Insufficient pitch + Autofeeder and /or LWCO = Overfilled boiler?

delcrossv

Now that the MIL's 4 flat is running well (thanks everyone!), her 2 flat is having issues. It's a parallel flow system with almost nonexistent pitch to the mains. She had the boiler replaced a while ago and the new boiler has a probe LWCO and an autofeeder.

Seems that when it runs the level drops enough to trigger the autofeeder, and then when the condensate finally comes back, the level is higher- a few cycles and the boiler is overfilled. Oma stops by and drains the excess water- lather, rinse, repeat.

Not looking forward to repitching the mains, so wondering if there was another fix. LWCO seems set to trigger with an inch of water still visible in the glass. too soon?

I'm familiar with the float type, but how do you set the cut in level on the probe?

Jamie Hall

The LWCO is in the right place, and you can't adjust the level on a probe. What you can do on most autofeeders is adjust the delay between the LWCO calling for water and the feeder actually doing anything about it. Most likely some combination of dipswtiches inside the feeder. Check the manual for your particular feeder.

delcrossv

@Jamie Hall It's a Hydrolevel VXT. I'll set it for 10 minutes and see what happens. When i tested it today, it had a very short delay
Thanks!

EBEBRATT-Ed

@delcrossv

make sure the delay isn't so much the water level gets too low.

If they are not getting any banging due to the lack of pitch first make sure the system is not going into a vacuum which might hold up the returning condensate.

Then the fix might be a surge tank installed at the boiler water level. Some of the boiler MFGs have a drawing that shows how to install one. Weil Mclain I think

delcrossv

@EBEBRATT-Ed 2 new vents, so I don't think vacuum is the problem, but I'll crack one to make sure. I'll be there to time it and add water if necessary.

I'm liking the surge tank idea, So not a pumped condensate tank, but just additional water tank? All the "surge tanks" I;m seeing have bladders etc.
Thanks!

JUGHNE

How about the return lines? If you have wet returns it is possible they are sluggish.
High returns (end of main or dry returns) probably have no flow problem.

I would check that piping first.
As Ed said if no water hammer, the mains must not be retaining water.

And of course you could always post pictures.

delcrossv

No wet returns, usual loop main with EOM venting. 
Pressures really low and we already replaced a rotted section, so I'll bet there's water there. I'm going over there today so I'll have more to report.  
I reset the autofeeder counter- it was at 300+ gallons, so something is going on.

Jamie Hall

Couple of things. First, the delay shouldn't affect the low water cutoff operation. If the water is low, the cutoff will still operate to shut off the boiler. What happens with the delay in the VXT is that, having received a low water signal. it starts to think about adding water -- but if the water level returns during the delay, it cancels the demand rather than adding. Nice feature.

What is meant by a surge tank is just a steel tank which is centered at the boiler water line and which the wet returns feed into, and from to which the Hartford Loop is connected. It is also connected to the boiler header, to equalize the pressure with the boiler. It is NOT vented to the atmosphere, and it MUST be centered more or less at the boiler water line to work effectively. Probably don' need it...

JUGHNE

(sorry about the wrong rotation on the second picture)

This is custom built surge/accumulator/reservoir "tank" to provide more water for the boiler to work with. (don't call it a tank....it is just a large piece of pipe).

It was fabricated from 5' of 6" SCH 40 steel pipe that was part of the old boiler header.
It is centered on the water line of the boiler with steam connection on the top and return on the bottom.
The far end has a cleanout nipple/cap on the top for flushing.

As you can see it is fairly involved to build and install.
I would try the time delay set up first.
If the water feeder is a VXT, there are a lot of delay options and amount of water added.

This is one of the few places where a Cyclegard LWCO may be helpful.

delcrossv

@EBEBRATT-Ed wins it. Closed rad valves that still passed some steam plus clogged vents kept GALLONS of condensate in the rads. 8 new vents and it all came down. Condensate return is still slow, so reset the VXT from 30 seconds to a more reasonable 6 minutes. 

EBEBRATT-Ed

@delcrossv

That's good but too much make up water will kill a boiler so keep your eye on it

delcrossv

@JUGHNE What a great idea, particularly with the new low water content boilers. At this location,  it'd be an easy add if necessary. 

EBEBRATT-Ed

page 23 is surge tank details

delcrossv

@EBEBRATT-Ed Awesome! Thanks!

delcrossv

EBEBRATT-Ed said:

@delcrossv

That's good but too much make up water will kill a boiler so keep your eye on it

No kidding!

312 GALLONS since last reset when tech replaced LWCO to "fix" problem (say a year? that's just nuts!)

12 Gallons since yesterday

0 gallons today after replacing vents (one LONG cycle)

MIL is stopping by tomorrow, so hopefully it'll stay at ZERO.

JUGHNE

This is a bad attempt at the accumulator.
This is a compression tank for an older type of

hot water system plumbed in.
The bottom port is connected to the return, but the top is not connected to the steam pressure.
So it just sat there with some water in it, not moving.

This was removed and after improvements on the steam system, it was not needed.
But it did nothing anyway.

This tank would work but has limited ports of only 1/2". Easy to sludge up and not very cleanable. Also is a true "tank" which is not ASME approved for steam.
Although it would have been used for 30 PSI water systems.

The next two pictures are of a probably oversized accumulator connected to a 500,000+ boiler.

The Hartford loop is connected into one end of the "tank" (second picture).
The equalizer of sorts is connected into the top of the tank.
The two bottom connections of the tank are connected directly to the boiler inlets.

It takes 95 gallons to fill the boiler and tank.

delcrossv

SUCCESS!! After 24 hours run time, water level is in the middle of the sight glass and added water off the VXT is ZERO! (a lot better than 12 gallons on one day!)

Thanks everyone!