Rancilio Silvia Mega-Mod part 3 Pressure gauge
Avi's Silvia Mega-Mod
My way to a better coffee...
DISCLAIMER - Important!
Silvia V3 has an OPV (Over Pressure Valve) that controls pressure.
It is not meant for daily use, only for calibration in case it is out of normal. Pressure reading helps to understand if pressure is correct for brewing. If you find your Silvia pressure is anything but 9 Bar, you can adjust the OPV to correct.
On a daily base, the pressure gauge serves mainly as an indicator that tells you if everything is OK.
Tip: For the way to adjust the OPV, follow Fig. 5 on page 8 and section 8.7 on page 35 of Silvia manual.
Tip: If you don’t have a gauge and want to measure your Silvia pressure, you can do it easily (though not accurately) by measuring the flow rate from the OPV pipe while using a blind basket.
In 1 minute of brewing operation (with blind basket) you should get 320cc of water if pressure is set to 9 Bar.
(you can measure it for 30 sec. and double the result)
This technique is based on Ulka pump’s specification graph which draws the typical flow rate vs. pressure.
Some sites suggest only 260cc based on the medium graph which I believe is a mistake.
I made the flow test after I completed the pressure gauge mod and when gauge showed 9 Bar, I got 320cc which is the value when looking at the Max. graph.
Some mods suggest it should be before the OPV, right after the pump exit or in the pump-OPV line.
Some mods suggest it should be after the OPV, to the boiler cold water inlet or along the steam pipe and some suggest it should be connected to the brew head.
So connecting the gauge to points 1, 2, 3, 4 or 5 should result the same. But measurements done by others suggested it is not consistent and that there are differences between readings depends on location.
In the steam mode, water in the boiler turn into steam and gets hotter in the top of the boiler, it is reasonable than that locating the gauge outlet in the steam path would give more precise and quicker response readings, especially when steaming.
In heat mode and standby mode, hot water flow to the upper part of the boiler, so measuring pressure in the upper position seems more accurate to me. Perhaps the most accurate location of all is inside the brew head. This measures the pressure closer to the coffee puck, but this installation requires the manufacturing of a custom adapter that I didn’t want to go into.
Connecting the gauge to the steam pipe means cutting Silvia’s steam pipe and shortening it and is more complicated than just connecting it to the pump for example. Nevertheless, I have decided to go with this location.
To start with this mod, you need the following:
A. A gauge that is Glycerin filled. This helps to maintain steady reading without any special connecting pipe.
Range should be 0-16 bar or 0-20 Bar (0-300 PSI) etc.
Tip: Decide if you want the gauge internal or external and get one with appropriate inlet, rear or right angle one.
Tip: Find out if the gauge needs ventilation when assembled inside Silvia.
Tip: There are many diameter size gauges, get one that you find comfortable with.
I got big 2.5” diameter with a rear inlet for easy panel mounting.
B. Pay attention of the gauge connector thread. Try to get something standard like 1/8 or 1/4 NPT. This thread will determine the connector you’ll need in order to connect the gauge to a pipe and the pipe to Silvia in the location you decide.
C. Get necessary fittings, connectors, tee connectors etc. Save your time and go directly to Swagelok company that has all the parts you’ll need. Swagelok had designed a fantastic patented locking mechanism that helps getting perfect connections without leaks.
Tip: Download Swagelok full line catalog and search in it for your needs.
Tip: Silvia steam copper pipe is 1/4″ OD and pump’s line to boiler uses 1/8 thread.
Tip: Cutting copper pipe is done with a special pipe cutter to get a clean sharp cut.
Don’t even think of using any other tool for this job.
Tip: I have used Teflon tape on all threads prior of fastening.
Tip: Don’t forget to get a mounting bracket for your gauge to mount it easily on the panel.
Comments, remarks and updates are welcome.
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