Hammering Noises in a Steam Boiler

Steam boilers are known to make a variety of noises at times, but that doesn't mean they should make noises. A properly installed and maintained steam boiler should in fact be a quiet system. Water hammer noise is a common issue in steam boilers, but how does water hammer happen?

Anytime steam and water occupy the same pipe, the amount of available space is decreased, and when we decrease the pipe size, the speed that the steam is traveling increases. Increasing the speed of steam causes water to be picked up by the steam and eventually creates a water slug in the pipe. The steam continues to build pressure behind the slug until it has enough pressure to shoot the slug downstream. 

That’s how the water hammer is made, but what causes this to occur in a steam system? Here are common reasons a steam boiler may experience water hammer.

1. Incorrect Near Boiler Piping

Modern steam boilers use the near boiler piping to produce dry steam. Dry steam is when no water is pasted through the steam mains to the radiators. Manufacturers use the near boiler pipe sizing and design to correctly achieve this. Each manufacturer has a set of specific installation instructions. Another common mistake on near boiler piping is the Hartford loop connection. This loop is to help prevent a boiler from being able to dry fire (light the burners without water in the boiler.) This Hartford loop connection must be done with a close pipe nipple. At Behler-Young, we stock some near boiler piping kits for the Utica PEG boilers.

2. Too High of a Boiler Pressure Setting

Many contractors may put the steam pressure of a boiler higher to help keep the steam boiler from short cycling. This may fix a short cycling issue but can cause water hammering later on. When a steam boiler for a residential application is set above 2 PSI, steam starts to leave the boiler too fast. This can cause the condensate to flood back to the steam mains and create water hammer.

3. Fail Steam Traps

Steam traps are used in two-pipe steam boiler systems. Their function is to separate the water from the steam by trapping the steam in the radiators and allowing the water to flow into the returns. When these traps fail, steam can freely travel through the return pipes that are filled with water. This allows steam and water to occupy the same pipe which can create a water hammer.

4. Pipe Insulation Problems

Steam pipes with missing insulation can cause the steam in the pipes to cool back to water before getting to the radiators. This makes steam and water prevalent in the steam mains and can create water hammer.

5. Dirty Boiler Water

The water in the steam boiler needs to be free from any oil, grease, or debris. Dirty water causes uneven steam distribution and can cause water to be carried up the steam mains. This creates "wet" steam in the mains and can cause both the water level to fluctuate and water hammer. Each manufacturer has instructions on how to properly skim the oil, grease, and debris off the top of the water line.

6. Incorrect Boiler Water Line

Each boiler manufacturer has a recommended water line. This is to ensure dry steam can be sent to the steam mains (along with the help of the proper near boiler piping.) Too much water causes a flooded boiler which does not allow the steam to "dry" before it enters the mains.

This video shows what happens in the near boiler piping on a steam boiler when it is not sized correctly or even has too high of a pressure. It is piped with glass tubes so we can see how modern steam boilers actually use the near boiler piping to “dry” the steam out before it gets to the steam mains.

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