The over-pressure valve limits the pressure the pump can build, dumping the excess back to the tank.
Why it is often set too high
Vibration pumps produce 15 bar or more. The OPV caps that.
Many manufacturers set it at 12 bar, and some market the number as a feature. Espresso is defined around 9 bar, and modern practice often favours lower still.
Higher pressure compacts the puck and encourages channelling. It does not make better coffee.
What adjusting it does
Lowering to 9 bar generally gives sweeter, less harsh shots with less channelling.
Some people go to 6 or 7 bar, which many find sweeter still — closer to what a declining lever profile produces.
How it is done
On many machines — the Gaggia Classic is the standard example — it is a screw or spring on the valve inside the case.
The method: fit a blind basket and a pressure gauge, run the pump, and adjust until the gauge reads the target.
Some machines need a modified OPV kit; on others it is a nut.
The caution
It means opening the machine, which voids warranties and involves mains electricity. Unplug it, and know what you are touching.
If you are not comfortable, do not.
Is it worth it
On a machine set to 12 bar, yes — it is one of the cheapest genuine improvements available, alongside a PID.
If your machine already runs 9 bar, leave it alone.
Last reviewed 8 August 2026