two pipe steam trouble

Unknown

Fix both pumps, then notice the excessive temperature of the water (and vapor) entering the pumps (which is likely what they died of), and find the bad traps in the system, and fix'em.




There is a certain minimum amount of maintenance required on all steam systems, weekly and periodically. Steam traps usually find themselves in the periodic category. Unfortunately, periods can be quite long, and viewed as an "all or nothing" venture. They get deferred frequently. There can be other alternatives to this, however.

There is nothing as easy as deciding to change every single trap and calling it cured, except not doing anything. Those are usually the two choices presented. The third choice is pretty labor intensive. It involves identifying exactly what is installed in the building, what is wrong with it, what it would take to fix it (broken down in stages), and what order to do it in, and what each stage would accomplish and cost.

This would chip expectations down to manageable and budgetable projects, and might give incentives to combine steps where it would save money to do so. It would help project for future budgets what the actual maintenance costs are on a large building with a seventy five year old heating system. It would maintain fuel consumption at predictable levels.

It would show how thrifty it is to keep up with steam trap maintenance. I'd like to help discover how to do this in layman’s terms. My experience is with four story brick residences with various vapor systems from 1910 through the 1960s. These were mostly two pipe vapor systems.

The very first thing to do is to identify the individual steps in an outline form that will bring the system back to working properly. Identify the system from trap names, unusual items in the returns or near the boiler, supply valve names, something to date the system with. This helps a little. Identify the height above the boiler water line to the lowest horizontal piping in the whole system that is above it. This is a B dimension, and is most important if there isn't a vented condensate tank or boiler feed tank. It defines what pressure the system was meant to be run at. Identify what vent is on the system and if it works, and at what rate it vents.

The first thing to address on the outline would be venting, as it has the biggest payback to cost ratio. Simply size the vent properly for the load and pipe lengths, and make sure it vents when it is cold, and it shuts when it gets hot. Make sure it is back from the end of the main about a foot or two, or more. It can even be right after the last radiator connects to the return main. There is likely to be a crossover pipe between the supply main and the return main there, with a radiator trap as the union and elbow on the return end. This is the supply main's air vent into the return. This flow is from supply to return to air vent. To keep the air and condensate all flowing the same way, the vent will be downstream and downhill from this crossover connection.

The next item on the outline will be to crank the pressure down to the pressure just above what it takes to get the main air vent to close. Identify that the control on the boiler might eventually need to be replaced with the one required to run this particular system at the design pressure. More on this later.

The next item to successfully tame the system is going to be insulation on all of the pipes. It simply must be in good shape to deliver all of the steam that they were designed to carry. If the steam condenses within the mains, the cross section of the pipe becomes reduced and the mains cannot carry the steam that they need to at reasonable velocities. The speed picks up and the water starts flying around, the noise goes up, the cost to run goes up, the vents and traps get hammered into little crumpled balls of metal inside. The insulation is mandatory. The mains are actually TWO pipe sizes too small, if the pipes are bare.

Along with insulating, the boiler piping must be right before the insulation gets applied. The first thing to do is to determine what the boiler needs to do, and if it will. We finally have come down to measuring the load connected to the boiler, and the size of the boiler, and to actually verify the firing rate and combustion efficiency. A filthy oil boiler that had been downfired beyond reason won't show up from a peek at the rating plate. It might make sense to look at the boiler size itself and it's piping, and start from scratch. It might be fine. Be sure the boiler piping matches the manufacturer's instructions, to the letter. Undersized piping might be the problem. Now is the time to decide.

If you have come this far, and have a working system to evaluate the steam traps with, you can move to the next step on the outline. You need a trap survey; a document that you make that shows what each trap model number is, and what room it is in. You need to group them by which branch of the RETURN main that they empty into. The return mains are groups of traps to be maintained and troubleshot as a group. It helps to begin thinking of them that way early. Along with this list of traps, a piping plan would be wonderful. These documents should be filed in a way that they outlast you on the job.

