Green Coffee Buying Club
Coffee Discussion boards => Hardware & Equipment => Topic started by: Tex on April 19, 2009, 12:41:12 PM
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If your espresso machine doesn't have a 3-way valve then it has a group valve.
Espresso machines will often leak when you steam or pull hot water from the steam wand. What you're seeing is normal for any machine without a 3-way valve. In it's place such machines use a group valve; a one-way valve that permits hot water to flow to the grouphead when a shot is pulled, but keeps coffee & grounds from being flushed back into the boiler before & after a shot is pulled.
The group valve is rated at ~1.4 bar. The OEM steam thermostats are set at ~300°F, a temp that corresponds to ~4 bar. As you can see, the pressure generated when steaming will force hot water & steam back through the group valve & grouphead. Here's a link (http://www.wholelattelove.com/articles/espresso_machine_repairs.cfm) that explains it in detail.
I get around this situation by using a blank back flushing filter basket when I steam.