# Water Pressure Differential Gauge
**URL:** https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752
**Category:** Factual Questions
**Created:** [July 11, 2025, 10:41pm UTC](https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752 "2025-07-11T22:41:43Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@MindsEye\_Watering](https://boards.straightdope.com/u/MindsEye_Watering)
#### Post date: [July 11, 2025, 10:41pm UTC](https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752/1 "2025-07-11T22:41:43Z")
I recently acquired and have installed a water pressure differential gauge [(this one)](https://differentialpressure.com/filter-indicators-overview/dpp975/) on my well system in order to monitor the state of my filters and when to change them. The filters are 4" x 20" five micron and plumbed in parallel.
A simple schematic [can be seen here.](https://imgur.com/a/m4tdE8k)
My question is did I put the sampling ports in the wrong location - installed at “Sample Point 1a and 1b” or should I have installed them at “Sample Point 2a and 2b”?
When I was planning this, I assumed pressures would be the same on ALL input piping regardless of the locations of the sample point (and same for output piping). I realized that assumption may be wrong and I had better ask someone more knowlegable than I.
_(It’s possible that this idea may not work at all because the filters are big, plumbed in parallel and the gauge has a range of 5 psi._
_If so…oh, well.)_
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### Author:  [@Snipe70e](https://boards.straightdope.com/u/Snipe70e)
#### Post date: [July 12, 2025, 4:42am UTC](https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752/2 "2025-07-12T04:42:34Z")
Either 1a or 2a is good for high side. 2b will give a better reading.
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### Author:  [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)
#### Post date: [July 12, 2025, 6:34am UTC](https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752/3 "2025-07-12T06:34:52Z")
I would tap at 1a/1b if you’re going to put a gage on each filter, otherwise at 2a/2b to measure the system as a whole.
If everything is working normally, your assumption is reasonable, but if one filter clogs (or blows out) then I think you’ll see bigger differences between 1a/1b vs 2a/2b.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [July 12, 2025, 11:35am UTC](https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752/4 "2025-07-12T11:35:39Z")
> [@abcdefghij](#):
>
> otherwise at 2a/2b to measure the system as a whole.
^ this. And I also have a well and two filters on it. This is an interesting system - the water pressure differential gage. Never seen one before.
My two filters are directly line, so a little different set up one right after the other. If I was keeping the house, I would definitely look into getting that gage.
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### Author:  [@MindsEye\_Watering](https://boards.straightdope.com/u/MindsEye_Watering)
#### Post date: [July 12, 2025, 12:44pm UTC](https://boards.straightdope.com/t/water-pressure-differential-gauge/1020752/5 "2025-07-12T12:44:39Z")
> [@abcdefghij](#):
>
> but if one filter clogs (or blows out)
Thanks. I always replace both filters at the same time as they should both get dirty at the same time.