Where's the OPV on an Astra Pro to adjust brew pressure?

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curmudgeon
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#1: Post by curmudgeon »

Hi,
Long time lurker, first time poster. This is going to be a fortress of text, so get ready!

The Background:
I've got a late 2015 model Astra Pro, which I've enjoyed since it showed up on my doorstep. The steam power is phenomenal! It was a huge upgrade from my Gaggia Pure, although the Gaggia served me well for many years and taught me a lot.

The Problem:
(This is where it gets tricky: I'm not entirely sure I have a problem, or if I really just don't understand this machine.)
The Pro only has a boiler pressure gauge; there is nothing to show me brew pressure. That really didn't matter (and I guess technically still doesn't - I can still make espresso without it) until recently when curiosity got the better of me and I wanted to know what my brew pressure is set to. I've done exhaustive research on the subject here and on other fora, and peoples' opinions of the Pro (as well as descriptions of brew pressure - as low as 5 bar as set from the factory) are all over the place. Enter the DIY portafilter pressure gauge. I was able to borrow two gauges and some fittings from work. This is what I found:
Video 1: https://www.youtube.com/watch?v=YoOnUhW4g1s
Video 2: https://www.youtube.com/watch?v=ewRoFCyazbo
Now, I know dead-head pressure is supposed to be higher than brew pressure, but ~16 bar is just plain high! I emailed back and forth with Richard of Astra, and he swears up and down there's no way the brew pressure could ever be that high. I want to agree with him, but it's hard to argue with the gauges. Why wouldn't the OPV kick in before then? From everything I've read, my dead-head should be more like 11-13 bar, and even THAT may be on the high side.

The Research:
I've been pulling my hair out on this one! I want to try to adjust the pressure down to a more reasonable level, but for the life of me I can't figure out how! I've read post after post and thread after thread of adjusting OPVs on various machines. I even found a post that showed three different style OPVs side-by-side. Now, I've pored over the internals of that machine for the better part of two hours, and as far as I can tell, the Pro DOES NOT HAVE ANY OF THESE!! I had the cover off the other day, so I got a good picture of the guts. I've labeled what I think are the air bleeder, vacuum break, and boiler relief valve, but no OPV! Picture is hosted here: http://imgur.com/PkPKf6y. If you're having trouble making out details, I can take more pictures.

Am I missing something? Have I mis-labeled these parts, or does the OPV simply not exist in this machine? I found some discussion from almost a decade ago with some guys discussing adjusting brew pressure on the Pro with the teflon slotted screw - as far as I can tell, they're discussing a Fluid-O-Tech style OPV, but there's nothing on mine like that!

The Mental Workout:
Now logically, the pressure will be lower with flow. That's always the given with a vibe pump setup. In fact, I pressure tested again with the portafilter purposefully not locked in 100%, and with some water leaking out, the pressure was closer to 14 bar. Could it really be that there is no OPV per se in this machine, and that all pressure regulation is purely up to the prep of the coffee puck? In my emails to Richard, he claimed brew pressure was not adjustable on this machine, but I also got the feeling he might not have been giving me the whole story. I just can't wrap my head around the fact that a machine of this caliber and quality with an air purge, vacuum break, and pressure vessel relief valve does not also have an OPV in the brew path!! There are a few check valves in the plumbing coming from the pump, and those are going to retard the flow a little in a dynamic situation, but surely that can't be the only pressure reducing-type device in the brew path!!...?

The Follow Up:
I'm waiting on some extra parts to add a needle valve to the pressure gauge setup. This will let me see my brew pressure when accounting for flow. Given that the pressure is still high, and given that no one here can tell me how I'm just overlooking my OPV (or confirm that the puck is supposed to regulate all brew pressure), I intend to take the following steps:
1) Buy an OPV from one of the various online retailers
2) Plumb the OPV directly downstream of the air purge
3) While I'm modifying the machine, I'm considering adding a dual boiler/brew pressure gauge so I can keep an eye on things from time to time.




TL;DR: Where's the OPV on an Astra Pro, and how do I adjust it?



Thanks for your patience! If you read through that whole thing and your eyes didn't glaze over yet, you're doing better than me!

EDIT: I should add I saw the very similar Bezzerra thread posted yesterday, and I've watched the video over there many times, but I can't find a simple adjustment like that!

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erics
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#2: Post by erics »

Nice post . . . where in PA are you located? Yes, more pics of the hydraulic path downstream of the deaeration valve would be helpful.

As far as I can tell, you have labeled the parts correctly. I would ask the mfg for a pdf of the parts catalog for your future/current use.

Assuming the brew pressure is not adjustable (as the mfg has said), then your brew pressure will be high given the capacity curve of the Ulka pump. Additionally, if the brew pressure is NOT adjustable, then you have no OPV.



An alternative course of action to reduce the brew pressure would be to install a restricting orifice in the hydraulic path.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

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curmudgeon (original poster)
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#3: Post by curmudgeon (original poster) »

Thanks for the quick reply! I live up in the glorious wilds of Pennsyltucky, near the home of the Little League World Series.

