Length of Injection Loop and Webstone Purge Tee

[bpirger]

Hi All:

A quick question regarding primary/secondary "connection". I'm hooking up my radiant tubing manifolds in my addition floor to the primary loop as the photo below indicates. I have closely spaced tees in both the primary and secondary. Does the length of pipe between the primary and secondary loops matter, i.e. the 3/4" copper with my mixing pump? In this layout I'm putting together, the distance would only be just a bit more than the pump with the iso flanges, i.e. less than 2 feet total, in the 3/4" between the primary 1.25" and the secondary 1". I'm a bit worried that the primary might pump through this short of a distance a bit, even though the tees are closely spaced.

Also, has anyone used those Webstone purge tees? A closely spaced tee with an integral valve, great for initial fill to purge off the air. They are spaced so closely, the return line is very close to the pump and the supply line. With the iso flanges on the pump, seems like things are within 1/4" of each other (some part of the pump and the return line). Is that just how it is? Steve, I know you have used thousands of these by now....

Thanks,
Bruce

 

[Morgan]

You should be alright, if the tees are very close together than the water should move straight ahead and not meander through the tees to your secondary loop, if you do notice some ghost flow then you could always add in a flow control valve (or 2) they are cheap and are basically a spring check valve........will prevent any unwanted flow issues if you have them, I would leave out for now, but allow pipe space to cut them in if needed down the road. Remember water is lazy, it doesn't want to take 7 mile detour if straight ahead (through a tee) will get it back to the suction side of the primary pump (point of lowest pressure)

 

[heaterman]

The rule, .......note that I said rule rather than rule of thumb,...... is to have any secondary tee's no more than 4 pipe diameters apart.

So: 1" main loop would be 4" center to center on your tees. 1-1/4" would be 5" center to center, 1-1/2" would be 6" and so on........

 

[bpirger]

Right, for the tee spacing. And the length of the "cross over pipe" between the secondary and primary loop doesn't matter at all? I understand that the pressure drop in each system across the closely spaced tees is near zero, hence no flow. But if the primary and secondary loops were piped by just a a foot of "cross pipe", seems like it might be easier for unwanted flow, i.e. only a foot of separation, and the "7 mile detour" is small. So maybe a small amount of unwanted flow....just have no first hand practical experience. But right, could always add the one way valves...the mixing pump has a IFC I'm sure anyways, and the secondary loop is a few feet below the hot primary....so no thermal flow downwards.

Thanks!

 

[heaterman]

Right, for the tee spacing. And the length of the "cross over pipe" between the secondary and primary loop doesn't matter at all? I understand that the pressure drop in each system across the closely spaced tees is near zero, hence no flow. But if the primary and secondary loops were piped by just a a foot of "cross pipe", seems like it might be easier for unwanted flow, i.e. only a foot of separation, and the "7 mile detour" is small. So maybe a small amount of unwanted flow....just have no first hand practical experience. But right, could always add the one way valves...the mixing pump has a IFC I'm sure anyways, and the secondary loop is a few feet below the hot primary....so no thermal flow downwards.

Thanks!

I see what you are referring to. Typically it is not an issue because it's the pressure differential from tee to tee that causes the unwanted flow. If you are concerned about thermal siphoning in the cross overs I would suggest creating a thermal "trap in your piping by dropping below the lower pipe and coming back up, entering the pipe from the bottom. Flow checks can be problematic on a loop with a variable speed circ due to very low head and flow rate developed.