AP racing fr brake m/cyl

Hi All. On my Norvil I have an AP racing fr m/cyl. When I stripped it I found that on the outlet side there is some sort of nylon spring loaded valve. I can't seem to find any reference to it or what it does, so wondered if a new 1 would come with a kit as I want to o/haul the brake, any ideas anyone?

Thanks in advance for all replies.

hayabusaman

Photo to Andover Norton to identify whether it is single or twin disc caliper and they will be able to tell you what the spares kit contains if they have one in stock. The M/C's have one or two rings to identify them, but this was copied across M/C's that were produced many years ago.