Low water cutoff Blowdown valve

Uthrid

First time posting to the wall. Been lurking for a while and have absorbed more information on steam heat systems than I thought I ever would. All it does is make me want to learn more about my system.

Anyhow, on to my question. I have a McDonnel Miller 67 LWCO on my boiler and the blow down valve seems to have siezed at some point in the past. The folks previous to us removed the handle and put a socket wrench on the body of the ball (packing nut?). This allows me to turn it and blow down the rust and sediment from the LWCO, but getting the valve body closed off is a balancing act. Tighten too little and it drips, tighten too much and it also drips.

My question is would I be creating a problem in my system if I put a new brass body ball valve below the LWCO valve and just leave the LWCO valve open? I don't particularly want to shell out $100 to replace the MI1015 valve, but I will if my other method will create any issues. The ball valve I am looking at has a temp rating of 400°F and 600PSI.

Thank you.

Jamie Hall

Should work just fine.

JUGHNE

That is commonly done.
Just be sure that the boiler is firing when you do the test and that it shuts down the burner during the test. It should fire back up unless more water fill is needed.
This is the most important part of blow down.

Also flow enough water to clear the bowl and avoid junk as you close the valve.

Chris_L

My McDonnel Miller 67 LWCO is so old it doesn't have a ball valve. The original valves weren't very good, and you used to be able to buy a square fitting with a 3/4" female tapping to install your own valve after removing the original. I am not sure if they are still available.

As @Jamie Hall says, your idea should work fine. I'd suggest a male x female brass valve. The cheapo Home Depot steel nipple I bought with a female x female ball valve rotted out after a few years. I found this out when I went to blow down the LWCO, and ended up with the valve in my hand as the boiling water drained out, overfilling the bucket I used for the blowdown.

EBEBRATT-Ed

a brass nipple and a ball valve. The prices M/M get for parts is $$$$$

Uthrid

Thank you all for the replies!

Motorapido

The original ball valve on my MM LWCO was allowing a few drips of water to escape each day. As a suspenders-and-a-belt type of mechanic, I figured why not leave that original valve in place and just add another valve to the original. The original valve terminates with a female threaded boss, into which I screwed the male threaded end of the new valve. Now, when I do a blowdown, when I open the new valve, an ounce or so of water drips out, which had escaped the aging original valve. I open both valves for the blowdown, shut the original valve and then wait to shut the new valve until all dripping has stopped. So now, if the new valve malfunctions, my backup is the original valve, which barely leaks.

Hap_Hazzard

Aren't you supposed to replace those MM float-type LWCOs every seven years or something?

ethicalpaul

Yes, 10 years

Uthrid

Good info all around. My cutoff still shuts off my boiler when I blow it down (weekly on Sunday). I don't know when this was installed, so if it is in need of replacement, any recommendations on where to get a new one? Should I look for the same LWCO or is there a better solution available?

Thanks!!

Chris_L

Uthrid said:

Good info all around. My cutoff still shuts off my boiler when I blow it down (weekly on Sunday). I don't know when this was installed, so if it is in need of replacement, any recommendations on where to get a new one? Should I look for the same LWCO or is there a better solution available?

Thanks!!

If your boiler is shutting down as it should when you blow down the LWCO, I wouldn't replace it even if it is older than 10 years.

Yes, that is the manufacturer's recommendation, likely written by their lawyers for liability reasons. It is not like they are going to turn into a pumpkin or suddenly fail when they reach 10.

I have a couple of these, both 35+ year's old. They ain't broke. I ain't fixing them (or replacing them). And as long as they work when tested, I have no reason to believe they won't work when needed.