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Flat vs Conical group seal

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  • Flat vs Conical group seal

    If a machine has the option of using seals of either kind, is there an inherent advantage of one type over the other?

  • #2
    Kaanage,
    My two bob's worth (Pre decimal (1966) term for my opinion,for what it's worth!)
    My two group m27 basic la Cimbali ,has both options for gasket/seal.
    I've always believed the conical gasket is the better design,I reckon the group basket gains a better seal regardless of the compression applied,possible incorrect assumption,but there you are,that's just me.
    What's your thoughts initially pondering the choice of either?
    cheers,
    Mick.

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    • #3
      Thanks Mick. I was thinking the conicals may work better but wanted confirmation before buying any (since I have to pay fixed postage, even for 1)

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      • #4
        I've done technical work on a few Boemas with slim conical seals. For some reason the pressure gauge/PF I use on all sorts of machines seems to blow out on only the Boemas (note: this is after replacing the old seals).

        I waiting for a NS or LM to do something similar but it hasn't happened yet. Maybe the expansion valve systems were shot on the Boemas but I rebuilt one so I know it was operating correctly.

        Any thoughts, anyone?

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        • #5
          Conical verses Flat!!

          Hello,
          I would presume the flat gasket/seal ,having greater surface/contact area upon the basket lip ...may possibly survive greater pressures when compared to the taper alternative,having that narrower contact with the basket!
          I simply replaced my seal/gaskets with what was already (identical-conical ) installed.
          Perhaps I'm just so used to this type and my technique has evolved and adapted to conical seals with La Cimbali.
          I had a Rancilio Techna three group volumetric ,until recently which used flat seals/gaskets....where is the logic?
          Kaanage,perhaps get both and see how they last! It's a funny world when things come down to this option of flat verses conical
          Cheers,

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          • #6
            That was my thinking. I've yet to blow out a La Marzocco but those conicals (like Nuova Simonelli) are pretty robust (I should upload some images of the different seals ... if anyone is interested).

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            • #7
              Originally posted by mulquemi View Post
              I would presume the flat gasket/seal ,having greater surface/contact area upon the basket lip ...may possibly survive greater pressures when compared to the taper alternative,having that narrower contact with the basket!
              Remember that the basket lip is rounded, so the contact area between seal and basket is the same, it's just at a slightly different angle.
              With all the machines I have worked on, I have never noticed any advantage of of conical over flat (or vice versa) in terms of sealing ability - where there is a choice of the 2 types for the one machine I fit whichever type best suits the level of wear on the handles and groups to ensure the handles lock in the right position.

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              • #8
                Originally posted by sprezzatura View Post
                I've done technical work on a few Boemas with slim conical seals. For some reason the pressure gauge/PF I use on all sorts of machines seems to blow out on only the Boemas (note: this is after replacing the old seals).

                I waiting for a NS or LM to do something similar but it hasn't happened yet. Maybe the expansion valve systems were shot on the Boemas but I rebuilt one so I know it was operating correctly.

                Any thoughts, anyone?
                The machine I'm having issues with (an old bezzera) also uses narrow group seals and is blowing them out when trying to slow shots beyond 25 seconds. It's currently using 66-56x6mm o ring group seals.
                I found that some Astorias also used these o rings but also have the flat and conical seals as options hence my enquiry. I'm now starting to lean towards the flat seals.
                If I lived in Sydney, I'd definitely get one of each to experiment with.

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                • #9
                  Flat vs Conical group seal

                  I'm working on an old Astoria next week so I'll check out the seals. Sometimes a Rancilio group seal works better in a CMA machine and vice-versa. The wear on the brass is always different and different seals are useful to have in the tool kit (as well as lots of packers).

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                  • #10
                    Old Bezzera's hate having any seals that aren't designed for their particular group. I had a BZ99 and currently have a BZ40E which had the conical shaped seals fitted by someone years back but came originally with the o-ring type.
                    The portafilters would not lock in properly and needed to be held on to to prevent spin out when extracting. This caused excessive wear on the portafilter lugs.

                    What model and approximate year is your Bezzera? They also came with a standard square shaped group seal which might work if the o-ring is having problems.

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                    • #11
                      Mine is old enough that when I called Baratzi and gave them the serial #, all they could tell me was that it was from before they became Bezzera's distributor.

                      From your experience, it sounds like the flat (square section) seals are the way to go.

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                      • #12
                        Well the two that I recently had were at least 15 years old and both used the o-ring seals. I would expect yours would use the o-ring as well but if it's leaking than I guess not.

                        I called Bezzera Australia about the BZ40 I had which has some really weird problems and they have no record of the serial number either it's that old.

                        This is a handy reference page, it lists the applicable seals relating to the model/year: Bezzera Group Seals
                        They say some differently shaped seals can be used for worn collars/handles so it might be possible.

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                        • #13
                          As with sprezzatura, the issue is not leaking but pressure forcing water past the inside edge of the groove behind the o-ring, causing it to blow out of the groove when trying to pull slow shots or backflushing. A packer has helped raise the threshold but not beyond a 25 second shot.

                          I'm hoping the straight sided seals will not be so prone to this. In theory, the conical seals should be better since the locking pressure will force the inside of the seal against the inside of the groove more than the flat seals, further reducing the likelyhood of pressure forcing water under the seal but from what you've said, they cause other issues.

                          My last resort will be to get additional brass brazed to the bottoms of the group handle locking tabs (with some filing to get the profile correct) so the edge of the basket/blind filter is forced up higher when locked in.

                          Here is the page where I have found the Astoria seals that I have been considering - the o-ring option is identical to the ones used in the old Bezzeras (+ Boemas, I presume)
                          http://www.coffeeparts.com.au/parts-...del-group-head

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                          • #14
                            Addendum - the Astoria I'm servicing tomorrow is 1.5 years' old so it probably has the square profile. If you want to PM your address I'll send you a couple of spare flat seals to try.

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                            • #15
                              A huge thanks to sprezzatura for helping me sort the issue with the Bezzera - the flat seal stopped the blowout issue and allowed the removal of the packer needed to improve the situation with the o-ring seals.

                              If the conical seals only reduce the effort need to lock the PF but introduce other issues, then I won't bother testing them and will get more of the flat seals like the one pass on to me by sprezzatura (not sure if this site will let me link his FB page so I won't risk it).

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