A Game of Inches
Every boiler system features pressure gauges somewhere in the system. Without them, you’d never know if you were operating at the right pressure for the system. Gauge accuracy, therefore, is fairly important. That’s where the Inches of Water Column comes into play.
Keep Your Distance
Ideally, to be most accurate, a pressure gauge would be exposed directly to the steam pressure in a boiler system. However, it’s not really practical to do that for two reasons. First, the gauge might not be at the operator level where it can be read. Second, the gauge itself would be exposed to the temperature of the steam, which would damage the gauge’s internals.
If you look at a pressure gauge, such as on a deaerator, you’ll notice that it’s often piped down to the user level for reading. As steam fills that pipe, it condenses into water due to the cooler environment, and this condensate acts as a buffer between the gauge and the steam itself. As the column of water gets taller and taller, it adds the weight of that “water column” to the actual steam pressure where it is connected to the system. This causes the gauge needle to display higher than the true pressure. But we can account for that.
Check Your Pressure
Because we know the mass of water, and we know the pull of gravity (welcome back to Physics class! Sorry!) we can figure out how the mass of the water will affect the pounds-per-square-inch reading on the gauge. We did most of the math for you (you’re welcome!), and we know that every 28 inches of water in a vertical column will produce 1 extra psi. Measure the drop in piping between the steam connection and the gauge, and see how many times you can divide it by 28. That’s how many extra psi the water mass is generating.
EXAMPLE: You have a gauge piped 80 inches below the steam connection. Dividing 80 by 28 produces a value of 2.86, which means the water is adding an extra 2.86 psi onto the true reading of the gauge. The next time the system is in startup or is idle, the gauge can be recalibrated, or “zeroed”, to account for the extra mass of the water.
If you want to make sure every gauge in your system is accurately calibrated, the experts at WARE are standing by. We’re experts at installing, maintaining, and servicing any steam pressure gauge out there, and have a full range of gauges for every application. Along with everything else your boiler will ever need. Let us know how we can help.