circulators and the vacuum created when system is cold and shut down

leonz

Greetings fellow board members,

Since I did not receive a reply from the B+G folks about my question I felt I should ask it here before I spent money on a new circulator.

I have a B+G NRF25 on speed one during the heating season with a steel compression tank.
The circulator has been in use for 7 heating seasons and I am wondering if its time to replace it?

Every time the system is left to shut down for the last two years or when its shut down during warmer weather it develops a huge vacuum of 7 inches Hg.+ that only goes away after the system reached 170+ plus.

One possible clue is the B+G NRF25 doe's not have a flow check and the 225 foot single loop system operates at zero PSIG as its all on one level.

I waddled into Lowes today hoping to find an TACO 007 with a flow check but they did did not have an TACO 007 with a flow check or a separate flow check to buy along with it.

The 2 stocking local supply houses will not be open until Tuesday and I will not be able to find out until then if they have small circulators with flow checks.

The heating system worked fine prior to this so I am thinking that a worn impeller is allowing a vacuum to be created.

One clue is the steel compression tank sight gauge stayed at its normal water level and when I cracked the boiler drain on top of the boiler it hissed and did not spit out any water until the boiler came up to a warmer temperature after I started the coal stoker fire.
While the boiler drain hissed the vacuum gradually disappeared and went back to zero Hg.

I guess $97.00+tax is not a lot for a good circulator- I have had the TACO 007 previous to this on my Buderus Logana G205 and never had an issue with them.

This boiler is the first one I have owned with a pumping away set up with the circulator above the steam chest.

thanks much,

Leon

mattmia2

Is this a boiler set up for hot water or is this a hot water loop on a steam boiler?

You talk about a conventional steel compression tank but then you say something about a steam chest.

Jamie Hall

The static system pressure should not be zero. Even with everything on one level it should be around 5 psi cold.

EBEBRATT-Ed

I wouldn't change the pump. That's not your issue a worn impeller will not cause a vacuum.

You have a pressure issue. Compression tank or water feeder issue maybe. Do you have any automatic air vents in the system. You shouldn't have.

leonz

Mattmia, the boiler is a hot water boiler for hydronic heating a single 225 foot baseboard loop;
Jamie Hall, the pressure has always been around zero as I have run the boiler at 170 high 150 low most of every season; the pressure has gone up when raised the high limit when it gets colder.
The steel compression tank has been operated at the 2/3 water to 1/3 air ratio.
Hello EBERATT-Ed; the water feeder is valved OFF; I have no automatic air vents in the system otherwise it would not work properly.

Jamie Hall

You should simply use your water feeder to bring the system to a minimum pressure of 5 psi cold. That will neatly solve your vacuum problem... and is the correct thing to do...

Robert_25

This is happening because you run such a low pressure at operating temperature.  Turn on the feed water and adjust the valve until you get some pressure in the system.  

I run 12 psi cold in my system, it goes up to 18 psi or so at operating temperature.

leonz

Hello Jamie and robert 25,

I will add more water to the system and report back.

EBEBRATT-Ed

@leonz

12-15 psi on the water pressure when cold. Your compression tank you should fill and bleed the system with the compression tank valved off. When that is done open the valve to the tank. Idealy the tank should be 1/2 water and 1/2 air

leonz

Hello EBEBRATT-Ed.

More food the discussion, in my system I have the following for pressure control/point of no pressure change.

1. Fifteen gallon B+G/Wessels Tank; I am using has a vertical sight glass gauge.
2. B+G Internal Air Separator
3. B+G airtrol valve

The siphon tube extends 2/3 of the way up the saddle tanks height maintaining the10 gallons of water 5 gallons of air blanket in the tank. This is all according to the B+G instructions for the pressure control system for the steel compression tank wherein you open the drain vent until no more water leaves the tank and air begins to hiss out of the tank when you are supposed to close the vent.

When the "heating season is really over" I will add water back to create 5-12 PSIG and see if the vacuum condition comes back.

I almost bought a $7.00 1/8" Maid -O-Mist air vent on Saturday to replace the key vent at the highest point in my system ONLY because it would be easier to vent with the knurled knob that can be closed all the way shut.

