So, I should've asked my question BEFORE going ahead and backflushing, using a handle from my Astoria Machine... BAH!
Here's what I've done... I put in the backflush and pulled down the lever, then released it back up. I let a few seconds pass, then went to twist off the handle- and woah- pressure! It spit water, the o-ring and the filter out of the machine.
What is the correct way of cleaning out a lever machine? (I purchased this machine 2nd hand and it didn't come with it's own backflush plate or manual... I will try to download one now.)
On typical pump-driven machines, backflushing is done to clean out the 3-way brew valve. Your machine does not have one, so there's no need. Don't attempt to backflush.
That's also worth remembering when you pull shots. There is no mechanism for relieving excess pressure, you simply have to wait for it to release on its own or deal with the consequences. This is especially important if you unintentionally overdose the basket or grind so fine that the shot totally chokes. There's no way to stop the shot - just gotta wait it out. If you have to remove the filter, wrap a towel around the area to catch the sneeze, proceed with extreme caution, and watch that lever!
Your idea of looking for the manual is good, though depending on the age of the machine you may not find much. You might also try calling the guys at the Simonelli tech desk.
Cleaning may just involve cleaning the screen, gasket area, and portafilter. IIRC, that screen can be tricky to remove and reinstall, so finding a way to soak it in-place may be your best bet. I know very little about this particular machine though. Hopefully someone else can jump in.
Feeling a bit silly! At least once I put the things back in place it continued to pull beautiful shots. I've only worked with pump-driven machines, so it's time to do my homework.
To relieve the pressure immediately, you can pull down on the lever a bit while removing the pf. The pressure comes from the spring inside the group head - if you re-cock it some, you take off the pressure to allow removal even of a blocked extraction. Then let the excess water flow into the drip tray.
There's little information about these machines. The biggest collection I have found is at homebarista.com. Also a few youtube videos of Napoli shops, where it interestingly seems everyone is getting shots and maccs.
I hope this information helps you, despite being 3 months late! :)
I work on a Victoria Arduino Athena manual machine at the Oasis Coffee Spot in FL. The group should be identical, since Nuova Simonelli basically = VA
When you pull the lever down, the piston recedes into the group head until it reaches the water inlet. The chamber can get caked with coffee oils (especially if for whatever reason you pull the lever down again in the middle of the shot).
This is what we do to clean out the basket, portafilter, group and piston:
1. Put some purocaff in the basket (regular basket, not blind!) and give the lever a super short pulse. This just gets a touch of water in the basket to let it soak into the basket and portafilter.
2. Find a wide mouthed cup or bowl that is big enough to fit over the group head.
Pull the lever down to fill the cup and empty the contents of the portafilter into the cup.
Remove the portafilter.
3. Put the cup over the mouth of the group head and pull down lever slowly until water just barely begins to trickle out. You will see the cup begin to fill.
When you release the lever, you will see the level of the contents of the cup go down as it is sucked up into the chamber.
4. After letting the initial pull soak, repeat step 3 repeatedly. Pulling the lever quickly gets the water moving more violently and may help break down any build up.
While the backflush will get most of the oil build up, you'll still get some gunk after a while that just needs to be scrubbed off.
If you're not in a cafe setting and can let your machine cool down, this is best.
1. Pop the dispersion screen off using a flat screwdriver
Give the screen a good wipe down. Hold it up to the light to see any holes that might be plugged by coffee oils or rubber from an aging gasket.
2. With the water turned off, pull down the lever until the heat exchange has been emptied
(If you're in a commercial shop and are unable to turn off the machine, you can cool the group down a little by keeping the lever all the way down and letting water flow until it runs cool before shutting the water off. This will help keep you from getting burned while scrubbing!)
3. With the lever still down, reach up into the chamber and scrub with a damp towel and purocaff. After you can wipe the chamber and the towel comes out clean, let the lever back down and scrub the piston head as well.
4. This process will strip your chamber of any lubrication it previously had. Be sure to coat the chamber with a food grade lubricant before letting the lever back up.
5. Replace the dispersion screen. These lever groups don't use a retaining screw but use friction to hold the screen in. Whenever you remove the screen, the prongs get bent out slightly. To replace, first inspect the screen and make sure no one tab is bent in or out more than the others. You'll probably have to bend all of them in slightly in order to get it to hold again. I do this by rolling it along our rubber tamp pad while lightly tapping on the prongs with the handle of my screw driver. Then, simply press the screen back in the group head. When installed properly, it should have some movement when you tap on it and it should be able to twist freely without falling back out.