Modifying a N. S. Ellimatic to include vacuum breaker & adjustable pressure release valve

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#1: Post by phreich »

Hi fellow espresso enthusiasts,

This thread is an attempt to document some modifications I am making to a Nuova Simonelli Ellimatic heat exchanger (HX) boiler espresso machine. Note that the same modifications can be made to it's precursor, the Elli, which suffers from many of the same issues as the Ellimatic -- basically, the difference between the Elli and Ellimatic models is that the Ellimatic automatically senses the water level in the boiler and refills it when necessary, and the Elli doesn't -- instead the operator has to keep an eye on a sight-glass and press and hold a button to refill the boiler to the proper level when the boiler water level gets low.

Through a mutually beneficial trade with a friend I received a NS Ellimatic as partial payment which I plan to use as my "backup" machine and as my "portable" machine for use when I go to gatherings at family and friends homes and want to offer espresso drinks. I am lucky enough to have found and restored a plumbed-in Elektra commercial single group machine as my main home machine -- it looks a lot like the current Elektra GL1. (I posted a restoration thread on that last year on the Coffeegeeks website, in case you are interested: ... ods/499708).

The Ellimatic is the immediate precursor to the current Oscar model. It has very similar good characteristics and some of the same flaws. It has two flaws that the Oscar remedied:
1. There is very little clearance between the portafilter and the drip tray, and a shortened custom portafilter (albeit 58mm wide) that somewhat helps with the lack of clearance -- but really doesn't help that much. However, having said this -- if you use shot glasses or demitasse or cappuccino cups you won't have an issue with this clearance.
2. It does not have a vacuum breaker (more on that below).

The good:
1. It is a HX machine and can produce some decent shots and you can steam and pull shots simultaneously.
2. It is well built, and should last a long time as long as it is treated properly -- never run dry and cleaned and descaled appropriately.
The not-so-good:
1. The low clearance under the portafilter. (This issue is fixed in the current Oscar model)
2. The lack of pressure regulation in the cold water side of the HX water path, leaving you at the mercy of whatever pressure the vibratory pump produces (which is usually way too much -- around 15 BAR). (I believe the current Oscar model still suffers from this shortcoming.)
3. The lack of a vacuum breaker on the boiler, which forces you to open the steam valve until the boiler gets up to at least boiling temperature before you can close it. If you don't open the steam valve, the vacuum that develops in the boiler will fool the pressurestat and it won't come up to the correct temperature. Another problem this causes is the common "bad smelling steam" issue that the Elli and the Ellimatic share with many other HX machines without vacuum breakers. A machine operator mistakenly opens the steam wand early while there is still a vacuum in the boiler, and sucks milk into the boiler causing rotting milk solids to contaminate the boiler (and then cooked rotted milk solids to form into nasty stuff when the boiler comes up to temperature -- yuk!). Or a machine operator accidentally leaves the steam wand in a pitcher of milk after the machine is shut off, the vacuum forms in the boiler, and sucks the milk up then, which causes the same nasty problem. When this occurs, the only real way I know of to remedy it is to open up the boiler, thoroughly clean it, and put it back together -- what a hassle....
(I believe that the Oscar has remedied this problem)

There has been some discussion on various forums about attempting to regulate the pressure of the HX water path on the Elli and Ellimatic machines by messing with the HX safety valve that is connected to the hot side of the heat exchanger. This is problematic for a couple of reasons:
1. On most of these machines, the HX safety valve is not built to be adjusted -- it is simply sealed with an o-ring, and loosening the end to attempt to relieve the pressure on the internal spring and thus reduce the pressure simply causes the o-ring not to seal properly.
2. Because the safety valve is on the hot side of the HX, if you were to replace it with an adjustable valve, you would be bleeding off hot water from the HX back into the cold water supply tank -- which will drop the temperature in the HX earlier than would otherwise occur when pulling a shot, increase the HX recovery time, and heat up the water in the water supply tank. I think none of these are good things....

Soooo, I determined to fix both problems and bring this home-brewing espresso workhorse into the present. I thought my adventure in machine modding might be of interest to a few of you.

