1.5" vs 2" piping, high but not high enough flow rates

Hilton

0
In The Industry
Jun 15, 2010
76
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?)
 
Short segments of 1.5" pipe do not cause significant flow restrictions. Long sections will cause some flow restriction, in proportion to the length of the segment. Longer runs of 1.5" cause more restriction, but it takes quite a bit of 1.5" pipe before that becomes significant enough to be noticeable. Six to ten feet of 1.5" pipe plus a few 1/5" fittings will not cause flow rate differences that matter in this situation. Replacing the entire multi-port valve with a hi-flow 2" equivalent would improve things, but not all that much, not as much as bypassing the heater.

Higher flow rates through PVC/poly pipe are not a problem other than wasting a little electricity. Metal pipe can be damaged by high flow rates, but not plastic.
 
I don't see any easy quick fixes to your problem, cheapest option I can think of that might work if you have room is add a second filter parallel to the primary filter that bypasses the heater, perhaps a cartridge filter of some type.

Ike

p.s. don't worry about higher flow rates in PVC unless they are WAY about the general engineering suggestion, many of those seem to be based on very outdated concepts before people knew how PVC would stand up to real world use since these would be easy to replace if the extra flow causes them to wear out if a few decades.
 
I don't think replacing just the 1.5" pipe is going to compensate for the heater head loss.

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.
Why can't you just run that way all the time? Even with the bypass open, the heater should be getting enough flow rate/pressure to operate.

If you need to bump up the flow rate further, I would look into replacing the multi-port valve with a 2". Most valves have quite a bit of head loss and the difference between a 1.5" and a 2" valve is about the same as a typical heater. But combining that with the heater bypass should give you plenty of margin.
 
Alright. I think I'm mostly concerned about the piece of spa hose now. It goes absolutely nuts when I open the heater bypass (due to the flow increase), and I worry that my glue job won't hold.
 
That kind of flex is not really designed for high flow rates so do yourself a favor and replace it before it breaks.
 
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