Published: August 30, 2016 - by Dan Holohan

Categories: Steam, Hot Water

water hammer

Discovering that water hammer has moved into any hydronic system, be it steam or hot water is never fun, but finding the cause of it sure can be. Hey, you get to be a detective.

            In the beginning, when steam water hammer first showed up, it broke pipes, flanges, and valves, and even killed people. The Dead Men gave it its name because that’s exactly what it sounded like.

            And since I spend a lot of time listening to dead people, I asked Mr. Hawkins, who left us more than a century ago, to give me his thoughts on the steamy side of this hydronic challenge. He said, “The fact that steam piping methods have not kept pace with the demands of higher pressures and modern practice is evidenced by the increasing number of accidents from the failure of pipes and fittings."

            I love it when he talks about modern methods. Gosh, it's 1902.

            “I think the cause of the bursting is undoubtedly water hammer or water ram, which accompanies large, long steam pipes, filled with condensed water. If steam be blown into a large inclined pipe full of water, it will rise by difference of gravity to the top of the pipe, forming a bubble; when condensation takes place, the water below the bubble will rush up to fill the vacuum, giving a blow directly against the side of the pipe. As the water still further recedes, the bubble will get larger, and move farther and farther up the pipe, the blow each time increasing in intensity, for the reason that the steam has passed a larger mass of water, which is forced forward by the incoming steam to fill the vacuum. The maximum effect generally takes place at a ‘dead end.’

            “In fact, under certain conditions, a more forcible blow is struck when the end of the pipe is open, as, for instance, when a pipe crowned upward is filled with water, one end being open and the steam pressure from the other, and the meeting of the two columns frequently ruptures the pipe."

            Boy, I wish he was still here. I once watched a video that a European manufacturer had made. It showed water hammer happening inside a glass pipe. You can see exactly what he just described and it's quite scary. The water moves quicker than my eyes could follow. I think he would have liked it, once I explained what video is.

            I next asked him how he dealt with water hammer back in the day.

            “The remedy for this is simple, the pipes must be properly located so as to drain themselves or be drained by rightly located drip cocks. The drip should be on the other side of the throttle valve, and if steam is left on overnight this valve should be left open enough to drain out all the water.”

            So when you're being a detective, look for places where water won't drain. The horizontal mains should pitch one-in in 20 feet in the direction of flow if the steam and condensate are going in the same direction and twice that if steam and condensate flow in opposite directions. And pay close attention to any place where the pipe reduces in size. Is that creating a place where water won't drain?

            Look for anything that can quickly cool the pipes because that will turn steam into condensate. In New York City, Consolidated Edison has to deal with heavy rains that get into their manholes. If you see those tall orange chimneys out on the city streets and they're spewing steam, realize that this isn't steam from the inside of the pipes. The steam you're seeing is rain water boiling on the outside of the pipe. The cooling on the outside of the pipe causes condensate to quickly form on the inside of the pipe, and if the steam traps aren't working properly, water hammer will appear. That happened in 2007 and the explosion destroyed an intersection of midtown Manhattan and put debris on top of the Chrysler Building.

            On a smaller scale, if you remove insulation from steam pipes, you're liable to get water hammer, and for the same reason. The steam cools too quickly when the pipes are bare.

            Pay attention to when hammering starts. If it's on start-up and then goes away, suspect the pitch of the pipe and missing insulation. Setback thermostats can also cause start-up water hammer because they allow the steam pipes to get cold overnight.

            If the hammering happens mid-cycle, check the wet returns. If they're clogged, condensate will back into the steam main and hammer. Unclog the returns.

            Hammering toward the end of the cycle and near the boiler is usually a poorly piped Hartford Loop that's allowing steam into the return as the water level in the boiler drops.

            So get out of the boiler room and wander around. That's what a good detective does. Ask yourself, if I were water, could I drain by gravity? Could I get out of the way of the steam? Think simply and methodically and you'll solve the case every time.

            The same goes for hot-water systems. In our house, we zone with four circulators. Two feed baseboard convectors. One serves a kick-space heater in the kitchen, and the last takes care of our indirect, domestic-hot-water tank. The reason we have circulators is because we used to have zone valves. The Lovely Marianne and I were sleeping peacefully one night when this loud BANG! caused us both to levitate.

            "What's that sound?" TLM asked, sitting up.

            "I don't know," I said. "You should get up and go check."

            As if, right?
           So I went to check and found the house secure.

            The next night, the same thing happened. I looked around and found nothing amiss.

            This went on for a while, and my bride began to lose faith in my diagnostic abilities, but then it happened when I was wide awake, and I now knew the sound was coming from the boiler room. I paid attention and found the culprits.

            We had these zone valves that powered open with a motor and closed mechanically with springs. The valve had a ball that would move into position and seat when the thermostat was satisfied. If one zone was on and the other zones were off, all was well. The hammering happened only when two zone valves were open and one then tried to close.

            Here, think this through with me: The thermostat sends a Go signal to the zone valve's motor. It opens the valve, and along the way, it trips an end switch that starts the circulator. The circulator moves hot water through the zone valve and out to where we need it. Nice and normal.

            So now the thermostat is satisfied. It cuts power to the zone valve. The springs go to work, pulling that ball toward the zone valve's seat. It trips the end switch along the way, and this is supposed to stop the circulator, but that thermostat in that other zone is still calling, so the so the circulator is still running.

            As the ball gets closer to the zone valve's seat, the space though which water can flow narrows, and as it does, the water speeds up. When the ball finally seats, the speedy water hammers into the closed valve with a wallop and all the pipes in our house shake. The Lovely Marianne gives me that look. You know that look?

            Before I switched to circulators, I tried to solve the problem by removing one of the springs from the zone valves, but that didn't work, so I gave up on them in favor of undisturbed sleep.  A smart pump would have solved the problem, but we didn't have smart pumps back when this was going on. It was up to me to be smart.

            I did my best.

            So whether it's happening in a steam system or a hot-water system, know that water hammer is just water moving quickly that suddenly runs into a wall. If you can see that picture in your mind's eye, you'll know where to look and you'll be able to solve even the toughest cases.

            Now go be nosy.