EBEBRATT-Ed

@leonz

Yes, you can use automatic vents as long as you close them after venting. But with a compression tank any air in the system should go into the tank. That's how they work

leonz

I under stand that the bleeding vents need to be closed and kept closed, I was just thinking the Maid-O Mist vent would be easier to use.
I wish I still had the original open to air water tank that was hanging in the ceiling when we bought this house as we never had to do anything to heat the house with the hot water baseboard that this house came with.
With the cold weather we are having I doubt I will be shutting down the boiler anytime soon.

Zman

The original tank was always keeping the system at positive pressure using gravity. Because it was open, the pressure could not go negative. Now that you have a sealed system, you need to put positive pressure on it to keep it from pulling a vacuum when it cools off. Why would you wait for the weather to get warmer? Just add some water....

EdTheHeaterMan

Amazing that the system is sealed so tight that it holds a vacuum. Many old systems would not do that with valve packing and the like letting air in. Your system was well built and maintained over the years. Just run it at a slightly higher pressure and you will be fine. 5 PSI cold should be enough to make your gauge happy and your relief valve tighter than a frog's butt underwater. Assuming someone added a relief valve when the expansion tank was converted from open to a closed system. *** IMPORTANT *** YOU MUST HAVE A 30 PSI RELIEF VALVE ***

Mr. Ed

jumper

Jamie Hall said:

You should simply use your water feeder to bring the system to a minimum pressure of 5 psi cold. That will neatly solve your vacuum problem... and is the correct thing to do...

Yes a closed system needs to be pressurized. But someday it may not be for whatever reason. Which is why I recommend that circulators are located below rooftop boilers and chillers. If the circulator experiences too low pressure it will not be happy. Check valve does not help. The OP should be able to hear the unhappiness. If she doesn't then first guess is that her gauge is fooling her.

Jamie Hall

jumper said:

Jamie Hall said:

You should simply use your water feeder to bring the system to a minimum pressure of 5 psi cold. That will neatly solve your vacuum problem... and is the correct thing to do...

Yes a closed system needs to be pressurized. But someday it may not be for whatever reason. Which is why I recommend that circulators are located below rooftop boilers and chillers. If the circulator experiences too low pressure it will not be happy. Check valve does not help. The OP should be able to hear the unhappiness. If she doesn't then first guess is that her gauge is fooling her.

Too right. Circulators -- or any centrifugal pump! -- with too low an inlet pressure will indeed be unhappy. Maybe very unhappy. Which is the real rationale behind the whole pumping away bit.

I've seen a cavitating centrifugal destroy the impeller in a matter of minutes. Not pretty.

leonz

Its supposed to get cold again on Friday so if it gets cold enough I will restart the coal stoker and in between that time I imagine the vacuum will recur.

Thanks for the help,

Leon

hot_rod

your static fill pressure is what fills but also raises the water to the highest point in the system 
.433 X whatever that distance is above the fill gauge.

At 0 psi it would be tough to purge?

ideally a positive 5 psi at the highest point, that is why 10- 12 psi is common.

Also even small wet rotor circs want to see some positive pressure, at least 2 psi static at the circ.

Jamie Hall

A bit stubborn here, are we? Just open the fill valve long enough to put 5 psi in the system. The whole thing will work much better and live longer and prosper...

leonz

I will add water to the system tonight Jamie.

Thanks much all.

leonz

About my my boiler and its vacuum;

After shutting the steel compression tank valve off then increasing the water pressure in the boiler to 5 P.S.I.G. cold and then shutting the water feed off then reopening the ball valve to the steel compression tank I can say after 7 days the boiler and near boiler plumbing have not gone in to a vacuum condition as of tonight.

I will keep track of the system while I wait for the heating season to start anew.


Leon

Jamie Hall

Working more like it should -- good!

GroundUp

Why did you isolate the compression tank when adding water? This is not a difficult theory, please don't overanalyze it. Add water until there is at least a few PSI at the highest point with everything open, and be done with it. Isolating the tank when filling removed the tank from the equation and ultimately dropped the system pressure you'd just added as soon as you reintroduced the tank to the system post-fill.