The Super Strega: Modifying preinfusion pressures and other functional improvements

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TomC
Team HB

#1: Post by TomC »

Taking a stock Bezzera Strega Top model and spending about an hours worth of time and about $15 in parts or less, can yield some really useful modifications that will greatly expand your extraction capabilities with various coffees. This is a thread that will serve to highlight ongoing improvements to the Strega. I have a few other ideas in the works that I'll plug in here later on as well. These for the most part, are John Borella's mods, put in easy to follow how-to's, along with a few of my own.

I'll break down the two steps to optimizing the Bezzera Strega with two very simple, step by step modifications. Anyone, even with little to no electrical/wiring know-how can easily accomplish this modification. It's all here in painstakingly boring detail. *Please note, modifying your machine is something you do at your own risk and you accept that any changes you make to your machine will affect your warranty and or create safety issues not inherent in the stock design. This entire modification can be easily reversed without permanent alterations to the machine, but you do so at your own risk.

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Vacuum Relief Valve Drain Line Modification

Unplug your machine, turn off any plumbing source if plumbed in.

Take the drip tray off, remove the portafilter and unfasten the upper hinged lid parts (4 screws). If you can unscrew your lever arm, that might make for easier moving around. Then remove the outer case (it's a pain in the @ss), loosen the two lower hex head screws underneath the rear feet and only slightly loosen the two extremely difficult to reach upper screws that are way up tight in the front upper corners of the faceplate. They're not easy to reach, they're even trickier to get a hex head wrench on. You should be able to get the case off with very, very subtle persuasion without having to back out those dang screws. Set the parts aside and take a look at what you have.

Your stock vacuum relief valve isn't barbed. It's just a poppet valve (for lack of a better industry term). Go to your favorite site vendor and buy 2 barbed vacuum relief valves. They're cheap, and it's much easier to swap out a clean fresh one and get back into pulling shots than waiting for the single unit you've bought to be cleaned and descaled in vinegar, so I highly suggest you buy two. Vinegar works perfectly well. Rinse well and you'll have no problem down the line, routine maintenance will be quick and easy. CCS sells them and their prices are great.

This is what your stock vacuum relief valve looks like.

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This is a shot of what the one you want looks like.

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Buy 24" of 1/4"flexible silicone tubing (you'll need less, but a bit extra helps when getting things placed). I often went back and trimmed as needed to make sure I was able to remove kinks, which happens if you have too much length and it gets kinked once being routed to and fro.

Buy one 1/4" Wye connector. Plastic is fine. One will be fine, it's not a high stress part and shouldn't be subject to any wear. John Borella bought a whole bag of them early on.


Starting with the simpler vacuum relief valve modification. All you're doing is replacing the stock vacuum relief valve that sputters and spits water all over your boiler and surrounding electronics/wires until it reaches its operating cut off pressure and pops and seats the valve; with one that has a simple barb nipple that you can run a line to the OPV drain and keep everything cleaner.

By replacing it with a barbed fitting, you can route a line from it, straight to your OPV's drain line where it tee's in, then routes straight to the drain nipple sticking out of the front of the machine over your drip tray.

Carefully using two wrenches to stabilize both the stock vacuum relief valve and the copper line that it mounts to, remove the stock vacuum relief valve and set it aside.

Use one wrench to hold the fitting marked by the blue arrow steady while you torque loose the vacuum relief valve with another wrench on the area marked with the red arrow. This will prevent strain and damage to the thin copper line that connects it to the boiler.

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Replace it with the vacuum relief valve with the barb and torque it only till it seats well. Moisten one end of the silicone tubing and slip it over the barb and seat it well. Let the slack run along the right side of the Strega (faceplate facing you) and down towards your OPV. From the top it will look like this now.

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Routing down the right side of the machine towards the bottom.

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From stock, the OPV drain line just exits to the nipple on the front into the drip tray. You're going to be cutting that line and splicing in the plastic wye.

Tee your 3 way wye connector one into the line from the expansion valve, one from the OPV waste line, and let the single tail side of the wye run the rest of the silicone drain line to the drain nipple in front of the machine (that goes to the drip tray). The tubing fits plenty secure and doesn't need zip ties. I haven't had a problem in over 5 months of daily use and I think John Borella has had his for several years of occasional use. I don't think he bothered with zip ties either.

