This item is located in the boot of my xj12. It’s also in some xj6. (Injection)
It has a one way check valve at the bottom that sends high pressure fuel to the fuel rail. The bottom gets filled with sediments and this valve (which is in the barb fitting) was becoming clogged and didn’t hold pressure well. Car ran this way but I can see it potentially creating problems. (Low fuel flow to engine). So if you have a chance open it up and see how clean the inside is and blow / clean the barb fitting (one way check valve) at the bottom. I was surprised to see how small the diameter of this feed barb fitting is. (1/4in) but with pump output pressure high I guess it works.

the air separator on top is just a very small jet. It lets pump fuel pressure seep thru (and air if any) and bleeds into the fuel return line. That small jet was clogged. It is so small it probably needs cleaning once a year. I know the system isn’t critical but I can see the barb check valve easily clogging the fuel output from the pump.

has anyone completely removed it ? Or drilled out the internals of then one way check valve to improve flow ? and decommissioning the pressure retaining function of it ?
curious to see if it affects starting and running.

the copper washers were not in good condition and I replaced them with fiber washers. Definitely a source of fuel “smell” if they barely even leak.