This week I replaced the non adjustable OPV of my old model Rancilio Silvia with a new adjustable one. I also ordered a PF with a pressure gauge (from a shop in Holland) to be able to measure the pressure and, if needed, to adjust the OPV. The PF w pressure gauge was delivered today and I tried to use it.
It was very difficult to lock the PF in and having no leakage but eventually I succeeded. I noticed that the biggest width over the ears (or do you call it wings ?) of the PF is a millimeter larger than the original Silvia PF, so maybe I have to file a bit off the ears.
When the pressure built up, the needle climbed up of course but then started to vibrate heavily over a 2 bar range, that is between 9 and 11 bar. Does this mean that the pressure gauge is faulty or is something wrong with my Silvia ?
And can I assume that the brewing pressure is in the middle of the range, in this case 10 bar ?
Btw, this is the one I bought:

If the gauge itself isn't liquid filled, the bounce is most likely those from the pump. Not sure how to interpret the reading of a dry gauge.

I am very familiar with that gage setup because it can also be equipped with a thermistor probe and a ball valve to reduce AVERAGE flow to that of a typical shot - 3 ml/sec and possibly try to measure temperature. In essence, they are attempting to mimic (poorly) the Scace II Thermofilter.

The needle flutter is attenuated by a tiny orifice in the gage port. I have vastly "more better" gages available - erics@erols.com - should you desire. I assure you that your flutter days will be over and the accuracy will be improved by a large margin.

Meanwhile I tried it a few times again and to my surprise suddenly the vibration of the needle is much less. It is still vibrating but only in a range of around 1/2 bar, so much more accurate.

@Eric: Because you are familiar with my PF/Pressure gauge and you apparently also own a Silvia, do you think I should file a bit off the ears/wings of the PF to be able to lock it easier in the group ? Would that help ?

Ton wrote:When the pressure built up, the needle climbed up of course but then started to vibrate heavily over a 2 bar range, that is between 9 and 11 bar. Does this mean that the pressure gauge is faulty or is something wrong with my Silvia ?

See Building a Portafilter Pressure Gauge for an explanation.

Do you think I should file a bit off the ears/wings of the PF to be able to lock it easier in the group? Would that help?

I bought that gage setup for a different reason - sort of wanted to see what else was out there - I do that sometimes, call it a whim. I am always disappointed when I buy a product and there is no pedigree to it. There's lots of quality gage manufacturers out there and this was not one. It did not prove to be accurate but, of course, I could have received the "one bad apple".

Silvia has, from what I experienced and read, always been a tough seal as compared to the standard E-61. I would not modify the assembly at all - perhaps return it and ask for one that "works" out of the box.