Pygmalion Is this a case of a bad OPV? How difficult is it to change out the OPV entirely?
it’s not difficult, but it’s very unlikely that the expansion valve (OPV) has gone bad. If it had you would probably be getting other sumptoms.
For the OPV to cause the behaviour you’re describing, it would have to be stiffer and open later for the first shot, then open a bit further when the pressure drops to 10 bar. Then as you do more shots…it is loosening up. That’ not really normal behaviour for that type of valve.
If it was sticky, then usually it would jam up on other shots, possibly randomly…it’s also very hard for it to stick. As you can see, the only bit that moves is the pad, held by the spring against the port. There is not much to stick or jam. The only par that could is the relatively loose fitting metal bit with a pad.