OPV before or after HX?

[DefaultIT]

OK so I'm changing a bit about the machine I'm overhauling (Brasilia Mini Classic) and find it a little curious that the OPV is branched off at the top of the heat exchanger (along with the shot pressure gauge), right where the upper connection to the group is. It seems to me the last few E61 machines I saw the insides of had a different flow path, with the OPV before the boiler/HX....which seems like a slightly more obvious place to put it.

I'm not sure it'd be worth the reconfiguring to move mine around, but I'm curious if anyone happens to know offhand if there is any functional difference between these configurations. I would tend to think that having it absorb some of the pump's vibratory pulses earlier in the flow path might be friendlier on the rest of the fittings and hardware...and might help to dampen out some of the buzzy noise these Ulkas make.

Anyone ever notice a difference here? Or have an idea why (apart from convenient placement) Brasilia might have opted to put the OPV between the HX/boiler and the group, rather than in front of it all?

[HB]

I can't think of any good reason to route heated water to the reservoir. My guess is they did it to save money, or they assumed that the OPV would only be open for water expansion, not while shot-pulling. That's not an unreasonable assumption at double espresso flow rates.

[DefaultIT (original poster)]

Interesting... The way mine was set, the OPV opened quite a lot during extraction; I backed it off, probably relying too heavily on the shot pressure gauge, given where it's tapped off (before all the jetting in the group/mushroom)

In my case, I've already replaced the yellowing plastic reservoir with a glass one, so I'm not too worried about the temperature of the water in it... But yeah now I wonder if that might have contributed to the occasional "pond scum" I had to clean out of there.

I almost have all the parts on hand to re-order the flow path while I have it all apart, but the bottom rear of this machine is crowded, given the room the pump needs to vibrate.... I suspect that's what led to the current arrangement and I'll probably leave it as is. Nonetheless I do wonder a little about noise reduction by damping out those pump impulses earlier. My friend's brand new Profitec is noticeably quieter than this thing