Steam Boiler

Unknown

Unit Heaters or coils usually need 2 PSI at the inlet coil unless the manufacturer says different.

That is why I said set a 3 with a 1 lb differential.

Look for the check valve that equalizes the steam & return piping

Jake

Donald

Losing Water in Steam Boiler

I'm having a problem with a commercial steam boiler. About 6 weeks ago the boiler was short cycling and would not maintain pressure. (Boiler was set to run between 5-7lbs.) When the boiler reached 1-2 lbs, the water level was dropping, it did not look like it was surging, just dropping, even after the condensate return pumps would start, the water level still continues to drop. The boiler goes off on low water, the pressure drops to zero, and the water that has left the boiler into the supply system begins to return to the boiler. (The water is not leaving through the condensate return line) The boiler continuously ran through this cycle for several hours, and then the problem went away. The boiler would now operate between 5-8 lbs, there was no problem with the water level. All I did was blow down the boiler several times and open and close the main valve. (The boiler ran without any problems with the valve closed)
The problem started again about two weeks ago. We drained the boiler, same problem. We drained the boiler, condensate return tank and vacuum system, chemically cleaned the boiler. The boiler worked for one day, the problem was starting again the day after but not as severe. (I can maintain the boiler between 5-7lbs.) The water level is still dropping in the boiler and I'm not getting heat to all the air handlers and radiators.
I also, at times have pressure in my return line; most of the traps are F&T. What would be the best way to check if the trap is working correctly? (Unable to achieve a vacuum)

Donald Barrette

Tony Conner

Does The...

...condenate tank overflow when the boiler is tripping on water?

Donald

The condensate tank overflowed several times per day.

Unknown

Boiler water loss

in a vacuum system can happen several ways.
Need some imformation.

Is there a zone valve for the building?

If you a zone valve exists depending on the size of the zone valve 5- 10 psi is ok as long as the zone valve operates with the heat panel in conjunction with the oitdoor temperature and indoor temperature sensor.

If the building does not have a zone valve and operates on a Heat Timer or similar control reduce the steam pressure to 3 psig with a 1 pound differential.

When the boiler shuts down and steam condenses in the system a vacuum is formed. If the steam piping and return piping do not equalize water can be sucked up into the steam side of the system thru the boiler equalizer.

Some place in the building there is a 3/4" or one inch check valve cross connected between the return and the steam main. That check valve is placed to allow the system to equalize. the check valve is installed to prevent steam from enterin the return and allow a balance or equal vacuum on both sides of the system.

Usually the the natural vacum that occurs in the steam main is greater than what the vacuum in the retrun side.

Find the chek valve and replace it.

If you have a zone valve in the system install a steam vacuum breake at the to of the boiler. You do not want vacuum in the boiler.

Jake

Unknown

OOPS

I missed this about the condensate tank over flowing.

When the water gets sucked up out of the boiler the water make up valve will replace the lost water.

When all water returns to the vacuunm pump and condensate tank the tank will overflow.

Need more info.

What kind of system is it? Manufactures equipment and temperature controls.

Steam traps come later.

At 5-8 lbs the returning condensate will be over 180 degrees.

You will have cavitation problems with vacuum pump.

First find and fix the problem associated with the boiler. All else may fix it self or you will need to replace steam traps.

jake

Donald

Thank you for replying;

The building is a four story building with approx. 5 air handlers/floor. Each unit has it's own zone valve.
The system is a 2 pipe system with a vacuum return.The vacuum system is less than one year old.
I have replaced the vacuum breaker on the boiler.
I was brought in on this prolbem about six weeks ago. They said the boiler always ran between 5-8lbs.
I agree with that we should be able to run this system between 2-3lbs.

Unknown

OOPS

Look at the manufactures installation instructions.

It should show where you need to put the check valve to equalize the vacumm on both sides of the system.

Jake

Tony Conner

In Higher Pressure...

...industrial systems, I've seen people install pumps to push water into boilers that have been selected so that their discharge pressure is the same as the boiler operating pressure. This, of course, always works badly, as no pressure drop, no flow. The boiler worked OK on low loads, as the pump could keep up. As soon as the load hit, the pump couldn't push enough water into the boiler, and a low water trip was the result. The condensate tank overflowed because the condensate just drained, or was pumped back to it from the rest of the plant. Since the pump that was supposed to push the water into the boiler wasn't making the cut, no water was leaving the tank, so it overflowed. Once they installed a pump with enough oomph to get the water into the boiler under all operating conditions, everything worked fine.

Jake knows way more about the specifics of this kind of system than I do. But I think you either need to get a pump with more discharge pressure, or drop the boiler operating pressure. Dropping the boiler pressure is likely the right thing to do. As soon as you drop it, I suspect you'll find out why those that were there before you jacked it up. (Likely an attempt to correct some other problem in the system.)

Donald

The main steam line in the building is 30-40 years old. The boiler is a Weil-Mclain cast iron sectional boiler. I could not read the model number. Input of 1,632,000 BTU. The boiler looks to be between 10-15 years old.
The steam main leaves the boiler room and eventually branches off to several different lines. On a system like this, I don't understand where there would be a check valve between the main and return.
As far as the pressure setting, I think any time they had a problem they just kept increasing the pressure. I will work on lowering it.

Donald

At different times under a large load, when the boiler is operating correctly the condensate return pumps had no problem keeping up with the damand. They would only run for a few seconds to satisfy the float. The boiler never came close to going off on low water. When the boiler is not running correctly, the water leaves the boiler at a very fast rate. I would guess that it takes only 5-10 seconds for the water at operating level would drop to 2-3 inches below the automatic shutoff.

[Deleted User]

Get the

manufacturer's name from the vacuum unit. Call or e mail them and ask for the recommended piping schematic. That will show you where to install the equalizing line w/ the check valve.

It is probable that the high pressure, combined w/ leaking traps, is raising the condensate temperature over 170 degrees. If so, the vacuum pump will cavitate, and not do what is was intended to do. Reduce pressure & check traps.
Also check condensate storage capacity w/ boiler condensate production capability. Recommended capacity is at least 20 minutes of boiler discharge rating. More is better.

Don't like that when the condensate pump(s) is working properly, water line is satisfied in a few seconds. Properly sized pump(s) should provide the required water to the boiler w/ 20# pressure in the pump discharge line. That normally results in a fairly long "pump on" time. Short cycles are bad on motors and can create problems associated w/ a lot of water returning to the boiler too quickly. Compare the boiler horsepower and pump size w/ a knowledgeable wholesaler. You might also want to check that the discharge line is piped properly.

Sounds like you have a bear by the short hairs. Or vise versa. Good luck.