Hi, I have a gas lift office chair which started slowly sinking when the weather turned cold a couple of weeks ago. I've dissassembled it but the gas lift bit is still connected to the tilt mechanism at the top. I can't see how to dissassemble it further for access the seals. Is there any way of repairing these ? I tried pouring oil down the valve at the top to improve the gas seal but it made no difference. If the cylinder has to be replaced, I can't see how it detaches from the tilt mechanism - anyone know how this works.
If this is OT or anyone knows a better group for this question, please let me know.
I recall some new chairs being delivered to my office. The top was just pressed onto a tapered spigot. A thump would dismantle such an arrangement - but never tried it.
is it not dangerous to dismantle these gas struts becuase they can be highly pressureised? I even recall that someone was killed by one which came a part and fired the steel rod upwards penetrating through the seat of the chair while he was sitting on it.
I think there is a spring in there, no gas pressure especially since it's got a leak. I thought it might be possible to replace a seal or use a lubricant to improve the gas seal of the existing seal. This must be a common problem with an appropriate bodge.
You can't fix gas lifts. If they've used a standard part, then you may be able to replace the gas lift cartridge with another one (there are on-line vendors with catalogues). This is often useful in big offices with standard chairs (strip the cartridge from the one with the broken arm, etc.) but usually it's difficult to buy a new compatible cartridge for less than the price of a new chair. 10-15 years ago was another matter, but now any retail-market stuff just arrives magically for almost nothing from the Chinese chair-pixies.
You _really_ can't repair gas struts themselves. They're made by roll- forming the top to lock the seal cartridge in, and that's a one-shot process. Even the factory couldn't open one up in a re-sealable manner.
Nor do gas struts necessarily fail because the seal has just failed. They fail primarily because their gas pressure has dropped, and that can happen slowly too. If you _could_ repressurise them, you might not even need to replace the seal, in order to get a few more years out of them.
Opening gas struts is too hazardous to discuss on Usenet, for fear of legal action by vendors of pressurised gas containers (those with long memories might remember what I'm talking about!). It's certainly hazardous though, same as opening up any hydraulic accumulator. Don't go there.
It is possible (as it has been done at least once to my knowledge) to re-pressurise a strut into working order again by refilling the gas and not touching the seal at all. Vent it, drill the back (away from the piston travel) solder in a pipe fitting, refill with high pressure nitrogen and then crimp seal. Not trivial though.
There are no credible reports for anyone ever being "harpooned" by a chair. Nor does the physics of it make much sense. Certainly I worked in a BT office in '86 where all our gas-lifts were modified to screw locks, after such an "incident". I can't prove the incident ever actually happened or didn't happen, but they certainly spent lots of money on chair conversions (A few days afterwards I obviously snuck my hidden cartridge back in - a geek has standards to maintain, after all).
PS - If you did do this, remember that they need to be filled with dry nitrogen not air, oxygen must be excluded and the lubricant grease must be non-combustible under pressure. The only vaguely credible explanation for the harpooning stories would be fatso flopping down heavily onto one, then having it turn into a Diesel pogo stick (as any airgunner will understand).
You know, I don't think I've been asking the right question - I assumed it was a gas lift because I heard the term and assumed that was what it was called beacuse gas goes in and out of it as it goes up and down but I'm pretty sure this one has a spring in it - you sit on it and pull the lever and it goes down or get off it, pull the lever and it goes up - I'm not even sure I know what a gas lift chair is now. Anybody clear up these 'conceptual' errors please ?
They're filled with high pressure gas (few hundred psi) but it's just trapped in one space, it doesn't "go anywhere". It's trapped in the bottom of the cylinder, the piston sits on top of it and the gas is merely compressed in situ beneath the piston.
The effective spring rate will change as the gas compresses, so you need to allow some ullage space at the bottom of the travel, i.e. the piston never goes all the way down. A 12" long tube might only allow
6" of useful movement. Some extra-compact designs wrap this extra space around the sides of the cylinder, so there's a smaller cylinder tube inside a bigger container tube. These can allow nearlly 11" of movement from a 12" tube.
Gas is cheap, metal springs are expensive. If you need to support a couple of hundred pounds on soemthing only an inch in diameter, then it's cheaper to use a gas spring. A metal spring this small and capable of supporting it is a high-quality bit of metallurgy and not cheap. It's especially difficult if you want to make a "chair", where the adjustment range is nearly comparable to the available height to fit the mechanism into. Chairs used to use metal springs in past decades, but these were nearly always high-force low-travel things used through some sort of lever mechanism.
Thanks, I get it now. I'll stuff a bit of wood next to the piston until I can organise a repair - It's a nice chair that works well for my back and I'm reluctant to change.
As a 17 year old, I spent a significant part of my waking hours trying to configure a piston latch and ether injection system to produce reliable Dieseling.
Fortunately, age, discretion and a firearms certificate intervened.
So do gas lift chairs require special handling when you want to get rid of them? I've got one whose gas strut is functioning just fine but the rest of the chair has fallen apart and so I was just going to throw it out with the normal household waste.
Its a combination of a right charlie and a chair who thinks that making posts about things they want to sell as if they have just discovered them is going to fool anyone. Be the product good or bad, who knows but this form of marketing is a bit stupid in my view.
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