High pressure and eyeball size

[eublet]

Hey guys. Searching has yielded a few discussions about pressure and eye size, but nothing that I feel like I can make decisions on.

I bought a house with a pool a few years ago. Water pressure was around 17-18 PSI when clean when I bought it. Pump died so replaced it with the same exact pump. Pressure has been 25 PSI when clean for close to 2 years now. No problems with this that I know of. Details about pool are in my sig.

I have two returns in the pool. Pump is a 1.5 HP through 1.5" piping. Any idea what eye size I should have in general? The eye in the shallow end looks to be a half inch, while the eye in the deep end is 3/4 inch. Wondering if I should open one or both of them up some more and get my pressure down?

Is there any science to figuring this out at all? Maybe take the eyes out completely, see what the pressure is, and then adjust eye size until it raises it to a certain level? Pool circulations seems to be pretty good, maybe too turbulent at times. I have eye's point downward at about 20-30 degrees to the bottom.

THANKS!

 

[Jimrahbe]

E,

I am not sure about the science, but I like your idea of taking them out and seeing what the difference is..

If your pressure drops from 25 to 24, you will know that it would not make much sense to screw with it.. On the other hand, if it dropped from 25 to 15, it would make a lot of sense to make the eyeballs smaller larger...

Thanks,

Jim R.

 

[eublet]

So I tried that and it dropped from 25 down to 21 with no eyes or caps. Just straight pipe. Still seems pretty high to me.

Today my SWCG is getting replaced. I’m wondering if the cartridge change will drop pressure any.

 

[duraleigh]

You have a good grasp of the subject. If your pump is a full rated 1.5 (say maybe 70-90 gpm), then you could be pushing the capacity of your sand filter to handle that much flow.

That flow is not horrible but you have more resistance on the pressure side than is normal. Does it hurt anything? No, but if it was my pool, I would be curious to find the source of that extra resistance........most pools similar to yours probably run closer to 12-15 clean psi?

Have you inspected your sand bed?

 

[eublet]

Thanks for the response! I replaced my sand last year "just because". No change. My new SWCG is in place as of this morning and that didn't change anything either.

Now my pool does have a spillover spa, which I haven't mentioned is shut off. When I open that, it does drop down 5 PSI to around 20. I have a 2nd pump just for the spa. It's shutdown b/c it has some leaks in the mortar between the tiles. But still, 20 PSI still seems kind of high to me, but maybe not that bad. I also have my Polaris cleaner completely plugged at the T connector that feeds the booster pump, and also have it plugged in the pool. It has never worked for me, and I don't plan on fixing it.

So maybe, all thing considering, if I had pool and spa running wide open (that's three eyes) plus the cleaner pump pulling extra water off the main return pipe, PSI would be lower? I've never really thought it through until now.

Side note, this site is awesome. Donating now! I learn stuff everytime I come here and mumble. haha

 

[duraleigh]

For what it's worth, the pressure running just a bit high doesn't stress the pump at all.....it's constant speed.

Also, not by much, but you actually use a little bit less electricity since the pump is doing less work.......always seemed counterintuitive to me but that's how it works.

 

[Jimrahbe]

E,

Since you no longer use the pressure cleaner, why not just take the booster out and plumb around it... this would give you and extra pool return and should lower your pressure, some.. Have no idea by how much.

Thanks,

Jim R.

 

[mas985]

Is there any science to figuring this out at all?

Absolutely!

Each piece of equipment adds to the head loss of the plumbing. The filter pressure is just a representation of the head loss after the filter gauge. It is possible to estimate the head loss in each section of the plumbing and the total flow rate. But to do it properly, you need a lot of detail about the plumbing (i.e. equipment, fittings, pipe lengths, etc).

If you replaced the old pump with exactly the same pump, you should not have experienced any change in the filter pressure. However, without knowing it, you may have replaced an up rated pump with a full rated pump and thus now have a higher flow rate with more head loss. What is the make/model of your new pump?

 

[JamesW]

Also, not by much, but you actually use a little bit less electricity since the pump is doing less work.......always seemed counterintuitive to me but that's how it works.

If the flow rate stayed the same when the resistance (head loss) was increased, it would take more power.

However, the flow rate decreases, which uses less power.

So, you have increased head loss, which increases the amount of power used and decreased flow, which decreases the amount of power used.

The net effect is slightly to moderately less power used.

 

[mas985]

It isn't just flow rate that determines the power used by a pump. Both head and flow rate determine the amount of energy a pump system uses. In fact, the energy delivered to the water is proportional to the product of head and flow rate (i.e. hydraulic power). The hydraulic power can then be converted to electrical power by dividing by both the pump and motor efficiencies.

Hydraulic Power (Watts) = Head (ft) * GPM / 5.3
Electrical Power (Watts) = Hydraulic Power / Pump Efficiency / Motor Efficiency

Wire to water efficiency is typically in the range of 40%-55% or about a factor of 2:1.

 

[JamesW]

I think that that's basically what I was saying.

Increased head loss increases power used assuming constant flow.

However, flow is decreased based on the pump head curve.

So, the net effect in most cases is reduced power used.

 

[eublet]

The replacement pump was an identical model. I did let the cleaner line provide some extra return for a while, but due to its location it seemed to interfere with the flow of water in the pool and how it skimmed. Things were much better when I just closed it up.

I have thought about opening it back up and putting one of those Infusion directional returns on it, pointed horizontally to help increase the whirlpool affect for better skimming

if you guys think there is nothing to worry about then I’ll probably leave well alone.