What the machine was like from the factory:
Here is a picture of the boiler plumbing as it originally was:

If you look at the picture, you'll see 4 connections on the top of the boiler (from front to back and left to right):
1. The first fitting you see on the left is the output of the HX. Connected to that is a tee that has the HX safety valve attached to it. This valve is supposed to open only when the pressure approaches 14-15 bar. It does activate (a little) when a blind filter is inserted in the portafilter and a backflush is done, dumping a small amount of heated water back into the water tank on the left.
2. The fitting in the middle is the boiler level probe that controls the boiler fill solenoid and pump circuit. When the water drops beyond the end of the probe in the boiler, the Gicar box on the right opens the boiler fill solenoid and turns on the vibe pump until the water level comes back up to the proper level. I discovered when doing the modifications, that this probe was set too low, and the last loop of the heat exchanger tubing was never being covered by the boiler water -- I fixed this by raising the probe up about 1/4 inch. There is still plenty of room for steam production.
3. The fitting on the right is the HX input line. You'll notice that it is connected via a brazed tee to the line coming from the vibe pump -- the other end of the tee goes to the boiler fill solenoid. I determined that this would be the best place to insert a tee and connect it to an adjustable pressure relief valve (PRV) (AKA adjustable over pressure valve (OPV)).
4. The fitting on the back of the boiler is connected to the boiler safety valve. Theoretically this valve should never be activated -- but it's there to make sure the boiler does not become a bomb should the pressurestat fail and keep the heating element on too long. I determined that this would be the best place to connect the vacuum breaker, and would do this by taking the 90 degree elbow off the safety valve, putting a tee in it's place and inserting the safety valve on the same side of the tee as the original elbow was oriented, and putting a street 90 on the other side facing up and inserting the vacuum breaker there. Clearance is an issue -- so even with the lowest profile vacuum breaker I could find, I may have to have to drill a hole in the top cover to allow the stem of the vacuum breaker to rise as the pressure rises in the boiler. I'll know more when the vacuum breaker I ordered arrives and I try it. It will be close either way. I may just be able to raise the top up a bit to get the clearance I need.

- Behind the boiler is the vibratory pump
- Behind the boiler and to the left is the cold water supply tank
- To the right of the boiler is the Gicar brand autofill circuitry. Directly below that (and not visible in the picture is the pressurestat).
- In front of the boiler is the boiler fill solenoid. Not visible in picture, but further forward is the 3way valve for the grouphead.
- In front and to the left of the boiler is the steam valve and wand assembly (not really visible in the picture either).

There are two connections visible on the picture (barely) on the upper portion of the boiler -- on the front (left side) and back sides. The one in the front left is the steam supply port, and the one in the back is the port for the line to the pressurestat. Both of these are above the waterline in the boiler.

There are two more boiler connections that are not visible in the picture. On the front lower side of the boiler is the boiler fill inlet, and on the bottom center of the boiler is a capped drain port. Both of these are below the waterline in the boiler.

Okay, so now to the modifications:
The fittings needed for the vacuum breaker were pretty straightforward -- a 1/4" tee and a 1/4" street 90 (both in brass). While the existing fittings are BSP, I know from past experience that 1/4" US Iron Pipe Thread (IPT) fittings will work okay -- they just have more aggressive taper to the threads -- but the size of the threads is actually the same (or close enough to work) as BSP. So these fittings could be bought in a plumbing supply store or a home improvement store. Note that most of the 90's you get in the home improvement stores are not made the same as standard pipe fittings -- they are drilled and tapped out of blocks of brass instead of being cast and then threaded. I don't like the drilled and tapped kind because they often have an area inside that is over-drilled and can trap water -- where the cast ones don't.

inserting the tee in the 6mm tubing was a bit more problematic. The difference in size between 1/4" US copper tubing and 6mm tubing is only about 10 thousands of an inch (the metric tubing is a bit smaller). I did not want to trust regular copper tubing compression fittings at the 130 pounds of pressure that the pump is capable of producing, so I determined to braise a tee in the line instead. However, the plumbing supply stores in my area did not stock 1/4" "sweat" tee's and I didn't want to wait for them to arrive (and I would probably have to buy a box of them instead of the 1 I needed).

