Causes of lower pool pump flow

[Turkish]

Long story short: what can cause low pump discharge pressure and flow? Since troubleshooting a noisy pump, disassembling and reassembling after finding/replacing bad motor bearings, flow is visually less than pre-replacement. This is from flow rate out of the spa. Discharge pressure I think is also lower, but I also had to replace pressure gauges during this activity. I don’t recall what discharge pressure the pump previously made, from a quantitative standpoint. I thought it was over 20, though. It’s making about 18 psi now.

Any common things to check? Disassemble and check impeller? What else? I don’t see signs of much air intake. It’s been running this way essentially unchanged for a few months. Filter has been backwashed. I do see a reduction in discharge pressure after backwashing, but I don’t notice a flow change as markedly as I used to. Tia

 

[mas985]

Long story short: what can cause low pump discharge pressure and flow?

DIrty Filter - Clean Filter (which you have done)

Clogged Impeller - Check the bottom of the pump basket first to see if anything is stuck in the inlet. You may have to separate the wet end from the motor to inspect directly.

Clogged Suction Line - Back Flush the suction line (eg. Drain King, garden hose with rag).

 

[Shapshftr]

I would check your impeller. It may be partially clogged. I have a small pool for my dogs with a small sand filter, and after vacuuming all of the floating fur and crud they track into it all the time, it has really slowed down. I checked everything else, so that's my next step.

 

[Turkish]

I’ll bump this before starting a new thread.

I’ve recently done more troubleshooting. Closing off any of the 3 pool suction lines gives me about 1 psi of discharge pressure loss. If one of these was plugged, I’d expect NOT to see any pressure loss upon closing it. With it only having suction from the pool and only discharging into the spa, I estimated 60-80gpm at 26psig discharge pressure, assuming 0psig suction pressure. According the pump curve I should see around 120 gpm of flow, so my my instincts based on visual inspection seem to be correct. If my suction pressure were really a few psig below 0, then maybe I match the pump curve better, but I can’t measure suction pressure.

 

[mas985]

Where did you get 26 PSI? I thought the filter was running at 18 PSI.

How did you estimate 60-80 GPM?

If you can give me details on the plumbing and pump, I can estimate both suction and return side head loss and flow rates.

Pump make/model#
Filter size
Distance pool to pump
Suction/Return lines diameters and number of parallel runs pool to pump
Number pool returns and eyeball diameter
Pool Water to pad level elevation

 

[Turkish]

Where did you get 26 PSI? I thought the filter was running at 18 PSI.

How did you estimate 60-80 GPM?

If you can give me details on the plumbing and pump, I can estimate both suction and return side head loss and flow rates.

Pump make/model#
Filter size
Distance pool to pump
Suction/Return lines diameters and number of parallel runs pool to pump
Number pool returns and eyeball diameter
Pool Water to pad level elevation

Really appreciate the response. I get 26 psi if I’m only discharging to the spa. 18 going to both spa and pool jets. I determined 60-80 gpm by timing the spa filling, after calculating the volume. I will work on remaining items.

I’m a process engr, so I understand pump curves and pressure drop, but I’m not perfect with applying it to this equipment and where common issues lie.

 

[Turkish]

Where did you get 26 PSI? I thought the filter was running at 18 PSI.

How did you estimate 60-80 GPM?

If you can give me details on the plumbing and pump, I can estimate both suction and return side head loss and flow rates.

Pump make/model#
Filter size
Distance pool to pump
Suction/Return lines diameters and number of parallel runs pool to pump
Number pool returns and eyeball diameter
Pool Water to pad level elevation

Pentair 346201 — 2hp Challenger
Tagelus TA-100D filter
Pump is about 24’ from one skimmer, 50-60’ from other skimmer, 28’ from pool drain, 50’ from spa drain. All distances horizontal.
4 suction lines are all 2” from what I can see above ground. All individually valved.
One return to spa, about 50’, pipe appears to be 1.5”.
2 return lines to pool jets, also 1.5”. I don’t really know the exact layout of these pipes. I have 2 jets probably 60’ from the pump.
Pool surface to pad is no more than 2’.

