Enrico of Italy....The O-Ring Solution
After numerous requests we have finally been able to come up with an economical seal replacement solution for an Enrico of Italy. We have found that the vexing problem of finding the proper U-cup seal for many vintage machines can be solved by the combination of careful measurement, logic, some trial and error, and of course, shims.
The central issue involved in many vintage machines is that the seal geometry of the u cups is rectangular....either the seal profile is taller than it is wide or wider than it is tall, and the modern U-cup cross sections are invariably square. For example a 1/4 inch tall U-cup will be 1/4 inch wide when looking at the cross section, 3/16 x 3/16 etc. For some of these machines there may be only a few dozen at most, worldwide, that are in use and need seals, so to have a special mold made for these rectangular seals is just too cost prohibitive to consider for any business dealing in espresso parts, including us! After a lot of experimentation we have found that one way to approach this issue is by the use of O-rings to replace the impossible to source U-cups.
As I mentioned, measurement, logic, trial and error and shims. Begin with the measurements. An O-ring is symmetrical in cross section, just as the square profile U-cups, but there is a far greater variety of O-rings available than there are U-cups. So we begin by measuring the cylinder, that is the first critical sealing surface. We select an O-ring that is as close as possible to the diameter of the cylinder and to the height of the groove (race) in the piston body. By working through the big charts from our suppliers we can generally come up with a ring that is close...once again, remember that we NEED a rectangular profile seal but can only GET a square one, so we have to adapt the square overall profile to the rectangular format of the piston race
Logic leads us to the next step in the process....we know we can seal the outer part of the seal to the cylinder but there is another equally important surface to seal, the inner O-ring surface, where it meets the piston body. This is accomplished by the use of shims.....our first attempts were done with aluminum tape but led to a haphazard application with no real technique of measureing the thickness of the shim. We then began using NSF high temperature adhesive backed silicone. This material is available in measured thinknesses, so can be used accordingly, to "build up" the piston race by controlled amounts to create seal between the piston race and the inner surface of the ring.
Trial and error then enters the picture since after measureing and calculating how much shim to add to seal, one must realize that for each shim wrap of material placed in the piston race that once the material meets, then additional shims can push out the OD of the ring too much, and not enough shim can result in a leak. One must have the motivation to fix the machine and the willingness to possibly repeat the process a number of times until the perfect combination of shim thickness, O-ring diameter and cross section has been achieved to give the end result of a working espresso machine hydraulic group.
We have applied this method to a number of different problematic machines and have long lasting success in all cases so far. The use of U-cups in hydraulic applications is preferred of course, but there are numerous espresso machines that use an O-ring or O-rings as the OEM piston seal and we feel confident of this solution.
Enrico of Italy Piston Seal Replacement
Replacing the seals on the Enrico piston proceeds identically to other spring piston machines......compress piston spring by use of a clamp, remove lever yoke pins, relax the spring by releasing clamp, remove piston, service the seals, and reinstall piston by compressing sping with clamp, intalling lever yoke pins. Done.
In this particular case, once the piston is removed, clean the piston body. The Enrico piston is made of aluminum and may have varying degrees of oxidation, remove the old seals, clean the piston races. The kit we are supplying contains 3 large O-rings and high temp adhesive backed silicone stips, cut to fit the width of the piston races. Each strip is long enough for one wrap around the piston race WITHOUT STRETCHING, The thickness of the silicone is .020" or about 1/32" or about .5mm. Each non stretched wrap will therefore increase the piston diameter by about 1mm. Of course, the silicone is soft, so we must allow for this compression as well. After placing one wrap on silicone in each of the races, install the O-rings. When installing the piston into the cylinder use plenty of Dow 111...there are no U-cups to foul with too much lubricant, so feel free to slather it on. The piston should slip into the cylinder fairly easily on installation. If it goes into the cylinder too readily, with no feeling of resistance, you may want to add the second wrap of silicone shim material now, before final assembly.
Please do not add both wraps at the outset unless you are sure that you will need them both....it is very difficult, if not impossible, to remove the second shim wrap....the adhesive is very strong and the entire job will be buggered. Just go slow, try one wrap first. Our machine was sealed with a single wrap of silicone shim. Upon heatup there were a couple of drips which stopped once the piston was warm and was moved up and down a couple of times to seat the seals. Keep the silicone just in case you need to later apply this second shim, or if the piston oxidation is extreme. As stated previously, there are other shim materials that can be used in a pinch, but we are supplying what we consider the best material for the job in our Enrico of Italy piston seal kit.
Click the links below to go to our products for the Enrico of Italy Espresso Machine:
Enrico of Italy Piston Rebuild Seal Kit
Enrico of Italy Portafilter Gasket
