Upgraditis: 2-group Grimac Commercial

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

JavaB, Ive kept a close eye on the vacuum break valve, testing it often to ensure it works, and it does -- or did.

Im hoping that is the problem so I dont have to look for other explanations.

Ill look at it tonight during powering up to make sure it doesnt prematurely trap air. I must admit though, I dont mind a 5-minute deadband on the pressurestat! But only if its genuine.

-Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Robusto

Even if it works perfectly..... and mine does...

Once pressure starts to build - the valve closes as it is supposed to..... but that pressure is due to a mixture of air and steam......

If you open a steam wand..... the exiting steam (under pressure) also draws out the air..... so you end up with just steam in the space above the water....

It is recommended (by trainers on these machines) to open a steam wand when you shut down and when you start up..... and because that is impossible to do this on a timer - mine is on 24/7....

You can test it by turning on a steam wand for a few seconds..... Does the pressure drop way down- possibly almost to zero? If so ..... air in the boiler!

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Robusto

You can test it by turning on a steam wand for a few seconds..... Does the pressure drop way down- possibly almost to zero? If so ..... air in the boiler!

Thats what made me suspect the vacuum break valve. Normally opening the steam wand barely affects boiler pressure. But this time, it quckly dropped from 8 bar to about 5 --almost instantly.

Mind you, there was still more than enough steam on hand to do a double latte without trouble.    

--Robusto

PS: that of course should be POINT 8 and POINT 5 bar. (edited 16.37)

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Thats what made me suspect the vacuum break valve. Normally opening the steam wand barely affects boiler pressure. But this time, it quckly dropped from 8 bar to about 5 --almost instantly.

Mind you, there was still more than enough steam on hand to do a double latte without trouble.

--Robusto

Yep.... thats air in the boiler - and it doesnt mean the vacuum break is faulty either.

The first time it happened to me - it was almost panic stations..... The boiler was apparently up to pressure really fast and, like yours, it was only on for a shot duty cycle (thats good I thought.... maybe one of the elements wasnt working before and has now kicked in.... )

But then I went to texture some milk.... seemed to start OK and then ran out of steam.... a quick glance at the gauge.... and it was down to a couple of Bars.... Oh no... something has broken

The heater had kicked in almost instantly (but for a short burst?).... and pressure came back.... only to disappear just as quickly.... It eventually twigged as to what had happened.... left the steam valve open for a while.... heater stayed on..... when there was the normal amount of steam, closed the valve.... and all back to normal : :

When I did the Commercial machine coffee course some time later, the trainer was very specific about opening at least one wand at shutdown (just in case the vacuum break doesnt work (it can- and does sometimes stick - and who wants a crushed boiler) and also opening at startup to remove the air....

I sat there with a rye smile on my face..... :-[ : :

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

That was a good learning experience, JavaB. Simple solutions to what appear to be at first glance deeply mysterious technical issues are always a welcome outcome.

As you say, leaving the machine on permanently obviates problems caused by air being sucked in by the vacuum break valve, not being expelled later .

I like to be asleep when the machine powers up on its timer. So if this occurs again, I can only manually bleed the air when I lazily arise an hour after start up.

If this gets to be a reoccuring problem -- its back to 24/7 operation. After all, running costs are the same, and there should be less stresses on the metal.

-Robusto

[Sparky]

Re: Upgraditis: 2-group Grimac Commercial


Ill just pick up on one thing that Robusto mentioned. I have disabled one element on the Pav and it seems to make an inordinately loud boiling sound with pronounced gurgling when the element switches off. However I havent run the machine with the full 4.5 kW heating capability, so I cant tell if it is louder than it should be.

I have also had a couple of wierd milk events as well. On occasion, opening the steam valve has resulted in a milk explosion and huge bubbles. However, it is mostly very predictable and well behaved, making silky smooth milk. Ive gotten to the point that the 8-10 secs of milk frothing seems like a long time.

[Dennis]

Re: Upgraditis: 2-group Grimac Commercial

Sorry, I know this is pretty OT but cant help myself. It is however, good advice.

Quite a while ago now I turned on the electric kettle and couldnt hear it start to make that underwater sizzling sound. So I took the lid off, reached in and pinched the element between index finger and thumb - DOH...it was working!

To make things worse, one of my daughters was watching at the time and couldnt stop laughing when she saw me recoil. I got cranky and asked why she didnt warn me, and she replied, I couldnt believe you would do something so stupid.

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Sparky / Robusto....

I agree with you both..... less elements more noise... (noticed that during post restoration testing). It is very quiet with all 3 elements working.