I got a chance to take more pictures over lunch. Hooray for living only two miles from work!
Here is a close-up of the pump output below the reservoir:
Here is a better picture of the plumbing above the reservoir:
Now, is it just me, or should the stem of the air purge valve be pointing up? Maybe when I'm digging around I'll cut some longer tubing and turn that stem.

Astra has a few pdf parts lists out there for their various models, but I haven't been able to isolate the valve I'm after.

The side of the pump indicates it is a Fluid-O-Tech - sorry not providing that information earlier. From what I've seen, the curve on the FOT pumps shows a little less flow at high pressure, and a little more flow at low pressure compared to their Ulka brethren. However, that doesn't make sense, as I'm seeing dead-head output numbers closer to the Ulka side of the spectrum. I'll try to figure out which one it is tonight.

Using a graph very similar to the one you posted, the output of the FOT should be 194mL/min, or 97mL in 30 seconds. (I typically pull a double in 30 seconds - VST basket, 20 gram dose, 1:2 ratio) That means (assuming no OPV) that I'm either necessarily going to have very large (97mL) doubles at 9 bar, or I'm going to be brewing around 10.5 bar (assuming a 2oz shot). Running the numbers for an Ulka pump means either a 130mL double, or brewing at 12.5 bar (again, assuming a 2oz shot). From what I've read, I could expect to see up to a 3 bar drop from static to dynamic flow with a portafilter gauge. Since I'm seeing almost 16 bar with no flow, I very well could be brewing in the neighborhood of 12.5 bar with flow. Hmmm.... now I'm even more curious to run the pressure tests again when my needle valve gets here.

Maybe there really isn't an OPV, and I've just been brewing at much higher pressures this whole time...!

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erics
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#4: Post by erics »

The side of the pump indicates it is a Fluid-O-Tech - sorry not providing that information earlier.
The pump looks like a typical Ulka EX5 to me. If you see the words Fluid-O-Tech printed someplace on the pump, that would be interesting to say the least.

The orientation of the deaeration valve output is not relevant.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

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curmudgeon (original poster)
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#5: Post by curmudgeon (original poster) »

Ok, correction: I was working from memory when I posted that, and in fact the words Fluid-O-Tech are printed on the mount, not directly on the pump. See here:
So it's an Ulka pump on FOT mounts?? That seems a bit mixy-matchy to me, or is that common in the espresso world?

I agree, it looks to be the EX5, judging from what I can find online. However, the sticker on the pump is mounted toward the frame, so I wasn't able to confirm. I'll have to pop the pump off to verify.

My needle valve and other parts should be here today or tomorrow, so I hope to be able to give a dynamic pressure test update soon!

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curmudgeon (original poster)
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#6: Post by curmudgeon (original poster) »

Alright, I've got a few updates:

I got the pump off and confirmed it is in fact an Ulka EAX5. Based on the graph above, this confirms my static (deadhead) pressure findings.

My fittings came in to do the dynamic flow test. I dialed in the needle valve for my standard double ~2oz/60mL in 30 seconds and ran a few "shots". Since this is a vibe pump, the needle never settled down, but it was buzzing around 12 bar consistently, which again, dovetails nicely with the graph above.

So, unless I'm completely missing something, the brew pressure on the Astra Pro is high (according to my highly unscientific experiments) and non-adjustable (according to the mfr). It blows my mind that the machine doesn't have some sort of relief or OPV, especially since i saw ~16 bar on my deadhead test - a number the mfr claims I should never, ever see. That said, I guess it's time to grab an OPV, plumb it in, and do some taste-testing!

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curmudgeon (original poster)
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#7: Post by curmudgeon (original poster) »

Well all the parts and pieces finally came in, and here's the final result: (brew path is green, OPV relief is red)
I spliced the OPV tee inlet just downstream of the air purge valve, and the OPV return splices into the reservoir feed, just upstream of where the air purge valve comes back in.

I wanted it to look as "factory" as possible. To that end, I didn't mess with any existing fittings; I just spliced into the existing tubing. This means this whole process is easier to reverse if I decide I don't like it, and not touching any other fittings means less chance of causing them to leak.

I don't have a good video of the OPV adjustment process. I set the deadhead pressure to about 9.5 bar and pulled a few shots this morning. They were...passable... but I need to spend more time getting used to the new parameters. The outlook is promising!

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icantroast
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#8: Post by icantroast »

What ever happened with this? Are the results better with an OPV?

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curmudgeon (original poster)
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#9: Post by curmudgeon (original poster) »

Honestly, I'm not sure I could say that whether it's better or not. At the very least, there's no change. However, knowing that I now have an operational OPV and knowing the plumbing in the Astra won't see ~16 bar of pressure on a choked shot or backflush gives me that much more peace of mind.

SJM
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#10: Post by SJM »

There are OPVs and there are adjustable OPVs.
If the OPV isn't adjustable, it is often labelled as a 'safety valve' and set to release pressure if/as/when and only when the pressure is really excessive, rather than just higher than is conducive to the production of a good shot.

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