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This is a copy of a post I put on another sub forum - not familiar yet with the amount of crossover, so please let me know if this is not a good practice
New to subs, so perhaps an old question about using bellows.
A piston system requires much energy to compress the air, to overcome the friction of the o-ring sealing on the cylinder, and to overcome the friction in the mechanical drive. Potential for leakage at the seals exists because of the high air pressure on that side of the cylinder. (Or low pressure if a vacuum is pulled)
A bellows provides a complete seal, has no seal friction (no moving o-ring seal) and if activated by a precision positive displacement pump, perhaps with two speeds for coarse and fine adjustment - offers precise volume adjustment with high mechanical efficiency. Potential for leakage across the bellows is minimized because water pressure on the pump fed side is equal to the compressed air pressure. The bellows is like a bag or BP cuff, but gives much better and more repeatable geometry control of the displaced volume. Also, the maximum bellows volume can easily be controlled by a stop ring in the cylinder or the bellows itself can mechanically activate a relief valve at the point of desired maximum travel.
Also, two bellows - fore and aft - could be operated by one pump, as pressure equilibration would ensure equal volumes of displacement in both bellows. Neoprene bellows are relatively cheap, come in various diameters and many lengths and could be custom fit better than innertubes and BP cuffs.
Just a rookie, but it seems a bellows provides some of the better features of both bag and piston systems, but I don't see mention of this approach when I do searches.
Thoughts?
New to subs, so perhaps an old question about using bellows.
A piston system requires much energy to compress the air, to overcome the friction of the o-ring sealing on the cylinder, and to overcome the friction in the mechanical drive. Potential for leakage at the seals exists because of the high air pressure on that side of the cylinder. (Or low pressure if a vacuum is pulled)
A bellows provides a complete seal, has no seal friction (no moving o-ring seal) and if activated by a precision positive displacement pump, perhaps with two speeds for coarse and fine adjustment - offers precise volume adjustment with high mechanical efficiency. Potential for leakage across the bellows is minimized because water pressure on the pump fed side is equal to the compressed air pressure. The bellows is like a bag or BP cuff, but gives much better and more repeatable geometry control of the displaced volume. Also, the maximum bellows volume can easily be controlled by a stop ring in the cylinder or the bellows itself can mechanically activate a relief valve at the point of desired maximum travel.
Also, two bellows - fore and aft - could be operated by one pump, as pressure equilibration would ensure equal volumes of displacement in both bellows. Neoprene bellows are relatively cheap, come in various diameters and many lengths and could be custom fit better than innertubes and BP cuffs.
Just a rookie, but it seems a bellows provides some of the better features of both bag and piston systems, but I don't see mention of this approach when I do searches.
Thoughts?
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