Pressure Build-up & Back flow operation

[Barton, John]

An operational question to those of you who have spent some time under the hood; how is Brewtus’ pump wired to divert between the brew boiler and the steam boiler?  Reason I ask is that I would like to understand what happens when there is to much resistance from the puck.

 

My experience over the weekend:  I over filled the portafilter a bit and compensated by tamping a bit over 30 lbs.  This was going to be a learning shot.  When I over filled the basket before with my old La Pavoni Lever machine, I would simply add the additional pressure needed (manually) to pull the shot.  I was curious how Brewtus would respond to this.  My expectation was that if the resistance was to great that the pressure release valve in the group head would open and the pressure and water would be discharged into the drip tray.  I turned on the pump at the brew group and waited.  After 15 or so seconds I started to get some espresso dripping through.  I watched the steam boiler pressure go up to 2.0 and then turned the pump off at the brew group.  In total I got about an ounce and a quarter in 60 seconds +/-.  When I turned off the pump with lever on the group, the pressure in the steam boiler dropped to 0.2.  Bleeding the steam wand yielded a constant stream of water – no surprise given the pressure.  Then the pump turned on by itself – as though the steam boiler was calling for water.  After about 30 seconds I shut off the power to stop the pump.  After about 1 minute I turned the power back on and Brewtus returned to normal operating mode.

 

What was going on behind the scene here?  I am guessing that the pressure build-up at the puck diverted the water from the brew boiler into the steam boiler.  This doesn’t seem like a desirable operation in the order of things.  Comments?

 

John N. Barton
Zimmer Gunsul Frasca Partnership
Architecture / Planning / Interior Design 
925 Fourth Avenue, Suite 2400
Seattle, Washington  98104
Direct: (206) 521-3444
Fax:      (206) 623-7868

 

[Sean Lennon]

Hi John,

read my post on "potential source of false pressure"

Essentially you pushed water back through the solenoid valve between
the brew and steam boiler and overfilled the steam boiler.

I have had the same issue with my machine once before as have others.
I have no answer as to a solution except to give Todd a call.
I have a different valve in my machine than everybody.

Sean

Sean

[Barry Corliss]

on 4/6/05 8:27 AM, Barton, John <JBa...@zgf.com> wrote:

> I over filled the portafilter a bit and
> compensated by tamping a bit over 30 lbs.

> In total I got about an ounce and a quarter
> in 60 seconds +/-.

John,

I always overfill and tamp (who really knows ;-)) maybe 40 lbs.

It would be impossible for me to achieve your volume/time result unless my
grind was extremely fine. So fine in fact, that I don't think I could make
coffee at all with a grind that fine!

It makes me scratch my head a little... My Mazzer is set quite close to the
factory start point with little daily adjustments for different factors. I
still time my shots - routinely getting 1.75 - 2 oz in 23 - 25 secs. It
tastes good as well, so I think my grind/fill/tamp/time parameters are in
the general ball park...

If I had a shot not flow fast enough to produce your result of 1 1/4 oz in
60 secs I would have stopped it at 20 secs and dumped it out. Then I would
have adjusted my grinder coarser and tried again.

I can't say what's happening with your setup but perhaps you are ginding
extremely fine and/or pump pressure is set too low?



______________________________________
Barry Corliss
MASTER WORKS CD Mastering
Seattle, WA (206) 282-2274
http://www.master-works.com
______________________________________

[Barton, John]

 

Barry,

 

I can see where too fine a grind could build the pressure, but when I fill the basket correctly and don’t tamp harder than the #30, my shots do run around 25 seconds.  Again, I am interested in how water being drawn by activating the brew lever is being diverted to the steam boiler.  It seems like there should be some type of back flow preventer to keep this from happening.

