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The 25 steps in the repair of a vacuum steam system

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Published
July 16, 2009
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1. Long ago, a Dead Man decided to heat a big building with a steam system. Since it was such a big building, and since pipe, valves and fittings have never been cheap, the Dead Man decided to use a vacuum pump to suck the air from the system. By doing this, he got to undersize every pipe, valve and fitting in that building. He also got to arm a heating land mine for you to step on long after he was dead. If nothing else, this Dead Men had a sense of humor.

2.At the beginning of time, Mother Nature decided that thermostatic radiator traps should last about 10 years. This is because thermostatic traps have these flexible metal bellows that open and close a gazillion times a year. Traps do the best they can, but they can’t last forever.When they die, they usually do so in the wide-open position because this is the position that will cause you the most grief.

3.Mother Nature also decided that most human beings will be either too cheap, too dumb, or too lazy to repair thermostatic radiator traps.She, too, has a sense of humor.

4. Without thermostatic radiator traps the condensate gets hotter and hotter. Vacuum pumps don’t like really hot condensate because they have a tough time pumping it. This is because, in a vacuum, water boils at a lower temperature than it does under atmospheric conditions. Since vacuum pumps produce vacuum (hence the name!), they have a good reason to be concerned about really hot condensate.

5.The red-hot condensate slugs into the vacuum pump, and flashes into great puffs of expansive steam as it hits the pump’s impeller thereby causing the pump to run dry. In a few hours, the pump’s mechanical seal cracks and spews lava-like condensate across the boiler room floor.

6.The building superintendent shuts off the vacuum pump, and opens the bypass line in hopes that the condensate will be smart enough to return to the boiler by itself. The superintendent has no problem making this decision because he sees no need for any system component he doesn’t fully understand. He would bypass the boiler if he could.

7.The condensate now takes its sweet time returning to the boiler. It may make it back by next June if all goes well. Meanwhile, there’s a lot of water hammer in the building, which everyone considers normal. It’s a steam system, right?

8. The boiler goes off on low water.

9. The superintendent curses under his breath, and then adds raw, icy water to the boiler. If he’s a real superintendent, he’ll also convince management they should hire a plumber to install an automatic water feeder. With this device, he figures he’ll have one less thing to do, and the tenants just might stop banging on his door in the middle of the night.

10. The automatic water feeder does its job, maintaining a safe, minimum water line inside the boiler. The boiler continues to run, sending steam up toward the undersized pipes that continue to hold back the condensate. At some point, the condensate stacks up high enough in the system to build the pressure it needs to return. When it does, it floods the boiler.

11.The superintendent curses the automatic water feeder. He drains water from the boiler and goes back to bed. Within minutes, the cycle begins again, and before you can say "oxygen corrosion" the boiler grows holes big enough to toss a tomcat through.

12.You get hired to install a new boiler. Naturally, you chose a modern,highly efficient, low-water-content steam boiler. Thirty seconds after you start it up, it goes off on low-water. The superintendent calls you a bad name in a foreign language and your sphincter muscle begins to do the mambo.

13. You call the boiler manufacturer for help. They send a guy in a suit and he tells you to add a boiler feed pump. He doesn’t explain to you who will pay for this new boiler-feed pump, so you approach management and try to get them to fork over some more cash.

14.Because you are so persuasive, management goes along with you, but only after several weeks of haggling that leave you with an "at-cost"installation. You’re delighted, though, that they’ve decided to stop the lawsuit. For now.

15.At this point, you’re still bypassing the vacuum pump, bringing all your returns directly to the boiler-feed pump’s receiver. But since every pipe, valve, and fitting in the building is undersized, the steam distribution stinks. You, of course, respond by raising the steam pressure. The urge to do this is greater than the sex drive. All this accomplishes, however, is to make the tenants who were already getting heat open their windows. The cold folks remain cold. Finally, you getit through your thick skull that the Dead Man must have had a reason for installing that vacuum pump in the first place. Maybe you should fix it.

16.You squeeze a few more bucks out of management and get the vacuum pump repaired, but you don’t do anything about the thermostatic radiator traps. It was tough enough convincing management they needed that boiler-feed pump. You don’t want to be the guy who tells them they now need to have their traps fixed. Life’s too short.

17. Because the steam traps are still broken, the newly repaired vacuum pump fails after two weeks.

18.You go to the supply house, buy the biggest float & thermostatic trap they have and install it at the inlet to the vacuum pump. You figure that this single trap will take the place of the hundreds of traps throughout the building. You do this in defiance of logic,mechanical history and physics. You do it because it’s cheap.

19.Your BIG F&T does nothing for the steam distribution. Nor does it keep the condensate from getting hotter than hotter. All it does is vomit steamy buckets of condensate into the vacuum pump. The pump screams in protest. You bite the bullet, go back to management and give them the bad news about their radiator traps. There’s no way they can get around it. They’ll have to have them repaired.

20.Five years later, management makes up its mind and listens to your advice. They hire you to do the trap replacement, which you do because you need the money, and because time has made you forget the pain. A good vacuum system repair can be a lot like childbirth - always less painful in retrospect.

21.You start up your refurbished system and learn (to your horror) that when your new steam traps close you’re winding up with a greater natural vacuum on the supply side of the system than the pump can pull on the return side of the traps. Hey, who knew? As a result, the condensate stays in the radiators. It also floods the boiler when it does eventually return. Just as it did before. This bad thing is happening to you because you forgot to add the equalizing line between the vacuum pump and the boiler. You would have known about this equalizer line had you read the instructions that came with the vacuum pump, but no one knows where those instructions are anymore.

22.You get advice from some old-timer, and you add the equalizing line.You try again. As things now stand, you’re returning your condensate to the vacuum pump, which is pulling a nice even vacuum all the way back to your boiler on start-up. The vacuum pump dumps its collected condensate into the boiler-feed pump, which waits until the boiler’s pump control senses a need for water. The controller then starts the pump. Life is good. All seems right with the world.

23.But it’s not. Since the vacuum pump is pulling a vacuum all the way back to the boiler, and since the boiler-feed pump is vented to the atmosphere, the vacuum in the boiler opens the feed-pump’s check valve and sucks all the water out of the receiver. The boiler floods and you’re now right back where you started.

24.You get some more advice from the old-timer. He tells you to add one more component to the mix. It’s a motorized valve, and you pipe it into the discharge line of the boiler-feed pump. The valve keeps the vacuum in the boiler from sucking on the boiler-feed pump’s receiver. When the boiler’s pump controller calls for water, it signals the motorized valve to open. The valve opens, trips an internal end-switch, and starts the boiler-feed pump. Just enough water enters the boiler, and everyone’s happy again. The traps work. The vacuum pump works. The boiler-feed pump works. The system works.

25. You get paid. With your pint-size profit, you buy as much beer as you can.