Pipe length before/after circ+IAS: real world example

SteamFTW

I want to make sure I'm not overlooking something

So we have some real-world data, let's use the following: 2" NPS Sch40 "iron" pipe, Taco 007-F5 and B&G Inline Air Separator. The 10-4 rule of thumb says: 10 pipe diameters length before the circulator and 4 pipe diameters length after, right? B&G says: 18" of straight pipe before the IAS. So, does that mean that, according to best practices, the whole stretch of [pipe + IAS + pipe + circ + pipe to next fitting] should be no less than

18 + 8.5 + (10)(2) + 6.5 + (4)(2) = 61 inches????

Really?

Is the IAS so disruptive that none of it (or the pipe that precedes it) can be considered as part of the "10 pipe diameters" of "straight pipe" before the circulator?

Thanks for clearing this up.

Jamie Hall

Not really. You can use the same length of pipe after the air separator as part of the length before the ciriculator and the same for the pipe after -- of course. So it adds up to 47 inches, not 61.

SteamFTW

Thank you, not only for answering this question, but for helping make my upcoming post a LOT shorter. Several issues have now become non-issues!

SteamFTW

@Jamie Hall Now that I'm home and have had a chance to draw this out, I'm curious about how to get "47 inches". From elbow to elbow (A - F) in the drawing I get 61". Which segments can be removed or shortened to reduce that to 47"?

Jamie Hall

I can't add. That's how. Your sketch is correct.

pedmec

i would not follow the 10-4 rule because you really got to think of what the reasoning for the 18" prior to the in-line air separator. the 18" allows for the air to separate from the water and rise to the top of the pipe and allow for capture at the air separator. This might be critical if you had high velocity circulator. But considering you are only using a taco 007 on 2" pipe air removal will not be a problem even if you don't get the 18". The velocity is reduced by the area of the 2" pipe. that air has no trouble separating with the water becoming laminar. The assumption with that is you are using a high velocity circulator and that you are going to be on the upper end of the velocity scale and the air bubbles still might be entrained in the water. Your really not going to use 2" pipe with 007. Waste of money. Considering that 2" pipe size is used for 400k.

The 4 pipe diameter upstream of the suction side of the circulator is to prevent cavitation. Again 2" pipe helps if you were to shorten it up a little i don't believe you would have a problem. Now if you had everything matching specs (400k boiler, 40 gpm circulator) i would most likely follow the 10-4 rule but not with a 007 on a 2".


sometimes

hot_rod

Would you consider an air seperator instead of a purger? No distance requirements on either side, and much better air removal performance

The purger are good up to maybe 4 fps, above that air blows right across.

The Steam Whisperer

Also, the IAS operates much differently and more effectively than an "Air Scoop". I don't think B&G shows any minimum distance into the IAS but I do like to keep 6 to 8 inches on the smaller sizes for residential work.

SteamFTW

@pedmec This came up because I was looking at a gravity-conversion. The conversion happened years ago, long before my friends bought the place. The 2" near-boiler piping and the Taco (on the return side) are what's currently there. I thought, "if this ever gets redone "pumping away," how crazy long a section are they going to have to try to fit in here?"

@The Steam Whisperer That's partly why I chose the IAS in my example. B&G's documentation for the IAS doesn't show any minimum distance, but their "CounterPoint Ready Reference" does. Make me wonder how important it is, if they don't put in the IAS docs. I've attached a photo of the current "air separator": a 2 x 2 x 1/2 tee. I don't see it doing anything, since the pipe to the tank isn't pitched up.

The Steam Whisperer

I thought I had seen something somewhere for the lead in length, but didn't see it in the instructions. I've found that when used pumping away that a shorter length works fine for the smaller IAS 1 1/4 inch or 1 inch. The 2 inch and up models probably should have the 18 inches reduce turbulence.

hot_rod

I think it comes down to how fast the water is moving through the device. The slower the flow, the less important the upstream distance. Make me wonder if any test was actually done on those suggested distances?

SteamFTW

pedmec said:

The 4 pipe diameter upstream of the suction side 

Isn’t it 10 on the upstream side? (Just making sure for anyone who drops in on this mid-thread.)

The Steam Whisperer

The IAS is rated for 15 GPM on 1 inch, 25 gpm on 1 1/4, 35 gpm on 1 1/2 and 50 gpm on2 inch. IIRC it uses the venturi principle to seperate air. For best operation, reducing turbulence is probably best, but velocity is what makes it work like it was designed.

