Calculating GPM

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One of my original concerns was a partially clogged impeller. I know that you checked via the pump basket but that doesn't mean it is completely clear either. I was trying to eliminate all other possibilities but more and more it looks like the impeller may be the problem. The reason I think this is because a partially plugged impeller acts as if the RPM is slightly reduced. Flow rate decreases, wattage decreases and the head curve shifts downward. All symptoms of what seems to be occuring. It looks like it is only about 5% reduction which is not much but could be more of an issue at lower speeds which I think you are experiencing. However, I don't want you to go to the trouble of taking apart the pump if that is not the problem but maybe your PB can do that if willing.

On high speed, does the pump seem to shake or vibrate a lot?
 
Would it be possible to use a very thin wire brush to check/clean the impeller vains? Like the kind used to clean the drinking tube for those water bladder things (I have two but their name is slipping me :( )

I'm at the same point with my issue - I'm down to suction blockage on both pipes or an impeller blockage.
 
That might work. Another thought if possible is to use a drain king in the pump outlet and back flush any debris that is stuck in the vanes out through the pump basket. That may or may not be enough to dislodge it but might be worth a try. Loweran has a union which can be disconnected but not sure about your setup.
 
I do have unions. I'll try both before I open it up. And while I'm at it I'll prob backflush the suction lines too since the pump will be disconnected.

Not to hijack, I think this is relevant, can you use a drain king in the pump for the suction lines Ie in the pump inlet? Will the drain king bend enough and still inflate properly?
 
Also, page 44 has a more specific list of steps for cleaning out the impeller only - second section: reduced capacity and/or head.

Hopefully I won't need to disconnect the pipes provided I have enough space behind the pump - I have a Dear Mr. Pool Builder situation :roll:
 

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Just want to recap:

I have reduced flow based on my head calculations, and especially based on the power consumption of my pump at a given RPM. The phenomena appears to be more exaggerated at lower RPMs. PSI reading seem reasonable, suction is reasonable at higher RPMs but low at lower RPMs.

Possible causes:

Plumbing design
This is not a probable cause as my lines are 2" and I do not have unreasonably long runs or elevations.
Check Valves in system
I only have a check valve in the spa return to prevent it from siphoning back into the pool.
Clogged suction line
I ruled this out by testing each suction line independently and noting pressure readings at the filter. As a precaution, I also tried to clear each suction line with a drain king. No debris was noted while using the drain king
Intelliflo not reporting accurate watt usage
I ruled this out by using my electric meter to validate power consumption. The pump appears to be reporting power consumption correctly.
Leak in suction line
This could still be a possibility. I do seem to collect air in the system over time, but this could be due to the ozone system that is installed on the suction side of the pump.
Clogged Impeller
I did a feel check of the impeller and there is nothing apparent at the intake of the veins. My next step will likely be to remove the motor and visually check the impeller.

Am I missing anything?

I still need to get my PB input. I have a tech meeting me to discuss the system on Friday. I really have no expectations of how that might go. It all depends on the tech I suppose. If I end up stumped, I will likely install a flow meter to get a validation that I have restricted flow and use that as a means to engage the PB on the subject.
 
New details

Tech was here. Did not think the impeller was clogged. He cleaned the DE Filter by removing the cartridges and hosing them down. After also noted that the air bleed tube in the filter was too short which is why we had so much air in the system. Here are the numbers now:
RPM/WATTS/PSI
1500/218/3
2350/847/10
3450/2640/20

I still might take that motor off and inspect the impeller. The filters were really dirty with tree seeds and pollen. Good chance that it could be partially blocked.
 
As I mentioned before, you have a union on the pump exit pipe that you could use to back flush the pump and see if anything comes out through the pump basket. That may be an easier way to clear the impeller without taking apart the pump.
 
Unfortunately, Pentair may not see anything wrong with what you are experiencing.

There could be one more explaination. The filter pressure only measures the pressure loss from the filter forwards. If there is excess pressure loss between the pump and filter, that would need to be added to the total head loss. Some DE filter backwash valves have a lot of the head loss but I don't know about yours. Do you know which valve model that you have? Did it come with the filter?
 
So, here is what I will do. I am OOT for biz this for a couple of weeks, but when I get home, I will spend some time getting pressure readings at the pump. If I get vacuum and pressure readings at the pump, we should be able to calculate the head exactly right? With that data, I should be able to discuss this with Pentair. Other than that, I am out of options.

One thought came to mind. If anyone knows a tech in the Austin area who is well qualified to diagnose this issue with this particular set up, I might be willing to pay them to take a look. At this point, I am simply aggravated by the power consumption of my pump at a given RPM. Also, I really want to be able to estimate the GPM within a degree of certainty, and can't really do that with these numbers.
 
The pressure at the pump should help determine if there is a lot of head loss between the pump and filter. Given that you have elminated everything else, that is probably the cause for the inconsistancy.

Also, keep in mind that knowing the actual flow rate is interesting and somewhat helpful but it is not totally necessary either. There are no hard rules as to the number of turnovers a pool needs so some trial and error would necessary either way. But if you really want to know the flow rate, you might consider a flow meter.
 

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