 

…and yes my dosing and tamping still need a lot of work to get to a consistent standard.  At present I am enjoying moderate success with the occasional just plain bad job!  =)

John N. Barton
Zimmer Gunsul Frasca Partnership
Architecture / Planning / Interior Design 
925 Fourth Avenue, Suite 2400
Seattle, Washington  98104
Direct: (206) 521-3444
Fax:      (206) 623-7868

[Deister, Eric]

John, I tried to find your original post and I can’t at the moment.  I don’t think, in fact, that water back flowed to the steam boiler.  I can’t recall why folks are suggesting that.  This can in fact happen when the steam boiler’s temperature is lower than the brew boiler’s temperature.  But what I remember of what you described was simply false pressure from the steam boiler (up to 2 bar and then down to .2 bar once you released water from the steam wand).  Had you steamed at all prior to doing this test shot?  False pressure can occur on any espresso machine (it did with my Isomac Tea) and normally happens (when it does happen) during the heat up process of the steam boiler.  Once you remove false pressure (by bleeding the steam wand, then giving the steam boiler a chance to heat up again) the problem should not occur again unless/until  you turn your machine off.

 

If you are not leaving your machine on 24/7, before beginning your brewing routine, bleed some steam from the steam boiler.  If the pressure suddenly drops way down, wait until it comes back up before proceeding. 

 

Eric Deister

 

---

[Barton, John]

Eric,

 

The actual drop in pressure reading on the gauge occurred (from 2.0 to 0.2) just by turning the pump off – before bleeding the steam wand.  I bled the steam wand expecting water given the pressure reading.  I am following your logic on the false pressure.  I guess what was causing me concern was the duration of time the pump was running once it turned on by itself – apparently responding to a fill command from the steam boiler.  I often draw 4-6 oz of water to warm larger mugs and am familiar with the time required for the pump to re-fill.  On this occasion the pump was running much longer than normal to the point that I got concerned enough to turn the power off.  Is it possible that false pressure could create that big of a gap in water volume? 

 

Thanks for the feedback Eric.

 

John N. Barton
 

[Sean Lennon]

Sorry guys,

I think I misread the post...thats what I get for trying to read the
thing on a blackberry.

Sean

[Deister, Eric]

I would have turned the power off too.  Pressure doesn’t have anything to do with water level.  The water level sensor calls for water at a certain fill point.  When you turned it back on, did the pump go on again for a brief moment?

 

John said:

            The actual drop in pressure reading on the gauge occurred (from 2.0 to 0.2) just by turning the pump off – before bleeding the steam wand. 

 

Was this after turning the machine on and letting it heat up?

 

FWIW, these water level sensors aren’t very accurate.  I’ve noticed that occasionally more water is called for than happens normally.

[Barton, John]

Eric said:  When you turned it back on, did the pump go on again for a brief moment?

 

My recollection is not….but I wouldn’t stake my life on it.  Back to the original inquiry, is the pressure relief valve on the solenoid only activated by moving the lever to the down position?  What happens if the system builds to much pressure for any reason?  Is there a different relief valve somewhere in the system?

 

Eric said:  Was this after turning the machine on and letting it heat up?

 

False pressure or not…the machine was up to temp for a couple of hours at the time.

 

One other question – is it the water level sensor that needs to see some minerals in the water to work, or am I mixing that up with some other sensor?

[Sean Lennon]

Hi John,

The gauge read 2.0 Bar?

Did you hear any hiss or pop from the top rear of the machine?

You watched the steam boiler rise in pressure during the draw?

You indicated you go water out of the steam wand...
how long did you get water?
did you ever get steam?

all the things you point out sound like the steam boiler completely
filled with water.

a rise in pressure during a draw..
Pressure generally drops during a draw because the feed water in the HX
cools the system. this can be significant in a long draw. the only way
the pressure would rise is if the the headspace was being reduced in
the boiler.

Water out of the steam wand...
The steam wand draws off the top of the boiler, some steam condenses in
the wand feed line during idle periods but if you get more than a
couple of seconds of water at the start of steaming; you have issues.
after you reset the machine; how was you steaming performance? did the
pressure in the boiler drop quickly the first few times before
returning to normal?

Pump just ran and ran...
that kinda tells me the water level sensor did not know to shut off the
water. could the water be such that the sensor is having a hard time
dealing with it's conductivity? (low mineral) the level sensor is
plus-minus half a brick in my experience.