TonKa

SteamFTW said:

@pedmec This came up because I was looking at a gravity-conversion.

Since the original pipe on a gravity conversation would now be way oversized, is there any reason why you can't just downsize this one section of the pipe in question and reduce the distances proportionally?

hot_rod

The Steam Whisperer said:

The IAS is rated for 15 GPM on 1 inch, 25 gpm on 1 1/4, 35 gpm on 1 1/2 and 50 gpm on2 inch. IIRC it uses the venturi principle to seperate air. For best operation, reducing turbulence is probably best, but velocity is what makes it work like it was designed.

Something about an internal "weir" to decelerate flow.

The Steam Whisperer

hot_rod said:

The Steam Whisperer said:

The IAS is rated for 15 GPM on 1 inch, 25 gpm on 1 1/4, 35 gpm on 1 1/2 and 50 gpm on2 inch. IIRC it uses the venturi principle to seperate air. For best operation, reducing turbulence is probably best, but velocity is what makes it work like it was designed.

Something about an internal "weir" to decelerate flow.

Yes I finally found a description and I was looking at the one I was going to put on my system. It looks like the larger than pipe sized body allows the water to slow dramatically and then it passes through the orifice (weir) into a second small chamber before exiting the casting. The vent opening in the casting is right after the water enters the first chamber, so I imagine the water hits the weir and causes it to roll back towards the inlet and with the low pressure point caused by the venturi effect of the high velocity water entering the large chamber, the vent point is probably at a much lower pressure. I would imagine the water flow inside the first large chamber looks a lot like the airflow behind the typical pick up cab on trucks with an open bed. The air behind the cab rotates due to the low pressure point just behind the cab at the back edge of the roof.

hot_rod

Horse and buggy technology🥴

Nothing comes close to a micro bubble type air Sep. All brands operate at high 90% efficiency. Even in over-pumped systems. No piping distance requirement

The Steam Whisperer

Yes, I used to do the microbubblers when they first came out ( early 1990's IIRC), but switched to the IAS. Simple and much more effective than air scoops.

SteamFTW

@The Steam Whisperer
Have you ever seen a cutaway drawing of the IAS? If so, please share. I recognize the drawing of the separator in @hot_rod 's attached image from Taco's TD11 tech doc, showing how their "Air Scoop" works. The bulge on the top of the Taco (and all the other brands that look the same) makes it pretty clear where the action happens inside, but the silhouette of the IAS isn't so extreme. I would love to see inside the IAS. If anyone has an IAS that is unfit for service, please send it to Gordon Schweizer (via @Steamhead, because I don't know if GS himself is on HH), and have him cut it open and do a YouTube video on it. I LOVE his "here's what's inside" videos!!!!!

They remind me of a great electrical engineering channel run by a guy in Australia who said something I can totally identify with. (The guy's accent makes it even more memorable.) If you have something that's beyond repair, and you've wanted to understand how it works: "Dant threow it a wahy; taik it apaht!" Words to learn by!

@TonKa
I have no info on the original boiler, only the fittings where the current supply was piped into the original mains. There are 3 mains, one of which is 3", the other two are 2.5", and those two share a 4" tee. (see big-tee-2-mains+air_annotated.jpg). IIRC, the rule-of-thumb for gravity conversion is to take the largest supply diameter from the original boiler, divide by two, and drop one size. Since all I have to go by is this 4" tee, I'll say the original supply was probably 4". That would make the "converted" supply diameter 1.5" (4/2 = 2; the next smaller pipe is 1.5" NPS). That makes the straight run 54" instead of 61".

I wonder if the fact that those two mains are tied together had anything to do with their choice of 2" for the conversion. Because I wonder what would happen if I took that big tee out and gave each of those mains their own tee off the header. The 3" main shows no sign of having had anything larger than a 3" supply. Maybe the original boiler had two outlets.

hot_rod

It becomes a challenge scrubbing air out of large diameter pipes at low flow.
In a 2" pipe you need around 20 gpm to get flow velocity above 2 fps.

Flow below 2 fps doesn't move air along with the water so well. This is especially true in vertical piping. Water flows down, air moves up through the barely moving water.
The best bet is manual air vents on the heat emitters as that air will collect at all high points.