Once you have identified a return main, and have the steam pressure cranked down as low as it will go, start the system up cold and see if the return main becomes steam hot at the vent, up on this end of the return. Since only air is supposed to be there, and cooler condensate, it should remain open and not be steam hot. If it gets hot within minutes, you have a trap blowing steam through. On a system with working steam traps, and on ALL pumped condensate systems, the vent isn't needed. It only sees steam if a trap lets steam through. An open pipe could serve as the vent.

Take it out, if it isn't too much trouble, while you troubleshoot. It will speed up the whole process. The way that we are going to discuss checking traps isn't the only way, by any means. My focus is on cost of materials, but admittedly it is very labor intensive. This isn't developing a free estimate for repairs, this is actually a very valuable part of DOING the repairs, and should be thought of this way. The reason for the trap survey in advance is, in part, so that some repair parts for traps can be brought in and kept on hand. This enables repair as the testing evolves.

The premise of this method of testing is to follow the steam as it expands into cool piping in the supply mains, and detect, by external pipe temperature, where the traps let steam pass through. I started by using my hands, but years later, infrared thermometers with laser pointers came along, and they cut the time in half.

Start up the boiler until you detect steam in the returns someplace. Shut off the boiler and follow the hot pipe back to it's source. You'll get near it easily enough; close radiator valves off to eliminate their traps; identify how the steam is blowing into the return. Shut the boiler off often because once everything in that return main becomes hot, the information to be gained is very diluted. Keep everything cool, and squirt steam through by firing the boiler once in a while to keep the path hot. This is more art than science.

After the return main stays cool, because all of it's traps are fixed and holding, or shut off from steam, open up radiators one at a time with the steam on. As you open a radiator, check the return for live steam. Condensate dripping into the return will warm it up. Steam blowing into it will make it a blistering 200° F plus, right away. Shut those back off. Mark those for repair.

Here's another note. On a return that you know has steam blowing into it, shut the boiler off with hot mains, and let the vent pipe draw air in until it stops. With all of the radiators and valves open, start up the system again. As soon as the system vent pipe gets hot, go through the building and find HOT HOT traps on radiators that have COLD or cool sections right next to the radiator trap. This will tell you two things. One, there is obviously steam in that return. Two, THIS TRAP IS WORKING!!! It won't let the air from the radiator into the return, which has an open vent on the other end. It is keeping the radiator from venting. Write this one down on your trap survey as good. Look for more. Cool it down and start it again. Check again. Shut some off in a pattern that makes sense along the return, to determine where the steam is moving around. Some of the radiator valves won't hold steam all the way off, but that's OK. As long as the radiator condenses what it does get, and the last section doesn't get steam hot, you'll be OK. The room will use that heat, anyway. It's temporary. Leave off whatever it takes to keep the returns from having steam in them. For temporary heat, crack open radiator valves to allow half the radiator to get hot, but NOT THE TRAP!!!! Fix the crossover traps and the F&T traps on the mains. Get your vent to be cool while the system runs.

Now make a list of the traps on radiators that are shut off. These are what you need to replace. Leave the radiators with bad traps off in the meantime, or mostly off, to save the remainder of the working traps. Budget your replacement costs, but remember that more will fail as time passes. It will often be fewer than expected, though.

Now that the system is tame, and half shut off, the boiler waterline will be pretty wild, due to overfiring. Get the traps fixed to get the load back on the boiler, and troubleshoot from there. Have a very clean system with clean water. This is a whole different subject, but very important.

If the system floods after it runs, or if it runs out of water and shuts off, suspect plugged returns that are below the water line. Don't waste any time on them, replace them. Pipe them so that you can remove an air vent and flush them with a hose to a drain valve that you put in at the boiler end. Use mud legs to collect debris.

Once you get an intimate knowledge of the system, a loving pat on the air vent while it's running will tell you if you need to check your traps again. It should run at virtually the same temperature all of the time, a little hotter in very cold weather.

If you want real economy, buy a vaporstat that operates from 0-1 PSI, and is graduated in ounces. Install it at the boiler, or even better, at the end of the steam supply main. Wire it to break one leg of the thermostat wire through it, and leave the pressuretrol as is, as a high limit. Set the vaporstat as low as you can and still heat every radiator.

