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Uploaded on Dec 6, 2010

There has been some debate about Gaggia (and other) espresso machines that do not have a solenoid valve and, instead, use a spring loaded rubber mushroom shaped valve in the group head. Typically this valve is called the "group valve". Some people insist that the valve has no effect on pressure at the brew head - these same people believe that you must install an OPV valve to bleed off the extra pressure to get down to the 9.5 bars that is desired for espresso. This video shows a Portafilter gauge on a Gaggia Carezza with the group valve spring removed and then with the spring installed. This test is performed with the spring not fully tightened and also with it tightened down as it comes from the factory - this not only demonstrates that the valve does, indeed, affect the pressure seen at the brew head but that the tension of the spring also affects the pressure. The tighter the spring, the more the pressure is reduced at the brew head.

Based on the results of this test, I believe there is no need to install an OPV on these type machines that don't have a solenoid valve. Further, I believe this video demonstrates that with a stock group valve there is barely enough pressure at the brew head as is without an OPV - in fact for a double shot volume the pressure is a bit lower than desired.

Relaxing the spring tension slightly, by not fully tightening the cap on the group valve, helps bring the pressure up at the brew head. However a softer spring will also mean a few more drips from the brew head when the boiler heats above boiling temps, like when you are steaming milk.

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