2.0 Bar...
I need to see where my machine blows the steam boiler relief valve and
how it behaves when it is in water.

Cheers

Sean

[Barton, John]

 

 

The gauge read 2.0 Bar?

Yes the boiler pressure gauge read 2.0 Bar.

 

Did you hear any hiss or pop from the top rear of the machine?

No pop or hiss sounds.

 

You watched the steam boiler rise in pressure during the draw?

Operation was normal when the pump was engaged – brew temp and pressure.  I didn’t watch the pump rise but when I looked at it after 50-60 seconds it was at 2.0 Bar.  I know is was at 1.2 before the pump was turned on.

 

You indicated you go water out of the steam wand...

how long did you get water?

did you ever get steam?

I did not perform a full bleed of the system – opening the steam valve for an extended period.  I only did about a 5 second check and then pulled about 6-8 oz out the hot water tap.

 

all the things you point out sound like the steam boiler completely

filled with water.

That is what I think happened.  What is curious to me is how calling for water at the brew group can lead to filling the steam boiler when there is to much resistance at the group head.  It seems as though the default operation in a case like this would want to be a relief valve not filling the steam boiler…..?

 

a rise in pressure during a draw..

Pressure generally drops during a draw because the feed water in the HX

cools the system. this can be significant in a long draw. the only way

the pressure would rise is if the the headspace was being reduced in

the boiler.

Agreed.  This would explain the drop in pressure down to 0.2 Bar when the pump was turned off at the brew group.  The pump was providing the building pressure in the steam boiler while engaged – pressure increase normally being provided by an increase in temperature – but in this case an increased volume being forced into the steam boiler….?  Make sense to you?

 

Water out of the steam wand...

The steam wand draws off the top of the boiler, some steam condenses in

the wand feed line during idle periods but if you get more than a

couple of seconds of water at the start of steaming; you have issues.

after you reset the machine; how was you steaming performance? did the

pressure in the boiler drop quickly the first few times before

returning to normal?

True.  It has been my experience that anytime that water is coming from the steam wand for an extended period that this is always associated with a low steam boiler pressure.  After turning the Power off, and powering back on, allowing time for steam pressure to get back to 1.2 Bar, all operations returned to normal.

 

Pump just ran and ran...

that kinda tells me the water level sensor did not know to shut off the

water. could the water be such that the sensor is having a hard time

dealing with it's conductivity? (low mineral) the level sensor is

plus-minus half a brick in my experience.

This could be the case, but in “normal” use I have not had this problem.  The pump seems to cycle on and off at appropriate times.  My water “mix” is roughly %75 RO water from our RO filter system and about %25 from the tap.  I should take the time to test my water mix to see where it falls.  We have quite a high mineral content in our area.

 

2.0 Bar...

I need to see where my machine blows the steam boiler relief valve and

how it behaves when it is in water.

Is there an additional relief valve other than the one on the brew group to relieve pressure in the system?  I know that the one on the brew group is specifically for releasing pressure from the group head.  Does this also function for the system?

 

Thanks for your input – more knowledge is more better!

 

 

-John

[Deister, Eric]

First off, I’ve noticed (the few times I’ve experienced false pressure) that false pressure does weird things.  It can jump up past the set value of the pressurestat.  It always kicks down to true pressure once you open up the steam wand.

 

At this point, all we can really do is speculate since we don’t know how much water was really in the steam boiler.  It’s possible that water backed into the HX portion of the steam boiler.  It occurs when the temperature in the steam boiler is lower than the temperature in the brew boiler.  This would have been caused by the false pressure that was reading 1.2 bar when it was really .2 bar.  I haven’t checked, but .2 bar surely translates to a temperature lower than that of the brew boiler.  You are correct that when the steam boiler isn’t up to full pressure you will get some water out of the steam wand.  Since the water doesn’t sound to be deficient of minerals, personally I’d nix the idea of a very full steam boiler.  After all, when you removed water, the water refilled for a very long time (longer than you expected).  It is possible you had a very full HX in the steam boiler.  But I’m not sure (Sean could answer this) how water could back out of the HX into the steam boiler.  I’ve always thought of the HX as a closed system.

