Pressure Issues

[canoebuilder]

If JackRafter is useing only one "Automatic fast fill", pre-set for say, 19 psi, shouldn't both boilers, when cold just reach this point and stop?
and then as you say LP, when one or the other heats, should they not increase at the same rate it all being a closed loop with just 2 boilers in the system???
Gerry
PS...Maybe a bad guage on one or the other boiler??????

[JackRafter]

CB,

I believe the gauges are working correctly, but I'm give them another check to make sure.

The point about the closed loop is interesting to say the least. If you look at it the loop is closed at the AFV and if that's the case then both boilers are on the same loop. Hence the point of my question.

[canoebuilder]

A closed Loop system, in Layman terms is simply a boiler system that can is filled with water and or anti-freeze (as many people in the North does) and it is isolated from the other plumbing from the house with either valves, backfloe preventers or physicaly cut pipes.
I run 2 boilers in my home, one a large wood fired boiler, used in winter and the other a smaller gas fired boiler, used when we go away for a few days or more.
I have on the water feed line, from the potable water lines this set up....
1 an isolation valve, which after boiler is full I close to insure against over filling if ATF fails. I then check water pressure regularly
2 a D9 Watts back flow preventer
3 a ATF set for 19 lbs
4 another valve....if ever need to replace one of these parts can shut off valves and replace without draining heat lines.

Both boilers have gauges and both read 19 lbs when cold, but I manually hold ATF open to attain 22 lbs, this aids getting water to upstairs.

When either boiler heats the water in thier boilers the pressure will raise in both boilers to 28 lbs...BOTH THE SAME.

I know of no way to check the valves unless they are checked on the same system with the same pressure and it sounds like this is just what you have now and one is not the same as the other.?.?

If I have your set up, in my minds eye correct?

Gerry

[LazyPup]

Based upon all the information that has been presented I would suspect that the gage on the second boiler is about 8 to 10psi out of calibration.

Consider the facts:
If the boilers are on separate loops, and further assuming that the feedwater check valve on the larger boiler is allowing some back flow to the smaller boiler, at best the pressure in the smaller boiler could only go to equilibrium with the larger boiler. There is no possible way that it could cause a 10psi increase in the smaller boiler.

If the boilers are on a common loop the pressure would always remain equal in each boiler.

It was also previously stated that when the larger boiler is firing at 22psi the smaller boiler pressure goes in excess of 30psi. A hydronic boiler T&P valve is factory set to discharge at the maximum allowable working pressure of 30psi. On the other hand, even though your gage is indicating in excess of 30psi, there is no mention of any water being discharged from the safety valve. This would lead me to conclude that the problem is in the gage.

In addition, both boilers should have a "high pressure cutoff switch", which is set at the maximum working pressure of 30psi. If the pressure in the smaller boiler was in fact exceeding 30psi the high pressure cutoff would prevent the burner from firing.

I would suspect that if you were to remove the gage on the smaller boiler you will find that it is reading 8-10psi instead of zero when laying on the bench.

[JackRafter]

So let's circle around to the original question. . . Should these two boilers for starters be on separate supplies or it doesn't really matter?

[canoebuilder]

NO ....is the simple answer to the above question.
Gerry

[JackRafter]

Gerry,

Thanks. So far I've had three other plumbers say yes. . . . , you say no and LP avoids answering any question directly. . .

I think for starters I'll check the gauges simply by swapping them. If one gauge is found to be defective, I'll change it. Then I'm going to put the boilers on separate feeds simply because this will with out doubt put them on their own closed loop.

[LazyPup]

The statement that I have avoided answering your question directly is totally false.

If you will go back and read my responses you will see that I made the following comment:

"Providing that both boilers are of the same type and operating at the same maximum working pressure there is no problem with supplying them from a common manifold and feedwater pressure control."

If you are asking me if I would personally operate multiple boilers from a common feedwater control the answer is "NO", but then I was trained in firing high pressure steam boilers where water level conditions are critical and when firing live steam you become paranoid about water level. Such is not the case with circulating hot water boilers.

[JackRafter]

LP,

Now don't you think your latest reply is a bit semantical?

Considering you gave the two opposing answers (no & yes)for the same question only differentiating it's presentation

Thanks anyway.

[LazyPup]

If you are asking will it work, the answer is yes. Is it okay to hook it up that way, again the answer is yes, providing both boilers operate at the same pressure.

On the other hand, If you are asking if I personally would hook feed water to two boilers with one feedwater valve the answer is, Not NO, but HELL NO!