peacecup wrote:One of the original HB Prestinas can be found somewhere down on Mogo's espresso page:

http://mogogear.webs.com/thingsespresso.htm

Apparently it started in with Bill in Texas, and went through Portland on it's way to Richard Penny's. Just above it is a photo of the first HB Caravel that MoGo imported from Italy. We had some fun discussions about these machines during the dawn of the lever resurgence. Now of course there's the Strega, L1, and the ES2, but the originals still have their charms.

PC

Yes, I was there at the cusp of interest turning back to small commercial levers at the moment the Strega appeared. See:

Moving Beyond Cremina Craze, Commercial Lever?

I posted about finding my Prestina and then a post on the next page of that thread split off to introduce the Strega.

RayJohns wrote:On the pilot lights, send me several close up pictures showing where they go into the panel and what you are dealing with presently. Then I can produce a technical drawing and you can provide measurements, etc. If you have a spare set of lights, sending them down here would help yes.

Will do both. Thanks!

erics wrote:I would have some second thoughts re that Sirai pstat considering the impact on "space arrangements". A MA-TER pstat is just fine, very easy to adjust, and supports the amperage requirements of that element. That Sirai should be easy to unload on our newly established B/S forum.

The gage should be easy to replace (just measure the case OD - 40 mm?). EPNW probably has the largest selection.

drgary wrote:I don't have to jump ahead with the Sirai with its 0.2 bar deadband to start. How much does deadband matter? I'm making delicious coffee with the original Sopac with its 05 bar deadband but obviously haven't spent time fine tuning. I researched the Jaeger PSTAT and it has a deadband of 0.35 bar.

I've thought more about this, especially my question about deadband. The best one to ask is my Prestina. Today I'll drill a small hole in a double filter basket and thread a thermocouple into it to measure temperatures inside the coffee cake along the range of pressures modulated by the PSTAT. Others use this method as a poor man's Scace.

For space management the Sirai will fit inside the case, and I have the fittings and brackets to install it. My main hesitations about the Sirai are its louder clicking, less convenient access for adjustment (the Sopac adjustment dial is accessible through the drip area), and its reputed tendency for widening deadband over time.

Because I'm using the Prestina at home and dial in different coffees, my need for fine tuning temperature could differ from typical commercial use. I won't know how much that matters before taking measurements. I'm also not sure how to temperature surf this machine or whether that's needed. So far, the shots on this across variations in boiler pressure are often so good that boiler temperature may be less critical than on a home machine with a smaller group.

Thanks, Doug. No worries about my cutting into the case. If I leave the screws out of the cup warmer I can lift it off for immediate access to the PSTAT dial.

I've done some measurements today. Here's my "Scace Lite." My new, larger drill wouldn't hold a very small bit so I punched a hole in the side of the basket with a nail and filed off the sharp edge.



Added: As I've thought about these temperature profiles it occurred to me that they show a trend that is very different than with home lever machines. In Tekomino's Cremina temperature studies the temperature rises and then begins a very slight decline during the pull. Watching the thermometers on my La Pavoni levers the temperature steadily rises during the shot. With my commercial lever the temperature declines after the preinfusion and drops in a fairly smooth, steep curve to make a far more nuanced espresso.

With apologies to the many disciplined engineers on this site, here's my first test run. Let's just say I'm discovering where the saddle is and trying not to fall off the horse at this point. I rigged my thermocouple to Artisan and used the magnification function to get some tracings. The test wasn't carefully controlled but it did show me some beginning temperatures at pre-infusion and that temperature during a pull has a fairly stable decline. I dosed 19 gm of an underdeveloped roast into the double basket, did approximately 15 second pre-infusion, then ran shots that often went well over one minute. This didn't stall the lever. As noted earlier I haven't fine-tuned shots in this machine. I could re-do some trace captures and perhaps fine-tune the grind. But let's see whether I have the information I need, which is whether a 0.55 bar deadband in a PSTAT on this machine is too wide a swing for my tastes.

My initial take with this rough testing is that the initial temperature varies by as much as 19 degrees over this range. The lowest initial temp was 183, the highest was 202. Even throwing out the 0.9 bar initial reading of 202, where the portafilter was locked in a bit longer at the start, and going with the 1.0 bar reading of 196, I get a 13 degree difference. What also stands out is a large and fairly steady decline in temperature, about 20 to 30 degrees in the normal course of a well-tuned shot of let's say 30 to 40 seconds. This tells me that this Prestina both softens the shot with lower temperature and reveals more layers of flavor that are shaded one into the next through a large temperature swing. The initial flavor accent of boiler temperature water settles steadily to much cooler temperature where the group is idling. This is in addition to a steadily declining pressure profile. The large difference in initial temperature that then declined more steeply was enough to change the taste on this failed roast from very sour at cooler pulls to slighly sour at hotter ones. I want a narrower deadband on my PSTAT to set the initial temperature where I like it, so I think I'll put the Sirai in there.