This is what the wye connector looks like down at the lower right side slightly underneath the boiler, near the OPV. Note the orientation of the wye. From the top is the line you just ran from the expansion valve, the OPV valve drain has a very short length of tubing that proved a bit challenging in order to get it just the right length so it was tidy, and didn't kink on me.

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Note here how the single "tail" side of the wye connector runs a line to the drain nipple to the drip tray.

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Check your fitment as far as length of tubing in order to prevent kinking. You want a smooth transition of lines from each location, to your drain without kinks.

By the way, this is what happens to components in your Strega with the stock vacuum relief valve in place. Water that manages to drip down or become water vapor that's trapped in the case of the machine promotes corrosion. Even the rubber mount has started to dry up and deteriorate on that side a bit. And these are stainless fasteners. My vibe pump has never leaked, and the other fastener on the far left side (not directly underneath the vacuum relief valve) has no signs of corrosion at all.

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And the other side, away from the OEM vacuum relief valve's dripping path. Looks good as new.

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Rotary Dimmer Switch Mod for the Vibe Pump

First off, buy this. About $5. You only need a single pole, 600w is more than enough than this vibe pump will ever need. Get a nicer dial and a pretty switch plate if you choose. I did, since I plan to mount the switch on an angle bracket I'll mount along the side (which only works because I added taller feet for the Strega [not for this mod specifically, but because I'm 6'3" and it makes it more ergonomic for me] the ability to mount the rotary dimmer switch along the side panel is only going to be an added bonus. If you choose to go that route and like the machine sitting taller Stephano's sells the 10mm thread, tall adjustable feet you need.

Buy about one or two feet of 12gauge/3 wire power cord. Home Depot sells them by the foot but it doesn't index on their website. It's about $3 for what you need. You'll only actually need about 8-10 inches total, but I liked having a buffer if I screwed something up.
This is what it looks like.

Before you get started cutting wires, you need to take a pair of pliers or channel locks and bend down the tab that Bezzera kindly provided us, for easy entry into the bottom of the case with out short length of power cord. Bend it down 90 degrees so that when you route your wire thru, it looks like this. This is the tab you need to bend.

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When it's properly bent down, it exposes a perfect sized pre-drilled hole that your new power cord will enter the machine to control the vibe pump remotely. So now your power cord shown here can be passed up thru the base of the machine. You should install a strain relief plug, which I've gone back and added and shown here. Orphan Espresso sells a great one that is at least 70% less than what I paid at the hardware store for a metal one. And I have a stubborn desire to have the things that don't need to be metal, not be metal, plain and simple. I prefer to minimize any chance of vibrations transmitting thru metal to metal contact and this is a good example. So pick one up from them the next time you need to re-order some dripper filters or something.

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Install a Romex style strain relief plug into the hole. The hole will need to be widened a bit in order for it to fit. It took me about 5 minutes and my Dremel tool to do the job nice and cleanly.

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Bored out a bit (about 1.5-2mm) with a Dremel with a coarse sandpaper wheel attachment.

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Installed.
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Take a look at the back of your rotary dial switch. You'll see 3 wires if you bought the right single pole switch. If you picked up a dual pole, you'll have 4 wires and more stuff to straighten out, so keep it simple and just get the simple single pole with three wires. One GREEN (ground) and two BLACK.

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Strip back and expose a good at least 3-3.5 inches of the three wires from your power cords outer black sheath, that you'll then snake up thru the base. After it's all tucked inside, it will sit here. You can easily do the wiring using a good crimping tool and wire connectors and heat shrink tubing etc, then tuck things back in the case. Use as much slack as you desire on this part, and you can just draw out the excess down thru the case and out to the rotary switch to keep things nice and tidy again. The arrow shows the power cord and it's 3 (BLACK, GREEN, and WHITE) wires coming into the case.

