During research on the 1906 MORRISS steamer and in a report by Mr. Frank Morriss he states that for boiler water level he quote " travelled many thousands of miles" depending soley on a WATER LEVEL gauge using a PRESSURE gauge as the indicator, I have mulled over this scheme and might consider some trials , but not having any further information as to the "modus operandi" I will have to rely on my own intuition/knowledge, but has anyone "out there" got any info about this ? I have few ides of my own but any input will be appreciated
I'm afraid this is thoughts rather than experience, but I always look upon a pressure gauge as a device to measure the difference between two pressures. If the reference pressure is to atmosphere it measures "gauge" pressure. If reference is vacuum, then it's absolute. If reference is bottom of boiler & test point is top, then it will measure the head of water.
The pressure difference will be less than 1 psi. Not at all the same device as measures working pressure, but still, a pressure gauge.
The sngg with thatis the resolution of the gauge. If it has to operate under a general pressure of 600psi it will be very hard to find a gauge on which you can read differences as small as one psi.
Mike, I don't see that as a particular problem. It's a sensor that's detecting a small force. Imagine a 2 opposing pistons say 1 sq in area. Deliver reference pressure on one side, pressure to measure on the other side. Measure the force needed to centralise the assembly. (< 1 lb.)
Actually the dynamic range is about 6 inches head of water, or ~ 1/4 psi, or 4 oz across a 1 sq in piston for the dynamic range of our force sensor.
We're measuring a head of water of about 6 in an environment of 600 psi. If you go to sea, that's only a depth of 400 metres, 1200ft - not particularly hostile. You might say "but the sea isn't @500 deg F" - quite so, but temperature decoupling is not a problem down a length of capillary tube. We can provide hydraulic (pressure) coupling along with temperature decoupling.
Is leakage across the boundary a problem? I don't think so. We can use a diaphragm - a total seal. The pressure differential is small, although absolute pressure is large.
I don't think I'm being too simplistic. Do I make sense?
I've been writing about what sort of pressure gauge could do the job, but I don't really believe that's what the 1906 author had in mind. I don't think Frank Morriss would have simply have said " ... travelled many thousands of miles ... using a pressure gauge as the (level) indicator", and left it at that.
I guess, when he talks about a pressure gauge, he is really thinking of a thing that measures gauge pressure - pressure relative to atmospheric. I'm stumped on the answer to that.
Greg - makes sense - after all the steam automatic is also doing a balancing act between two strong forces, the position of the valve plunger depending on a very small difference in force applied. What I wonder is whether you will find a ready made instrument out there which will do the job.
Working on a temperature of 250 deg C, which gives water density of 0.8, the maximum pressure variation works out at 0.113 PSI. on a boiler level difference of 4 inches (the length of the usual water gauge). Assuming that you want a reading that stays somewhere in the middle of the glass I think that you are probably looking at a pressure differential of about 0.06 PSI.
I doubt a gauge that can give an accurate and reproducible reading of 0.012% of its working pressure, even if it is a well designed differential one, attached to the top and bottom of the boiler, is available at any price.
Some bright spark may be able to come up with a super duper electronic gizmo. But is that what we want on a 95 year old steam car?
I think I'll stick to the Klingers, they work for me some of the time.