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Someone was chatting about a acrylic/pmma cylinder developing stress cracks which they thought may be due to internal pressure from the piston ballast system.
I think this is very unlikely, as a piston ballast system is unlikely to develop the kind of high pressures required inside the cylinder as a jack screw becomes exceeding inefficient when working against a high load, and to cause enough stress to crack the cylinder would need to be pushing tens of psi to bust the cylinder walls.
My main suspect would be internal stresses in the material. Acrylic/PMMA is highly variable in quality, and in conjunction with the stresses imparted in the extrusion process during manufacture, cracks can form if inferior grades have been used and also if the material has been machined poorly and/or not normalised after being worked.
I personally think clear cylinders are overrated- they look very slick, but the cons can outweigh the advantages. Generally a transparent cylinder will mean using acrylic/pmma or polycarbonate/lexan. The latter is much tougher, but is notch sensitive and expensive. Acrylic is stiffer but more brittle.
PVC tubing is far more forgiving, it’s very tough, machines nicely and is cheap. Usually it’s filled making it opaque, some say they like a clear cylinder to spot leaks, however my experience is that clear cylinders tend to turn silver underwater, and once it’s inside a hull you certainly can’t see anything unless that’s transparent too, also it’s very difficult to spot where the leak is entering unless the cylinder is pressurised in which case an opaque cylinder gives a telltale of bubbles just as capably.
If PVC has any disadvantage it’s simply that the range of sizes commonly available tend to be a bit more restrictive than other materials, however most common sizes are usually suitable unless you’re building something very specific, and a collar can be machined or printed if you need to step the tubing size down to fit an existing endcap.
I think this is very unlikely, as a piston ballast system is unlikely to develop the kind of high pressures required inside the cylinder as a jack screw becomes exceeding inefficient when working against a high load, and to cause enough stress to crack the cylinder would need to be pushing tens of psi to bust the cylinder walls.
My main suspect would be internal stresses in the material. Acrylic/PMMA is highly variable in quality, and in conjunction with the stresses imparted in the extrusion process during manufacture, cracks can form if inferior grades have been used and also if the material has been machined poorly and/or not normalised after being worked.
I personally think clear cylinders are overrated- they look very slick, but the cons can outweigh the advantages. Generally a transparent cylinder will mean using acrylic/pmma or polycarbonate/lexan. The latter is much tougher, but is notch sensitive and expensive. Acrylic is stiffer but more brittle.
PVC tubing is far more forgiving, it’s very tough, machines nicely and is cheap. Usually it’s filled making it opaque, some say they like a clear cylinder to spot leaks, however my experience is that clear cylinders tend to turn silver underwater, and once it’s inside a hull you certainly can’t see anything unless that’s transparent too, also it’s very difficult to spot where the leak is entering unless the cylinder is pressurised in which case an opaque cylinder gives a telltale of bubbles just as capably.
If PVC has any disadvantage it’s simply that the range of sizes commonly available tend to be a bit more restrictive than other materials, however most common sizes are usually suitable unless you’re building something very specific, and a collar can be machined or printed if you need to step the tubing size down to fit an existing endcap.
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