I got to thinking and remembered that compression tee's have a "well" or "socket" in them that is about 1/4" deep to allow some tubing to be inserted within the fitting to stabilize the tubing when the compression sleeve is being tightened by the compression nut. I realized that I could utilize this area in the brass compression tee to braise in the tubing instead. While this might not work for larger diameter tubing, for small tubing like this (6mm & 1/4"), it should hold well. I consulted with a friend who is a journeyman plumber and has extensive experience with both water and high pressure boiler pressure lines and he assured me that for this small diameter tubing, I could use standard plumbing lead-free solder for the braising -- I always use the "better" stuff that has some silver in it so it flows better and is stronger anyway. He assured me I did not need to do the braising with silver/nickle braising rods as would be necessary for larger diameter tubing (like 3/4" or 1" would require). Soooo, happy not to have to find a welding supply house for special braising rod, I went to work with the standard plumbing stuff that comes in a coil. I marked where the new tee would go, cut out the section that the tee would replace, "cleaned" the tubing and sockets in the tee with sandcloth, applied flux, and got to braising with a mapp gas torch.
ASIDE: (Mapp gas is much hotter and easier to use for braising plumbing fittings than standard propane bottles -- you just need to make sure that the torch can handle the mapp gas temperature. When I first started doing copper plumbing I used a standard propane torch -- my plumber friend introduced me to mapp gas, and I've never looked back since).

On the other end of the 1/4" line I added via the new tee, I braised on a 1/4" compression to 1/4" male pipe thread adapter, and I attached a 1/4" coupling to that. I'll screw the adjustable PRV to that and route it's output back to the cold water tank with the same flexible silicone tubing as is used for all the other lines to the cold water tank. I could have used a 1/4" compression to 1/4" female pipe thread adapter, but I had the other stuff on hand already....

I have the PRV and silicone tubing on order along with the vacuum breaker. I'll post a picture of everything mounted and in place once it arrives next week.

The results of the plumbing mods are shown in the pictures below (three different perspectives). Note that I have left off the HX safety valve assembly so you can see the modifications -- that assembly goes over the new plumbing and would hide it from view. The 4th picture below shows it mounted back in place:
View one:

View two:

View three:

View four (with HX safety valve back in place):

There was one other minor modification I did while I had the machine apart. The Elli and Ellimatic group is attached to the boiler by some heavy copper plate that is about 1/4" thick -- it acts as a passive heat transfer conduit to keep the brewhead hot. They decided to support the brewhead by bolting this conduit to a steel cross-member attached to the frame of the machine. The issue was that this caused a lot of boiler heat to be wasted heating up the steel cross-member. I thought that if I inserted a piece of neoprene between the "conduit" and the steel member, that would dramatically reduce the contact and heat transfer -- all that would remain was the heat transferred through the two bolts.

We'll see once I get the machine fired up again if it is noticeable, and I'll update the thread with the results.

More pics to come once the vacuum breaker and adjustable PRV arrive and are installed.

I hope this is helpful to other Elli and Ellimatic owners, and may be of interest to others facing similar issues....


UPDATE: The adjustable pressure relief valve and the vacuum breaker have arrived, I installed them and they are working just fine. As before, the first two views are taken with the HX pressure safety valve and its' tee removed to show the added fittings. The last picture shows this reinstalled and shows the leak-free tested and working modifications. Pictures are below:

View one showing installed Vacuum breaker and PRV

View two

View three, showing the completed and tested modifications with all plumbing reconnected, and the silicone tubing routing the "relieved" cold water back to the water tank (I had to drill a new hole in the tank). :)
NOTE: When drilling in this kind of material, it is necessary to put a block of wood inside the tank to support the side being drilled (in my case a piece of 2x4 plus a shim of 1/4" wood to make up the difference. Otherwise you are likely to crack the old plastic as you attempt to drill through it. Also, drill slowly and steadily -- don't push real hard and take your time -- you'll get a cleaner end result....

Original unmodified view (again)....
And, just to give you a side-by-side comparison -- here's the original factory setup again

The end.

