Originally Posted by
spinner
An interesting thread. I'll reserve judgment on the practicality and safety of a project like this and offer the following observations for your consideration. You are combining several different elements in uses they were not designed for. The presta valve has a rubber o ring that was designed to seal against air pressure, but not designed to work in a hydrocarbon rich atmosphere. Try to determine the effects of long term exposure to gasoline on this o ring. If it should break down while the stove is lit it could have serious consequences. As far as I know there are no stove manufacturers using plastic fuel tanks for pressurized fuel systems. In a market that is driven by weight saving and manufacturing costs, there has to be a reason for this. Try to determine what the reasons are and see if they are valid in your own application. In response to one of your earlier posts, metal gas cans are actually making a comeback. Many large industrial sites no longer allow plastic gas cans on site, for a number of reasons, and metal gas cans are required. I would urge you to use the smallest quantities of gasoline that you can in you experiments. Remember you are basically dealing with a bomb that only requires an ignition source. Gas burns are Nasty
Good observations there. I do believe in redundant levels of safety.
As for the HDPE (the word 'plastic' tends to set off too many cliched reactions in many minds): I believe it is engineered to withstand enough pressure when it is made for shipping and selling hazardous materials to the public. I have seen it hold more pressure than I will be needng or using.
The stove manfacturers have a very CYA way of approaching things in a litigious society. One issue for them is the melting of the plastic if the container is set inside a windscreen, for example, or in some burning gas from a leak, or from overpriming, or from a valve that someone neglected to close when priming (just read of a case of that). Or if someone cross-threads the cap, or leaves it insufficiently tightened. These companies really need to chimp-proof things as much as they can.
However, MSR engineers have told me that their reasoning behind the plastic pumps is that the plastic will melt, in case of some kind of a leak that ignites. Old or damaged o-rings are another cause of leaks, and they know of cases.
They said that the fuel would spill out but at least it wouldn't behave like a bomb. They considered a metal pump to be significantly more dangerous.
Sun exposure is also a concern with outdoor materials. I am very alert to UV degradation issues.
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A bike mechanic told me that there are nylon seals inside the Presta valves. I will be taking some apart and replacing anything that needs replacing.
Thank you for some specific engineering-oriented, intelligent and constructive points.