Problem with watchman condensate tank

gcp13

Installed new steam boiler on a 2 pipe steam.added a drop header, repiped Hartford loop, 2” equalizer.
after testing,the watchman condensate pump came on to return water to boiler but kept running and didn’t add the water.
After the boiler shut off on low water the condensate pump still running finally started to add the water.
We opened the check valve on feed line from pump and it was clean and working.
We ran the pump with check valve cap off and water flowed out just fine.
We did find a vacuum in the boiler, no crossover trap could be found so we added a vacuum breaker to the top of boiler. But still had the condensate pump running without filling the boiler until the boiler shut off.
Any ideas? the pressuretrol is working and set to 1.5psi. And when the problem happens there is no pressure.
Thanks

ScottSecor

Is your condensate tank properly piped?
https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1344859213284/77277_PROD_FILE.pdf

Is there any chance the tank is empty and the pump switch/float is acting up?

gcp13

The pump hasn’t been touched and is piped correctly.pulled off vent to make sure it’s clear and could see water and float inside.

Jamie Hall

Where, and what type, of vents are there on this system? (I won't even ask why you need a condensate tank and pump...). Unless your vent(s) are the type -- such as Hoffman 76 -- which is designed to hold a vacuum on the system, there should never be a vacuum on the system. That said, I have seen vents which got stuck closed, and I have seen the systems in that case fail to return water to the boiler (or, in your system, the condensate tank). You have added a vacuum breaker to the boiler (steam main side) which you almost certainly don't need -- but how about the venting of the dry and wet returns?

gcp13

we replaced old leaking grossly oversized 700,000 btu weil mclain with a proper 500,000 btu boiler at the last minute,condensate tank is the old existing one. haven't had access to all units to check for vents.if any,they are at the end of mains probably hoffman 75,
i see only 2 small ventrite 35 on drip returns near f&t traps.
i think your rite about stuck vents.a few minutes after boiler shuts off you can hear water rushing back down from one of the ft traps near the boiler..what i don't get is the pump doesn't move water while its running until boiler shuts off, then moves condensate back to boiler.i need to install lower pressure gauge to better check.after the traps at the radiators closed it caused a vacuum in the boiler,when i flushed the lwco no water came out only air rushed in and sight glass water level went crazy.
boiler would probably be fine without condensate pump.

dopey27177

Try this. Remove the master vent when the pump is running. (no steam pressure) if the vacuum occurs in the system water will be held in the piping until vacuum is broken. If you are a real two pipe system (no vacuum) the master vent valve should be installed before the steam traps.

Or a float and thermostatic trap should be on the end of the steam main.

If you have an f&T trap on the end of the steam main the thermostatic element may be broke in the closed position.

This condition will cause vacuum to occur in the piping until the float valve opens to let the water out and break the vacuum.

Jake

Jamie Hall

Oops. Well, there are two pipe systems and two pipe systems. Most -- if not all -- vapour systems (very low pressure) were designed to provide venting by means of crossover traps from the mains into adjacent dry returns. Those dry returns (which also took the return from the radiation) were then vented by one or more main vents located at, or very near, the boiler. In many, but not all, cases there were (and are!) also wet returns beginning near the ends of the steam mains and dry returns, as it was common for the steam mains at least to be parallel flow.

If this was the original design, it is not such a bad idea to make sure that "upgrades", such as adding additional vents, were done with the original in mind; additional main venting in places where it doesn't belong can do far more harm than good, and was sometimes done when the crossover traps had failed.

It's worth noting that a closed crossover (or radiator) steam trap may fail to reopen if there is a substantial vacuum on the return side (or excess pressure on the supply side, which amounts to the same thing).

F&T traps are useful gadgets. They are not, however, a substitute for correct venting nor correct draining of condensate into wet returns.

Pumpguy

Sounds to me like your pump was air bound.
The pump's case needs to be vented of air so the impeller is submerged in water (primed).
Most pumps like this have a copper bleed line running from the pump's shaft seal cavity back to the receiver tank, above the seal cavity.
Some pumps don't have this external bleed line, and rely on internal passages for venting. With this design, these passages are small and prone to clogging.
I would check that the bleed line or passage is clear, and vents air from the pump case and allows water to gravity flow into the case and cause the impeller to be submerged.

EBEBRATT-Ed

I agree with @Pumpguy

Also, make sure check valve in pump discharge is not sticking. Install a pressure gage on pump or pump discharge, check boiler feed line from pump for restriction

gcp13

Thanks for all the reply’s. Check valve is working and clean. Air bound pump sounds good but when boiler turns off on low water pumps starts to move water every time.
I’m leaning toward traps and f&t traps stuck.
Will check out and follow up.
Thanks again

Pumpguy

What is returning condensate temperature, and is tank vented to atmosphere?

If tank is not vented to atmosphere, as condensate is pumped out, the air inside the tank will expand causing an ever increasing vacuum to occur. This vacuum caused by the removal of water from inside the tank will increase the pressure drop across the pump.

This increased pressure drop just might be more than the pump was sized to perform at, in which case it will stop pumping.

If the condensate is too hot, the spinning impeller will cause the water to flash into steam, and stop pumping.

gcp13

No it’s vented and clear. Unit is old and was installed correctly. It’s been a few days and it seems to all be working smooth now.
Not sure if at start up returns were not filled yet or what.hard to get in to see unless people complain about no heat.
Thanks for all the ideas.