Kystdesign, the best quality comps i’ve seen, small and large, PSS, Hydrovision/SMD and ye olde truck air suspension bladders/Firestone are crap in comparison.
On one of our subs (the not working EB ROV) we have a huge Firestone tyre which is pretty crap because after one year you’ve to throw them in the garbage bin. Other comps on that sub are from Sub-Atlantic with volume indication. These comps start leaking after a few weeks and the volume sensor breaks off easily.
Best comps we use are the 15ltr compensators from Seatools. They also make smaller volumes.
Sub Atlantic comps generally good but one word of warning, change out the pish push fit connectors for some decent QC/QD’s, the only weak point I’ve found they have.
BTW
These Firestone bladders (the air spring) where developed late 1930’s as a more efficient spring (vibration isolator) for use in vehicle suspensions.