Filling the boiler for better temperature stability?

[hbuchtel]

So if you have a Gaggia Espresso (w/out a 3-way valve) and you want to reduce the intrashot temperature drop ('cause of the incoming un-heated water), could you first open the steam valve, turn on the pump till water comes out the wand, completely filling the boiler, then pull your shot?

A Gaggia boiler holds 120ml, but if it has an air pocket at the top it may only have 100ml or so of water in it... so filling it to capacity should reduce the effect of the incoming cooler water, right?

This should also be true for Silvia's 300ml boiler, but I think you'd have to disable the 3-way...

Henry

(please excuse my uneducated questions, I'm about to receive my first 'lectric pump machine and I'm a bit excited...)

[luca]

Hey Henry,

Typical temperature surfing involves running water out of the boiler to when you're kicking the element on. So, yeah, full boiler.

Cheers,

Luca

[hbuchtel]

Hey Luca, I understand that keeping the element on during the shot would help, but this full boiler thing . . . let me try to explain what I mean here-

Here we have an empty boiler, as if the machine were new. Two things to explain, the tube in the middle of the boiler (described better here) leads to the coffee (the PF). Between the tube and the PF there is a valve held by a spring. Normally this stops water from leaking out of the boiler. If there is pressure in the boiler the valve will open.


So you want to fill it up, right? The reservoir is full and you turn on the pump. You have two choices, leave the steam valve closed (A) or open it up (B).

You are pumping water in, and because the steam valve is closed pressure builds up enough that the spring valve opens. At this point the only thing coming out is air. (2.A)


Here the steam valve is open, so the air is going out at the same rate that water is coming in and there is not enough pressure to open the spring valve. (2.B)


Now back to the 'steam valve closed' example, the water level has raised to the point that the air above it is trapped and water is coming out of the PF. At this point you would stop! (3.A)


In the 'open steam valve' example the water level keeps going up 'cause the air is escaping out the top of the boiler. (3.B)


Once the boiler is completely full water will start coming out the steam wand. At this point you would stop. (3.a.B)


So here is example A- The water level is at or just above the tube (standpipe) and there is a pocket of air trapped above the water. If the boiler capacity is 120ml then there is maybe 100ml of water in the boiler. (4.A)


Here is example B- The boiler is completely full (120ml) of water. (4.B)


Assuming the water is at the temp that you want, you pull a shot-

In example A the incoming (cold) water will compress the air pocket until there is enough pressure to pull your shot. So you have 100ml of Hot water, about 60ml of Cold water (for the espresso+saturating the puck), and another ~20ml of cold water to take the place of the compressed air. 100 to 80 Hot to Cold.


In example B the incoming water will meet a full (120ml) boiler. As water does not compress much (compared to air) the pressure required to make your shot would be met immediately and only the amount of water that makes your espresso would enter the boiler. 120 to 60, a much better ratio, and hopefully would cause less of a drop in temp during the shot.


Steaming is another way to create an air pocket, so the boiler would have to be filled after steaming. Would keeping the element on during a 'full boiler shot' actually cause the intrashot temp to raise? Dunno...

Well, that was fun, I hope it made sense!

Henry

[hbuchtel]

After using my new machine (SYL-100) for a couple days I think I know why nobody worries about filling their boiler like I described above... cause I was wrong!

When it is at brewing (not steaming) temp and I open the steam valve a full 2 oz of water squirts out- indicating that the boiler is pressurized and full at least to the level of the steam wand port.

So no silly filling procedure is necessary!

Henry

[oofnik]

The only time I need to fill my boiler back up the way you described is after steaming. Otherwise it's always full. What do you think of that machine? I've seen one but I haven't brewed with it... looks pretty promising for its price.

[hbuchtel]

The only time I need to fill my boiler back up the way you described is after steaming. Otherwise it's always full.

After steaming I fill up the boiler the 'natural' way (ie just turn on the pump till water comes out the head). Opening the steam valve during pumping doesn't seem to get any more water into the boiler...strange, that.

One more piece to the puzzle- after the machine cools to room temperature no water comes out the steam wand! I thought the pressure in the boiler was created by the pump + the one-way valves but it appears that it comes from the expansion of the water when heated... ??? wait that doesn't make sense...

What do you think of that machine? I've seen one but I haven't brewed with it... looks pretty promising for its price.

My sentiments exactly! I've only had it for 4 days so I'll keep my trap shut

Henry

[jesawdy]

After the machine cools to room temperature no water comes out the steam wand! I thought the pressure in the boiler was created by the pump + the one-way valves but it appears that it comes from the expansion of the water when heated... ???

If anything, on a single boiler, once the machine cools to room temperature and you open the steam wand it will suck some air into the steam wand/boiler. A vacuum is created when the water in the boiler cools. Most heat exchanger machines have a vacuum breaker valve that prevents the formation of a vacuum on cooling. More importantly, the vacuum beaker prevents false pressure in the boiler at startup, since the vacuum breaker valve doesn't close until pressure builds up in the boiler.