Oversizing PEX runs

Now I'm kicking myself, because I could have bought a set of ProPEX exandering heads and expander for $190 last night on Fleabay...
I went back this morning and they were G-O-N-E!

Thanks for all the advice and help. I think the PEX will substantially reduce the downtime for my baths and kitchen.As for the Biofilm... I imagine within the next couple of years, someone will come out with a way to deal with that as well.

"Chlorine doesn't kill as much as you think. Those of use in the Metro Milwaukee area experienced that a few years back with the Crypto outbreak. It ended up killing my dog actually (older dog that had kidney failure due to the crypto...)"

One way to take care of crypto is with a filter. It is about a 3 micron organism (the cryptosporidium oocyst).

The Milwaukee outbreak occurred because of failure of the chemical pretreatment system necessary for effective filtration with a sand filter.

The Harmsco 1 micron absolute filter has been approved for removing at least 99% of the crypto oocysts. It actually removes more than 99.9%. http://www.harmsco.com/uploads/pdf/harmsco_polypleat_catalog.pdf

In addition to the Milwaukee outbreak, there was a serious crypto outbreak at Seneca Lake State Park in New York in 2005. There were more than 2000 cases before they were done. It was in a recreational water application; not drinking water.

Crypto is usually not fatal for healty people but it is deadly for those with compromised immune systems.

Legionella is another organism that is resistant to chlorine, because it is often protected by a biofilm.

The protection provided to organisms by biofilm and dirt is why filtration is considered an essential part of the process of treating surface water. Lakes, ponds, rivers, and shallow wells and springs are considered surface waters.

If you are using surface water for showers or any potable use, you should filter and chlorinate it.

Cass said:

Bob NH I think the flow % should be based on the ID size of the fittings as it is smaller than the pipe. I have searched online but could not find the PEX fitting ID sizes anywhere.

Click to expand...

This is interesting. Some flow reduction is due to the length of the pipe itself, some to the elbows, and some due to spot constrictions, like the miniscule openings they give you at the ends of flex lines.

Each has some impact. None is a limiter. A single small opening is not a limiting factor; it is friction and it does reduce flow, but it does not cause a limit.

david

Only X amount of water will flow through a given diameter at Y pressure. PEX would have a least/minimum of 2 fittings(possibly more) on each run using a manifold system. 1 at the manifold (beginning of the run) and 1 at the fixture(end of the run). The fitting ID is reducing the flow right from the start.

Yes

yes, Cass, the fitting reduces the flow. Right from the start, and at the other end. Two fittings; therefore two reductions in flow. And yes, this has to be included in calculations. Also true that only X amount of water will flow through a given diameter at Y pressure. This statement applies to elbows and to lengths of straight pipe too. You already knew that, I am sure.

Yes, it is good advice to look at the ID of Pex fittings and see how small it really is. Very small. And include this in all calculations, if you are doing the math.

When I saw the size of the fittings I coudl get with nominal 3/4" Kitec, I bought them. They are huge.

Fittings of all kinds will cause pressure loss proportional the square of the velocity in the fitting, and related to some characteristics of the fitting. Branch flow of tees are the worst and elbows nearly as bad. Globe valves are so bad that they should never be used if you care about pressure loss.

I don't have fitting bore diameters for PEX, but here are some things to consider:

A fitting that goes in an expanded pipe is probably larger than one that doesn't require expansion of the pipe. If pressure loss is important, check the diameters of the ferrules that go in the pipe.

Chamfering at the inlet of the fitting is very important to reduce pressure loss. A sharp internal corner is bad. Check the fittings. I wouldn't expect your plumber to take time to knock the sharp corners off a PEX fitting, but if you are doing your own and care about pressure drop, consider chamfering the inlets of fittings if they are sharp edged.

Elbows in rigid pipe produce a lot of pressure loss. Elimination of elbows with PEX will make up for a lot of the loss in the fitting bores.

Thanks Bob NH, your summation was excellent. Now I just need to win an expander set on Fleabay cheap...