 

In the end, who knows?  It will probably never happen again.  In the meantime, it’s a great idea to bleed the steam wand after the steam boiler has come up to full pressure, just to be sure you don’t have false pressure.

 

As far as extra pressure from brewing a shot…the OPV (overpressure valve) activates a spring to release the extra pressure by returning water to the water tank.  That is why you have two lines to the water tank.  On a ristretto shot, if you look at the lines to the water tank, you’ll see water coming back to the water tank as excess pressure is released.  These OPV valves exist on better home machines.  Lower end home machines do not have them and the shot suffers as the pressure moves well beyond  9 bar  and peaks at anywhere from 10-15 bar).  It results in a harsher taste.

 

Eric Deister

 

---

From: Barton, John [mailto:JBa...@zgf.com]
Sent: Thursday, April 07, 2005 7:37 AM
To: bre...@googlegroups.com
Subject: RE: Pressure Build-up & Back flow operation

 

 

 

The gauge read 2.0 Bar?

[Deister, Eric]

Oops, I didn’t answer these questions.  I have a nasty habit of yakkin’ away and forgetting to answer the original question.  (Sorry!)

 

John said:

My recollection is not….but I wouldn’t stake my life on it.  Back to the original inquiry, is the pressure relief valve on the solenoid only activated by moving the lever to the down position?  What happens if the system builds to much pressure for any reason?  Is there a different relief valve somewhere in the system?

Pressure relief from the manual “solenoid” is in fact only activated when moving the lever down.

 

Both boilers are required to have pressure relief valves for safety reasons.  These is different, of course, from the OPV overpressure valve I mentioned in my earlier post.

 

John said:

One other question – is it the water level sensor that needs to see some minerals in the water to work, or am I mixing that up with some other sensor?

 

Yes

 

Eric. 

-----Original Message-----
From: Deister, Eric [mailto:edei...@spu.edu]
Sent: Wednesday, April 06, 2005 4:31 PM

To: bre...@googlegroups.com
Subject: RE: Pressure Build-up & Back flow operation

 

I would have turned the power off too.  Pressure doesn’t have anything to do with water level.  The water level sensor calls for water at a certain fill point.  When you turned it back on, did the pump go on again for a brief moment?

 

John said:

            The actual drop in pressure reading on the gauge occurred (from 2.0 to 0.2) just by turning the pump off – before bleeding the steam wand. 

 

Was this after turning the machine on and letting it heat up?

 

FWIW, these water level sensors aren’t very accurate.  I’ve noticed that occasionally more water is called for than happens normally.

 

Eric Deister

---

From: Barton, John [mailto:JBa...@zgf.com]

Sent: Wednesday, April 06, 2005 3:38 PM

To: bre...@googlegroups.com
Subject: RE: Pressure Build-up & Back flow operation

 

Eric,

 

The actual drop in pressure reading on the gauge occurred (from 2.0 to 0.2) just by turning the pump off – before bleeding the steam wand.  I bled the steam wand expecting water given the pressure reading.  I am following your logic on the false pressure.  I guess what was causing me concern was the duration of time the pump was running once it turned on by itself – apparently responding to a fill command from the steam boiler.  I often draw 4-6 oz of water to warm larger mugs and am familiar with the time required for the pump to re-fill.  On this occasion the pump was running much longer than normal to the point that I got concerned enough to turn the power off.  Is it possible that false pressure could create that big of a gap in water volume? 

 

Thanks for the feedback Eric.

 

John N. Barton
 

-----Original Message-----
From: Deister, Eric [mailto:edei...@spu.edu]
Sent: Wednesday, April 06, 2005 2:51 PM

To: bre...@googlegroups.com
Subject: RE: Pressure Build-up & Back flow operation

 

John, I tried to find your original post and I can’t at the moment.  I don’t think, in fact, that water back flowed to the steam boiler.  I can’t recall why folks are suggesting that.  This can in fact happen when the steam boiler’s temperature is lower than the brew boiler’s temperature.  But what I remember of what you described was simply false pressure from the steam boiler (up to 2 bar and then down to .2 bar once you released water from the steam wand).  Had you steamed at all prior to doing this test shot?  False pressure can occur on any espresso machine (it did with my Isomac Tea) and normally happens (when it does happen) during the heat up process of the steam boiler.  Once you remove false pressure (by bleeding the steam wand, then giving the steam boiler a chance to heat up again) the problem should not occur again unless/until  you turn your machine off.

