Results 1 to 18 of 18
Like Tree14Likes
  • 3 Post By robusto
  • 1 Post By Dimal
  • 1 Post By Lyrebird
  • 1 Post By robusto
  • 1 Post By Dimal
  • 1 Post By robusto
  • 2 Post By EspressoAdventurer
  • 1 Post By EspressoAdventurer
  • 2 Post By robusto
  • 1 Post By EspressoAdventurer

Thread: Sirai Pressurestat Cycles on Grimac machine

  1. #1
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644

    Sirai Pressurestat Cycles on Grimac machine

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    These cycle times may be of interest.

    They were taken 30 minutes after I switched on the machine. Ambient temperature 22C

    Machine: Grimac Eclisse commercial 2-group with 10-litre boiler

    Pressurestat contactors close: 0.65 Bar. For 21 seconds, supplying 2300 watts to the heating element.

    Pressurestat contactors open: 0.85 Bar. For 1 minute 50 seconds during which no electricity flows to the heating element.

    Water temperature at shower screen: 93C


    For 11 years this bullet-proof machine has worked away without a problem. No parts have been replaced.

    I did clean the contacts on the touchpads which can corrode and make them a little sticky. https://coffeesnobs.com.au/brewing-e...tml#post535152

    A few months ago I dissassembled the contactors on the Sirai pressurestat, and removed the build up of carbon deposits.
    Perhaps surprisingly, the diaphragm of the pressurestat was still very supple and working well, so the Sirai continues in its original state giving solid reliable service with a deadband of 0.2 Bar.
    Attached Images Attached Images
    Dimal, flynnaus and gordons like this.

  2. #2
    Mal Dimal's Avatar
    Join Date
    Oct 2004
    Location
    Warwick, QLD
    Posts
    16,760
    Can't keep a good machine down mate, with a modicum of maintenance...

    Mal.
    robusto likes this.

  3. #3
    Senior Member Lyrebird's Avatar
    Join Date
    Jun 2018
    Posts
    505
    Quote Originally Posted by robusto View Post
    Machine: Grimac Eclisse commercial 2-group with 10-litre boiler

    Pressurestat contactors close: 0.65 Bar. For 21 seconds, supplying 2300 watts to the heating element.

    Pressurestat contactors open: 0.85 Bar. For 1 minute 50 seconds during which no electricity flows to the heating element.
    FWIW the boiler temperature is swinging from ~114 oC to ~118 oC.
    robusto likes this.

  4. #4
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644
    While I'm seduced by modernity with computer-controlled bells and whistles, for longevity, cast-iron (or should that be brass?) simplicity works best.

    My latest car is a 6.4 litre computer on wheels and I need my wife as co-pilot to operate the touch-screen gadgetry while I concentrate on the driving.

    My oldest engine is a 6.3 litre 1970s built cast iron monster diesel still chugging away on my boat --no electronics apart from the alternator which it doesn't need anyway.

    So yes, Grimac built their machine (after building parts for other companies) for durability based on good design simplicity.

  5. #5
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644
    Lyrebird, that would appear to be a nice "even" deadband for a 10 litre boiler.

    It should not affect brew water going through the heat exchanger.

  6. #6
    Senior Member Lyrebird's Avatar
    Join Date
    Jun 2018
    Posts
    505
    Quote Originally Posted by robusto View Post
    Lyrebird, that would appear to be a nice "even" deadband for a 10 litre boiler.

    It should not affect brew water going through the heat exchanger.
    Not sure I agree with that.

    The water out of the HX will be a mixture of the water that has sat in the HX between shots and inlet water that is being heated by the HX.

    We can assume that the water in the HX has equilibrated to somewhere close to the boiler water temperature.

    For the inlet water, energy gain in a heat exchanger is U.A.ΔT*, U and A are fixed by the design and materials of the HX so the functional variable is ΔT. If the incoming water is at a nominal temperature (say it's 20 degrees) then by definition there will be more heat gain when the boiler water is at the top of the band than at the bottom as the initial ΔT has increased from 94 oC to 98 oC.

    Accordingly, there will be a temperature difference in the water being fed to the group which is created by the boiler swing. The thermal mass of the group will serve to push the temperature of the water towards the group temp but it can't completely equilibrate because the system is passive.

    * U = heat transfer coefficient of the media and surfaces, basically it is the inverse of the more familiar R value used for insulation.
    A = Area of heat exchanger surface
    ΔT = temperature difference. Note that you can't use the simple temperature difference for a single flow heat exchanger as ΔT diminishes as the water flows through. IIRC you need to use the log mean but since the exit value depends on the initial value the problem becomes iterative.

  7. #7
    Mal Dimal's Avatar
    Join Date
    Oct 2004
    Location
    Warwick, QLD
    Posts
    16,760
    Quote Originally Posted by robusto View Post
    Lyrebird, that would appear to be a nice "even" deadband for a 10 litre boiler.

    It should not affect brew water going through the heat exchanger.
    I take it that you have been very happy with the performance of the lovely Grimac up 'til now mate?

    Mal.

  8. #8
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644
    Mal, Yes, very much so.

    Every time I take the cover plates off to dust the insides I am reassured of the indestructible build quality and how thoughtful engineering design makes it all happen, rather than electronic sensors everywhere (nothing wrong with those, mind you).

    Especially so in the thermosyphon system where the tuned length of pipes ensures thermal stability in the group heads.

    The sirai pressurestat is tough, long-lasting and very sensitive. Just the beginnings of a turn of the steam knob and you can hear the pressurestat kick in. No latency.

