I have a pressure gauge I bought to measure air pressure. Can I use it to measure water pressure?

It was a gauge from Home Depot to verify a natural gas line was properly installed and did not leak. I pressurized the line with air and then left it for 48 hours to see if it held the pressure. Now I need to measure my water pressure. Can I use this gauge?

 

Yes...pressure is pressure...but the range on the dial may not be adequate for water. Water may also cause some issues with the gauge for later use. Connecting it with adapters may also be a pain. You can get a water gauge to screw on a hose bib for about $10.

 

Pressure gauges used on water lines in the home are usually mounted upright and quite often with a nipple or other fittings. This traps a pocket of air so even though it's installed on a water line, usually the water does not actually enter the gauge (except for condensation), so they can even be surprisingly resistant to freezing.

 

I have been getting an odd behavior on this gauge. It is connected to a hot water boiler to measure system pressure. For example, it shows 17# consistently. I am trying to regulate the system to 15# so I let out a small amount of water, less than 4 ounces. The gauge plunges to 5# +/-. Then I heat the boiler and the gauge rises again to the 17# or maybe 16#. So I know the gauge is accurate. The 3-4 ounces of water was not enough to truly lower the system pressure to 5#. So, why does the gauge drop like this, and then later rise back to where it was? The make up water supply is shut off. I was thinking maybe the gauge was an air gauge, not a water gauge. Guess I'll just ignore this odd behavior as over time the gauge looks to be accurate.

 

Ahhh well a boiler is kind of a different animal than a domestic water supply. Water supply is kind of static w/o any usage, boiler has many things that could affect a reading. Just draining the water could release pressure somehow...never had one, can't tell you.

 

As you heat water it expands, the pressure in the system goes up.
As the boiler runs hot and cold over time the pressure is going up and down all the time.
Albeit that the boiler has its own pressure vent to avoid explosions.