flow increasing when closing a return?

[padlock]

so this one is a puzzler for me. Normally, even with my 2 speed pump on low, my gas heater still gets enough flow to come on. Of course, when my filter gets dirty, the flow diminishes, and the heater switches off.

What I don't understand is that when this happens, I found that by closing some of my returns (specifically a waterfall that flows into the pool), the heater was able to come back on.

That seems counter intuitive to me. Wouldn't closing a return, reduce the flow even more and make it less likely for the heater to switch on? Does anyone have an explanation as to why that might be happening?

 

[borjis]

I think you might be thinking it backwards.

For example if you have low flow on a return jet and put a smaller eyeball on a different jet
it is forcing more pressure to equalize in the other. (we just solved that exact scenario last week for someone that had a weak return jet
in their shallow end)

so blocking a return...that pressure has to go somewhere, so naturally it will come out stronger
on the other.

make sense?

 

[Richard320]

Not if it's a pressure switch instead of a flowmeter.

 

[padlock]

I think you might be thinking it backwards.

For example if you have low flow on a return jet and put a smaller eyeball on a different jet
it is forcing more pressure to equalize in the other. (we just solved that exact scenario last week for someone that had a weak return jet
in their shallow end)

so blocking a return...that pressure has to go somewhere, so naturally it will come out stronger
on the other.

make sense?

Well, the waterfall doesn't have any eyeball, just 2 open pipes pouring over some rocks into the pool. Elevation wise, they are about 2 feet higher than my other returns, could that account for the difference?

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Not if it's a pressure switch instead of a flowmeter.

Is that likely? My heater is a Sta-Rite Max-E-Therm.

 

[Richard320]

Is that likely? My heater is a Sta-Rite Max-E-Therm.

Figure 26 (schematic) shows a pressure switch. So does figure 27. https://www.pentairpool.com/~/media/websites/pool/downloads/heaters%20and%20heat%20pumps/manuals/max-e-therm_owners_manual_english.pdf

 

[padlock]

Figure 26 (schematic) shows a pressure switch. So does figure 27. https://www.pentairpool.com/~/media/websites/pool/downloads/heaters%20and%20heat%20pumps/manuals/max-e-therm_owners_manual_english.pdf

Thank you Richard, that seems to explain it. In your opinion, could this be something I should worry about. I mean wouldn't it be possible to have very low flow but adequate pressure, simply by closing most of the returns?

I know the obvious answer is simply not to do that. But I sometimes keep my other returns partially closed so that when I open the waterfall, I get adequate flow even on low speed. Now I'm thinking that if I close the waterfall return and forget to fully open the other ones, I might be introducing a situation that could potentially damage my heater.

 

[Richard320]

Thank you Richard, that seems to explain it. In your opinion, could this be something I should worry about. I mean wouldn't it be possible to have very low flow but adequate pressure, simply by closing most of the returns?

I know the obvious answer is simply not to do that. But I sometimes keep my other returns partially closed so that when I open the waterfall, I get adequate flow even on low speed. Now I'm thinking that if I close the waterfall return and forget to fully open the other ones, I might be introducing a situation that could potentially damage my heater.

If that happened, the high limit switch would kill things. Or the flue temperature switch.

 

[borjis]

Well, the waterfall doesn't have any eyeball, just 2 open pipes pouring over some rocks into the pool.

But turning it off means that extra pressure has to relieve itself elsewhere.

 

[padlock]

If that happened, the high limit switch would kill things. Or the flue temperature switch.

Ok, that's great to hear. Sounds like they build these things with a fair bit of redundancy. Thanks again for your help.

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But turning it off means that extra pressure has to relieve itself elsewhere.

I'm no expert, but I was under the impression that closing the returns would be like adding head to the system, thus reducing the overall flow. I readily admit that I don't fully understand fluid dynamics though.