# OPV Bypass problem



## Ghostrider (Jul 3, 2008)

I wonder please if anyone could help? I am at my wits end. We have an eleven year old handfill with a rotary pump and an OPV as a balanced bypass valve, both Fluid-o-Tech.

She has been out of action since just before Christmas. The problem relates to the OPV. It became noisy like a loud rasping sound which lasts until brew pressure is reached then stops, and the coffee became sour. We changed the OPV but made the mistake of trying to adjust it. I have since read DaveC's excellent article about the Fluid-o-Tech not adjusting well and believe we may have inadvertently damaged the new OPV. We are trying to source a brass screw Expobar/Brewtus replacement but note the threads have changed and it may be a problem to retro fit.

Currently, shots begin all viscose and sweet but you can visibly see at the head a sudden change to thin sour output, it's like a switch and we end up with shots of two parts. The shots are like tasting marble cake in that it's two polar opposites together, half the mouthfeel is viscose and sweet, with thin sourness also present in other areas on the palate. I believe it correlates with the opening of the OPV as the change occurs later when it is tighter and earlier when it is loose. Is this typical of a faulty OPV "letting in" as per Dave's article? If so, could someone describe the actual phenominum that is occurring at that point?

We have a head manometer and know the pump is set at 9 Bar, it was checked with the old OPV closed so we are sure. We reach brew pressure instantly at the head. The issue is when the OPV reaches bypass pressure and lets water out. I think!

We have reached desperation point. Thanks for any input.


----------



## El carajillo (Mar 16, 2013)

Does the gauge pressure drop or fluctuate at the change in tone or sound ? That would add weight to your conclusion, sudden changes in pressure to the head.


----------



## Ghostrider (Jul 3, 2008)

Hi El carajillo, thank you.

No, the only fluctuation at the head occurs if the OPV is too far open during testing. Under normal circumstances it is stable at 9 bar. The additional noise actually stops the second 9 bar is reached and the line is at pressure. Reaching pressure is almost instant. However, there is subsequently a visual loss of pressure at the point the coffee thins during the shot, I suspect at the point the OPV releases excess water flow.

My only thought as to why is perhaps because the line is closed with the manometer present and able to retain enough pressure to stop it letting in, but during a shot it is open and the ground coffee alone is not enough once the OPV opens to prevent it also letting in?


----------

