gregE
The pump is delivering 9.5 bars of pressure.
You are attempting to control pressure by reducing flow between the valve and the puck.
Its a concept that interests people but you have to understand the flow control valve is just a valve . It doesnt control what the pump is delivering.
Control of flow and control of pressure require different control parameters.
The valve only controls flow and you attempt to control pressure via the permeability of the puck and restriction given by the valve masking the pressure in the system. Its not an ideal situation but with practice you can do what you need, sort of.
On the other hand, without a flow control valve, the acs will produce great espresso with less hassle and frustration.
When i had the synchronika i read a lot about the flow control valve. I have had a lot of dealings in the past priming high pressure pumps in much larger systems than an espresso machine. The more i read the more questions i had and wondered how much practical use a flow control valve could be when what i actually wanted to do was control the pressure . I by then had a vesuvius pressure profile machine as well which actually controlled pressure using the pump. Not the only way to control pressure but a real way of directly controlling pressure by changing delivery against the resistance. So to see if i was missing something i went ahead and fitted the flow control valve to the synchronika for a couple of weeks and sold it on after returning the machine to stock control.
With practice you can achieve what you are aiming for but requires you to preempt when to adjust the valve. When you want pressure to drop you need to close the valve further than you think to allow pressure to drop due to the lack of flow but start to open it very slowly prior to hitting aim point as you now require some extra flow to restore the pressure .
I’m not the best teacher or at trying to explain this and hope it sort of makes sense.
You are not changing pressure between the pump and valve, just between the valve and puck which is permeable so you seem to be controlling pressure by actually controlling flow…..