    The procon pump is also still original (I bought an aftermarket spare about 9 years ago and it's still in its wrapping waiting for the fateful day of deployment).

    Steaming milk is an absolute delight with the 2-hole tip. I must say I make silky microfoam (most of the time!)

    And-- oh yes, the espresso is better than ever, and more consistently so, now as I get the hang of the new Baratza grinder.
    Dimal likes this.

  9. #9
    Mal Dimal's Avatar
    Join Date
    Oct 2004
    Location
    Warwick, QLD
    Posts
    16,760
    Have always liked the design and engineering of the Grimac machines too mate.
    An awful lot of thought and consideration has gone into it, and as you say, made to last...

    Mal.
    robusto likes this.

  10. #10
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644
    Lyrebird: All that reminds me of my secondary school days in science class, and the mandatory experiment we all dreaded: the continuous flow calorimeter.

    While I understand the physics of what you wrote, the reality is that the temperature of exiting water through the large heat exchangers and the E61 groups is very stable, especially so for the 25-30 seconds for which water is forced through.
    gordons likes this.

  11. #11
    Senior Member
    Join Date
    Sep 2009
    Posts
    301
    Kinda reminds me of a recent experience watching a very high end multi group multi boiler - 13L steam boiler plus individual 2.3l brew group boilers
    - and each of the G/H boilers were set to 121deg.
    *Sorry I'm so old school I don't even know how to bring uo the fancy '0' in upper line to denote degrees ;( .
    Maybe I shouldnt got one of these fancy pads....reminds me of grade 1 with a slate n chalk !

    Anyway back to the ???....aah now I forgot...aa damn it I'll have to post another day when it comes back to me
    Dimal and gordons like this.

  12. #12
    Senior Member
    Join Date
    Sep 2009
    Posts
    301
    Yeah I remember ....watching this electronacry trickery being setup and bench tested.....
    Well 121deg...at the boiler ...yes ok not HX but stay with it ...resulted in a very consistent 94.2deg at the scace 2 device.
    The PID had a cycle variance of 3deg...But then how could I trudt my memmory !
    So I'd hazard to say Robusta given your taste buds are ok that your Grimac might be pulling a very nice 93+ deg or thereabouts shot

    Bit like A.Grice at Bathurst aka 1990 In his old school CastIron block V8 with analogue Carburetion etc etc. Up against the Nissan Godzilla / Ford Sierra electricary..... A sad day for the new kids in town !
    PS LB you left the 6+ Lbs of Good 'Ol Skool Brass AKA the GH out of the brew path / thermal calculation.
    gordons likes this.

  13. #13
    Senior Member Lyrebird's Avatar
    Join Date
    Jun 2018
    Posts
    505
    Quote Originally Posted by EspressoAdventurer View Post
    PS LB you left the 6+ Lbs of Good 'Ol Skool Brass AKA the GH out of the brew path / thermal calculation.
    No I didn't.

    Quote Originally Posted by Lyrebird View Post
    The thermal mass of the group will serve to push the temperature of the water towards the group temp but it can't completely equilibrate because the system is passive.
    BTW an E61 grouphead has less thermal mass than 400 ml of water
    Last edited by Lyrebird; 7th September 2018 at 03:58 PM.

  14. #14
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644
    Some time ago before electronic management systems began transforming pregnant skateboards of cars into 200 kw fire-breathing but still pregnant skateboards, we used to have a saying: there's no substitute for cubes.

    The E61 group head has been around since...well, since 1961. More than half a century and still going strong.

    Must have something going for it.
    Dimal and burr like this.

  15. #15
    Senior Member
    Join Date
    Sep 2009
    Posts
    301
    Yep choices choices choices....
    Would you choose a current KoreAmMexCzechSpan build, German design
    Twin Turbo 1.3L 4WD Electronic Twin Clutch Trans whatever...
    or
    An 351 Cleveland V8 'SuperRoo' GT Falcon....
    No Decision really


    I still remember as a 13yrold sitting in my older bros XW GT 'Burmese Gold' and hoping he decides to
    tromp it thru 2nd into 3rd...aah it was glorious...as you would sink back into the bucket seat....

    SO much for Toyota's current Ad with the Drooling Dogs eyes receding back into their sockets ...
    gordons likes this.

  16. #16
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,644
    Hell, I must have dementia. Did I say my machine has a 10 litre boiler? Halve it. 4.9 litres.

    EspressoAdventure: Bite your tongue. 1.3 litres...in my garage? Never. That few cubes amount to 2 cylinders worth of my 5 litre Ford V8s...and even less of my 6.4 litre Chrysler hemi. 0-100 in 4.something seconds without strain.

  17. #17
    Senior Member
    Join Date
    Oct 2012
    Posts
    182
    Quote Originally Posted by Lyrebird View Post
    No I didn't.



    BTW an E61 grouphead has less thermal mass than 400 ml of water

    Sorry if I got lost somewhere, but where did 400 mL of water come into the equation? Water flowing at a <2 mL/s for ~30 s?

    I think the intricacies of cooling flushes are going to have more serious implications for brew temp (for most HXs, anyway), the location on the pstat cycle won't be noticeable.

  18. #18
    Senior Member Lyrebird's Avatar
    Join Date
    Jun 2018
    Posts
    505
    Quote Originally Posted by burr View Post
    Sorry if I got lost somewhere, but where did 400 mL of water come into the equation?
    About the same place as cast iron engine blocks



Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •