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Flex PVC

Zman
Zman Member Posts: 6,989
Does any one have any info on the friction coefficient or a head loss table for 2" flexible PVC?
I was called on the troubleshoot a spa that altogether too much of it running at too high a pressure.
It turns out that the pool knuckleheads make the heating knuckleheads look like geniuses.
Thanks in advance..
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein

Comments

  • Gordy
    Gordy Member Posts: 9,514

  • hot_rod
    hot_rod Member Posts: 15,033
    Is that chart referring to straight length PVC or coiled type well or geo Polyethylene pipe?
    I would think that sort of corrugated ID of flexible PVC would present a bit more pressure drop than PVC or smooth walled PE?

    I know the corrugated SS solar tube has substantial pressure drop.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Zman
  • Zman
    Zman Member Posts: 6,989
    hot rod said:

    Is that chart referring to straight length PVC or coiled type well or geo Polyethylene pipe?
    I would think that sort of corrugated ID of flexible PVC would present a bit more pressure drop than PVC or smooth walled PE?

    I know the corrugated SS solar tube has substantial pressure drop.

    Thanks Guys,
    Hot Rod,
    That was my thinking exactly. The pipe is not smooth on the inside it has gentle ripples every 3/8" or so.
    I have heard references that indicate a 40% increase in resistance from schedule 40 but nothing concrete.
    The pool industry is kind of all over the map with specifications.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gordy
    Gordy Member Posts: 9,514
    Not a huge difference at 50 gpm. Less than 2' difference in 100'.

    How many feet is involved?
  • hot_rod
    hot_rod Member Posts: 15,033
    Zman said:

    hot rod said:

    Is that chart referring to straight length PVC or coiled type well or geo Polyethylene pipe?
    I would think that sort of corrugated ID of flexible PVC would present a bit more pressure drop than PVC or smooth walled PE?

    I know the corrugated SS solar tube has substantial pressure drop.

    Thanks Guys,
    Hot Rod,
    That was my thinking exactly. The pipe is not smooth on the inside it has gentle ripples every 3/8" or so.
    I have heard references that indicate a 40% increase in resistance from schedule 40 but nothing concrete.
    The pool industry is kind of all over the map with specifications.
    Zman said:

    hot rod said:

    Is that chart referring to straight length PVC or coiled type well or geo Polyethylene pipe?
    I would think that sort of corrugated ID of flexible PVC would present a bit more pressure drop than PVC or smooth walled PE?

    I know the corrugated SS solar tube has substantial pressure drop.

    Thanks Guys,
    Hot Rod,
    That was my thinking exactly. The pipe is not smooth on the inside it has gentle ripples every 3/8" or so.
    I have heard references that indicate a 40% increase in resistance from schedule 40 but nothing concrete.
    The pool industry is kind of all over the map with specifications.
    We worked with a Pool Bath and Spa company that jetted all the tubs and spas we put in custom homes. They would only use that flex stuff at the pump connections, for service and removal ease.
    They would heat and bend PVC with one of those roller machine that electricians use to bend PVC conduit if they were doing a round or octagon tubs.

    I'm not sure if it was pressure drop, cost, or the glue fittings not holding as well, maybe that it just looked sloppy, but they sure avoided that flex PVC.


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    I would think with the expansion cycles, and spa temps you would want to avoid as many glued connections as possible. At least in a stand alone unit.
  • hvacfreak2
    hvacfreak2 Member Posts: 500
    I was told by a pool / spa guy that flex pvc was found to be susceptible to termite damage , and that was the reason that it is not used as much as it was five years ago. Sounds ridicules to me but he believed what he was saying. I have a few feet of it at my pool pump and have not noticed any termites messing with it , lol.
    hvacfreak

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

    Gordy
  • Zman
    Zman Member Posts: 6,989
    These tubs have over 50 feet of 2" flex each way. The pipes are failing at a rapid rate.
    They are contemplating replacing it with the same because they can snake it though a sleeve under a slab.
    I am wanting to document the existing setup and show them how much energy they would save and how much more efficient the system would be if they tore up the concrete and put in properly sized hard pipe, with properly sized pumps. Right now they need a 3 hp jet pump. Around 90 gpm and 90 feet of head...
    Would the ideal pipe be schedule 80 pvc spray foamed in a trench?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 15,033
    90 GPM in 2" PVC! There's your problem, Vern.

