One-pipe primary-secondary systems

FrankieJ

Is there a rule of thumb for the distance of piping between pairs of closely spaced tees? I am attempting my first P-S piping system. I am currently in the design stages.

Brad White_9

As closely as you can

Often a close nipple will do. Taco has a fitting series where they enter and leave in one fitting with a divider between. Yes, that close.

Having 5-7 diameters at least of straight pipe upstream and downstream cannot hurt either.

The idea is that the space between the tees should have no appreciable pressure drop; take away any excuse for flow in that circuit to want to leave of it's own accord. Flow in one circuit should never affect the flow in the other.

Sometimes if the tees have to be a distance apart for some reason, (obstruction for example) increasing the tee assembly one size for that installation is a good idea.

FrankieJ

Should the distance between the closely spaced tees of circuit A and circuit B be as close as possible also?

Brad White_9

Yes,

For the very same reason, that one circuit not affect the other.

Here is another way to look at it. Suppose each pair of tees in each circuit had a ball valve between them, a tee on each side of even a full port ball valve. There is more pressure drop between them then a short nipple. Some flow, -not much, but some- will be induced to take a side-trip just because it is lazy. Even a trickle, until the pressure drops of the straight path and the branch path become equal.

Now start closing the valve and what happens? Flow will be forced from one circuit to the other, affecting flow in it even more.

Make sense? Works both ways, too.

Cheers!

Brad

zurnie

Closely space tees

The rule of thumb is no wider then 5 times the pipe diameter for the tee spacing.