All of this would be done with the service person AND the weekly operator. The more involved with the system that the operator becomes, the more known and less costly will be the maintenance plan.

Along the way, you'll both learn the system. You'll find that return that's ALWAYS hot, no matter what. It'll drive you nuts, looking for the cause. Eventually, you'll find the crossover trap in the wall at the end of the main in the finished basement. It'll be behind a wall hung radiator.



You'll find the F&T trap that works, but it has a 3/4" bypass around it with a very painted plug cock in it; wide open.

You search the building and find two more. Guy's have been rebuilding these traps for 90 years, yet the bypasses never were closed. Originally, this system made heat and electricity by coal, the bypasses are from those days.

I want to close with a story. It is very relevant, and it was costly. It was a four-story residence, and the bottom floor was four feet in the ground. The returns ran around the bottom floor ceiling with the supplies, until they were pitched down to a point 30" above the floor, then the return split into a high and a low return back to the boiler room, the same on both ends of the building. The west end had steam in the front return, as a door on the ends of the building split the returns into a back and a front on each end of the building.

This front, west return had steam in it near the boiler end, the low end. The rooms all had thermostatic radiator valves on the radiator inlets, so each had control. The front door entry was always cool, and the radiator always hot. The next room had his thermostat off, because his room was hot enough, and the trap was hot and the radiator burbled steam into it through this hot trap. The radiator would fill with condensate until the system satisfied, when everything would cool off and drain back to the boiler. He opened and closed his window for temperature control.

The next room had the same hot trap and shut-off thermostat, but he was roasting. He NEVER closed the window. He went away every chance he got. One weekend when he was away, it was very cold. The whole weekend never saw above zero temperatures. The guy in the end room by the door called for no heat. Even with the valve open, no heat would come from the radiator. His walls were FREEZING. The hallway wall, the entryway wall, the outside wall, and the room next-door wall.

The radiator was full of water. No steam could get in. Draining it by shutting off the boiler got the radiator to heat but the room didn't heat well.

The wall to the next room was freezing. Uh - oh. In the maintenance guy went, to check on it. Everything was frozen. Bottles on the dresser had broken. The window was open. The radiator had exploded. He shut it off, shut the window, left the door open and went to call in some help. He was gone for a short while.

The frozen and split 1" sprinkler had thawed out while he was gone. The whole time he was gone, a 1" sprinkler pipe filled the west half of this building. About 11 people lived in the lower level, and they were displaced. The water was a few feet deep. Several people on the next level were also displaced to hotel rooms, until the building was renovated.

The steam traps were repaired right away. The rooms were comfortable, after that.

M. Klenck

Water sucking out of steam boiler

I recently installed a burnham V-88 in a local resturant. System is two pipe steam. Most of the piping is in an old part of the building, the last two boilers have been located in another basement. The two joining via wee little crawl space. When I fire the new boiler within two minutes the water falls out of the sight glass and the lwco kicks off. The boiler tries to refill itself. If, durring this period I open the skimmer valve the pressure drops and things seem to equalize and the water rushes back into the boiler, and we begin again. There are two zone valve, one for each side of the building. They are not used anymore and are both manually open. The water seems to be going up the suply towards the other basement because those pipes get warm.(not hot)
Now on the old side of the cellar there is a condensate pump. Yesterday I realized that this pump isn't working. So question #1 is, would this pump not working cause the water to suck out of the boiler. Also when the system locks up there is enough vacum that I can open a ball valve below the water level and nothing comes out until I open the skimmer.
To paint the picture alittle more, the boiler that I took out had three sections rotted out on top. Too much fresh water? I belive this problem has existed long before I was hired to replace the rotten boiler, but now it's my problem and the owner is holding final payment until he has heat. Any help or ideas would be great.
One more thing, there is another pump right behind the new boiler, which also doesn't work.
I can attach a diagram if needed.

M. Klenck

thanks

Thanks for the info, although that's alot to soak up for someone who has only replaced a half dozen steam boilers in 10 years and hasn't ever dealt with two pipe systems until now. But I think I can push through it now. Up here in the catskills I can't find anyone who really knows what they're talking about. thank again.

tim smith

Thanks Noel for the detailed description.