fresh water accumulator tank replacement

[blue-max]

I think after 25 years the original accumulator tank next  to the fresh water pump is beginning to  fail - the newish  pump has started to take longer to  shut  down  after water has been drawn. There is no nozzle to  pump it up so  I am thinking to  replace . However I am not sure of the spec. Whatever was written on the bottle has become obscured.
I am thinking to  go  for bottle shaped plastic tank with 15 mm hose connectors but what Psi should I have?  Don't  have much  space in the locker where this is fixed so  hopefully  can find a suitable one the right size. Anyone experienced about this?

[Yngmar]

Was it this one? https://www.imara.es/en/water-pumps/1095-pressure-tank-comet.html

[blue-max]

Its very similar. If I knew how to attach  a photo I could show you (insert an image icon does not let me browse my files). I want the replacement to  have a valve at the top so  the air pressure can be maintained  but I need to  the Psi

[Diverphil1]

ours has something like this on it. easy to find in caravan shop or parts store on line

FIAMMA A20 ACCUMULATOR - EXPANSION TANK