Partially draining hydronic system to work on plumbing

gliptitude

I have a hot water heating system with threaded black pipe and cast iron radiators. I have done a bit of work on this system in the past to get it working after past freezes, replacing and eliminating sections of pipe and radiators.

I'm trying to open up two pipes that are currently capped in the basement and I want to know how to determine the least amount of water to drain.

There are no valves to isolate these particular pipes and there is a minumum number of valves in the system.

Being in the basement I would think it would just drain all out if I opened these pipes, but I heard otherwise a while back and was told I drained a ton of water beforehand unnecessarily on a previous occasion.

The purpose of my work today is to install valves at the end of these pipes so I can more easily extend them later on to a new radiator without draining. It is warm today so I don't need heat and I have a little bit of time.

Jamie Hall

How wet can you tolerate your work area? If you are quick at your work, and this is threaded pipe, and don't mind working with a bit of a fountain, you may be able to take those caps off and slap on a new valve without draining.

gliptitude

Heh, it wouldn't be the end of the world if I messed the area with water but I'm afraid I won't get the work done acceptably in such a hectic scenario.

In other previous ridiculous scenarios where I was testing experimental repairs to cracked radiators, (which held water fine until I fired up the boiler), the water didn't all drain at once or ever drain completely. That wasn't in the basement though.

STEVEusaPA

Get the water going out a hose from the boiler drain, pull a little vacuum, open cap get a swet-jet in there, then spin on a ball valve...repeat for other pipe.
Someone else mentioned before (I think Alan) about using the device that freezes a small section of the pipes.

gliptitude

swet-jet, interesting. I don't have one though.

Would it help or somehow hurt if I turn the fill water supply off?

Jamie Hall

If you don't turn the water supply off, you're going to have an ocean rather than a lake...

I think I'd resign myself to partially emptying the system and purging when I got done...

gliptitude

Jamie Hall said:

I think I'd resign myself to partially emptying the system and purging when I got done...

Yes I figured on partially emptying I just don't know where to draw the line or how to tell.

If I close the fill and open the drain could I maybe just start working and experience a more manageable flow?

JUGHNE

Fill valve off.
Isolate exp tank if possible.
Drain valve open.
Pressure should drop.
If you have a pressure gauge that also shows altitude in feet that would be the height of the water above the gauge.
Being in the basement your pipe might be only 7' above the gauge.....hard to read on a probably not completely accurate gauge.


IIWM, after dropping the pressure I would loosen the caps to where the dripping is tolerable, dope the exposed threads, dope a little into the valve threads.
Someone holding a bucket for the pipe water to shoot into and then run down to another bucket on the floor will lessen the mess.
Open the valve, remove the cap and get the threads of the valve started on. Then close the valve. It is easier to start threads with the water running thru the valve than you fighting the pressure.
FWIW

gliptitude

I was able to do get it done. There was suprisingly little water that came out. Filling back up and bleeding air took a little while, but nowhere near the time to fill from empty.