Dave, I'd point to Ian's analysis:
cafeIKE wrote:Steam production and foaming milk successfully rely on several interelated factors.
It's the velocity of the steam that produces the foam.
The velocity of the foam is related to the hole diameter, steam volume and pressure.
More water, i.e. higher level will produce more steam when the pressure is released. The potential volume of steam is directly related to the water volume and temperature above the local boiling point at the boiler pressure. The down side of a high water level is the initial volume of steam is reduced and the pressure drops more rapidly when the valve is opened, reducing velocity.
The capacity to continually produce steam is related to the heat input, the input water temperature and the pstat setting. The water level has no effect. Water level affects how quickly the system can recover once the valve is closed.
The water level probe can be adjusted by loosening the small upper nut slightly and pulling up on the probe.
cannonfodder wrote:[...]With all the steam talk, I was thinking about playing with the water level as a possible fix. More water = higher pressure but less volume, lower level get you more volume but with less pressure.
More volume = higher pressure? The discussion reminded me of some of the saturation physics. The equation would not be true, I think, but am not 100.000% sure the water/steam are in saturated condition as per physics definitions.
I would say, more water creates more heat inertia so you suffer less from incoming cold water and the effect of losing steam maybe even. Losing steam however has serious cooling effect and must be compensated by switching on the steam heater a.s.a.p. In this sense, pressurestat deadband may be part of the equation.
Less water would mean more (saturated) water damp, at least initially.
cannonfodder wrote:[...]The key is matching the volume, heating element and steam tip to provide sustained steam.
From Ian's analysis I became aware of another aspect of the steam tip. Personally I never steam, so I have to discover these things, reading around. Most discussions I read on steam tips seem to focus on nr, size and angle of the holes. In fact, most of that discussion is an optimization problem that will differ per machine and where the discussion implicitly is about (flow) speed of the steam. The question then is if less holes or smaller holes in the steam tip could still maintain flow/speed of the steam, even when passing less quantity and what the effect would be on the time needed to heat the same amount of milk.
As to the VBM DB, part of the "not enough steam" discussion should then focus on nr of holes and diameter.
Having seen the photos and this debate, I would want to insulate that steam boiler btw. Being small, its surface area relative to its contents is larger than would be the case with a larger boiler. If it really would extend the steam life of the boiler is still to be seen though.
HB wrote:Some of the espresso machines I've tested included the factory inspection sticker showing it passed pressurization. They're not as high as you might think - only 2.0 bar, if I remember correctly. Personally I would sleep better knowing it's idling well below the factory pressure test: [youtube movie]
I am sure the leading people in these fora are aware of this and most certainly Dan/HB, but what you see in the movie is supposed not to happen with your espresso boiler
because it has an over-pressure valve (OPV). The experiment in the movie requires the OPV to either be sealed (made dysfunctional) or replaced by a permanent cap. It seems to me the boiler was prepared for the experiment as you can see one of the end plates has nicely come off for it to behave like a steam driven rocket.
In your espresso machine, if the OPV is opened, I wonder if it would close again when the pressure drops. I would expect it needs replacement, in which case you need to stay away from the maximum pressure it was designed to open at.
Regards
Peter
Netherlands
Europe