Collapsed pipe

[Onmartin]

Hi
I have a problem with a pipe running between sand filter and heater ( approx 450mm) has collapsed ( sucked almost flat). It happened last year too, I thought then it was inferior pipe but this time it was good. I have a chlorine feeder that inlets between the pump and sand filter and outlets after the heater. There is a 1 way gate valve to stop chlorine flow back into heater.
Any advice/explanation as to the cause and prevention??
Has worked all season without issue. Chemical levels are checked and kept. Constant ( PH 7.4 chlorine 3ppm) TIA

[Denniswiseman]

Does the diagram below represent your layout. It may not be exactly as drawn. I suspect you are talking about the section between F and H with NRV being the non return valve
What type of pipe is it and how close to the heater
If the diagram is accurate then the water passing through the chlorine feeder is unfiltered and will slow the flow through the filter and heater although I assume that is stated how in the installing instructions
I would have been inclined to remove (service)the NRV as it may be restricting flow through the heater
The system is under pressure throughout and I don't see how the pipe could be sucked flat. Are there any other valves in the system
Just had a thought what if the MPV is set to backwash or recirculate you could have negative pressure heater side with the NRV stopping equilibrium

IMG_0408.JPG (18.06 KiB) Viewed 1843 times

[Onmartin]

Hi
Your drawing is spot on. The NRV was put in place to prevent chlorine feeding back and sitting in heater matrix ( as per the Hayward CF installation instructions)
The pipe is 50mm PVC piping. The pool has been in 12 years and never an issue before last year, though does coincide with the CF installation.
I wasn't sure if there was negative pressure when pool pump shut off. Possibly caused by chlorine feeder?
The only other valves are pre pump on feed from skimmer and pool wall inlet

[Denniswiseman]

I still suspect the NRV seeing as the problem coincided with the CF installation
Also the pipe would have to get hot with a negative pressure for it to collapse
Does the heater have a pump overrun to dissipate residual heat left in the heater when the pump should shut down
Is it worth speaking to Hayward to see if they have a solution with the NRV in place