Expansion Valve Drip - Aha Moment

[chas]

There used to be many comments on this forum about dripping from the S1 Expansion valve. (This doesn't apply to the MIni.) This seemed to happen only when the group boiler was on, usually just a few drops each time. Chris got enough complaints that he finally asked LaSpaziale. They told him that this was normal behavior. Still I always had my doubts.

Now that I have the GS/3, I've had an "aha" moment and agree that it is normal. On the GS/3, the group pressure gauge shows the pump pressure when the pump is on and the group boiler pressure when the pump is off. The expansion valve is set while the group boiler is on with the pump off so that the boiler pressure never exceeds 12bar.

On the V2, if you look at the water flow diagram in the User's Manual, you will see that there are one-way valves between the group boiler and the group pressure gauge so that, when the pump is off, the group pressure gauge reads the street pressure rather than the group pressure. This plumbing difference between the two machines of where the group pressure gauge picks off the pressure is why the setting of the Expansion valve has to be done with the pump pressure of the S1temporarily increased to 12bar.

However, the bottom line is that when you get a few drips from the S1 Expansion valve while the group boiler heater is on, the group pressure actually has exceeded 12bar and this is why the expansion valve opens and drips. This fact is just invisible to the S1 user because the group pressure gauge never shows the actual boiler pressure.

[cruiten]

On the surface your explanation makes perfect sense; in fact, it was an "Aha!" moment for me as well.

However, I started to think about it all and one question just kept bugging me:

• On my machine the intermittent dripping starts almost immediately after I turn on the machine; how could the pressure ramp up to approximately 12 bar so quickly from a "cold" start?

I am not attempting to challenge your explanation; however, I would greatly appreciate any input as to my nagging question so that it all makes sense to me...

Thanks,

[Endo]

Just a thought:

The OPV on the Vivaldi uses a huge, stiff spring (compared to other machines) and likely doesn't require much displacement to generate the seating force to resist 12 bar. Could it be that the stiff spring or rubber seat needs to warm-up a little and expand in order to seal properly?

I can't tell from my Mini since the overflow is sent back to my pump.

Another thought: Could you try removing the rubber OPV seat and flipping it over just to be sure it isn't grooved (like a head gasket) over time? I expect it might need to be changed as well after 2 years or so.