Pressure gauge running high at low RPM, sanity check please

Started by Marcus Reed · · 3 replies
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#1
Running my IntelliFlo at 1500 RPM for the 8 hour filter block, filter side gauge is sitting at 12 psi where it used to sit around 7 to 8 at that speed when the cartridge was newer. Cleaned the cartridge two weeks ago so it is not that. Affinity laws say head should drop with the square of speed so I expected way less than this.

Only thing that changed is I added a check valve on the return line after some chemical feeder plumbing last month. Wondering if that is adding more head loss than I am accounting for, or if I have got a partially closed valve somewhere I forgot about. Anyone dealt with a new check valve eating more psi than expected. Before I start pulling unions apart I would rather rule out something dumb first.

3 Replies

#2
Had almost this exact thing happen when I added a check valve after my chemical feeder tee, gauge crept up more than felt right for such a small fitting. Turned out mine was a spring loaded check and at low RPM the spring resistance is a bigger percentage of your total head than it is at high speed, so it shows up worse right where you are running, at 1500. The affinity laws math you are doing is for the pump curve itself, it does not know a new fixed restriction got added downstream, that is just extra head tacked on at every speed but you notice it more at low RPM because your margin was thinner to begin with. Worth checking if yours is spring check versus swing check, spring ones eat more psi than people expect for something that small. I would not tear into unions yet, just pull that check valve and see what the gauge does with it out of the loop, cheap test before you go hunting for a closed valve that might not exist.
#3
Spring loaded check eating psi rings true, my heater bypass valve did something similar years back and I never would have guessed a valve that small could move the gauge two or three pounds until I saw it with my own eyes on the binder notes.
#4
Only thing I'd push back on is jumping straight to pulling the check valve before checking where the gauge actually sits relative to it. If that gauge is on the filter itself and the check valve is downstream on the return side after everything, it shouldn't be adding to your filter psi reading at all, that gauge only sees what's between the pump and itself. Spring check on the return past the chemical feeder would show up as more resistance the pump has to push against overall but I wouldn't expect 4-5 psi jump on a filter gauge from that unless I'm misreading your plumbing layout.

No IntelliFlo here so I can't help with the RPM side, but for what it's worth a 4-5 psi jump after two weeks with a fresh cartridge is more than I'd expect from a spring check valve alone even if it is eating some head. I'd pull the cartridge back out and actually look at it under water before blaming the valve, sometimes they look clean dry but still have channeling or a torn pleat you can't see till it's wet. Cheap test either way, your mileage may vary.