# Water pressure measurement

• posted

Is there an easy/inexpensive way to measure water pressure? I'm installing a new water treatment setup at home and would really like to monitor the pressure drop across the various filters so that I can generate the necessary alarm to indicate they need to be changed/cleaned.

I've done a search on Google, but can't seem to find anything a couple of hundred dollars.

Thanks,

Randy

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Well, the cheapest way is to use a 5 gallon bucket and time how long it takes to fill it!

Martin Custer

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I have the same interest. I've been experimenting with my 5-stage RO system. I put a pressure gauge after the pre-filters and just before the membrane, but it never really shows any drop in pressure. Not enough flow to show the effect of a really dirty filter. The carbon filters are actually used up long before it would show as a pressure drop.

Another way to do this would have been a FLOWMETER. This way one can measure the amount of water that has passed. Filter replacement would be triggered based on the capacity the filter manufacturer states.

For whole house filters and high flow rates, the pressure gauge would seem like a good idea. A differential type pressure switch could automate this?

In the end for the RO system, I got a chlorine detection kit that turns the water pink if chlorine is present. At six months, I tested the water after the first, then second carbon stage and found that chlorine was beginning to appear on the output of the first carbon filter. So I now change the first carbon every 6 months, and both carbons and the sediment filter every year.

On ebay, you can also get in-line TDS meters relatively cheap. But if one waits to see the effects of a failed membrane, it is too late!

Good Luck!

• posted

So filling a 5 gallon bucket in say 1 minute translates to how much pressure :)

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I think you could derive an equation starting from fluid flow equations that predict flow (eg Darcy-Weisbach).

known flow: 5gpm need: what size pipe? assume: general characteristics of similar pipe derive: reasonable approxmation of pressure

some equations:

all kinds of calculators, maybe one to do the job:
But it might be easier for to buy a pressure guage and measure static and dynamic pressure and calculate the filter restriction.

sdb

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If the water comes from another 5 gal bucket, then it's pretty low. If the water is coming from a drinking straw, that's pretty high. So, you need to identify another variable before this works out. :-)

-John O

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If you are good with electronics, you might be able to hack a digital tire pressure guage and get an output to work with. WalMart has a small digital tire pressure gauge for \$5.88 that might be a starting point.

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What device are you using to fill the bucket? (This is an automation site right?)

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The pressure drop is strongly related to the flow rate. When all taps are closed, the pressure throughout your system -- both before and after the filters -- will be equal to the line pressure (whatever your household pressure regulator is set for). There will be zero drop across the filters.

To do what you want, I think you'd have to arrange to measure the pressure drop with a tap open, *to a standard flow rate*.

Isaac

• posted

Grainger has a \$45 box that connects before and after a RO membrane filter to tell when it's time to change it.

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