Group Head Parts: Gasket, Shower Screen and Dispersion Plate
Water drips down the side of the portafilter, or the coffee looks unevenly wet. You look up into the group head and see a ring, a perforated disc and a screw. Which is which?
The gasket
This is the ring around the rim. Your manual will say what yours is made of. The portafilter forms a seal with the espresso machine's gasket1, so when you lock the handle in, the gasket is what stops water escaping at the edge.
Grounds collect on it. One guide says coffee grounds love to collect on that rubber edge2.
One retailer's service page for one espresso machine model lists replacing the gasket and screen as a yearly job3. Look for your own maker's interval.
The shower screen
It's the flat metal disc with small holes. Wikipedia says the grouphead contains many holes, which it calls the shower, that attempt to distribute the pressurised water evenly1. So the screen's job is to spread water over the coffee instead of letting it fall in one stream.
That's why a screen kept clear matters. Holes are small, and anything that sits in them gets in the way of that spreading job.
The screw and the dispersion plate
On most machines a single screw in the centre holds the shower screen2. One retailer's help page for one machine model calls it a dispersion screw and says it holds the screen in place3.
Some machines also have a dispersion plate behind the screen2. The sources saved for this site don't explain what that plate does, so we won't guess. If your manual shows one, read what it says about it.
Names change from maker to maker
Makers don't always use the same words for the same part. If your manual has a parts diagram, use the maker's words when you ask for help or look for a spare.
| If you see | It's most likely |
|---|---|
| A rubber ring at the rim | The gasket1 |
| A disc with many small holes | The shower screen1 |
| A single screw in the middle of the disc | The fixing for the screen2 |
Who touches what
How to clean the gasket and screen is for your own maker's manual to say. We haven't saved a maker's manual that allows owners to take the screen off, so follow your manual, and leave removal to the maker or a qualified technician.
Opening the machine's case, or touching anything electrical, is for the maker or a qualified technician. Please don't try it yourself, even if the group head looks simple.
Dirt on these parts has a cause, and knowing it helps you decide how often to clean. Read about it on the buildup page.
Where the facts come from
- Espresso machine, Wikipedia
- How to Clean an Espresso Machine That Can't Backflush, Seattle Coffee Gear
- La Marzocco GS3: Group Cleaning and Maintenance, Clive Coffee Help Center
More group head pages
What Is an Espresso Group Head?The group head is the fitting where the portafilter locks in. Here's what it does, what's inside it and why makers ask owners to keep it clean.
Why Group Heads Get Dirty: Coffee Oils and Fine GroundsBrown buildup around the group head comes from coffee oils and grounds. Here's how it forms, what it looks like and what makers say to do.
What Is Backflushing and Which Machines Can Do It?Backflushing pushes water or cleaner back through the group head with a blind basket. Here's what it means and how to tell if your machine allows it.