While shopping for sources of SDR-11 pipe, some manufacturer's only offer 3608, a few others offer 4710. I understand that the numbers refer to their resistance to their respective categories so 4710 is better than 3608, but is there any advantage to having 4710 pipe for geothermal loops? The main advantage thrown out for these is that 3608 has an operating pressure of 160 psi at 73 degree F, and 4710 is 200 psi. Do operating pressures in a closed loop system ever come close to 160 psi? Some of the explanations for the technical details between 3608 and 4710 mention surge pressures, but that all seems to be in reference to irrigation or drainage (open systems). Does a closed loop system experience pressure surges in normal operation? The manufacturer of my heat pump throws out this in their design guide: "NOTE: The expansion and contraction of earth loop piping will cause a 50 to 60 psig water pressure change in system between summer to winter." I can imagine that polyethylene pipe will contract radially in winter, but the loop fluid is not going to compress. Would the pressure drop calculations for PE pipe be based on winter temps? (so it is already accounted for when selecting a circulator pump) Or, do closed loop systems require an expansion tank?