Also, I pulled and inspected the impeller before updating the thread. There was some debris in it that was removed. Since, absolutely zero bubbles in strainer and return water, so I think the impeller is good.

 

[mas985]

My estimate of filter pressure is about 17.7 PSI so pretty close to what you are getting.

Sounds like everything is working as it should. Is there any other particular issue other than what you remembered being the filter pressure? Note too that filter pressure will change with both the suction and the return side valve settings. So if you had previously had them in a different position, then that could account for any difference.

 

[Turkish]

My estimate of filter pressure is about 17.7 PSI so pretty close to what you are getting.

Sounds like everything is working as it should. Is there any other particular issue other than what you remembered being the filter pressure? Note too that filter pressure will change with both the suction and the return side valve settings. So if you had previously had them in a different position, then that could account for any difference.

17.7 psi at filter inlet or outlet? And roughly what would the pressure be at the pump suction?

2 particular issues concerning me are that flow rate does not seem to match the pump curve. Also, visually my waterfall rate is less than it used to be before the wintertime motor issues.

 

[mas985]

Filter pressure is 17.7 PSI. Suction at the pump basket would be about 4.5 in-hg. But these are estimates based solely on what you have told me but they shouldn't be too far off.

The estimated operating point is 86 GPM @ 56' of head. What head curve are you using?

The 2 HP uprated pump is curve J.

 

[Turkish]

Thanks s a ton! I’ve been referencing the curve here, which is quite a bit different. https://images.inyopools.com/cloud/documents/pentair-challengerpumps-highpressure-datasheet.pdf

And what would be an estimate of pressure drop across the sand filter?

 

[mas985]

Those curves are for full rated pumps. You need to use the 1 1/2 HP full rated curve to match the 2 HP uprated. They are the same.

The plumbing curve constant I am using for the sand filter with a 2" Multi-port is 0.0025.

Head Loss = 0.0025 * GPM^2 = 18.5' of head.

 

[Turkish]

Now I’m lost. My motor says 2hp with a 1.1 SF, giving a rated output of 2.2. Why would I use a curve for 1.5?

 

[mas985]

2 HP with a 1.1 service factor is an up rated pump. The curves in the brochure are for a full rated pump which usually has a service factor of around 1.65. So 1.5 * 1.65 = 2.475 THP and 2 * 1.1 = 2.2 THP so close to being the same. Manufactures often use the same head curves for the full rated as the up rated versions. You just need to make sure you are using the proper curve. If you look at the parts list for the full rated 1.5 HP vs the uprated 2 HP, you will find that they use the same impeller which is what determines the head curve.

 

[Turkish]

Gotcha. That’s pretty important info not to state in the brochure. Ultimately, I’m ready for a new motor or pump/motor. I wanted to verify I didn’t have other issues going on keeping me from getting the flow I expect before buying. If I’m getting the correct flow according to the curve and my pressure drops look reasonable, then my visual triggers must just not be real.

If I want more flow, I just need to go up in HP.

 

[mas985]

It is a bit moot now because the DOE banned single and dual speed pump manufacturing for anything above about 0.711 HHP. So if you are upgrading, your only real choice is a VS pump. But that is not a bad thing.

 

[Turkish]

I was looking at the Century VGreen VS since it’d be a drop in replacement for this motor, and keeping same wetted parts. They have a 2.25 and a 2.7. Now I’m confident a 2.7 would be needed for any increased performance.

 

[mas985]

Putting a larger motor on the same wet end does not change the head curve performance. Again, the impeller determines the head curve not the motor.

However, a VS motor will be a little bit more efficient at full speed and much more efficient at lower speeds.

 

[Turkish]

Yep, yep. Thanks for reminding me. I’d forgotten that. It won’t spin any faster on the high end.