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The Strega has a ground screw that has a few ground wires on wire connectors from the pump and other electronic components. It is located about an inch away from where you see my power cord coming in, and is mounted to the frame. You're going to take the GREEN wire from the power cord you fed into the machine and crimp on a forked or closed loop wire connector and secure it with heat shrink tubing for a clean install. This new GREEN wire with connector will get grounded under this highlighted ground screw in the picture here below. Make certain that all the other components that need to be grounded remain so. This is the one fiddly bit of the whole job, since it's not the easiest spot to access. At least if you have big fingers and are trying to wrangle 3 random small wires that all need to be secured with one tiny little screw.

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The following steps are for tapping into the neutral side of the pump. For those wishing to tap into the hot side (works exactly the same but is more "correct", ignore the next few parts and only follow the steps that I've numbered 1,2,3, etc. immediately following these photos. I want to leave these original photos here for clarity sake, and since I don't feel like unmounting my back end off the Strega again just for a few pictures of what it looks like in its stock configuration, you'll get a better idea of how everything is situated.

Take note of a few things. This is your connection block that supplies power to your vibe pump. The red arrow shows the connector as it will look after you've connected the WHITE wire from your power cord. Using a spade connector and heat shrink tubing for a clean install, it will slide in place of the stock dual BLUE wire connector that occupies this spot normally. The blue arrow shows what the connectors look like for reference sake. You will not mess with that connector. The only one you're splicing into is the upper right one that has the black heat shrink tubing(around the WHITE wire) shown in the photo.

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Here's another shot showing the stock clear plastic connector (highlighted with a red arrow) that I removed and let sit there momentarily while I secured the WHITE wire (highlighted with a blue arrow) in it's place. That clear plastic connector with the two stock blue wires coming out of it will be connected to the BLACK wire from the power cord.

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The clear plastic connector you removed from the connection block (shown by the red arrow) is now spliced in with the BLACK wire from your power cord using a spade connector and heat shrink tubing again. The BLACK wire is indicated in the photo by the small blue arrow).

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*EDITED*
Although I haven't had a single problem in 6 months and John hasn't had a single problem in close to 3 years, for the sake of completeness, I'll include the following steps for tee-ing into the pump on the hot side, to avoid the scorn of the electrical engineers amongst us. ( I totally agree that things should be done properly however, which is why I went thru the added work of all the heat shrink tubing, etc), but if we're going to build it, we might as well do it according to code and keep everyone happy.

1) You're not going to remove the stock dual blue wired connector that is on the right side. Leave it alone.

2) You're going to remove the stock thinner dual brown wire connector on the left side and set it aside briefly.

3) You will now connect your WHITE wire from your power cord with the wire connector secured and with a heat shrink tubing (in my instance, black shrink tubing) for a nice clean install, where the BROWN thin dual wires were originally connected, as shown here in this photo. The blue arrow indicates the stock dual BLUE wire connection that you're not altering. The red arrow indicates the WHITE wire connection from the power cord now in the place of the thin dual wire brown connection.


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4) The only parts left that can possibly be connected is your remaining BLACK wire from the power cord, that you've installed a spade connector to, and slide it into the stock clear plastic connector- the OEM thin BROWN dual wire connector, as shown in the photo below.


The blue arrow indicates the clear plastic OEM connector (with the thin dual brown wires) while the red arrow indicates the BLACK connector that inserts into it.

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Now all necessary wiring connections are made within the case. We turn our attention to the end of the power cords three wires and how they wire up to the rotary switch. Gently tuck and tug the lines in the case so that they're arranged cleanly and organized and gently take out any excess slack thru your access hole in the bottom which leads to at least a foot of power cord. For my installation, I realize I only need about 6-8 inches of power cord, since I'll shortly be mounting the rotary switch along the side of my case.

Taking a look at the wires from the power cord, using twist connectors, splice together GREEN to GREEN.

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Next twist connector, you splice together BLACK to BLACK and BLACK to WHITE. It does not matter which black from the rotary dimmer switch goes to which black power cord wire. The only remaining black wire from the rotary dimmer switch now connects via twist connector to the only remaining white wire.

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After plugging the machine back in, and turning on the water supply, I turned on the switch and verified the pump engaged to fill the boiler. Turn the rotary dial to hear the decreasing voltage slow the output of the vibe pump to ensure proper installation. Once proper installation is confirmed, power it down, unplug the machine and wrap the twist connectors well with black electricians tape. These connectors are very close to your steam wand, depending on how much slack you've given yourself. You want them protected from a wet or steamy environment. This setup will eventually be mounted in a small project box and mounted alongside the frame under the drip tray.

