Did I buy wrong low pressure gauge?

Motorapido

I bought this Wika gauge https://www.valworx.com/product/low-pressure-gauge-25-0-15-ozsq-in to get a more precise reading than the other gauge I also have on the boiler, which is 0 to 3 pounds. This Wika gauge I bought drops below 0 when the system shuts off, which either indicates vacuum or some sort of defect with the gauge. My 0 to 3 psi gauge has a pin that stops the needle from reading less than 0. After four or five weeks with this new gauge installed, and I should mention both gauges are mounted above a snubber and up on high brass nipples, much higher than the water line and above the vaporstat, the 0 to 15 ounce gauge now usually shows 15 ounces or so when the system is off, and when it fires up and gradually builds steam, the needle moves clockwise to zero and then up through the range, but it shows lower pressure than the 0 to 3 psi gauge. Did I buy the wrong gauge, or is mine broken? That's a short life for an expensive gauge.

Jamie Hall

Something is not right with that new gauge... when the system is firing, assuming it builds any pressure at all, the two gauges should read exactly the same.

Take the 25/0/15 gauge completely off, and see what it reads. It should read 0.

Fred

Is this gauge on a pigtail? Operating temp range is -4 to 140 degrees. Temperature Error:
Additional error when temperature changes from reference
temperature of 68°F (20°C)
+0.4% for every 18°F (10°C)
rising or falling. Percentage of span.
Also, have you actually watched the gauge through a heating cycle? If you have it on a pigtail, it may drop into a vacuum that looks like it is at 15 ounces when in fact there is a vacuum in the pigtail, between the gauge and the water in the loop. I have seen my 0-3 PSI gauge drop well below the zero but it usually recovers to zero by the next heat cycle. Check to make sure the pigtail or the orifice on the gauge isn't clogged .

mikeg2015

Most will briefly go into vacuum after shutting off. On vapor systems could be a fairly deep vacuum. Mine gets to 5” hg but I have a heck valve that opens.

Normally the gauges have a stop at0 a you mention. Guess that one doesn’t.