Upgraditis: 2-group Grimac Commercial

[Thundergod]

Re: Upgraditis: 2-group Grimac Commercial

Moi? Mais non?

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Just for peace of mind, this morning I dismantled the big Sirai pressurestat to check the membrane and contacts, mainly.

The membrane appeared to be in pristine, excellent condition. No sign of hardening.

The contacts, I cleaned of any surface carbon, and they didnt appear pitted. (I was looking for similarities to spark plug pitting)

Also removed and cleaned the vacuum break valve.

And the dipstick for water level. The final 15 mm or so looked dirty, rusty, and I sanded it clean so water makes a better contact and turns off the pump.

Everything back together and working well.

Im not certain whether the pump pressure gauge oscillation is normal.

When brewing, it oscillates within a 1 mm range, which translates to about 0.2 bar.


-Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Robusto

Generally oscillation of the pump pressure is a sign that the pump is on the way out...... probably only good for a few thousand more coffees.....

I wouldnt worry about it at the moment - just keep an eye on it and if it starts to get a lot worse, you might have to look at a replacement.

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

1. So the pointer should be absolutely still during pours, then?

2. The brew cycle confuses me (its volumetric). Its as though its trying to mimick lever-style pre-infusion.

First, the pump comes on for a second at around 6.0 bar. The 3-way valve kicks in and some water is flushed into the drip tray.

Then the pump comes on again, and gently ramps up to 8 bar and out pours the coffee.

Any ideas?

--Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Robusto....

1. Yep, on a site where I collected info on testing potential commercial machine purchases.... that was one of the "tests"......and mine does remain stationary.

2. Mmmmmm that seem strange! Normally preinfusion is provided by the solenoid opening which allows mains pressure to build up in the PF. The pump also starts but the flow is restricted by the group jet (mine is 0.8mm)..... and that causes the pressure to increase slowly from mains to the 9 Bar.

The 3 way venting water to the drip tray sounds unusual......

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Gulp. A thousnad coffees left. Pump is good for only another 7 months then!  I dont know about rotary procons supposed to be whisper quiet, either.

Mine  emits an audible "hum"-like noise when operating.   Not a metallic rumble or anything, just what Id expect a pump to sound like.

--Robusto

[Sparky]

Re: Upgraditis: 2-group Grimac Commercial

Robusto,

Yep, pump pressure should be rock steady.

Your preinfusion sounds wierd. Id expect a pump spurt to say 4 bar (or that area, then a pause to let the puck expand and then on again for the duration of the shot. But I would not like the 3-way to exhaust during the process as this can damage the surface of the puck resulting in channelling... This pump pulse pre-infusion is common to a few machines including the new La Marzocco GS3 superhero home machine. None of them involve exhausting the 3-way during the process.

Oh and my new pump is whisper quiet. It actually goes Shhhhh if theres too much noise in the room

Cheers,

Mark.

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

The opening of the 3-way valve into the drip tray happens when I use the volumetric buttons. If I use the emergency rocker switch or non-volumetric button it doesnt happen.

--Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

I agree with Mark, releasing the pressure on the puck at that point would not be good for its uniformity...... and I cant think of any good reason why it would be designed that way......

Maybe the program in the volumetric computer is a little scrambled.... and operates the three way when it shouldnt be.

I dont know your particular machine at all, and each manufacturers machine has its little differences in operation.... which the designers believe makes it work that little bit better than the others - but I cant see opening the 3 way at that point having any positive effect.

[Sparky]

Re: Upgraditis: 2-group Grimac Commercial


Id be using the emergency rocket switch...

Does the pump pulse during manual operation?

Youve heard of explosive decompression in a space-craft. Just imagine how your puck feels under the same circumstances. Maybe its a natural selection procedure where only the strong pucks survive?

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Id be using the emergency rocket switch...

rocket switch?

5,4,3,2,1 - fire!

coffee machine entering orbit in 30 seconds ;D ;D ;D

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Theres no pulsing of the pump. Its just an audible hum. The pointer on the gauge doesnt do wild oscilations, but very tiny, almost invisible ones. Could also be due to my jury rigged fix inside it.


Ill have to observe whether the explosive decompression into the drip-tray is clear water or from the puck.

May be it is some odd by-pass thing within the group, where water already inside it is forced out without affecting pressure on the puck.

--Robusto

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

Id be using the emergency rocket switch...

rocket switch?

5,4,3,2,1 - fire!

coffee machine entering orbit in 30 seconds ;D ;D ;D

....For a taste sensation thats truly, "out of this world"

--Robusto

[robusto]

Re: Upgraditis: 2-group Grimac Commercial

The mystery deepens.

Ive pulled a double espresso, and observed the colour of the water from the 3-way-valve into the drip tray. It was very clear.

With the exhausted puck still in the group, I emulated a backflush routine as though the blind basket was in. Water emerged very clean and clear each time, no sign of having mixed with the grounds.

Im ...er...baffled.

--Robusto

[JavaB]

Re: Upgraditis: 2-group Grimac Commercial

Robusto....

That is strange indeed....

The 3 way is also a pressure relief valve (which normally releases supply water into the drip tray at 15 Bar)..... I wonder if it is malfunctioning.... and releasing at pump pressure.

Do both groups do exactly the same?