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#2: Post by benpiff »

Beautiful work my friend! That's so cool to see my first serious machine about to get a whole lot more serious.

phreich (original poster)
Posts: 78
Joined: 13 years ago

#3: Post by phreich (original poster) »

Parts have arrived and been installed in the modified plumbing -- the first post has been updated to show the end-result. It is all working well, with no leaks, and I have proper pressure at the group head and no longer have to open the steam wand when heating up the boiler. :)

I will have to raise the cover up about 3/8" or cut a hole in it to allow room for the vacuum breaker -- but that's not a big deal. I'll show a picture once that has been done, and the whole machine buttoned up (front, side, back and top panels in place).


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#4: Post by doubleOsoul »

benpiff wrote:Beautiful work my friend! That's so cool to see my first serious machine about to get a whole lot more serious.
+1 Elimatic was my first too. Had mine for 15 years.

phreich (original poster)
Posts: 78
Joined: 13 years ago

#5: Post by phreich (original poster) »

Well, another wrinkle in the process -- the boiler safety valve started to open too early and so pressure was not where it needed to be. I opened up the safety valve, noticed that the red neoprene or buna (I assume) rubber seal was pretty well indented by the plunger, and got ready to go to the plumbing store to replace it (it's just a round, flat valve seat washer), and got to thinking -- if it was flat on both sides and was still pliable, maybe I could just turn it over.... Well it was pliable and flat on the other side, so I turned it over so what was the flat backside would be the sealing surface, reinstalled it, and, viola, it worked. Note, this is not a new concept -- a plumber showed it to me years ago for doing a quick repair to older faucet valves -- but it's the first time I had an opportunity to try it on a boiler safety valve. Maybe this "fix" will save someone else some time by avoiding a trip to the plumbing store.

Now the last things I need to do is to get some tubing and hose clamps, and a fitting to hook up a gauge to the steem wand to get an accurate reading on the boiler pressure so I can adjust the pressurestat to the appropriate pressure.

I am finding that the shallow portafilter and filter basket for the ellimatic is a bit of a pain -- it is much more susceptible to grind and tamp variations, and am having to adjust my grind to be finer so the pour at 9 bar has the correct timing (it's coming out too fast now). I am going to make a bottomless portafilter out of a spare commercial one I have (I will have to do some grinding on the flanges to make it fit), so I can use a standard double basket -- should be able to pull better shots and not have to mess with my grinder settings hopefully.

I do have a question for other Elli and Ellimatic owners....
Since the heat exchanger in these machines is a simple coil of copper tubing, it seems to heat up in the boiler a lot faster than a commercial hx does. Do you find yourself always pulling cooling flushes, and how long do you pull them since the HX is smaller than a commercial machine? I don't have one of those handy (but expensive) portafilter temperature gauges or I'd be able to answer this question on my own.
If I don't get a response in this thread, I'll post it as a general question so the title will get noticed.

Once I have the pressurestat adjusted, I'll button up the machine and post pictures of the completed project.


phreich (original poster)
Posts: 78
Joined: 13 years ago

#6: Post by phreich (original poster) »

Okay, I've been a bit remiss and not posting the final results of the modifications...

I completed the modifications, and have calibrated the machine to produce the shots at 9 bar of pressure, and it is pulling great shots....

Here are some pics of the buttoned-up machine:
The first is a front view:

The second is a top angle view showing the modification done to the cup tray on the top allowing room for the vacuum breaker.....
I put some ink on top of the vacuum breaker, put the drip tray back on it and wiggled it around a bit so I could find the mark left behind by the ink on the bottom of the drip tray. I then drilled a 1.5" hole in the drip tray, and made the custom cover for the hole by using a couple of standard schedule 40 PVC fittings -- a 1.5" male threaded adapter, and a 1.5" plug. I cut most of the threads off of the male threaded adapter and cut all but 1/8" of the glue-in female hub on the other side off. and used a 1.5" conduit nut (they are very shallow) to hold the fitting in place in the hole I drilled in the cup tray. I then cut all but 1/8" off of the 1.5" PVC plug, and used that shortened plug as a removable cap to cover the opening in the male threaded adapter. It worked beautifully, looks good, and only cost about $3 for the parts.

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#7: Post by Coffeefix »

I have a question about the pathetically shallow drip tray on the Ellimatic.

My tray fits rather snugly in place, but when I try to remove it, it tips backward, spilling the contents under the machine. The front of the tray has a lip that fits over the front edge, but the back is smooth. Is this normal?

Thanks for your excellent posting on the modifications!