Modifying Gaggia Classic OPV to 9 Bar

This week I decided that, to pass the time, I would modify my Gaggia Classic in pursuit of the “God Shot”.  Now by all means I will be years from my “God Shot” as I barely understand the variation in beans, freshness, grind, the requirements of temperature and all manner of tamping skills.  However, I know that my machine has been delivered ready for POD compatibility and the Internet more or less commands me to reset the OPV (Over Pressure Valve).

Previously I have discovered that my Gaggia Classic came delivered with baskets which are specific to using POD’s.  This in itself set me back a few months as because I have never had a Coffee machine before I did not realise that there was anything wrong with these baskets.  When researching why my shots were so poor I came across a description of how the Portafilter basket should look and realised that I should have many holes in the bottom of my basket not just 1 and a plastic frother.

So I ordered a new basket from coffeehit this was promptly delivered and I put this in machine.  My shots changed instantly and although far from perfect the taste changed instantly.  They also flowed very fast even on the finest grind of my Gaggia MDF.  (I will post something about this issue, here)

Walk-through of Modification to Gaggia Classic

(CAUTION All of the things that I describe in this walk-through are of my own doing and will have invalidated any warranty I have with Gaggia, I am fully aware of the risks and Hazards.  If you decide to try to replicate any of the described modifications you do so at your own risk and I cannot take any responsibility for your actions or any injuries, damage and any other outcome due to you performing the modifications and the risks you expose yourself to (Electricity, Water, High Temperature Metal))

  1. Hopefully no one is reading this without knowing that this is purely an experiment and my Gaggia Classic is now an engineering toy.
  2. Ensure that the Gaggia Classic is disconnected from the Electricity supply and that the Machine is has been allowed to cool for 1 hour. (Machine gets to over 100 Degrees Celsius and can cause severe burning to skin.  Ideally only attempt after leaving machine off for several hours)
  3. Remove the lid to the Gaggia Classic by removing the two Philips Screws on the top
  4. Remove the Earth wire from the cover whilst lifting the cover away from the Main unit

    (Optical illusion here due to Stainless Steel, but remove clip by depressing the “tang” and pulling on the crimp)
  5. Locate the Over Pressure Valve (OPV), centre of the unit with rubber tube, for return, leaving through the top and high pressure line from pump entering from the left through red Bung (as viewed from rear of Gaggia Classic)
  6. Remove the Overflow tube from the top of the OPV, do not try to touch any other tube.
  7. Using 17mm socket or 17mm Spanner, carefully remove the the OPV cover by unscrewing Anti-clockwise (CAUTION: The 17mm head is made from soft metal and using a spanner may lead to damage to the Nut head)
  8. Here is the OPV with the Adjustable 5mm Hex pressure control visible, there will be water present
  9. Insert the 5mm Hex key and turn the Anticlockwise 270 degrees.  (This was a setting initially found after trawling the forums, some further tinkering can be done if this initial setting is not enough)
  10. Now perform the actions in reverse to put the Gaggia Classic back together, remembering to connect the overflow tube onto the OPV
  11. Reconnect the Earth lead to the cover and replace the cover onto the Gaggia Classic
  12. Test the machine by reconnecting the Electrical supply and trying to pull a shot

Observations / Comments

  1.  I have performed the modification on the commonly posted 270 Degree’s anti-clockwise technique.  I have not used a pressure gauge.
  2. However, I have tested using the flow technique.  This involves putting the overflow from the OPV into an empty glass and measuring the amount of flow over 30 seconds with the Portafilter blanked (i.e. blocked)  To block the portafilter, either get a special portafilter or press the steam button which actuates the 3 way valve and perform the same function.  This is not perfect, because each valve and pump combination will have differing overflow volumes.  You are looking for ~125ml in 30 seconds.
  3. When I got close to these values I then tested the espresso by pulling a shot and checking it’s formation and flow.


The modification has made a phenomenal difference to the taste of my espresso shots and I have been getting far better flavour and consistency.  Also my pour is taking around 25 seconds rather than 15 before.

I’m using very fresh beans, 1 week since roasting, and still have the MDF set to the lowest setting, this has surprised me, however if I don’t I get horrid espresso.  (I get the feeling this is where my next research should be focussed)

This did take numerous tweaks of the OPV valve and I think I ended up nearly 400 degree’s anti-clockwise of the factory setting point.  Each valve will be different due to the pump, valve combinations.

I have been very poor in my measuring of pressure and I know that I may well not be getting 9 Bar.  Therefore I will have to modify my portafilter and measure the pressure at the Brew Head to find anymore improvements.

Overall it’s been a fun experience and my espresso has improved.  Within a few more years I may get good at it.