La Marzocco Expansion (Over-Pressure) Valve - 12 Bar This expansion valve bleeds off excess hydraulic pressure into the drain cup, set to release at 12 bar. Water occasionally trickling from this valve during brewing is completely normal operation. SPECIFICATIONS 1/4" M BSP thread 12 bar relief pressure COMPATIBILITY Fits: La Marzocco machines using this drain-cup expansion valve design INSTALLATION DIY - threads into the group/hydraulic block. PRO TIPS A few drips from this valve during brewing is normal, not a fault - it's only doing its job. The opposite is actually the concern: if it never trickles at all, that can mean the valve is stuck shut and pressure has nowhere to bleed off.