seized pump--steam boiler hot water loop

dhelmkamp

Recently added a hot water loop to a steam installation to heat a basement space--about 100 feet of 3/4" copper and 25 ft of baseboard radiation. Adjusted to operate at or below 180 degrees, and used a TACO 006-B4 brass pump.

After a couple of hours of operation pump seized. I was able to free it manually by dis-assembling it, but a couple of days later it happened again. Not an issue of dirty water, it
was just internally stuck.

Photo attached--boiler is located immediately to right of photo. This is my first installation of this type--I'm scratching my head.

Thanks
dave

ethicalpaul

That's up pretty high. How does it compare to the water line? For a steam boiler water loop you have to rely on the static pressure of the water to supply water to the pump, so it's a good idea to have the pump like right on the floor.

Also you'd want a nice short path with minimal bends and a reasonably large supply pipe IMO

dopey27177

All the installations I did the pump was put below the boiler.
As was said by EthicalPaul the pump needs some static pressure to keep its prime.

I can see this happening, the boiler water is at based on the steam pressure 212 degrees to 232 degrees on average. Although the the pump is all brass there are different coefficient of expansion of the pump parts. The impeller will expand faster than the body of the pump, as each part expands they will eventually touch and the pump will seize.

All of the piping should be installed at or below the boiler water lines. That area has the cooler water. All the steam in the system is spent and comes back as much cooler condensate. The condensate is mixed with the hot boiler water which lowers the water temperature passing through the pump. The cooler the water the less expansion will occur to the impeller and the body of the pump.

Jake

P.S. mount the pump vertically as is shown in Dan's sketches.

EBEBRATT-Ed

You can't mount a wet rotor pump vertically

dopey27177

The wet rotor pump can be mounted in any position except for having the motor upside down.

jake

pecmsg

dopey27177 said:

The wet rotor pump can be mounted in any position except for having the motor upside down. jake

I believe Lon systems twitch 20 PSI standing pressure!

dhelmkamp

Thanks all--some follow-up:

1) pump height, and tap into boiler, and condensate return, are about 12" below water line. I can increase that to about 24" if I move pump to floor level. Worth doing?

2) regarding pump orientation, Taco instructions read "circulator must be mounted with the motor in
the horizontal position. It may be mounted vertically with motor up if system pressure is at least 20 psi"
So I think I am OK on this one.

3) should I be replacing the pump cartridge at this point, or can I assume it will be reliable if I can get it
operating again?

Where should I look for Dan's sketches referenced above?

thanks,
dave

ethicalpaul

I would lower it yes. I would also have it closer to the boiler with as few bends as possible in the pipe.

Also, are you feeding the boiler water directly to the pump (at possibly up to 212 degrees) or are you mixing it with a bypass from the loop in order to temper the water down to something more reasonable like 180?

If you try to pump 212 degree water, and there is not very much static pressure on the supply side of the pump, the pump will lower the pressure enough there that the water will become steam and your pump won't like that.

dhelmkamp

i will lower the pump and see how it does. it's about 3 feet from boiler, which is as close as I can get. the water temp has not exceeded 180 at any time I was watching it; that's with the mixing valve partially open (see photo).

thanks for the advice

-dave

mattmia2

Side note, gate valves shouldn't be used for throttling, they should be fully open or closed. Use a globe or a ball valve. The threads on the stem and gate don't like the gate fluttering in the flow.

Greybeard

I'm not sure why your pump is seizing, but you should be using a 3 piece bronze pump, not the Taco impeller. I believe Dan discusses this in his article on hot water loops.

That said, more than 20 years ago our oil company replaced a three piece cast iron pump with a cast iron Taco impeller. When the Taco seized I just replaced the impeller, and it has been working fine on our hot water loop for more than 10 years. By the way, a complete pump cost no more than just the impeller.

dhelmkamp

Where can I find that article?

-dave

ethicalpaul

https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

dhelmkamp

So Dan's article recommends a 1700 rpm 3 piece circulator. Is the Taco 110 stainless steel a good match?

https://www.supplyhouse.com/Taco-110-24S-110-Stainless-Steel-Three-Piece-Circulator-Pump-1-12-HP

I have not seen any bronze models in this series.

-dave

Greybeard

Stainless steel should be at least as good as bronze, but you should check with the manufacturer or supplier to see if that pump is good for condensate.

Bell and Gossett has a bronze three piece circulator that is crazy expensive. You should check to see if the flanges are compatible with your Taco flanges. Here is the link: https://www.supplyhouse.com/Bell-Gossett-106192LF-1-12-HP-Series-100-AB-Bronze-Circulator-Pump .

mattmia2

I suppose there is some point of crazy expensive that it makes more sense to make it a closed system with a tankless coil.

ethicalpaul

I’m using a cast iron grundfos, I know I’m not supposed to but it was too cheap to resist trying. I have treated clean water and a screen in front of it. One year, so far so good

EzzyT

I’m my opinion you have the wrong pump installed, it needs to be a 3 piece oil lubricated bronze pump like B&G 100. 

dhelmkamp

Happy to report success after upgrade to a three section pump and lowering of piping. One week of operation with no issues.

Thanks all!

ethicalpaul

To my eyes, that's a nice layout! Congratulations on the successful change!

You might consider a screen at the hot water output from the boiler (prior to the bypass)