Ounces of steam?

Warsaw

Hello all - here's 2 basic questions on venting: I purchased the "Balancing Steam Systems" pamphlet and have been measuring my mains, runouts, etc. to figure out how much air (roughly) I need to push out. First question - when measuring, how do I account for the run of pipe between the main and the actual point where the individual runouts branch off. For example, I have a branch off the main of 1 1/2 pipe that goes about 4ft before the first radiator runout, then another 6ft before the second radiator runout. And what about fittings? Should I just round up on everything? I know it's not an exact science, but I'd like to get the right thing if possible. Sort of seems like Gorton C's are the way to go, but...



Second question is how many ounces of steam should I figure on using? According to the charts, the venting is pretty different at higher pressure. Using Dan's method in the Lost Art, my longest run is only about 25ft, so doubling that means that the pressure drop is still less than an ounce, right? So does this mean I should figure on using the 1 ounce scale?



And by the same token if I set the cut-in on my pressuretrol to 1/2 and the diff at 1, doesn't that give me closer to 15 ounces of steam at the radiators?



It seems as though I am missing a step somewhere.



Thanks in advance!

Jamie Hall

Round up

and approximate things.  Venting is not an exact science -- but the bottom line is that it is almost impossible to over vent with main vents.  Radiators, yes you can.  Main vents, no.  In fact back in the bad old days, some systems were vented through an open pipe to the atmosphere!



On pressure.  Keep in mind that the pressuretrol is there to limit the maximum pressure the boiler will create, and does not control the actual operating pressure for most of the cycle.  Until all the radiators are full and all the vents are closed, the actual pressure -- even at the boiler -- will be an ounce or two at the most.  Only when the radiators are full and all the vents closed will the pressure begin to rise -- then the pressuretrol will cut off the boiler until some steam condenses, then turn it back on to make a little more, then off again and so on until the thermostat is happy.  So use the one ounce scale...

jpf321

my normal SOP

mains are mains .. runouts to rads become part of rad vents calculation

i usually use 1oz pressure because I figure when you need the steam to be moving fastest, you are at 0oz

the tricky thing to figure is Minutes To Vent .. that's a personal preference thing .. and it is unlikely that you will ever vent anything in 1min.



please have a look at the venting worksheet linked in my signature .. it should be somewhat helpful. any questions about it feel free to contact me directly or through this thread.



enjoy

Warsaw

This is great

Thanks very much. I had begun creating a much less sophisticated version of this myself. This is very helpful and conforms to what I had been figuring myself.

Cheers!

Warsaw

EDR of main

Quick question on this: how do you figure the sqftEDR of the main? I haven't see any figures about that out there - though I am probably just looking in the wrong place.

Thanks again!

jpf321

for worksheet..

you don't enter edr of main. just length and chose main a s the radiator type. If you really want to know edr of mains there is a table. I can tell you for 2.5" pipe..1 linear ft = 1 sqft edr

nicholas bonham-carter

figuring venting needs

if you have a low-pressure gauge on the boiler, it will show you the pressure inside the boiler. assuming the vaporstat is maintaining the pressure between 2, and 8 ounces, that will be the same pressure more or less as in the returns, next to the vents. this is really the back-pressure, and will be lower if your venting is capacious enough to let the air out quickly. conversely, if the venting is non existent the back-pressure will be much higher, as the gas company is pumping extra gas through your meter to force the air out, and pumping money out of your wallet to pay for it. 

my take on the venting issue is to make an antler, with several ports for vents, and keep on adding vents, until the back-pressure is in the 2 ounce range.

as the main vents close, the pressure will rise a bit as the steam enters the risers pushing a little harder on the air inside them and the radiator, but the steam will have arrived at each radiator at the same time.--nbc