Detroit wrote: ↑Fri Dec 15, 2017 7:59 am
So, before I go into it, it's important to understand steam heating systems. Steam heat progressed through the 1800's to the 1920's. In the early days, boilers blew up (yes actually exploded), killing many people and building a reputation of being unsafe. The name of the game became reducing pressure to make boilers safer. I won't get into the different types of systems, but in my case, I have the most "advanced" steam heating system that was developed in the mid 20's. Shortly after, forced air became the norm because steam heating systems were so damned expensive. You had to have a dedicated engineer plot out the system in a new house (which was
) and all the parts (pipes, radiators, valves, traps, etc) were expensive to buy and install. None of that was an issue with forced air, so steam heating systems like mine came and went fast. The result is that nobody knows how to work on my system, so I taught myself. I'll focus on our system from here on out...
Water hammer occurs when water gets into the steam lines, or steam gets into the water lines. Effectively, the steam crashes into the water, and that collision is heard in the pipes as a bang. There's many ways this can happen.
At first glance, we have a 2-pipe steam system. Radiators with a supply pipe coming up to the top, and a return line coming out the opposite side on the bottom with a steam trap. The steam trap separates water from steam...and as such is a critical part of water hammer. When I started researching my system, everything I read said to replace ALL of the steam traps to prevent water hammer. Steam traps tend to fail open (so as not to build up pressure), and when that happens, steam gets into the water return lines and before you know it, there's an army of elves tapping on your pipes with hammers (that's what it sounds like).
So I replaced all the steam traps. Proud of myself, I ran the boiler and it was fine. No water hammer for the first few days. Then one night, the elves showed up.
I read deeper and inspected my system closer. To combat pressure, there should be air vents at the end of the steam mains. Mine didn't have any. Too much pressure means steam will push it's way anywhere...including water pipes. I assumed that someone at some point removed the steam main vents because they were leaking, and plugged the holes...so I set out to add them back. When examining the boiler, I saw an odd cluster of pipes labeled as a "differential loop" with a vent on top. I hadn't read a thing about this, so I did some homework. This is when things got crazy.
The differential loop is a mechanical series of pipes that controls the water level through pressure. Too much pressure, the water level rises, and it pukes it out into the return line to the boiler. On top of this is a vent. When digging further, systems with a differential loop were the last iteration of steam heat. They run on less than 1 PSI or pressure (
) and rely on only one main vent to let all the air out of the system...the one on top of the loop. The pressure is so low, and the vents are designed in such a way that they continue letting air out after the boiler is shut off, which creates a slight vacuum. Then, when the boiler turns on, the steam rushes through the pipes because it always travels to low pressure first. This means the house heats faster, and is completely silent. In theory...
I looked up what vent was on my loop, and someone...not knowing what the system was...put a vent on that was about half the venting capacity of what it should be. They even left the original dead vent on the floor, which I confirmed has much higher venting capacity. The small vent was letting the system build up too much pressure, and as a result steam was finding it's way to places it shouldn't, and causing hammer. The crazy thing was, I could let water out of the system to stop hammer for a few days. I couldn't understand why until I realized that dropping the water level also dropped the pressure level. But as pressure slowly built up due to insufficient venting, the hammer would return in a few days.
I bought the proper vent, and installed it in place of the small one. It was $80, and we've been water hammer free ever since. We had three different "experts" come out over the years, and just take a look at the boiler and say "it's old, needs to be replaced. That's causing the hammer". Yes, the boiler is old, but that's not the culprit of the water hammer. Most had no idea what they were looking at, so they just went to the obvious.
I've become fascinated with steam heating ever since I went through this journey. If I ever lose my job, I legit will get certified in HVAC and specialize in repairing steam heat systems. There's a bunch in my area, and nobody I could find knows much about them.