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Thread: PEX for higher pressures

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    Sprinkler Guy Wet_Boots's Avatar
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    Default PEX for higher pressures

    What pressure ratings are available for PEX, if considered for usage at higher pressures, in instances where pressure regulation won't be workable? I don't think the 160 psi ratings I see will provide enough of a safety margin. Do they have standards for thicker-walled tubing than SDR-9?

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    In the Trades kordts's Avatar
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    Call the manufacturer or supply house. 80 psi is the highest allowable domestic pressure. Industrial or commercial is usually speced by an engineer or architect.

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    Sprinkler Guy Wet_Boots's Avatar
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    80 psi would be about as much as I'd want to expose a 160-psi-rated tubing to, although Zurn, for one example, suggests a 50-percent pressure margin.

    This inquiry is for a few homeowners who have thoughts of adding secondary water meters to feed existing lawn sprinkler systems, and are looking at long runs of copper, some of them in finished basements. Since the systems are using every last psi of water, there isn't an opportunity to reduce the supply pressure to a safe 80 psi.

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    In the Trades kordts's Avatar
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    80 psi is way plenty for lawn irrigation systems. If the system is designed and installed properly tha's all it needs. If the system was designed figuring on pressure over 80 psi, then the designer was a moron. 80 psi is code all over the US. I have installed lots of RPZ's for lawn irrigation systems where it was 50 psi. If you are a licensed plumber, and you know the pressure is over 80, you better reccomend a PRV, if they don't want one, walk away. The lawyers will come after you if anything bad happens. Helping somebody do something against code is a lose-lose.

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    Moderator & Master Plumber hj's Avatar
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    Default Pex

    The pressure rating for PEX goes down as the temperature goes up, so you have to know the ambient temperature of the area before you can decide whether it is adequate or not.

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    Sprinkler Guy Wet_Boots's Avatar
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    Quote Originally Posted by kordts
    80 psi is way plenty for lawn irrigation systems. If the system is designed and installed properly tha's all it needs.
    In the sprinkler system itself, I fully agree. But the static supply pressures often go beyond 100 psi.
    If the system was designed figuring on pressure over 80 psi, then the designer was a moron. 80 psi is code all over the US.
    Designers tend to use what they have, and watering restrictions can require them to get the sprinkling done within a certain time frame, so nobody likes to leave any potential flow unused. That's what makes cutting in a PRV a no-go, since the system reworking could involve time and material exceeding the cost of doing the new supply work in copper
    I have installed lots of RPZ's for lawn irrigation systems where it was 50 psi.
    I also do RPZ retrofitting, and often have to inform a homeowner that they have inadequate, or non-existent, backflow protection, and that I won't be able to do any repairs unless the backflow protection is brought up to code. RPZ retrofits can cost more than a homeowner with one broken sprinkler head is willing to pay.
    If you are a licensed plumber, and you know the pressure is over 80, you better reccomend a PRV, if they don't want one, walk away. The lawyers will come after you if anything bad happens. Helping somebody do something against code is a lose-lose.
    There are too many thousands of houses without PRVs, with pressures beyond 100 psi, for me to believe that authorities around here consider it a public safety hazard. It's bad enough when someone signs off on a home inspection where the backflow protection is missing. (they seem to spend most of their time looking for sump pumps draining into the sewer system - those they catch)

    My searching for higher-pressure PEX didn't turn up any specific examples yet, but I think there are some out there, according to an NSF approvals page. Funny thing, is that there is now a higher-pressure form of the 'ordinary' polyethylene tubing, made from a new resin. Unfortunately, nearly every mention of polyethylene tubing states that it is not intended for indoor usage.

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    In the Trades kordts's Avatar
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    It ain't the authorities, it's the lawyers you gotta worry about.

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    Moderator & Master Plumber hj's Avatar
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    Default Pex

    If PEX came with a thicker wall, then it would have to have an entirely differenent line of fittings because the internal diameter would be smaller than conventional PEX and the fittings would not be insertable.

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    In the Trades Bob NH's Avatar
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    Quote Originally Posted by Wet_Boots
    What pressure ratings are available for PEX, if considered for usage at higher pressures, in instances where pressure regulation won't be workable? I don't think the 160 psi ratings I see will provide enough of a safety margin. Do they have standards for thicker-walled tubing than SDR-9?
    The specified pressure rating of pipe is the working pressure. The burst pressure is usually 3 to 5 times the working pressure.

    If your water system operates above 160 psi then you are wasting energy. The only application for higher than 160 psi is with wells that are very far down to the water level, or if you have a submersible pump with some kind of throttling or control valve between the pump and the pressure tank.

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    Sprinkler Guy Wet_Boots's Avatar
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    Of course, on a sprinkler system with diaphragm zone valves, there is a distinct possibility of water hammer, and the pressure spikes that go with it. I suppose the PEX has expansion capabilities to dampen the effect, but it's another concern that makes me unwilling to overstep any manufacturer's safety margins.

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