Here's the tracing for 0.45 bar. Initial temp is about 183 and it declines to about 155 after a minute.



0.6 bar (the Amprobe data logger had shut itself off and I had to restart, so missed the starting number). This one isn't that useful and I would have to redo it:



0.7 bar. Initial temp is about 185 and it declines to 155 after one minute:



0.8 bar. Initial temp is about 192 and goes to 158 after a minute:



1.0 bar. Initial temp is 196 and goes to 156 after a minute:



I didn't capture the tracing for the 0.9 bar pull but did record the numbers in Artisan, as follows, which tells me it started at 202F and declined rapidly once I released the pre-infusion. That must be where it moved from 187.3 to 182.1. It eventually declined to 160.6 when I turned off Artisan.

202.0, 200.9, 198.8, 198.7, 197.4, 193.5, 191.6, 188.9, 187.3, 182.1, 181.9, 179.8, 179.3, 177.8, 177.7, 176.5, 175.3, 175.1, 173.2, 173.0, 172.8, 172.5, 172.1, 172.0, 171.6, 170.7, 170.5, 170.3, 169.4, 169.0, 167.6, 167.5, 167.3, 167.2, 167.0, 167.1, 167.0, 166.9, 166.8, 166.8, 166.6, 166.4, 165.4, 165.2, 164.0, 162.8, 161.2, 160.9, 160.6

Added: Discussion of this temperature profile yielding flavor differences seems worth continuing on my Conti Prestina Owner Experience thread. There's an old thread where I've added this observation. It's here:

The temperature profile of a commercial lever group

Staggering Toward the Finish

Today I did more piecing together and advanced this project further. It feels a bit like what I've watched through TV coverage of marathon finishers. Some wizards like Paul Pratt, Doug Garrott and Doctor Espresso look spent but run across. I'm staggering toward the finish, but it looks like the end is near.

I've just received some pre-cut stainless pieces for completing the drip grate, sourced from Speedy Metals, an online source that advertises willingness to sell in small quantities, some cutting included. These two pieces cost about $25 shipped and arrived in a week with the outer dimensions, at least, plasma cut. The one laid on top is wrong side up. The other side is coated like the strip on the right. I'll cut the big piece into a wide, square U to cover the edges and extend the back. The narrow strip will go underneath to extend the back at the level of the existing workpiece. I expect to get to that this week. When we arrived home tonight some steel trim arrived that should attach to the back edge, along with a roll of ceramic insulation for the boiler. I've also sourced a deeper bread pan made of stainless steel that will replace the shallow aluminum one that will now serve as an ice tray in my office fridge.



My main project today was figuring out the assembly for plumbing in the vacuum breaker and that huge Sirai PSTAT. After much head scratching I came up with a very simple support bracket design for the Sirai. This will support the front while the back is supported by the steam pipe underneath. This simple bracket was not store bought. I had to cut the ends off and smooth them on a grinder. I also drilled a hole in the thick steel inner frame and threaded a screw in there with a lock nut and washer to hold the bracket in place. That's why there are metal filings underneath. To cut it I used sturdier metal disks and a quick release mandrel for my rotary tool. It worked well and I'll use this for part of my drip grate cutting chores.



Here's where the Sirai PSTAT will fit, as Doug originally advised and facing in the direction suggested by erics.



By reading Paul Pratt's entry on PSTATs I determined that my hot lead can go into any normally closed (NC) terminal and exit the terminal directly across from it. The same is true for the neutral lead. But there's a grounding screw hole that puzzles me. Do I need to use this in any way?



Here's that grounding port from the bottom where the hot and neutral leads also enter inside the chassis.



Next I started assembling the steam pipe connecting the PSTAT to the manometer knuckle. Large compression caps went on each end, with compression nuts fitted over the tube that will lock them in place. We'll see if my attempt at "sweating" these joints with silver solder will hold up to steam pressure. I'm about to bend that pipe in place so it can attach. Eric was right. It's a tight fit, but I'll get it in there for a narrower deadband. I started bending pipe by hand and ending up using the vise for an assist, being careful, very careful, not to crimp the pipe.



A replacement manometer is on the way thanks to Dave at Allann Brothers. It's original equipment, fortunately. The existing one has started to stick.

Next staggers will be documented tomorrow or the next day.

Thanks, Ray. That's the input I needed. Will do.