Injection tee spacing

MikeDurigon

When injecting a boiler primary loop into a secondary loop I’ve been told to keep the branch of the tees no further apart then 3 x the pipe diameter. No further then 12” centre to centre. Recently I’ve had another journeyman informing me that spacing the tees further apart works better as it gives the secondary loop more area to scrub heat off the primary loop. I was of the understanding that if you spaced the tees too far apart that you will not get return flow back into the primary loop. 

hot_rod

The tee spacing on P/S has to do with keeping the pressure drop as low as possible. The more distance between the more chance of ghost or induced flow. A close nipple, regardless of the pipe diameter.

It has nothing to do with heat scrubbing, that is a new one on me, however.

EBEBRATT-Ed

When you say "injection" I assume you're using a pump to do the injecting If that is the case i don't think the spacing is critical but i would keep it within 10" or so. Same thing if using a three-way valve.

The only reason to keep the tees close is to prevent unwanted "ghost flow". If you think ghost flow is a problem, keep the tees close.

On larger commercial jobs with large size pipe the tees are so large you can't keep them 12" or less center to center. These jobs still work fine. There is no magic to the 12" number.

STEVEusaPA

Closer is better. Journeyman is wrong.
You couldn’t possibly be on this site without reading a few of Dan's books-which explains it simply and perfectly.

hot_rod

Here it is in a visual.

Mad Dog_2

Sounds like your Journeyman friend may be conflating the Air Eliminator (Microbubble Air  scrubber)  with P/S Tee distance.  His next stop on the Journey should be here.  All of us will benefit.  Cross-Training and an infusion of  new blood is a good thing!  Mad Dog 🐕 

MikeDurigon

Hot Rod. Your last drawings notes 4 x diameter, Interesting. Scrubbing is my piping slang 😁 as the injection flow is backwards to the building loop. I’m calling the boiler loop primary and the building loop secondary. Primary and secondary loops both have Grundfos pumps. Boiler pumps into a Calefi hydraulic separator. 

MikeDurigon

Correction on my late night post. There is actually 3 loops. Boilers pump into the hydraulic separator. The the hydraulic separator pumps into the building loop via injection tees. The building loop has pumps on its own.

hot_rod

MikeDurigon said:

Hot Rod. Your last drawings notes 4 x diameter, Interesting. Scrubbing is my piping slang 😁 as the injection flow is backwards to the building loop. I’m calling the boiler loop primary and the building loop secondary. Primary and secondary loops both have Grundfos pumps. Boiler pumps into a Calefi hydraulic separator. 

It shows a maximum of 4 pipe diameters, less is fine.
For threaded pipe I use a close nipple. For sweat a nipple to allow enough gap to solder.With a tee drill you can get them really close together.

EBEBRATT-Ed

@MikeDurigon

You mentioned "injection flow is backwards to building flow"

This does not sound right. can you post a sketch??

MikeDurigon

MikeDurigon

EBEBRATT-Ed

From what I can make out from the piping diagram the piping looks fine to me. I am not seeing "injection flow is backwards to building flow".

The spacing between the supply and return tees is not that critical with pumped injection in my opinion.

Rich_49

MikeDurigon said:

Hot Rod. Your last drawings notes 4 x diameter, Interesting. Scrubbing is my piping slang 😁 as the injection flow is backwards to the building loop. I’m calling the boiler loop primary and the building loop secondary. Primary and secondary loops both have Grundfos pumps. Boiler pumps into a Calefi hydraulic separator. 

Boiler pump should pump away from Hydro Sep . If you have a Hydro Sep why do you have CSTs ?