In this month’s column, we will cover steam trap maintenance for low-pressure heating systems. These steam traps are typically found in schools, apartment houses, churches, and light commercial buildings. There are certainly some very large homes with steam traps as well.
We will start with the purpose of the steam trap. The low-pressure steam boiler receives a call for heat and the burner fires. After a short period of time, the water in the boiler begins to boil and changes state from water to steam. Once this occurs, steam begins to fill the steam mains in the building. Inside the mains, the air is being pushed through the pipe by the steam pressure behind it. At the same time, some of the steam condenses inside the relatively cold piping and drools towards the end of the mains. Something must allow the air and condensate to escape, this is where the steam traps (float and thermostatic in most cases) at the end of the mains come in.
These F&T traps are designed to allow the air and the condensate out of the steam main while preventing (trapping) the steam from entering the drips that connect to the returns. From the F&T traps, the water and air go back to the boiler, often via a condensate station.
In most of these buildings, there are also steam traps on the end of each heat emitter. These heat emitters might be cast iron radiators, recessed convectors made of cast iron or copper with fins, or blower-type units often seen in large classrooms or gymnasiums. In most cases, you will see thermostatic traps connected to the opposite side from where the steam enters the heat emitter. These thermostatic traps work very similarly to the F&T traps, except they are much smaller and have fewer moving parts. Like their counterparts, they allow air and condensate out of the heat emitter while trapping the steam inside.
Ideally, the maintenance crew would perform steam trap maintenance every year and fix or replace the problem traps as needed. Instead, in almost every type of building I mentioned, no one ever does any trap maintenance. The reasons for the lack of maintenance vary — for example, churches rarely have a maintenance staff these days, many apartment building owners only worry about the steam heating system when there is no heat and the school maintenance staff may not have the time, budget or expertise to take care of the steam traps.
For example, we were recently asked to take care of some heating issues at a local building. The heating system is a typical 70-year-old two pipe steam heating system in a school with six very large classrooms, a few bathrooms and an office. The school is used as a nursery school during the day, aftercare for older children and a religious school on Sundays. For the last few years, two classrooms had no heat, two classrooms heated almost perfectly and two classrooms had the windows open every day of the heating season.
We started by examining the existing steam traps and nearby piping. The traps on the heat emitters and the ends of the steam mains all appeared to have been replaced in the last 20 years. Originally, someone installed a wye strainer before each F&T trap, these appeared to be untouched and about 70 years old. Some of these strainers were retrofitted with blow down valves, some were not. Since they were on a tight budget, we focused on the F&T traps and ordered new replacement heads. We planned on testing the thermostatic radiator traps afterward.
We turned the boiler off and locked it out so no one could accidentally turn it on. We opened the blow down valves if there were any, and drained whatever came out into a bucket. Some allowed debris and red hot condensate to come out, in others, nothing came out but some black muck. Next, we found the correct impact socket with an 18-inch breaker bar for the hex bushing or plug on the strainer and attempted to remove the fitting. In every case, this was not enough to break the fitting loose on the strainer. Next came out the battery-powered impact gun, and within seconds, we were able to remove the fittings. Unfortunately, the dirty condensate and debris all came out at once. Let’s just say I was happy I was wearing my eyeglasses.
We removed the screens/strainers and found most of them completely clogged with debris. We washed them in the janitor’s sink and reinstalled them along with the fittings. This time, we made sure to install blowdown valves in all the strainers.
The reasons for the lack of maintenance vary — for example, churches rarely have a maintenance staff these days, many apartment building owners only worry about the steam heating system when there is no heat and the school maintenance staff may not have the time, budget or expertise to take care of the steam traps.
Next, we used a socket wrench to loosen the bolts on the F&T traps. We gently tapped the edge of the face of the trap and loosened the trap cover, dirty water drooled out for a few seconds. We then removed the face that holds the moving parts, namely the thermostat and the mechanism (float assembly). We wiped any residue from the inside of the housing, removed the face gasket and wire brushed the interior to remove any debris or rust. In the base of the trap is a relatively small passageway that often clogs, we cleaned this with a small gauge glass brush. Next, we installed the new trap cover assembly and tightened up the cover bolts.
It was now time to test our work. We started the boiler and began to flush each strainer individually. We got a lot of debris and dirty condensate that came out of the strainers, be very careful not to burn yourself.
We also noticed some unusual noises coming from the steam mains. I suspect at least one of the mains has not drained in years. The nearby condensate receiver ran much more than normal, and for the first time in a long time, every main got warm. We checked for leaks in the areas we had just worked in and found none. We then went upstairs and checked every recessed convector, and smiled. For the first time in years, every classroom had heat.
When we returned to the building a few days later, the staff was pleased that the whole building was now comfortable. We used our infrared temperature gun on the inlet and outlet of each of the steam traps, we found at least a 10-degree spread on every unit, this implies all of the traps are working correctly. Hopefully, the school will notice reduced utility bills this year and realize the importance of steam trap maintenance in the future.