Vacuum Breaker Valve

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Ascaso W..517 1/4" Threaded Bleeder / Vacuum Breaker ValveEvery heat exchanger espresso machine (except the Nuova Simonelli Oscar) has a vacuum breaker valve on the top of the boiler or a pipe that comes from the top of the boiler. Another name for it is a vacuum bleeder valve. A sample of the vacuum breaker valve looks like the picture to the right.

There are different types of vacuum breaker valves that look like this. They can be bigger/smaller or come in different colors, like silver. The middle pin insert can be narrower/wider or longer/shorter. Typically, the taller the middle pin insert, the heavier the middle pin insert will be. Even the C-clip on the end can be different.

Please note that this part has nothing to do with pump pressure. You also won’t find this part in smaller home espresso machines.

Purpose and Impact of Types

The purpose of the vacuum breaker valve is to release the vacuum pressure in the espresso machine boiler. Specifically when it cools from a very hot state to room temperature. Without this part, the boiler will create a false vacuum pressure. As a result, the pressure regulator will read this as true pressure and not allow the unit to fully heat. Without the proper functioning of this part, you may notice the boiler pressure gauge will move up quicker than normal. You will also notice that the boiler pressure gauge drops to zero immediately upon opening the steam or water valve.

The vacuum breaker valve sometimes will and can stick. The lighter weight valves will stick sooner than a heavier weight vacuum breaker valve. The fundamental reason is that limescale prevents the middle pin insert from dropping to relieve the false vacuum pressure. Some of our competitors believe they are putting the heavier weight valves as a convenience to their customers. However, there are two schools of thought that the customer should decide:

  1. Lower weight vacuum breaker valves – Although they stick more often, they will notify you sooner that limescale is building up. As a result, you will need to soften your water. Since the limescale build up is so light, we do not recommend to descale.
  2. Heavier weight vacuum breaker valves – Although they stick less often, there is usually more limescale at this point of sticking. As a result, you will need to descale your espresso machine as well as soften your water. Limescale can affect the pressure regulator longevity, the heating element effectiveness, and the potential clogging of the internal valves. The purpose of the descaling is to remove the limescale build up.

What to do

If your espresso machine experiences the fault of not relieving the false vacuum pressure, power off the machine. Allow it to fully cool and open the steam wand to remove all the pressure out of the boiler. Remove the body panels to get access to the boiler and remove the vacuum breaker valve.

Carefully remove the c-clip, and soak the c-clip, middle pin insert, and nut in white vinegar or descaling solution overnight. Make sure to not lose any parts since they are not for sale individually. Rinse the parts the next morning. Use a very, very slight amount of olive oil on the shaft of the middle pin insert. Reassemble the vacuum breaker valve and place back on the machine. You can re-use any existing O-rings or metal washers.

You will notice water spritzing out of this valve during warm-up (but before the middle pin insert rises). Please consider this as normal operation for every machine that has this vacuum breaker valve working as it should. Water will never spritz up when the pin is in the up position during limescale.


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