and now for something completely different - a clear polycarbonate steam gifford loop return test

archibald tuttle

So this is pretty friggin cool:

https://www.youtube.com/watch?v=GCv7iKi0xgg

This is 1" ID 1/16" wall polycarbonate (mcmaster carr was the most convenient source i found for a small order) so it fits 1" sharks. i also bought 1" ID 1/8" wall and a couple brasscraft 1 1/4" tubing compression by pipe thread fittings in case the thinner tube was not up to it when i put the shark on, but fortunately the thinner wall and sharks worked like we the people for a 3 hour test. The Material is rated for like 248 fahrenheit i think and given that we're talking next to no pressure although i guess 15 lbs as against the safeties if you were going to leave it alone you'd have to check. no clue how it would really fair in longer service if there were some reason or curiosity to leave it in place longer. and don't know what would happen if i propressed it. i'm going to try that with a piece at some point and will report. It's really funny, when you look up this material they say it has high strength and heat tolerance characteristics for fluid piping but there are no fittings for it. i had to make this up as i went along.

so now the interesting part, if you don't get too bored - or distracted - watching this plumbing porn you'll get to where i start measuring the relative height of the steam in the return vs. the weir of the gifford tee you'll notice that i'm running about 7.5" of steam but the difference in the heights is about 5". i'm trying to wrap my mind around this. the weir is fairly high compared to the boiler operating water level, i.e. about 10.5" above, according to various representations of 'how to make a gifford loop' but these are very vague on appropriate ranges other than not below the operating water line, and since this was just a test and not the permanent install and this was a very convenient spot to get into the piping i just went with it to see what would happen.

but noodling on this i feel like the upper piping in the small equalizer for the fill float assembly from the existing condensate pump system (which i'm looking to do away with) should be seeing that 7.5" of steam from the boiler so i ought to have a height in my clear column that is more or less 7.5" higher than the gifford weir because the whole assembly is the same size, i.e. 1" pipe", up and down both sides of the loop.

and i didn't even see much if any increase in the column height when the system was fully warm and the pressure rose to about 16 or 17" of water which is typical of this system when it is completely warm (and until i institute two-stage operation and the dwyer-stat which, sadly, the extensive thread on the design and schematic for creating a dwyer stat was lost in the celestial infindibulum of heatinghelp posts that ceased to exist for some reason). As you can see from the height of the clear column, even if it responded with a heightened water level on a per inch of water column basis i've got like 30 more inches before i hit the drop from the horizontal mains so i'm pretty much thumbs up on the condensate pump goes in the off season. but i'm still a little mystified on the results i'm getting. maybe there is some phenomenon the cooler return water dripping through actually reduces the pressure in the gifford loop entry where - as here - it is a one inch tangent. I do notice that when the condensate pump runs, just hitting the main boiler with that hot but not steaming return water in a burst drops the steam pressure like 5 inches and it takes about 15 seconds to recover. and of course the gravity return is constantly dripping so maybe it is constantly reducing the pressure in its immediate zone by further condensate? or ? steamhead? dan? anybody want to play. i would have done this for nothing just to see it but i figured it was defensible work to perform before repiping 6 separate F&Ted returns.

brian

archibald tuttle

PS - don't ask me why the youtube gif image comes from the middle of the 'broadcast' so it shows my black pipe gifford intercept but not the clear return drop described. what can i say. it is like a teaser for the weather, you gotta actually watch the video i guess.

archibald tuttle

duh, i need to put a second vapor meter at the end of the return because there surely is a little steam pressure there, i've got a vent right at the drop. so whatever pressure that is would counteract boiler pressure, so it seems by emperical demonstration here that having as many inches of gravity return as you have water column of steam actually gives plenty of margin unless you wicked undersize the returns or something. thoughts?

EBEBRATT-Ed

I think all boilers should be piped with that stuff LOL.
Sure would make troubleshooting a lot easier.

The way I think of it mostly all the water in the boiler has to be at 212 or you get no steam.

Return water weather from gravity, boiler feed or condensate tanks or cold make up water will quench steam production.

But

Boilers are tested with a certain condensate temperature to produce their rating. I don't recall the exact temp but I think it is 160 deg. Feed colder water than that the boiler produces less steam feed hotter water than that and your basically overfiring the boiler and it produces more steam

nicholas bonham-carter

When the pressure in the boiler causes the water in the wet returns to rise up 1.75 ounces for every ounce of pressure, it also presses down on your Gifford loop level, so I think that’s what you are seeing in your experiment.
The heights of displacement will be the same: plus height in the wet return, and lower height in the G-loop, and both heights will return to the same level, when the boiler is off.—NBC

Voyager

First, I am not a steam person, but I find this very cool. Nice work.

Second, I will venture a guess, but keep in mind I am an engineer, but NOT a steam person. If you have 7.5” of pressures on the steam supply side, I would expect lower pressure on the condensate return. The phase change complicates things compared to the flow of either air or water, but the fact is that anytime you move anything through a pipe there will be frictional losses. I suspect the height difference you are seeing is simply a measure of the pressure loss of the steam flowing through the system until it condenses and falls back with gravity.

If you could put a pressure port on the return, you could measure the delta P and I suspect you would see this directly.

ChrisJ

Very cool.

That boiler piping though..........