PEX flow queston

[Jarniscipus]

Hi all, I'm a little worried about a job and I have asked 3 other plumbers live who do not know the answer so I don't feel so lost at least...hoping the knowledge is here. Plan is to run a 1" PEX service line about 60 feet from meter to house to replace blown polybutylene service. I am concerned about using 1" PEX as I normally would because I am worried about flow rate on this 3/2 standard house. Obviously 1" can service this house but there are irrigation zones on 1" PVC up a hill that I think are using the full 1" flow available - too many heads on some of the zones. Thus I need maximum flow and minimal pressure loss on the service line to feed the 1" PVC at max flow for the irrigation. I'm worried the PEX could be less flow than existing PB, I don't know because PB is before my time so I don't know it's flow rates and pressure loss as I have never installed it. Even if the smallest drop in flow/pressure caused the rotor heads to throw water 1 foot less it would be a disaster for the plants and lawn and I would be hosed on the job.

Some questions, basically I am looking to confirm that I can get the same or better flow and pressure loss with 1" PEX as existing 1" PB with the right fittings:

1. How does 1" crimp PEX compare to 1" PB flow with the old QEST compression fittings, is it the same flow or less on PEX because PEX is thicker walled and the crimp fittings are smaller? Am I right on that? Would there be any difference on the maxed out 1" PVC irrigation line?

2. How much more flow and pressure can I get out of the pro-PEX expanding fittings vs the crimp? Would that help and be similar to the 1" PB? I can use either system, I have both, but homeowner prefers crimp - thinks metal is stronger than plastic. Nevermind what is true on that topic, it is what it and it is a specific request.

Am I overthinking this? Again it's because the irrigation is at absolute max flow, this is a not a question of whether I think 1" PEX can service a 3/2 house and more about I don't know how to compare 1" PB to 1" PEX.

Also not sure what pressure is at house because service line is leaking, but generally it's 85 in this neighborhood at the houses unregulated.

ThankS

 

[Jadnashua]

The ID of PEX is 22% less than PB, then add the internal fittings, and the pressure drop will be greater than with PB.

What you really need to do is figure out your maximum volume needed, then using the PEX industry's guidelines for distance, diameter, fittings select what size pipe you need.

Figuring out the pressure drop is fairly straightforward if you know the volume, starting pressure, distance, and ID of the piping involved.

1" PEX will not flow as much as 1" PB did. Other than cost, it never really hurts to go up a size or two. 1" PEX should be sufficient for many homes, but not an irrigation system that is expecting more volume and pressure.

 

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[Reach4]

You can get a 100 ft roll of 1-1/4 inch PEX for $200. You can get the stainless steel clamp rings. You can get some adapters.

One inch SIDR 160 PSI polyethylene would be an alternative. That uses 'insert" barbs and stainless steel hose clamps.

 

[Jarniscipus]

Thanks guys, this is what I was afraid of...22 percent diameter reduction is a lot. I think i will go to 1 1/4 to be safe, same difference installing it and not much more in cost as you mentioned . One thing I should have tried is to watch the irrigation zones with the most heads run and see how much I can reduce the flow on the valves...that would tell me how much reserve there is left in the system. This stuff makes me crazy. you can spend all the time in the world planning a well designed system in new construction and then the irrigation contractor creates impossible situations that the service won't support to save a few bucks on PVC, valves and timer wire.

 

[Jeff H Young]

Absolutly run 1 1/4" and it dosent nessesarily take care of if the 1 inch pvc is too small but should / could help and not hurt anything

 

[Jadnashua]

It would potentially make sense to run 1-1/2" line to the house. Feed the irrigation system with near zero pressure losses. That does not mean you need a meter that size. You can calculate the pressure losses of various pipes at different flow rates with free calculators on-line. The longer the run, the smaller the pipe, the more dynamic pressure loss. Keep in mind, too, that elevation differences could make a constant static difference...if the source and the point of use are at different elevations, the pressure change just from that without flow or restriction impacting things is 0.43#/foot change. Say the house sits up 20' from the street connection, that's nearly 9# pressure loss just from the elevation change forgetting dynamic (friction) losses.