

First thing is checking they’re rated for your weight. If they are, I think the problem is not a loss of pressure because I would’ve gone soft very fast in a couple up-downs. So imo (not a specialist in pneumatic things, but I’m pretty good with machines in general) it must be the valve you move with the lever not closing properly. I have a couple chairs at work that don’t have spring-loaded levers and you have to push down them for the chair to stay at the chosen height, so try pushing the lever a bit. If it’s an outside problem—something bent or badly adjusted, dirt or something that stops the movement of the mechanism— then you might be able to fix it, but if it’s an inside problem with the valve itself, it’s worn out or gets stuck, then I’m afraid you’ll have to replace the whole piston assembly.
To answer your questions, as I said I don’t have that much experience with pneumatic parts, but parts in general are never too standard nor very custom, that is they usually are standardised but there are so many standards and specifications and variations that yours may be hard to find. Look for references/codes printed on the cylinder, the specifications you’ll need to find another one would be diameter(s), length(s), displacement, pressure/force, there could be also different kind of fastening types and ways to actuate the valve.
How hard it’s going to be, I can’t tell, but it’s most likely possible to do.










First mistake. For crumbly material you should use a 9.5 or a 9. The plug should fit tightly, as tight as possible while still getting in with some gentle hits with the butt of the screwdriver or even a hammer.
The screws are alright, I guess. For a 10mm plug, you’d use 5-7mm screws (read the instructions on the packaging, sometimes on the plug itself). It should be at least a bit longer than the plug, and the hole a bit deeper than the screw length.
Now there might be a solution to the hole too wide. You need to get the screw a bit screwed in, as it gets in the plug will spread and hold to the wall. If you can do it with the plug out of the wall it’ll be easier, depending on what you’re fixing to the wall and how, once it opened a little and it’s a tight fit, hit them all together (with any braces or whatever that needs to be with the screw) into the hole until the plug is flush with the wall, screw it all the way in, and then tighten it. If you cannot and you have to do it with it in the wall, another trick is to try screwing in the screw with fast, short bursts (hand screwdriver or electric / power drill). If the plug don’t even have enough grip for this and it keeps spinning in the hole, try to keep it from moving with the tip of a small flat screw driver or electrician scissors, once the screw is going in it’ll start to hold by itself.
The part where you tighten it after the screw is all the way in is important. This makes the screw pull from the end/middle of the plug and deforms it, shaping it to the hole so it gets a proper hold.
The plug doesn’t need to be flush with the brick, you can see that part of the plug is completely flat and smooth, and doesn’t make anything for support or grip, is there because of the plaster. The hole needs to be deep enough for the screw tho, or it will push the plug out.