The Water Column Column

The Water Column Column

If you know anything about boilers, you know how important it is to maintain proper water levels inside the pressure vessel. If the water gets too low, the boiler can get damaged from heat stress. But if the water level is too high, the boiler won’t be able to make steam efficiently. But it’s not like you can just open a door and look to see how much water you have in the boiler, because then you’d lose pressure and steam production would drop. So how do you know the water level? Welcome to the water column. 


To help visualize the purpose of a boiler’s water column, let’s think about it this way. If you have two containers full of water at two different levels, and then you connect them with a tube, something interesting happens. Due to the universal pressure of the atmosphere, the level of water in the now-connected containers will equalize so they’re at the same level. 

This is basically how the water column in a boiler works. If you can’t see inside the boiler, but you have another container that’s connected to the boiler, the level of water in that second container is going to equal the water level inside the boiler. 


A typical water column will have a few standard pieces to it. First, you’re going to have a sight glass. Sight glasses are the clear cylinders that actually let you see the water level. A water column is also going to have metal pipes leading to the boiler to let the water equalize through to give you a sight glass reading. The water column will also have valves between the boiler and the sight glass.

While these sight glass valves are normally left open during boiler operation, they can be closed to isolate the water column for sight glass service. The sight glass assembly will have another valve that functions as a drain, to depressurize the glass or aid in clearing buildup. Sight glass valves should not be left closed while the boiler is in service - this is a code violation on boilers below 400psi.

The overall water column has a blowdown to clear the float, probe, and sight-glass columns. This should be blown down daily to keep the column clear and to test the level safeties, but the sight glass should only be blown down as needed to reduce wear and tear. Remember though, the bottom blowdown valve is the primary way to get sediment out of your boiler. 


While the water column allows you to check the water level of your boiler, it can serve another important purpose as well. If the sight glass water is milky or cloudy, it’s a good indicator that your water softener may be having an issue. You will want to check that function immediately.


The water column is a reliable way to check your water level, but because it’s outside the main vessel, it’s also one of the primary places that water leaks can develop. Give your water column a regular visual inspection to make sure there’s no leaks or drips, especially around the sight glass. 

f you are having problems with your water level, or if your sight glass is getting cloudy and hard to read, remember, the professionals at WARE are standing by to help get everything fixed and running properly. That way, you can have the right amount of water you need to maximize your steam output and your energy costs. If you need help with a new or rental boiler, or if you need any other boiler services, WARE is always here to help. Just let us know what you need. 

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