All about adding vacuum breakers to older hx boiler machines without them

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#1: Post by phreich »

I originally posted what is below as part of another discussion, but it grew to become kind of a primer on adding vacuum breakers to older heat exchanger (HX) boiler machines so I thought it would be better in it's own thread. I hope it is helpful to those debating whether to add a vacuum breaker or not, and wondering what is involved in adding one.

What the heck is a vacuum breaker anyway?
A vacuum breaker is a device that was originally designed for plumbing applications to break siphoning action in plumbing -- some typical uses are: drain lines for dishwashers so that dirty water from the sink drain doesn't get sucked into the dishwasher, main valves for most lawn and garden sprinkler systems have them to keep water from the underground sprinkler plumbing from being sucked back into the building's potable water supply lines, and all newer garden hose spigots have them for the same reason.

In espresso machine boilers, they have a different function -- as the boiler cools down and loses pressure, the vacuum breaker opens the boiler to the atmosphere, preventing a vacuum from forming in the boiler as it continues to cool down to room temperature and the air and vapors inside the boiler loose volume due to this cooling. The vacuum breaker also allows the expanding air in the boiler to escape as the boiler heats up the water and the initial boiling of the water starts to generate steam. Once a bit of steam pressure builds, it overcomes the vacuum breaker's ability to stay open and it seals. That's why on modern HX boilers, as the boiler heats up to initial boiling, you will start to hear a hiss, and then "phhht" sound as the vacuum breaker seals. The pressure then can build up in the boiler to the appropriate point (usually about 1 bar above atmospheric pressure more or less depending on the altitude where you live) and the pressurestat turns the heating element off.

So, why add add vacuum breakers to older machines?
1. Convenience:
I've done it to a number of machines. The simple reason is that I don't want to have to be around when the machine is heating up in the morning to monitor the air escaping from the steam wand and then closing it once steam starts to appear at initial boiling. I would rather install a vacuum breaker and then be able to hook the machine up to a timer so it could be turned on, unattended, 1/2 hour before I wanted to pull my first shot (so the machine would have time to heat up and temperature stabilize).
2. Avoiding the milk contaminated boiler:
The addition of a vacuum breaker, as was mentioned before, also prevents a forgetful or novice operator from opening up the steam valve too early with the steam wand in a pitcher of milk and getting the milk sucked into and contaminating the boiler (due to the vacuum formed when the boiler cools down without a vacuum breaker). (Or, the other way -- by leaving the steam wand in a pitcher of milk after turning off the machine -- which has the same effect as the vacuum forms). The vacuum breaker, when functioning properly, prevents this from happening.

As one tech mentioned elsewhere -- cleaning out a boiler contaminated with milk is no trivial task -- it has to be removed from the machine, requiring disassembly of all plumbing and wiring connected to it, then opening up the boiler (if possible), or if the boiler can't be opened up, removing the heating element to gain access to a larger opening and then thoroughly cleaning it. It takes a lot of time and is expensive due to this. Also all boiler fitting gaskets have to be replaced -- which may take a long time if they are out of stock -- especially if they have to come from overseas. This delay is a headache for machines used in the home, but it is a serious problem for commercial establishments that may only have one multi-group machine. This is one reason why commercial establishments have their machines serviced usually at least every 4-6 months, usually including a thorough cleaning, descaling and checking of all valves and fittings to make sure they are all working properly.

Aside: if you are wondering why you need to keep the boiler vented to the air until steam starts to be generated at initial boiling, see this thread:What is the purpose of a vacuum breaker valve

What's involved in adding a vacuum breaker?
If there is room under the cover (usually a cup warmer tray) for adding a couple of fittings, it is a pretty simple task to add a vacuum breaker. There should be a port on the top of the boiler that has the boiler overpressure safety valve attached to it. The safety valve can be unscrewed, and then a close-nipple of the same size is screwed into the hole, with a tee screwed onto that, then the safety valve attached to one end of the tee, and a street 90 put on the other end of the tee and the vacuum breaker attached to the street 90. Sometimes it may be necessary to put a flat gasket between the vacuum breaker and the street 90 if the joint leaks. I had to do this on a couple of the machines. If the surface of the 90 facing the vacuum breaker is machined you can use a soft copper gasket washer -- if it is not machined use a paper gasket. In neither case do you need to use gasket cement. Often you can simply take the vacuum breaker out, clean off the old teflon thread seal tape and add a couple of layers more than the first time and effect a good seal without a gasket.

The safety valve does not need to be installed vertically -- which is why it can be installed on it's side attached directly to the tee. However, the vacuum breaker opens due to the force of gravity pulling down on the seal (once the boiler pressure is eliminated by cooling) -- so it must be installed vertically. That's why the 90 is needed. You could use a regular 90 (which has female threads at both ends) and a nipple between the tee and the 90, but that would require more room to add the extra fitting and a regular 90 is usually taller than a street 90. What is a street 90? A street 90 has male threads on one end, and female threads on the other -- making it more compact (albeit a bit more expensive than a regular 90). The threads on all tapered thread brass fittings should be sealed with teflon pipe thread sealing tape (although pipe dope/paste rated for potable water and steam fittings will work, it is a lot messier to use and can leave an unpleasant flavor/odor behind that may take a while to fade).

Is there room to add the vacuum breaker?
If the boiler safety valve was originally installed vertically, there is likely room to do this modification. If not, it might be difficult to find room to add the tee or you might have to cut a hole in the cover/warmer tray to accommodate the height required.

What about the cost?
The total cost for parts should be less than $20 for the close-nipple, tee, street 90 and the vacuum breaker (all fittings should be brass -- not steel). (Don't forget to pick up some teflon pipe thread sealing tape if you don't have some on hand.)

Some words of caution regarding tightening threaded brass fittings when using teflon thread sealing tape:
1. When using teflon thread sealing tape, you need to be careful not to overtighten the fittings. The teflon tape is very slippery and a great thread lubricant -- which means that it can be very easy to overtighten a fitting and crack the female fitting the male thread is being tightened into. This is not a big deal when it's a simple fitting to replace like a tee or a 90. However, if you overtighten a male fitting going into a boiler and crack the boiler's female fitting -- you'll need to take the boiler out and have a new female fitting braised in place by a welder -- a big hassle (and possible expense if the repair is beyond your capabilities and you have to send your machine in to a service place to have it done). Bottom line -- tighten until good and snug -- but don't tighten until there's a lot of resistance. If you fire up the boiler and it leaks a bit, then you can always tighten a bit more until the leak stops.
2. Also -- don't decide to loosen a fitting a bit to make it look/fit better.... It will most likely break the seal on the threads and cause a leak. If you need to do this, take the fitting completely apart, clean out the old teflon thread seal tape, put new tape on, and then re-tighten from scratch remembering to stop tightening when the fitting gets to the desired position, or tighten it more until the position comes around again (but not to the point of breaking).
3. Be careful about where the tape is wound. Make sure the tape goes only on the threads and does NOT overlap and go over the bottom of the male threaded end. If you get it below the threads, it can come loose inside the female fitting and work it's way into the valves and that can cause leaks and require disassembly.
4. Wrap the teflon pipe sealing tape only on the male pipe thread and in the correct direction. What is the correct direction? Make sure you wrap the tape in the opposite direction to the way you screw the male thread into the female fitting. Another way to look at this is to wrap the pipe tape onto the pipe in the same direction as the threads are cut into the pipe -- going upward from the cut end to the unthreaded part of the fitting or pipe. Both perspectives cause the tape to be put on in the same way -- so that it stays in place and doesn't unwind as the fitting is tightened.
5. Use a liberal amount of tape -- it's thin stuff and multiple layers help lubricate and seal the threaded joint. By that I mean 4-8 wraps -- not 20. You don't want too much either.
6. ASIDE: (Never use teflon tape on compression fittings -- only on regular threaded fittings -- teflon tape can and will interfere with the sealing of compression fittings which must be strictly metal-to-metal). If needed, it is okay to use a small amount of silicone plumbers grease on the threads of compression fittings to make sure they don't bind -- that won't interfere with the metal-to-metal joint.

