kelly51 wrote:
They do make opd cylinder valves with magnetic gauges but they clip on the valve and seem to work ok. Look at page 4 of the pdf. We install them where I work and cost around $20 to swap out.
http://www.gasequipment.com/catalogs/Catalog_8_PDF/23-Cylinders.pdf
Sorry, but Canadian Tire here in Canada sells that exact gauge, I've got one, and it's all but useless because it's measuring vapour not the level of liquid propane left in the tank, which is what you want to know. The most effective method is to weigh the tank and subtract it's tare weight which is stamped right on the collar ... then you
will know how much liquid propane is left in the tank.