the pressure has dropped the heating element will start to turn on again.

    But it is possible that this pressure switch fails, so now you have the situation that the power to the heating element isn’t turned off anymore. And will keep heating the water inside the boiler and increasing the pressure of steam inside the boiler.

    In some cases there is also a boiler thermostat or heating element thermostat installed. This will shut off the power when it reaches a pre-set temperature and needs to be reset manually.

    But if the thermostat isn´t present or fails as well the safety valve will open at a pre-set pressure and will release the over pressure out of the espresso machine. This prevents that the boiler will explode.

    How does a safety valve work?

    The safety valve itself has a brass body, with threads on the in- and outside. Inside this valve are 4 components(note this can vary from model and brand). The first item is a brass gasket holder with a gasket inside. This gasket normally seals off the boiler from steam escaping. This gasket holder is held in place with a conical shaped spring holder. On top of this you will find a stainless steel compression spring. Finally to keep everything in place you will have a brass set screw. The opening pressure of the valve is factory pre-set. When you want a high opening pressure, the setscrew is screwed inwards. When you want a lower opening pressure it is screwed towards the outside.

    What type of safety valves are there for espresso machines?

    There are numerous of configurations for safety valves. Things like, thread type, sealing material, pressure, valve material, certification, spring type, testable.

    Thread type:

    On most espresso machine safety valves it is a male thread. The most standard type of thread used is a 3/8” BSP-G, but you will also also find a ½” BSP-G and ¼”BSP-G on various brands. There are some brands which also use metric threads, such as La San Marco, Gaggia and Pavoni.

    Calibration

    Boiler safety valves for espresso machines are normally set at 1,8 bar. But this does also depends on the brand of espresso machine it is used on. they range from 1,5 bar all the way up to 2,1 bar. When these safety valves are certified, they are in sort of a way fixed and can´t be adjusted. This is done for instance with cover plates or copper/lead seals so that they can’t be changed.

    There are some models of safety valve which don’t have certification. With these models you can adjust the opening pressure. But most models are CE, PED or auto certified

    Sealing material

    For safety valves there are various types of seals which can be used inside the safety valve. This can be nbr, fkm, silicone and PTFE. With espresso machines you mostly find Viton seals.

    Testing safety valves

    In some cased you will find a ring on top of the boiler safety valve. When you pull this ring you will pull a shaft which opens the valve. With this procedure you can test if the sealing material isn’t stuck to the mating surface.

    Sealing off the safety valve.

    The safety valve can be sealed of with various sealing materials. In most cases a copper crushable gasket is used. But in the field you do see the usage of PTFE tapes or liquid sealing materials as well.

    Replacement

    How often do you need to replace your boiler safety valve? You should replace it every 2 year. A boiler safety valve is a relatively inexpensive item, which can have big consequences if it fails.