OK. If there's supporting documentation to confirm that it is a PMV, then here's what I think is going on. This is a different story from the one in my earlier post.
If there's lots of air in the bank, air will flow from the bank into the charging panels. During this phase of operations, the pressure just upstream of your 207 bar PCV (let's call this manifold pressure) is roughly the same as your bank pressure, and drops as you discharge the bank. The pressure immediately downstream of the PCV is 207 bar The difference between 207 bar and the pressure in the empty bottles plugged into the panel is dropped across whatever device it is that limits the charging flow - on manually controlled charging panels, this is often one of the isolating valves on the panel which is kept cracked just open - or if you're lucky, a needle valve provided for the purpose. In your system, it may well be those orifices drawn just downstream of the panel isolation valves. Upstream of the orifice: 207 bar. Downstream: Whatever is in the bottles you're charging. (This probably answers one of your questions).
As the bank pressure drops below 285 bar (if I read the fuzzy figures right), the first compressor kicks in - followed by the second one a bit later. Assuming that you're still drawing air out the charging panel faster than the compressors can put it in, the bank pressure will continue to fall, with both bank and compressors putting air into the panel. Although it makes no difference at this point, the PMV closes as the manifold pressure drops below 260 bar.
For as long as the bank pressure stays above 207 bar (and if you're only charging two or three sets of bottles, there should be enough air in a 366 litre bank starting at 310 bar to make sure it does), then the charge time depends only on the size of the orifice, the 207 bar above the orifice, the volume of the bottles you're charging and the amount of air that was already in them when you started. It doesn't depend on the compressor setpoint.
As the manifold/bank pressure drops below 207 bar, the PCV opens fully and the top of the orifice sees manifold/bank pressure instead of a steady 207 bar. This is a key moment as it's only at this point that the bottles begin to fill more slowly than before.
The PMV really comes into its own when the bank/manifold pressure equalises with the bottles you're charging. Now you're relying on the compressors alone to finish the fill. With no PMV, the compressor would try to put air into both bank and charging panel - a total volume of 420 litres - and it would all get very slow indeed. Instead of this, the closed PMV (coupled with the NRV between bank and manifold) isolates the bank and ensures the entire compressor flow is dedicated to the charging panel. Manifold and bottle pressures rise together, but the bank pressure does not.
Once the little bottles reach 207 bar, the PCV closes and, with no outflow, manifold pressure rises quickly until the 260 bar PMV opens - at which point, the compressors start to recharge the bank - continuing until the last compressor trips out with 310 bar at compressor, manifold and bank.
So what does this mean for your problem? I understand you are proposing to wind back the trip pressure on the lead compressor by 20 bar to step back a little from the final stage relief pressures. This will almost certainly entail adjustment to the cut-in pressure and also to the lag compressor settings. The main effect will be to reduce the amount of air stored in your bank when the system has finished topping it up and this in turn will affect the time it takes for the system to switch from (fast) filling by decanting from the bank to (slower) filling direct from the compressors. With the bank and client cylinder sizes you've described and a change from 310 to 290 bar, that switch won't happen until maybe the very end of the charging cycle of your third set of six bottles or (more likely) partway through the fourth set. For the first couple of sets, you shouldn't see any difference at all in charging time.
A.
