A Heated Exchange
For want of a vacuum breaker, water hammer destroyed this heat exchanger.
The call came in when I was young, eager, and paying close attention to the grown-ups. I had been working for the manufacturers’ rep for a few years, where my father was the Service Manager. When we sold a product, we held the bag for the first year. If something went wrong, the contractor didn’t have to fix it; we did.
So here was this steam boiler in Manhattan that was feeding a steam-to-water heat exchanger that we had sold. The boiler-feed pump, which we had also sold, was overflowing and the contractor had a telephone, so he used it. My father sent Richie, who was very capable with the tools and who knew every curse word ever muttered, as well as some of his own making. Walter, who was our mechanical engineer, decided to join Richie. A product of the Merchant Marine, Walter was forever curious, and as good as Richie was with the muttered words. I was along to represent the next generation.
So we got in Richie’s Chevy station wagon and headed for the City. Richie cursed every driver around him as Walter and I listened, appreciating the verbal virtuosity and creativity of the man. He hated everyone, and when we were about 20 minutes from the job, Richie had decided that whatever was wrong with this job was the contractor’s fault. He was superb at that. He hated everyone who bought our products, but he was very good with the tools.
Anyway, we got to the job, met the contractor (whom Richie brushed by) and headed to the boiler-feed pump, which was vomiting hot water out its receiver vent and all over the floor. The contractor made a comment about the quality of our products, which caused Walter to glare and Richie to growl. I just watched and kept my mouth shut.
Richie picked up a wrench, which caused me to take a step back, but he used it on the receiver’s float valve instead of the contractor. The float valve was holding. Its job was to maintain a minimum water level so the boiler had feed water for the first start-up. Once the condensate returns from the system, the receiver wouldn’t need the feed valve again. A bad feed valve could cause what was happening, but this time it wasn’t the culprit. Richie mumbled some words that were made of acid and barbed wire. “Excuse me?” the contractor said. “Nothing wrong with the product,” Richie said, and then mumbled some more. Richie could have made Lil Wayne blush.
“Let’s look at that heat exchanger,” Walter said. It was the shell-and-tube type, and it was sitting on a rack about six feet above the steam trap and condensate-transfer pump, which moved the condensate from the heat exchanger to the boiler-feed pump. There was a steam regulator on the feed line to the heat exchanger, which is normal for this set-up. Walter later explained to me that the reason why the heat exchanger was mounted as high as possible over its steam trap was because, when the steam regulator closed, the only pressure available to shove the condensate though the steam trap was the weight of the water in the vertical pipe between the heat exchanger’s outlet and the steam trap’s inlet. That made sense. I mean a steam trap just sits there like a meatloaf. Condensate won’t move through it unless there’s differential pressure. The trap’s outlet connected to a receiver that was vented to the atmosphere, so all we needed was a few feet of stacked water on the trap’s inlet side to build weight and we were good to go.
Walter watched the transfer pump, which was quickly cycling on and off, even though the steam regulator was closed at the moment. That seemed like a lot of condensate. Or was it?
And that’s when Walter noticed the pipe plug. It was screwed into a three-quarter-inch tapping in the shell of the heat exchanger. Next to that plug was a large, bright-red sticker that read, INSTALL VACUUM BREAKER HERE! “Sir, do you see this?” Walter asked the contractor. Richie snarled. I watched in wonder.
“Yeah,” the contractor said.
“Please read it to me,” Walter said.
The contractor smirked. “It says, INSTALL VACUUM BREAKER HERE!”
“And what is this?” Walter asked, touching the pipe plug.
“Pipe plug,” the contractor said. “That’s the way it came.”
“Why didn’t you do what the sticker says?” Walter asked.
“I didn’t have a vacuum breaker,” he said. “Besides, plugs cost less and don’t leak.”
Richie reached down into a bushel basketful of dirty words I had never heard before. They drooled from his mouth like obscene lava.
“Richie,” Walter said, “please pull the tube bundle. Dan, help him.”
‘Wadda ya doin’ that for?” the contractor asked.
“To show you what you did,” Walter said. “They teach this in the Merchant Marine Academy.”
Now pulling a tube bundle from a shell-and-tube heat exchanger involves a lot of nuts and bolts but it was worth it because when we slid it out and looked at the curved end of the tubes we saw the holes. Those tubes looked like someone had taken a hammer and chisel to them.
“There’s your problem,” the contractor shouted. “You make lousy heat exchangers. Look at those holes! And this thing is just a few weeks old. Piece of crap!”
Walter nodded. “Yes, the water from the hot-water system is leaking into the shell of the exchanger. That’s what’s flooding the boiler-feed pump. The transfer pump is just dumping that water into the feed-pump’s receiver. As I said, they teach all this at the Merchant Marine Academy. They call it basic physics. It involves stuff like atmospheric pressure and gravity. You know about gravity?”
“You’re gonna pay for this, “the contractor said.
Walter gave the guy a Jack Nicholson smile. “Dan, he said, “there’s a deli downstairs. Go get me a bottle of water and a straw. We’ll wait for you.”
I did what I was told and was back quickly. The contractor looked more annoyed than ever. Richie was deep-breathing. Walter took the bottle of water and the straw. He unscrewed the cap, slipped the paper off the straw, dipped it into the bottle, placed his finger over the top of the straw, pulled the straw out of the bottle, extended his hand with the straw so it was in front of the contractor’s face, lifted his finger, and just smiled as the water slid out of the straw and onto the floor. Then he did it again. And again. “Atmospheric pressure and gravity,” Walter said. “Basic physics.”
Richie mumbled words that even Lil Kim wouldn’t say.
“What’s your point,” the contractor said.
“My point is that my finger is the vacuum breaker,” Walter said. “When I lift it, the water leaves the straw. If I don’t lift it, the water stays inside the straw, or inside the shell of the heat exchanger. And when water, which we call condensate, stays inside the shell of a heat exchanger, the steam is going to find it the next time the steam regulator opens. And that steam is going to hammer that water off the back of the steel shell. Then the water is going to bounce back and smash into the tube bundle at the exact point where the tubes are curved and at their weakest. That’s why the tube bundle is leaking and that’s the source of your problem here. And notice I said your problem.”
“You mean all of this is because of that pipe plug?” the contactor said.
“Yes,” said Walter. “That’s why the factory puts that sticker on the shell. It reads, INSTALL VACUUM BREAKER HERE!”
“Who’s supposed to pay for this?” the contractor asked.
“You are,” Richie hissed.
“Why me? I didn’t know.”
“So true,” Walter said. “You didn’t know. So just think of the cost of the new tube bundle and the vacuum breaker as tuition.”
Richie had much more to say once we were back in the Chevy. He got that contractor out of his system and then went back to cursing the other drivers.