    That must be near 9fps, screaming fast. I think 3" would be a better choice? Or two runs of 2"?

    This table show choices at 4 fps.

    Larger than 2" the pipe get sized a bit differently, based on head loss per 100'

    This is from Idronics 16

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Gordy
  • Gordy
    Gordy Member Posts: 9,514
    Funny with Kurts chart that would seem to be at the upper end of an exceptable flow rate for 2" flex pvc.

    However I like the notes at the bottom of my chart which touches on pump surge, etc.

    That will tear some stuff up with a spa.

    How old is the present system?
  • SWEI
    SWEI Member Posts: 7,356
    The pool & spa industry often tends to treat friction losses as a pump sizing issue.
  • Gordy
    Gordy Member Posts: 9,514
    True Kurt. A hatchery scenario which your chart seems to cover is far more different than a spa.

    Water temps, on/off cycles etc.

  • Zman
    Zman Member Posts: 6,989
    edited August 2016
    Hot Rod,
    Yah Vern, looks like the water is moving pretty fast. I quick calc says 2.5" supply and 3" return would be about right. I am surprised it is not cavitating. The inlet pressure is surely sub atmospheric. The pump being 14' below the tub helps.
    We will need to leave some of the 2" flex on the tubs and knowing how to calc it would help. It is going to look a bit funny going for 2" to 3" and back again but so be it. The tubs will be replaced in about 2 years so we are trying to plan for that.
    I think the newly purchased 3 hp pumps will need a freq drive or perhaps replacement after the piping is updated.


    Gordy,
    The tubing is dated 2011. It is bulging and failing at the spirals.

    SWEI,
    The spa industry is way behind the times. Finding any meaningful specs on anything but circulators is difficult. The attached manual is very helpful.

    Does anyone have opinions on schedule 40 vs 80 or PVC vs CPVC? Other options?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gordy
    Gordy Member Posts: 9,514
    The concept is that most people who would own pools, or spas efficiency is hardly high on the list unless it's heating the water.

    Until the bills roll in.
    Zman
  • Gordy
    Gordy Member Posts: 9,514
    Carl keep in mind the filtration gpm needs, and turn over of the spa volume.
  • SWEI
    SWEI Member Posts: 7,356
    I'm guessing the pumps are existing? If not, the Pentair Intelliflow stuff is surprisingly affordable.
    Gordy
  • Gordy
    Gordy Member Posts: 9,514
    I was just looking at the Pentair Intelliflow. You would be a hero Carl once the utilities rolled in.
  • Zman
    Zman Member Posts: 6,989
    Yes,
    I am going to look at all that once the pipes are correct. It is a bummer they just bought new ones.
    The filters are separate from the jet pumps so they can be evaluated on there own.
    I got away with not looking at the disaster spa setup for about 6 months. Then one day they asked....
    It should be an interesting one!
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 15,033
    Wow those are crazy high velocities they list.

    Here is a sample of a sizer from the Aquatherm site. I think they recommend staying below 5 fps in their plastics.


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    Aquatherm actually leaves a bit of wiggle room within limits:

  • Gordy
    Gordy Member Posts: 9,514
    I would think the sole act of turning the pumps on can wreak havoc on pvc pipe, and fittings. Couple that with spa temperatures.
  • hot_rod
    hot_rod Member Posts: 15,033
    I think that 4- 5 fps in hydronics has a lot to do with noise and air removal. It gets harder to scrub micro bubbles out at those high flow rates. In metallic pipe 5 fps is where it starts to be heard.

    3.4 mph doesn't sound fast but trying to watch that velocity in my clear pipe demo..

    So fast it will make your head spin.
    d trumf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 6,989
    I am actually psyched about this one. I think you size for 4 ft/sec and over sized the returns a bit to avoid cavitation. That will future proof it a bit. I think I would be comfortable with 6 ft/sec max if they upgrade the tubs.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    SWEI
  • Zman
    Zman Member Posts: 6,989
    edited August 2016
    3
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein