BES900 and the brass OPV…

As many of you already know, from early on we had the idea of changing out the plastic OPV for a more heavy duty OPV.

People asked why, my answer to that is 1. because we didn’t feel that the plastic OPV would stand up to the test of time and the ups and downs that we all have when it comes to playing around with our coffee settings, getting chokers, gushers, getting it right.  Yes it may has withstood 10 thousand times in testing but that is at one constant setting not the multiple settings a coffee lover goes through.  As we all know different beans need different settings and we often don’t hit the right setting straight away, I felt that a plastic OPV wouldn’t withstand those sorts of changes for long.

Oh and 2. because we can 😀

Now first off I have to say that this wasn’t an easy changeover, I guess the first time someone does something new there are almost always causalities, in our case it was our pump (more of that later), don’t be alarmed though if done carefully anyone else attempting this shouldn’t have the same trouble.

Normal disclaimer before I go ahead: BE SAFE AROUND ELECTRICITY, UNPLUG BEFORE YOU FIDDLE !!!


I took the covers off the same way that I did for the adjustment, you really do need to take the back cover off to give you more working space and accessibility.

First off here are photos of the original OPV, I’ve joined everything back up just to show you what you are looking at, you can see the threaded section where the OPV screws into the pump.

The original OPV and attachments.

The small section on the far right hand side is the end of the tube that has been cut off to allow for insertion into the new elbow that fits into the brass OPV.

Yes I can hear the questions already, what brass OPV did you use?  Where did you get it from?

We had chosen the new OPV we wanted very very early on during an OPV discussion on the Crema forum.  When it came time to make the final decision I was actually guided by Richard, one of my fellow Crema members who had just changed over his old OPVs in his Expobar.

So there you have the answer to the first question.  The new brass OPV is what Expobar call an expansion valve, part number E614.

Where I brought it was sourced from the same supplier that Richard bought his from, Espressobits in Victoria, I will get in contact with them and check that it is ok to put their details up before I do.

…and here it is…

Unlike the older Expobar OPV this one doesn’t have any plastic in it, a comparison can be seen here, the centre OPV being the most like the one both Richard and myself are using.


I needed to find a new attachment for the small hose that goes to the group, at present it is an airline fitting, I’m hoping to source a better fitting than this, it is only rated to 70 degree Celsius, in knowing what I do about fittings though this would be a constant temperature rating, for the purpose of what we are doing I felt that until we sourced a food grade part this would service.

I do have to say this about the fitting though, it is priced the same as the similar part from Espressobits that fits the Expobar machines, so I’m not sure that theirs would be rated any differently.  Oh why didn’t I buy theirs, well theirs fits a 6mm tube, the BES900 has a 4mm OD tube.


Here I come to the causality of the conversion, our pump.  What we neglected to recognise when first looking at the two OPVs was that the thread on the new OPV is longer than the old OPV and there is a reason for the old OPV having a thread as short as it is…by looking at the above photos of both new and old you can see the differences.

Yahoo we thought, detached the old parts, attached the new parts and off we go.  In the process of adjusting the OPV the pump sounded, well, wrong.  The OPV worked, that wasn’t an issue but the pump definitely didn’t sound like that before the changeover.

After Steve pulling the pump apart, putting it back together, definitely nothing wrong there, we tried again, and again it sounded not right, it was then on closer inspection that Steve figured out what had gone wrong.

The length of the new OPV had engaged and pushed into the top of the valve of the plastic section of the pump and caused the pump to mis-fuction.

After a discussion with my fellow Crema mates and a phone conversation with AM (he really is worth more than all the tea in China) I discovered that the free Breville machine we had picked up a year earlier was going to help us out again, it has exactly the same pump in it.

So out with the old and in with the old and the process began as to what was going to be the best approach to fitting the new thread into the pump thread without hitting the valve.

We tried washers and o-rings of different sorts but nothing was working, it would seal correctly, so finally we came to the conclusion that the end of the thread had to come off.

There are two ways (probably more) that the thread can be taken off, a lathe or a hacksaw and file.  Steve has the access and ability to use a lathe so that is what he did, measured up the plastic thread lenght matched it up with the brass thread length and took off the appropriate amount.

Below is what the brass OPV now looks like.

Also a comparison photo with the old plastic OPV.

Now the fun could really begin, putting everything back together again.

So the parts I used are:

Expobar expansion valve E614

1/8 BSP male to 4mm tube swivel elbow

6-16mm hose clamp

o-ring to fit 1/8 thread

It was then a very simple process of adding the o-ring and thread tape to the thread attaching the OPV to the pump, remembering to attach thread tape in the opposite direction to the direction that you screw the thread in and screwing it in.

Next step attaching the overflow hose back onto the OPV, now using the hose clamp as the hose is actually too large for the OPV attachment and without the new clamp it will leak as it’s not closed tight enough and the small tube to the elbow at the top.

The last thing you need to check for are leaks, please please be careful…

I don’t recommend doing this by yourself if you are not qualified to do it.

Once you have checked for leaks and found none, then comes the fun part of adjusting the OPV, I say fun because it is SO SO SO EASY.

Here you see the adjustment end of the Expobar OPV, a flat head screwdriver or something similar and someone to tell you up or down is all you need.

I’ve adjusted my gauge to sit at 10 bar as I did with the old OPV adjustment, I just find that this suits myself and my ability at this stage.

It took me a few shots to get the grind right, I find that I am grinding finer now than I was before, I also have to say that when I finally got the grind and tamp right (well for the first go anyway) the result was amazing.  I’ve been drinking mycuppa’s roasted Tanzania and have never tasted it like I got tonight, smooth, sweet cocoa as a cappuccino, I also have to say that the bean was roasted over a month ago, who would have thought huh 🙂



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