 

If you are not leaving your machine on 24/7, before beginning your brewing routine, bleed some steam from the steam boiler.  If the pressure suddenly drops way down, wait until it comes back up before proceeding. 

 

Eric Deister

 

---

From: Barton, John [mailto:JBa...@zgf.com]

Sent: Wednesday, April 06, 2005 2:09 PM

To: bre...@googlegroups.com
Subject: RE: Pressure Build-up & Back flow operation

 

 

Barry,

[Sean Lennon]

"But I'm not sure (Sean could answer this) how water could back out of
the HX into the
steam boiler. I've always thought of the HX as a closed system"

Hi Eric,

The only way for water to go from the HX to the steam boiler is to go
through the solenoid valve underneath the brew boiler.

we'll figure this thing out eventually :-)

Sean

[Randy Rusch]

When I was dialing in my grinder today, at one point I was choking the machine. I noticed the steam gauge rising slowly while pulling the shot. The only way for this to happen is for the valve to be leaking under high pressure. Looks like they need to upgrade to a solenoid valve with a stronger spring or a smaller opening.

--
Randy

[Kitt Johnson]

Sean, I have studied the diagrams you posted on water flow in a lock-up and
I can not determine the temperatures implied in the water flow ... What are
you suggesting the water temperature is in the steam boiler when it shows
purple and how did it get to that temperature ... the same color as the base
of the brew boiler? What is that solenoid valve doing normally and what has
it done when it sins? Can you amplify your working hypothesis at this
point? Kitt

[Randy Rusch]

IMO, It comes down to the point of least resistance. When the machine is choking, the easier path for the water from the pump is through the valve isolating the boiler. Unfortunately the solenoid valve spring can only hold off so much pressure and some vales will have a weaker spring than others. If this starts happening under normal shot tweaking I would get a replacement valve. WLL may want to think about a better valve in the future.

 

Randy

[Kitt Johnson]

Thanks Randy, that makes sense ... I was still trying to tie this problem (Lock-up after choke) to the earlier problem of Lock-up after idle time...  Two separate problems with no temperature-pressure dive in the steam boiler in the latter case.  It is clearer now... the improper water movement is driven by the pump, not steam or heat.  Kitt

[Sean Lennon]

The only other obvious relief valve I know about is the one on the top
of the steam boiler to protect from overpressure.

I will need to review the E61 diagrams to see if it has a mode that
will allow pressure relief.

sean

[Sean Lennon]

Hi Kitt,

I apologise

I Just realized the PDF docs do not have the second page that
explained the illustration...I do not have access to my laptop where
the document is until tomorrow...I will repost then.

Sean

[Sean Lennon]

exactly the issue I believe happens.

Sean

[Barton, John]

 

I contacted Todd S. about this on Friday afternoon.  His first thought was that the water was backing into the steam boiler through the solenoid valve – as Randy stated – nice diagnosis Randy.  I am taking my machine in to Home Espresso repair on Monday to have them give it a once over.  Operations are normal when the machine is not choking.  This morning I tried to recreate the problem by putting the back flush disk in and back flushing.  I took the cup tray off to monitor the OPV tube back into the reservoir.  I let pressure build-up for about 20 seconds – this is longer than normal for typical back flush for me on my machine, normally 8-10 seconds.  The first two back flushes seemed normal with the steam boiler pressure reading a slight drop down to around 1.0.  In both of these cases it didn’t seem like much water was working its way back into the reservoir through the OPV tube.  The third time I went through the back flush procedure the steam boiler pressure gauge began to shoot up very quickly after about 10-13 seconds – into the red around 2.0 when I quickly switched off the pump.  Shutting off the pump was followed by what I would call a gentle pressure release from under the boiler cover.  I saw a wispy rise of steam and heard a soft pressure release.  Not the type of pressure release I would expect to hear in a catastrophic pressure release situation.  Perhaps it would have been more if I had let the pump continue as the pressure gauge shot up.  This test was done after the machine had been on for about 3 hours and I had made the morning drinks – both espresso, and steamed milk.  I think that would rule out any false pressure issues…

 

I’ll keep everyone posted with the diagnosis.  If it is the solenoid, I think that Todd will have the entire machine replaced.

