Squiffy
Forum Member
I'm going to mention and talk about what some may say is a controversial subject, which it really should not be and this post is purely for information and I except no responsibility if folk act on this demonstrated post.
I have recently changed my underslung 25ltr gas tank for a new one as the original was ten years old and had varying degrees of corrosion showing, not knowing how thick the walls of these tanks are I began to be concerned and so to be on the safe side I replaced it and the flexible feed pipe from the filler point back to the tank. I then proceeded to go to Portugal and back over the next 5 weeks. All went well and filled twice at various garages, apart from the filler adapter for Spain and Portugal did seem to have a connection problem.
However now we've been back for several weeks I decided to remove all the gubbins from the old tank and check out the valves and floats and what they do etc. What follows is a photo of them roughly in order of their removal.
The first valve is the 80% float valve which operates when the float reaches a certain position and drives a mechanism which creates a pressure build up in the supply tube from the gas pump, in turn the pump feels this pressure build up and shuts off.
The second unit is the magnetic mechanism that when the float starts to rise it operates a pinion type gear which turns a shaft and at the other end revolves a disk with a magnet attached and this revolves in a circular movement which in turn through the brass plate turns a needle encased in a plastic case rather like a compass, the higher the float the further round the dial it drages the needle on the scale behind it.
The third one is the pressure relief valve and will operate under extreme stress, I'd have thought it's set to unload at just below the pressure which would rupture the integrity of the tank.
The fourth one is the supply valve that incorporates a shut off turn screw valve, the base tube I think never dips into liquid gas as it operates in the 20% zone of the tank and so supplies vapour and not liquid.
These float mechanisms are the reason these tanks have to be orientated at a precise angle of 105 degrees so that the cut off float cuts off the pumped supply gas at exactly 80%.
Now the reason I removed these valves apart from interest as to how these tanks and valves work is because I wanted to know just how thick the walls of these tanks actually are. I wanted to see just how bad the rust and corrosion had to be before the integrity of the tank would be affected. Well the rust to me seemed quite bad, hence why I replaced it after ten years, however on feeling inside with my figure and thumb trough the holes now available by the valve removal, I can say that the corrosion would have to have been far far worse than that showing on this tank, with a scraper and wire brush the depth of corrosion was insignificant to the thickness of the wall of the tank. I haven't got a calipers that enabled me to measure the exact thickness but it was significantly thick and had I known I would not have bought a new tank. Having Said that I'm happy that I have changed it as I would never have been comfortable having seen the outer corrosion of the old tank in the first place, but I'm certain there was many more years of serviceable life left in it, especially if it had been scrapped off repainted and wax oiled or equivalent.
I have recently changed my underslung 25ltr gas tank for a new one as the original was ten years old and had varying degrees of corrosion showing, not knowing how thick the walls of these tanks are I began to be concerned and so to be on the safe side I replaced it and the flexible feed pipe from the filler point back to the tank. I then proceeded to go to Portugal and back over the next 5 weeks. All went well and filled twice at various garages, apart from the filler adapter for Spain and Portugal did seem to have a connection problem.
However now we've been back for several weeks I decided to remove all the gubbins from the old tank and check out the valves and floats and what they do etc. What follows is a photo of them roughly in order of their removal.
The first valve is the 80% float valve which operates when the float reaches a certain position and drives a mechanism which creates a pressure build up in the supply tube from the gas pump, in turn the pump feels this pressure build up and shuts off.
The second unit is the magnetic mechanism that when the float starts to rise it operates a pinion type gear which turns a shaft and at the other end revolves a disk with a magnet attached and this revolves in a circular movement which in turn through the brass plate turns a needle encased in a plastic case rather like a compass, the higher the float the further round the dial it drages the needle on the scale behind it.
The third one is the pressure relief valve and will operate under extreme stress, I'd have thought it's set to unload at just below the pressure which would rupture the integrity of the tank.
The fourth one is the supply valve that incorporates a shut off turn screw valve, the base tube I think never dips into liquid gas as it operates in the 20% zone of the tank and so supplies vapour and not liquid.
These float mechanisms are the reason these tanks have to be orientated at a precise angle of 105 degrees so that the cut off float cuts off the pumped supply gas at exactly 80%.
Now the reason I removed these valves apart from interest as to how these tanks and valves work is because I wanted to know just how thick the walls of these tanks actually are. I wanted to see just how bad the rust and corrosion had to be before the integrity of the tank would be affected. Well the rust to me seemed quite bad, hence why I replaced it after ten years, however on feeling inside with my figure and thumb trough the holes now available by the valve removal, I can say that the corrosion would have to have been far far worse than that showing on this tank, with a scraper and wire brush the depth of corrosion was insignificant to the thickness of the wall of the tank. I haven't got a calipers that enabled me to measure the exact thickness but it was significantly thick and had I known I would not have bought a new tank. Having Said that I'm happy that I have changed it as I would never have been comfortable having seen the outer corrosion of the old tank in the first place, but I'm certain there was many more years of serviceable life left in it, especially if it had been scrapped off repainted and wax oiled or equivalent.
Last edited:
. Phil
.
, so I was lucky in that one day I walked into Suresh's work shop and caught him at it, that's when he finally showed me the whole process. Phil