Measuring pool piping water flow and/or pressure

Dan (electron) said:

So today I got home, and noticed that due to a series of events, the skimmer door was blocked, making the pool pump suck mostly air all day. Since this isn't too healthy for the pump, I would like to detect these kind of problems with the Arduino controller I am building (designing it to monitor 3 pool temp probes). Question is, what is the most efficient way of doing this? Is there such thing as a simple analog pressure gauge? My filter pressure dropped big time whenever this happened, so I am hoping measuring flow or pressure would allow me to detect these kind of issues.

Since I am redoing all the plumbing, I have some wiggle room, so I am all ears.

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AnthonyZ said:

There are certainly pressure and flow monitoring devices with analog outputs (most I've worked with are 4-20mA) but, they're often times just crazy expensive. A flow switch would be considerably cheaper. I know that there are flow switches that you could harvest from an old washing machines, too.

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ano said:

I think an oil pressure sensor from just about any model car should work. I think they trip in the 5-10psi range.

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WayneW said:

Something like this should be all you need (there are cheaper sources & alternative models, maybe ask at yout local pool store).

http://www.aqua-man.com/row_num.asp?Ic=16643
Hayward part number HAXPSA1930 - Pressure Switch Assembly

These are used in heaters as a safety switch to make sure the heater won't kick in when there isn't water flowing. If the pump isn't pumping, then there is no pressure. I don't know why more pumps don't have these built in to the pump to prevent the pumps from running dry and wasting energy and/or ruining themselves.

You probably don't need an analog sensor, unless you want to monitor more than basic on/off. I have the heater safety switch wired to an Elk input via a relay, so the Elk can shut down the pool pump if there is a pressure problem after 2 minutes (usually enough time to re-prime itself). The Elk can also then announce when the heater turns off, indicating the hot tub is ready

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WayneW said:

Something like this should be all you need (there are cheaper sources & alternative models, maybe ask at yout local pool store).

http://www.aqua-man....um.asp?Ic=16643
Hayward part number HAXPSA1930 - Pressure Switch Assembly

These are used in heaters as a safety switch to make sure the heater won't kick in when there isn't water flowing. If the pump isn't pumping, then there is no pressure. I don't know why more pumps don't have these built in to the pump to prevent the pumps from running dry and wasting energy and/or ruining themselves.

You probably don't need an analog sensor, unless you want to monitor more than basic on/off. I have the heater safety switch wired to an Elk input via a relay, so the Elk can shut down the pool pump if there is a pressure problem after 2 minutes (usually enough time to re-prime itself). The Elk can also then announce when the heater turns off, indicating the hot tub is ready

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Lou Apo said:

Oil pressure sending units can be had for $15 with lots to choose from. Speaking on behalf of GM, they put out voltage from 0 to 5 in the range of 0 to 130 psi. I don't doubt that they would work, however, I do question whether they would not fail as a result of corrosion. Since they are designed to be immersed in oil, rust isn't a concern in the design. Maybe you want to play with it? When these fail, my experience they "peg", or, in other words, short out.

The suggestion about monitoring amps on the pump is a good one. If the line gets plugged up and the pump is working against higher pressure, the amp draw will go up. I wouldn't be surprised if it wasn't a good correlation between psi and amps. You might even be able to convert that amps to psi. Certainly you could put a $7 standard psi guage on one of the pipes and then close down a valve and watch to see how close amp draw changes with psi.

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JonW said:

For a flow switch, I'd look at the ones used for the salt systems. They come with a 2" PVC T fitting for putting them inline wherever you need it. Here's an example one: http://cgi.ebay.com/...l-/180669778323

Another thought is to take a look at your existing pool heater to see if it is using a similar pressure switch to what was shown above. You might be able to tie into it to get the status you need without any additional equipment investment.

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