John N. Barton
Zimmer Gunsul Frasca Partnership
Architecture / Planning / Interior Design 
925 Fourth Avenue, Suite 2400
Seattle, Washington  98104
Direct: (206) 521-3444
Fax:      (206) 623-7868

-----Original Message-----
From: Sean Lennon [mailto:sean....@sympatico.ca]
Sent: Friday, April 08, 2005 9:08 PM
To: bre...@googlegroups.com
Subject: Re: Pressure Build-up & Back flow operation

 

 

The only other obvious relief valve I know about is the one on the top

[Barry Corliss]

on 4/10/05 11:34 AM, Barton, John <JBa...@zgf.com> wrote:

> I am taking my
> machine in to Home Espresso repair on Monday to have them give it a once
> over.

I've seen this place for years... It would be interesting to hear how they
treat you, and what they think of the Brewtus. Let us know what you think of
their expertise...

It's good that Todd will replace the machine, how long have you had it?

Good luck!

Barry

[Barton, John]

 

Barry,

 

I took delivery of my Brewtus on March 18^th.  Home Espresso Repair is a questionable looking establishment from a drive-by point of view, but by all accounts they are widely known and do very good work.  Todd knew them and spoke with them before I called to arrange to drop my machine off.  Will – the repair guy – hasn’t worked on a Brewtus before, but is familiar with Expobar and had Todd’s vote of confidence.

 

I’ll let you know how it goes.

John N. Barton
Zimmer Gunsul Frasca Partnership
Architecture / Planning / Interior Design 
925 Fourth Avenue, Suite 2400
Seattle, Washington  98104
Direct: (206) 521-3444
Fax:      (206) 623-7868

-----Original Message-----
From: Barry Corliss [mailto:bcor...@master-works.com]

Sent: Sunday, April 10, 2005 12:10 PM
To: bre...@googlegroups.com
Subject: Re: Pressure Build-up & Back flow operation

 

 

on 4/10/05 11:34 AM, Barton, John <JBa...@zgf.com> wrote:

[Barry Corliss]

on 4/10/05 12:15 PM, Barton, John <JBa...@zgf.com> wrote:

> I took delivery of my Brewtus on March 18th. Home Espresso Repair is a
> questionable looking establishment from a drive-by point of view, but by
> all accounts they are widely known and do very good work. Todd knew
> them and spoke with them before I called to arrange to drop my machine

> off. Will - the repair guy - hasn't worked on a Brewtus before, but is

> familiar with Expobar and had Todd's vote of confidence.

I was in there years ago, before Will bought it. I agree, looks aren't as
important as the work they do. ESI over on Leary Way is a really impressive
establishment, but last I checked they won't touch a home machine. (but you
can buy parts, LM baskets and such there).

Not at all a surprise Will never saw a Brewtus before, seeing as it's brand
new. It's good that he is familiar with Expobar (and Todd's go ahead would
be good for me as well).

> I'll let you know how it goes.

I'll be most interested to hear what happens.

Best,

[Deister, Eric]

Home Espresso Repair is a well known establishment with an excellent
reputation. I've been going to them for years. People from across the
country send their machines in to Will (the owner) for repair with good
results.

It can take up to two weeks to get a machine repaired, depending on how
backed up he is. Hopefully he'll give the Brewtus top priority.

Eric Deister

-----Original Message-----
From: Barry Corliss [mailto:bcor...@master-works.com]
Sent: Sunday, April 10, 2005 1:38 PM
To: bre...@googlegroups.com
Subject: Re: Pressure Build-up & Back flow operation