So here's my story. Please bear with me. To visualize it better, I've put photos of the equipment room on Imgur at http://imgur.com/a/W0N3p rather than attach them to this post (for which I would have to reduce the photo resolution). Click the gear icon in the top corner of each photo to view it at full resolution.
I've got this pool that I just started taking care of this year. I walked into it being told that a new filter head was required; I ordered the current model to replace the old one (no longer available) without really looking at the overall setup. They also had a flow meter mounted just above the pump, without anywhere near the required pipe length around it, so while replacing the head I also rebuilt that portion of pipe.
What I failed to notice is that the filter head on this Hayward S-310T filter had 1.5" ports, where the entire rest of the system - intakes, pump, heater, and output - had 2" piping (or larger). At some point in the past, someone installed this filter head with 1.5" ports, and a 1.5" pipe from there, to the heater, and back out to the chlorine feeder. This seems to be causing quite a restriction. Unfortunately, replacing the head with a 2" version and rebuilding all the pipes isn't really an option now; the connection inside the filter was so tight that I had to pound it into place with a hammer and a block of wood. I doubt I could get it off without wrecking the pipe inside the filter.
This is a nearly 200,000L pool by my best estimates. (I plan to do an alkalinity change test to get a better idea of the volume.) The system is currently moving around 230 LPM - a 14.5 hour turnover rate. Health regulations here require a maximum of 12 hours, with 8 hours preferred. Here's the kicker. If I open the Heater Bypass valve (in addition to leaving the heater open, of course), the flow rate jumps up to 275 LPM, which gives us very nearly a 12 hour turnover rate. In addition, the filter pressure drops from ~150kPa down to ~110kPa.
So here are my questions. I'd like to get the higher flow rate, especially since I've already had a couple of clarity issues in the first month. The filter specifies an operating flow rate much much higher than what we've got, but that number probably assumed a filter head with 2" ports - is it okay to push that much water through the smaller filter head, or is there a chance of it causing damage or wrecking the gasket? What about the existing 1.5" piping - can I safely leave it (especially the chunk of black spa hose) with that high of a flow rate? The water velocity in some parts of the piping would be over 13 ft/second - way above the recommended specs for PVC that I've seen. What about leaving the 1.5" filter head, but replacing all the piping with 2"? (and on that note - the Hayward chlorine feeder originally had 2" connections, but the "pipe" through the bottom of it restricts to less than 1.5"...if I replace the rest with 2", is this going to still have a restriction?)