If you're looking for BIG servo power then this could be the answer.
But be warned. They are HUGE and HEAVY.
3.4 : 1 power boost ratio at 600mm Hg vacuum.
Canister diameter 270mm. Overall length 360mm.
Vacuum inlet 12mm O.D. push-on hosetail.
Fluid inlet and outlet female threads on cylinder 1/2" UNF.
Cylinder piston diameter 7/8"
Five 3/8" UNF mounting studs on canister flange and one on rear of canister. Weight 7 kg.
LARGE HIGH POWER SINGLE REMOTE SERVO #RS270