jackson@ttidcb.UUCP (Dick Jackson) (01/16/86)
* * * For the nth time I used one of those pocket tire gauges last night and wondered how they worked. You press the "valve" end onto the valve, there is a quick hiss (which then stops) and the graduated rod shoots out to a length proportionate to the pressure (with some offset I think). I tried to see if there was a taper on the rod, if so it was very small. The gauges are inexpensive, therefore relatively easy to make (no high precision?). I cannot figure out how they work. Anyone know? Dick Jackson
jim@alberta.UUCP (Jim Easton) (01/21/86)
Dear Dick, The funnest way of finding out how they work is to take one apart. Some are even built for it but I will tell you. There is a spiral spring attached inside to the end which goes onto the valve. The other end of the spring is attached to a piston. When air comes into the cavity it pushes the piston down the tube, stretching the spring, a distance proportional (approximately for the purists) to the pressure. The rod that comes out the other end of the gauge is a rider on the piston and stays when the pressure is removed. Jim Easton (..!alberta!jim)
jp@lanl.ARPA (01/24/86)
This reminds me of a question I asked once before, but got no reply. How do the automatic shutoff's on gasoline filler nozzles work. They seem to be very sensitive to the slightest change in back pressure. I wouldn't mind taking one apart, but all the nozzles available to me are in use at my local service station. Thanks, Jim Potter jp@lanl.arpa