Here's the setup without the electricians tape.

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With

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You'll notice that I have only a very short amount of sloppy black wire sticking out from under the machine. When it's mounted, it will look almost as if it came that way from the factory. I will add even more electricians tape and form up a very close to waterproof enclosure before I mount it, but I honestly think the risk of water getting into the wrong area to be quite small. It's more exposed now as it sits than when I'll have it mounted.

Here's my matching polished stainless rotary dimmer switch plate (not that easy to find) along with a much prettier and easier to read dial instead of the plain round marker-less knob. I picked up the nicer knob with the pointer line from my local hardware store in the fastener aisle along with various lamp switches and oven knobs and other generic replacement knobs. It was only about 0.50c.

Nicer switch plate waiting to be mounted at some point down the line.

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Please refer to the pre-infusion pressure profiling thread for tips on use. If you dial in your plumbed in unit, to a set 1.5 or 2 bar pressure, that's essentially the pressure you'll have at the group when you have the rotary switch turned all the way to off. I find that I can grind finer and use slightly lower doses and get much better extractions with a lot more forgiveness factor inherent in this modification. There's a multitude of options this modification allows. Please don't use this thread to discuss shot extractions.


I hope you enjoy doing it. All together, it took about an hour to do, start to finish.

erik82

#2: Post by erik82 »

Thank you very much for this detailed description of the Mod.

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bostonbuzz

#3: Post by bostonbuzz »

Thanks for getting around to doing this Tom, great work. I wonder if there is a convenient place for a needle valve in the brew path? Maybe this isn't needed or perhaps it could be an alternative to achieving the same ends as this pump control?
LMWDP #353

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JohnB.
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#4: Post by JohnB. »

TomC wrote:The tubing fits plenty secure and doesn't need zip ties. I haven't had a problem in over 5 months of daily use and I think John Borella has had his for several years of occasional use. I don't think he bothered with zip ties either.
Nice write up Tom. Thanks for putting it together. I didn't use zip ties to hold the drain line onto the fittings but I did use a couple to clean up the install as you can see in the following photos that were buried in the Strega Owner's thread. I also tidied up the wiring mess down by the vibe pump.

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I would suggest adding either a strain relief or cable clamp where the Dimmer switch power cord enters the bottom of the Strega. I opened up the existing hole & installed a standard Romex cable clamp as that was what I had on hand.

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LMWDP 267

IMAWriter

#5: Post by IMAWriter »

Awesome posting, Tom! Totally considerate, and much appreciated.
Mr Borella and I have discussed the expansion valve mod. I have the parts, excepting the "wye" connector, which I wasn't aware of. My bad, I'm sure.

NOW, All I need is someone in middle TN to DO THIS FOR ME!! (I live in Brentwood, residence of numerous songwriters and artists but sadly most of us electronically challenged! :lol: )
I perhaps the most challenged of all. It's amazing I did my Cremina maintenance, and hardly ever had any parts left over. :oops:
Rob
LMWDP #187
www.robertjason.com

WSH

#6: Post by WSH »

Outstanding!

Thanks

kmills

#7: Post by kmills »

Very cool! Just to be clear, if I want to replicate on an arbitrary vibe pump machine, I can use this dimmer switch on the Neutral leg from the pump, right?

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JohnB.
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#8: Post by JohnB. »

I don't believe that it matters which of the two wires on the pump you break into but don't quote me on that.
LMWDP 267

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another_jim
Team HB

#9: Post by another_jim »

The convention (and electrical code rules) is to put all controls on the hot side. This technically applies as a rule if the wiring and dimmer are outside the machine.
Jim Schulman

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Eastsideloco

#10: Post by Eastsideloco »

Correct. You don't want to ever open an intentionally grounded current carrying conductor (aka the neutral or grounded conductor). Switches, over-current protective devices, and similar go on the ungrounded current carrying conductor (aka the "hot" wire). All connections to ground, whether for equipment or system grounding, are made for safety purposes, to mitigate shock or fire hazards.