And my guess is.....

Because you have less surface area transferring heat into the water- to reach the pressure required for cutoff- the element/s are on for longer, they can get a little hotter (thermal gradient from the core to the outside surface of the element reduces), the water close to the heater is boiling more furiously.... when there are more elements operating the heat transfer into the water is over a larger area and is therefore more effective.... less local boiling and less noise.

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

I couldnt believe you would do something so stupid.

;D ;D ;D ;D ;D ;D ;D ;D

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Sparky, when my element switches on, the unmistakable but gentle sound of water being heated starts immediately.

But once the pressurestat cuts off power, the sound also stops, virtually immediately. Not with a bang, but a whimper.

Thats the normal operation. But yesterday it misbehaved, having been switched off while we were away a few days before Easter. That heating noise was very pronounced. Now that I have bled air out, its back to normal.

Could your milk explosion have been caused by a rush of air-driven steam?

I do love the infinite steam power of these commercials. And the sound of frothing is sweet --once mastered.

-Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Could your milk explosion have been caused by a rush of air-driven steam?
-Robusto

Or air mixed with the steam..... steam gets condensed in the milk.... air blows big bubbles and milk everywhere

I dont know how either of your HX work.... but in a La Cimbali HX (and many others) part of the HX is in water (good thermal transfer).... part in steam (reasonable thermal transfer).... the two combined determine the HX dynamic temperature. Now if you have air (poor thermal transfer) rather than steam in the boiler.... this will reduce the HX dynamic temperature..... it will in fact wreck the tuning of your HX....

Another good reason to make sure you have bled out all the air (and it takes quite a while even with a steam wand open)..... the vacuum break wont do much at all as it closes far too quickly (mine is closed at about 0.1 Bar - or even less)

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

JavaB, I could be mistaken, but I dont think that extra noise came from less power .

I only had the machine operating with less power for a day or so last week before we went away. But I cant recall that it was any different from the full 3200W version.

The noise, I suspect, is somehow related to the trapped air, which tricks the pressurestat into remaining on for longer. A full minute instead of 20 or 30 seconds. Perhaps all that extra heat causes the water to emit that groan?? :-/

Dennis, you should be proud of your daughters perspicacity. ;D ;D


-Robusto

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Ah, strange you should mention about the HXs JavaB.

When I first got the machine the boiler pressure was set to 1.1 bar. The cooling flush took forever, about 200 mls.

Now, at 0.8 bar, I am not so sure I need to do any cooling flush.

Im not familiar with the ritual, but from the videos and descriptions Ive seen, the shower screen water in the Grimac now appears to be quite stable. No spitting.

Ive used a cut-down polystyrene cup and thermocouple to take temperature readings.

And they come out at around 92/93 degrees. Thats after long periods at idle, with no flushing.

Ill have to repeat the experiment several times to prove its no fluke allied to ambiant temperature and other variables before I can be secure in the knowledge that the flushes are definitely not needed, though.

I cant determine how much of the HX tube is submerged. I wouldnt think the sight glass level is directly related to actual boiler water level.

--Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Im not familiar with the ritual, but from the videos and descriptions Ive seen, the shower screen water in the Grimac now appears to be quite stable. No spitting.
--Robusto

Well Id say you are probably correct - no cooling flush required...

Mine does a water dance (with steam) for about 150 ml if idle for 5 minutes or so (at 1.1 Bar also).

I cant determine how much of the HX tube is submerged. I wouldnt think the sight glass level is directly related to actual boiler water level.

Mmmmm.... now when I went to school, (admittedly a LONG time ago ), water found its own level... so if both the ends of the sight glass are open to the boiler - as they should be (not blocked with scale) - then the water inside the boiler will be exactly at the same height as the water level in the sight glass.... and that should allow you to determine how much of the HX is in water and how much is in steam (or air :)

[Sparky]

Re: Upgraditis: 2-group Grimac Commercial


err, the sight glass is directly related to the boiler water level. It is infact that level. My HX is about 50% exposed. The average pressure is about 0.9 bar and the water dance is minimal. At 0.8 bar average there was no water dance, but the groups ran too cool. At 0.9 bar (average, as the PS is set to 1 bar, with a 0.25 bar deadband) the group is about 92 oC idle and the water dance is very minor. At the original 1.1 bar (or 1 bar average) setting the water dance was dramatic and went for longer than I cared to flush.

As for the air/steam scenario, thatd be my guess as well. Note: bleed air out of boiler before steaming....

Im very happy with the way my machine is running and the tweaks are now just an endevour to take my espresso to the next level.... the fabled red crema zone.