I am hoping for some clarity and to add some useful info for future tinkerers.
I have read several threads referring to the idea of an OPV in an Olympia Maximatic/Coffex/Livietta.
How do I add an OPV/Gicleur to Olympia Maximatic?
Olympia Maximatic brew pressure sans OPV
I've seen this article talking about and comparing a few common OPVs.
http://myweb.tiscali.co.uk/coffeetime/u..._Valve.pdf
Seen photos:
http://www.flickr.com/photos/26907910@N...hotostream
and here:
Olympia Maximatic. Stick to old or change to new?
video (accompanying first photo)...


Yet I still have some uncertainty.

Fact: 60ml in 30 seconds from my 22 year old Fluid-O-Tech vibe pump yields a group pressure of about 10.3 bar as measured on my portafilter gauge. a little tighter flow pushes it up to 11.
The choices:
http://www.orphanespresso.com/Fluid-O-T..._3975.html
pros: made for this pump, small, cheaper
cons: cheaper
http://www.orphanespresso.com/14-Adjust..._3974.html
pros: much beefier
cons: twice the cost (including additional fittings)

Opinions on which one to get? I am going to get the second one unless someone can give me a good reason why I should get the cheaper (FOT) one instead.

Secondly I need some advice on mounting.
After the pump there is a restrictor orifice (somewhere around .5-1mm diameter), a check/1-way valve, teflon tube, heat exchanger.
1. Where in this mix should the valve be introduced? I saw in the first photo where they used the FOT valve, it is mounted to the metal line connected to the HX, but I thought this wouldn't be best because the valve would then be heated. Is this a concern or not? My instinct is to mount it before the check valve and thus before the orifice (because it uses a funky thread so I'd have to go one fitting further upstream). Is this right or should it be downstream of the check valve.
2. Does the valve need to be decoupled from pump vibration via teflon hose? I know the FOT valves come standard attached straight to the pump. What about the bigger one? Could it be too massive for the vibrations? I know welone mounted the swagelok valve with plastic tubes but that one seems bigger yet and his pump's snout is plastic whereas mine is brass...
3. Should the discharge go back to the tank? I have heard advice against teeing back into the line feeding the pump. What is the concern and is it valid?

Thanks in advance for taking the time to help me out! I look forward to some more info and some tinkering!

You have succeeded in constructing a well written post - lots of effort in just the writing.

Anyway, I would question the need for an OPV given the FOT pump and the restriction orifice. Without researching past things I have said about that particular combination, it puts you very near an optimum point as regards flow & pressure. A pic of your PF pressure gage setup would be nice - seems as though you incorporated a needle valve to regulate the flow?

But, if you insist , the FOT OPV is, hopefully, designed for the flow characteristics of their pump. If I had an installation that was 22 years old, I would buy the pump with the OPV attached (I have a new one if you want) assuming it can fit or that you can relocate the pump horizontally a couple of inches.

When the FOT OPV is NOT attached to the pump, it requires an adaptor because the inlet threading is M12 (I don't recall the pitch) while the outlet is standard 1/8" BSPP.

erics wrote:You have succeeded in constructing a well written post - lots of effort in just the writing.

Thank you, Eric!

erics wrote:Anyway, I would question the need for an OPV given the FOT pump and the restriction orifice. Without researching past things I have said about that particular combination, it puts you very near an optimum point as regards flow & pressure. A pic of your PF pressure gage setup would be nice - seems as though you incorporated a needle valve to regulate the flow?

I had read a few times about the pump already having nice characteristics (and a few times suggesting otherwise), but seeing that ristretto pulls push the pump to 11 bar, shouldn't it be worth at least the $14 OPV to take that from "near optimal" to correct? Also I have been enjoying normale shots more and more but on the maximatic, they can be messy with the bottomless and if I use the spouted portafilter, I feel like I am just hiding a problem I know is there. This mod would be in hopes of also making it a little more gentle on the puck. The video I shared, shows a beautiful shot without blonding early, which often is not the case for me. If anything I thought it would be a good experiment!

Here is what the plumbing guy and I were able to construct The flow is (accidentally) controlled by the threads leaking at a convenient rate of 120 ml/min.

erics wrote:But, if you insist , the FOT OPV is, hopefully, designed for the flow characteristics of their pump. If I had an installation that was 22 years old, I would buy the pump with the OPV attached (I have a new one if you want) assuming it can fit or that you can relocate the pump horizontally a couple of inches.

When the FOT OPV is NOT attached to the pump, it requires an adaptor because the inlet threading is M12 (I don't recall the pitch) while the outlet is standard 1/8" BSPP

I thought about replacing the pump but it has been completely rebuilt and meticulously cleaned. I wondered, why it should be replaced if it is nice and clean and, being built like a tank, still going strong. By eye-balling, it appears that the FOT OPV should fit about right in the space the adapter takes up. I could be wrong, but it doesn't look as huge as the second valve.

A couple more opinions about these two OPVs would be nice to hear, and if the exhaust should drop into the tank, or if it is safe to tee into the line before the pump.

The adaptor you speak of and the FOT OPV are a match.

I would simply route the OPV "excess" back to the reservoir. If nothing else, you could then always estimate where you are on the curve. Keep in mind that the restrictor orifice provides about a 0.2 bar loss.



Technically, it should not matter as pump relief/regulating valves are frequently led back to the suction side, e.g., all espresso machine rotary pumps.