What about the difference between BSP fittings used on most espresso boilers, safety valves and vacuum breakers, and US IPT fittings?
Luckily, the major difference between the British standard (BSP) and US standard (IPT) threaded pipe fittings is the taper -- the US standard having more taper than the British. What this means is that you can mix the fittings in some cases successfully. In the case of the female threads on the top of the boiler -- the extra taper in the US male thread will seal quite nicely and not do damage to the fitting. The male British thread on the existing boiler safety valve will screw nicely into the more tapered US IPT tee female thread too, this is also true for the male BSP threads on the new vacuum breaker fitting into the US female IPT street 90. Just make sure to use a liberal amount of teflon thread sealing tape when you assemble the fittings (see section above for tips about using teflon thread sealing tape). I don't recommend mixing BSP and US IPT in fittings connected to copper tubing because it may not work. The reason for this is that the British standard uses the same threads for compression fittings as they do for plain threaded connections. The US standard requires the threads be different between compression fittings and threaded connections. (If you are confused by this, go to your local home improvement store or hardware store and ask the sales associate to show you and explain to you the difference between compression and threaded connections and fittings. However, don't expect them to know much about BSP fittings -- that's usually beyond their experience, since most US home improvement, hardware and plumbing stores don't deal with BSP (or metric) fittings.)

Of course, if you want to do it all in BSP fittings you certainly can do it. You'll need to order them from an espresso parts store or a specialty fittings store, will pay 2-4 times more for the fittings, and will have to pay for shipping and wait for delivery (unless you have shop in town that will sell them to you). Here's two reasons NOT to be concerned about mixing BSP and IPT fittings: You don't need to be worried about voiding warranties because you are working on an older machine already out of warranty , and the modification should be obvious and understandable to any technician that may see it in the future -- in fact doing this was recommended to me by a technician.

Here's an example of how it has been done?
If you want to see a picture of this being done to an older HX machine, take a look at the before and after pictures in this thread I posted on doing this for to Nuova Simonelli Ellimatic: Modifying a N. S. Ellimatic to include vacuum breaker & adjustable pressure release valve.

The part of the thread to pay attention to for the purposes of this discussion is the addition of the vacuum breaker. (I mention this because in that thread I also describe adding an adjustable pressure relief valve which allowed me to regulate the pressure at the group head. That portion of the thread is not applicable to this discussion.)

Here's another machine that I've done this to (after image only): ... 283#501283

I hope this is helpful,


Posts: 304
Joined: 15 years ago

#2: Post by Billc »

Just a note of caution mixing NPT and BSP threads types.
The thread pitch for 1/8, 1/4. and 3/8 are different.

1/8"-28 BSP VS. 1/8"-27 NPT
1/4"-19 BSP VS. 1/4"-18 NPT
3/8"-19 BSP VS. 3/8"-19 NPT

Additionally the thread angle is 55 degrees for BSP and 60 degrees for NPT. This usually causes early interference and galling. Just be careful especially with parallel threads (i.e. 1/4G or 1/4 BSPP).


Posts: 637
Joined: 17 years ago

#3: Post by aindfan »

Phillip, excellent write-up!

A tip for those following this procedure but feeling lazy: stop by your local Swagelok office with the thing that was attached to the boiler and the thing that will be attached to the tee, and let them work their magic. I spent 15 minutes in a Swagelok office when getting a tee to sneak a thermocouple probe past my pressure safety valve, and an expert quickly figured out (and solved) exactly I was trying to do. Definitely time well spent, especially with the added confusion of IPT, BSP, and any other acronyms.
Dan Fainstein
LMWDP #203
PSA: Have you descaled lately?

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

#4: Post by phreich (original poster) »

Great tip Dan -- if you live in a city of significant size, there probably is a Swagelok dealer and they will have fittings to fit bsp (or can order them). However, if you live in a smaller town -- you are probably out of luck for this kind of help....

Bill -- the details on the thread differences is very informative -- the threads are close enough it does seem to work on tapered fittings. As the poster mentions -- the untapered (parallel) threads (usually used on BSP compression fittings) are problematic -- that's why I strongly discourage mixing thread types on tubing fittings. I am only suggesting it on the threaded boiler flange and that it works to screw the tapered BSP overpressure valve and the vacuum breaker valve into IPT fittings. Note that there is no tubing or tubing fittings involved in this modification.

Thanks for the comments folks -- it helps to round out the thread.