Puck remains on shower screen after removal of portafilter

Matthew Hoffman

Recently, I find that the spent puck often remains on the shower screen after I remove the pf, following the pulling of a shot. I think this probably started after I put a new-style seal on the bottom of the piston. Probably, the sucking force is just that much greater when the lever is lifted.

I use VST baskets, but I switched to an IMS basket of the same size to see if that would make a difference. It does. The effect disappears with the IMS basket. This is not surprising, as VST baskets are very easy to dump after a shot, with their slippery straight sides. I suppose they offer very little frictional resistance to being sucked upwards.

I don't know if the shots are worse for having the puck sucked up on to the screen; it seems reasonable to expect that they would be less well-extracted than otherwise. They are also messier to clean up.

Matt

Reiss Gunson

hi matt

i suspect your dose - grind combination for the VST is causing the puck to compress against the shower screen when you fit the portafilter to the group; trying leaving a bit more headspace - i suggest 17g doses for an 18g VST basket

the IMS is likely to have a slightly greater internal volume, depending on which model you are using

i dont think the new seal will be responsible as the sucking effect that you refer to would be minimal as air can be drawn through a dry coffee puck quite readily, and in any event the vacuum only exists for the first few millimetres that the piston is raised until the piston seals clear the inlet ports and water rushes in at boiler pressure. after that you have the piston coming down at circa 9 bar into a wet puck rather than a dry one, so a lot more downward force on the puck that any initial upward force on a dry puck

kind regards

reiss.