The Steamboating Forum

I have two gauges to chose from for my boiler pressure. My safety is set for 150 psi. I run anywhere from 100 to near the pop point in use.

The existing one is a rather prosaic looking 200 psi unit and the one I am considering installing is 160 psi. The 160 unit is a much nicer looking unit but I am reading here and there that a gauge that tops out a 1 1/2 to 2 times the working pressure is recommended.

I would be using a different gauge for hydro testing. I'm interested in reasons to have a gauge that reads so far beyond the safety set point? I wouldn't think that it would be hard on the gauge to use it near the upper end of the range.

My belief is that any gauge should be able to read at least 150% of working pressure, but I can't remember where that came from.





Some might say it's old age!

The ASME Code for Boilers now requires a pressure gauge reading at least 150% of MAWP, older versions of the code did not have this requirement. I very much prefer a gauge that ranges up to the safety valve setting, so on my launch (100 PSI MAWP) I have a nice old brass gauge that reads to 100 PSI, and a smaller one ($5 commercial 2-1/2 inch gauge) that reads to 160 psi.

Thanks, Fred.

I wonder why? Must be some reason. Traditions often come from some previous bad experience. Sometimes advances in technology have made them less applicable. Some times they are based on nothing much at all. Sometimes they can save you a lot of grief!

For now, I'll use my 160 gauge with a 150 safety setting and see if I'm killed right away. (grin)

My Grandfather - who was "old country German" - was a blacksmith/boilermaker in the logging camps in the Puget Sound area of Washington State in the 1920s through 1940s. He told me that most "donkey engine" operators (as well as the logging companies) preferred to have boiler pressure gauges that were twice the normal opoerating pressure and mounted vertically. If the operator and/or fireman saw that the needle was vertical, then they knew that the pressure was ok. No fancy 'rithmetik or need to read or 'rite.

I like that explanation Ron.

In my case, any green horns on board will see the gauge well past 12 o'clock when I'm at 100 psi and think we are really going places.

If the gauge only read upto safety valve release pressure, how would you ever know if the SV got stuck...? The pressure gauge would just be reading it's highest pressure and you wouldn't know any different- in th UK safety valves are allowed to release upto 10% above MWP (although it is frowned upon and you are expected to get it as close as possible), with on a 200psi WP boiler would be another 20psi- a not inconsiderable increase.

Greg

That is a thought. 'Though I am an enthusiastic fireman and all too often get to hear the safety pop. It lifts right at 150 by the present gauge.

Part of the temptation is that the present 200 psi gauge is liquid filled and I have designs of putting it at the feed water pump output where the damping and the extra head room would be nice.

The other gauges I have laying about are 400 psi 6 inch monsters that would look silly on this little power plant. One big brass antique even says Locomotive on it. What's next? A horizontal fire tube boiler? Anathema!