Rotary Pump: OPV vs. Retention Valve

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Larz
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#1: Post by Larz »

I thought maybe Eric or someone else in the know could clue me in on this: Yesterday I decided to fix the dripping from my plumbed in Expobar commercial's OPV valve. I dug into my parts bin to grab a new OPV but found I had Expobar's new model OPV that had replaced the old Fluid-O-Tech (the one with the nylon screw that make them unreliable once adjusted). The new and old OPVs are not compatible without an adapter which i didn't have, but I found a Retention Valve that fit and that I had picked up from Cafe Parts for an earlier project, so I stuck it in in place of the OPV. This leads me to my question and the purpose of this post: why do i need an OPV with a rotary pump since I can adjust the brew pressure with the acorn valve on the pump? I only know enough about these machines to be dangerous but the little that I do know tells me that a Retention Valve is all that is necessary. That being said, Expobar's parts schematics for this machine have one diagram of the pump showing just a retention valve used and on another diagram for the same machine, both a OPV and a retention valve in series. To make it even more confusing, my machine originally had just an OPV and no retention valve, and now in its current iteration, just a retention valve.... seems to work like a charm in either of the two later configurations and I have to assume would work in the 3rd and 4th configurations shown in the manual. If anyone can shed some theory on this and also offer their opinion on any risk/disadvantage running with just the retention valve that I have put in place, I'd appreciate it.

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Bob_McBob
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#2: Post by Bob_McBob »

Rotary pump espresso machine designs still need to account for thermal expansion when the machine heats and other situations that could produce excess pressure.
Chris

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HB
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#3: Post by HB »

Exactly. An OPV serves double-duty with a vibratory pump (max. pressure and expansion), but only serves as an expansion valve for a rotary pump. Manufacturers recommend adjusting the expansion valve to 12 bar; the pressure of the hydraulic system will quickly reach that as soon as the pressure release valve closes and the (newly introduced) cold water heats up. The expansion valve only has to let out a few drops for the pressure to remain below 12 bar.
Dan Kehn

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erics
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#4: Post by erics »

See page 12 of this: /downloads/ ... arts01.pdf .
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Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

jonr
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#5: Post by jonr »

but only serves as an expansion valve for a rotary pump.
Why? Ie, what is special in the design of the valve that it won't release pressure to the input side of the pump if the output side exceeds some pressure limit for any reason?

My guess - because it is effected by supply input pressure. Ie, for espresso, we want a pressure relative to atmospheric, not to inlet pressure. But they are approximately the same whenever you use a tank.

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

OK, got it, thanks all. So that answers the question as to why an OPV/bypass valve is also used on a rotary pump. In Eric's download link above (thanks BTW Eric), it shows both a retention valve as well as a bypass valve used in the Expobar Office Leva; that is one of the multiple configurations that I spoke of in my rather noisy earlier post. I have similar pdf documentation for other Expobar machines (Megacrem , Markus, etc.) which I could upload if I knew how, that shows machines with the other configuration that I mentioned, specifically, retention valve only (no OPV). And I purchased my machine from the original owner who said it had never been modified (to the extent of his knowledge) and the machine had ONLY an OPV bypass valve and no retention valve when I purchased it. So it seems Expobar manufactures the machine in at least 3 different configurations. With the exception of this bypass valve/retention valve issue, the rest of the hydraulic circuitry is the same for all machines in all the Expobar documentation I have.

So I have since Saturday been running the machine with just a retention valve which I used to replace the bad OPV and it works fine...for how long I don't know but Expobar seems to be OK with that. Below is documentation from Expobar that shows the same machine offered with and without OPV, both having retention valves, so you can see why I am still confused as to the ultimate need for an OPV valve in these machines. Sorry for the poor documentation quality; its the only way I found I could upload them.




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erics
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#7: Post by erics »

So it seems Expobar manufactures the machine in at least 3 different configurations.
I would say "manufactures/manufactured." It is important to keep in mind that Crem (Expobar is part of their product line) - http://www.creminternational.com/ manufactures machines for a worldwide market as do manufacturers of other machinery. Regulations and certifications inherently vary depending upon the end use. Although it would be a cost analysis nightmare, I believe a uniform hydraulics system for any given make/model espresso machine makes for good practice.

A retention valve ( check valve) is designed to allow flow in one direction only. HB (Dan Kehn) has posted several times about a local ordinance which requires the installation of a check valve to prevent the reverse flow of machine water back into the main water distribution network. I am unaware of any machine originally fitted with a rotary pump that is not so equipped. The original (?) OPV utilized by Expobar was, I believe, manufactured by Fluid-O-Tech and this particular valve has a check valve in the main fluid path - see this: /downloads/Brewtus_OPV.pdf .

For machines (yours) that are not fitted with an OPV, there may be something in the hydraulics that, after factory testing, demonstrated that it was unnecessary. That would require an exhaustive study of your particular machine and/or communication with Crem as to whether or not they now recommend the installation of same. BTW, Lars, exactly what Expobar model do you have ?
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Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

Larz (original poster)
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#8: Post by Larz (original poster) »

Eric to answer your question, my Expobar in the picture below, is called an "Inter Mini" according to the Expobar factory folks...their standard E61, 6 liter single group commercial Gicar HX with Cunill grinder. They say it was manufactured in 1986 but is no longer being made...although very similar iterations such as the Markus, Mega etc., continue to be made and differ largely from mine cosmetically only.

In the picture below that, on the left you can see the old OPV. This is the one that originally came with the machine (the old fluid-o-tech you mentioned) but was leaking and so I replaced it with a retention valve I had kicking around mainly because it didn't have one and it fit and allowed me to use the machine without leaking. The OPV beside it is the new Expobar one and as you can see is configured differently. I was unable to use it because I did not have the right size adapter fitting to connect it to my main water line (I live in no man's land) and didn't know where to get something to adapt. Now, with what you, Dan and the others have explained, I would like to install the OPV on top of the retention valve exactly as the new Expobars have (see schematics in earlier post above). To do this I will need to find an adapter to connect the male 3/8" O/S nominal diameter OPV to the male 5/8" O/S diameter retention/check/non-return valve. I know next to nothing about thread sizing, be that NPT, BSPT or other.,...can you tell me what I should be looking for and where? Thanks very much. Oh, and Eric, I guess you can not see any way I can adapt my machine to accept your thermometer/thermocouple given that the group is hidden beneath a panel beside the gicar panel(??)




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erics
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#9: Post by erics »

Skål,

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

Larz (original poster)
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#10: Post by Larz (original poster) »

Excellent piece of work; thank you Eric.

Lars

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