Lucca M58: Adjusting the Expansion Valve

Follow these instructions to set the pressure on your Lucca M58's expansion valve (aka over pressure valve or OPV).

Tools Needed:
- #2 Phillips head screwdriver
- Flat head screwdriver
- 12mm crescent wrench or adjustable wrench
- Portafilter with back flush blank

The expansion valve, sometimes called the OPV, is designed to allow the water in an espresso machine's brew boiler room to expand as it heats. On espresso machines equipped with rotary pumps, the expansion valve has no affect on brew pressure, but should be adjusted to open 1-2 Bar above the set pump pressure. An expansion valve that is adjusted too low will leak from the drain port into the drip tray while brewing or back flushing.

1. Start by removing the panels from the machine.

2. You can operate the machine in this configuration without the side panels attached.


3. Temporarily set the machine's pump pressure to ~1.5 Bar higher than your desired brew pressure.

Lucca M58: Adjusting Pump Pressure

4. Remove the reservoir and undo the indicated Phillips head screw so you can set aside the reservoir tray and access the expansion valve.



5. You may need to remove the silicone tube from the expansion valve to prevent it from kinking while making adjustments. Alternatively, you can simply un-kink it as you go.



6. Use the 12mm wrench or an adjustable wrench to turn the expansion valve adjustment cap. Turning the cap clockwise (tightening the expansion valve) raises the pressure at which the expansion valve releases, turning the cap counter-clockwise (loosening the expansion valve) lowers the pressure at which the expansion valve releases.

More often than not, you'll be adjusting the expansion valve tighter in order to address a leaky valve or set the pressure on a freshly serviced valve. 

7. Check the expansion valve adjustment by replacing the reservoir tray and reservoir and then back flushing the machine. Adjust the expansion valve until it just barely stops leaking while back flushing.

8. Don't forget to lower the pump pressure back down to your desired brew pressure!