New pump, very low suction

[dlukin]

Hi All -
I replaced old 3/4 HP single speed pump (fried motor) with a new 1 HP dual speed pump. Issue is that the new pump has very low suction - when running on high speed the pump basket is barely half full, on low speed maybe 25% full of water. Old pump
This happens regardless of suction lines openings (both open, only skimmer open, or only main drain open).
Any advice is welcome - I'm at my wits end, since old pump worked without issue, and now I've got a several hundred $$ replacement that isn't working correctly.

Equipment info:
in-ground 20,000 gal vinyl pool
all plumbing 1 1/2", underground
no add-ons (heater, spa, fountains, vacuums, etc.)
single skimmer/no weir, main drain
Sta-Rite S7D75 DE filter, max flow rate 74 GPM, pressure 10 PSI (recently backwashed/recharged, this is normal pressure when clean)
replaced Sta-Rite pump, motor @10yrs old, Centurion B2661 3/4HP single speed 3450RPM 230v
with Inyo Pool Pureline PL1608 pump, 1HP dual speed 1720/3450RPM 230v
skimmer and main drain suction lines join together into single 1 1/2" line going direct into pump
pump is wired from 2 20amp breakers

I've checked quite a few things based on other posts I've seen:
pump basket, skimmer basket clean
pump drain plug tight
pump basket lid tight, O-ring lubricated
pump is @25ft from pool, about 1ft below pool level
checked all unions, joints with soapy water for leaks
checked tightness of all unions joins
have not checked voltage at pump (I'm assuming ok since old pump had no issues)
no air entrapment in filter
do not think there's any blockage in any line (incoming suction, outgoing discharge, any lines between pump & filter, etc.)

 

[Lbray812]

Hi All -
I replaced old 3/4 HP single speed pump (fried motor) with a new 1 HP dual speed pump. Issue is that the new pump has very low suction - when running on high speed the pump basket is barely half full, on low speed maybe 25% full of water. Old pump
This happens regardless of suction lines openings (both open, only skimmer open, or only main drain open).
Any advice is welcome - I'm at my wits end, since old pump worked without issue, and now I've got a several hundred $$ replacement that isn't working correctly.

Equipment info:
in-ground 20,000 gal vinyl pool
all plumbing 1 1/2", underground
no add-ons (heater, spa, fountains, vacuums, etc.)
single skimmer/no weir, main drain
Sta-Rite S7D75 DE filter, max flow rate 74 GPM, pressure 10 PSI (recently backwashed/recharged, this is normal pressure when clean)
replaced Sta-Rite pump, motor @10yrs old, Centurion B2661 3/4HP single speed 3450RPM 230v
with Inyo Pool Pureline PL1608 pump, 1HP dual speed 1720/3450RPM 230v
skimmer and main drain suction lines join together into single 1 1/2" line going direct into pump
pump is wired from 2 20amp breakers

I've checked quite a few things based on other posts I've seen:
pump basket, skimmer basket clean
pump drain plug tight
pump basket lid tight, O-ring lubricated
pump is @25ft from pool, about 1ft below pool level
checked all unions, joints with soapy water for leaks
checked tightness of all unions joins
have not checked voltage at pump (I'm assuming ok since old pump had no issues)
no air entrapment in filter

Is there any air in your pump basket window?

 

[dlukin]

More air than water.
At 3450RPM the basket will be roughly 50% filled with water, I can see the input stream coming in from the suction line (it's a pretty strong stream coming in, not like it's just dribbling in, but not enough
to fill the basket completely). So there's a lot of turbulence in the basket and consequently quite a bit of air bubbles coming out of the pool jets.
At 1720RPM the basket is less than 25% filled with water, so it's useless to run the pump at the lower speed.

To re-iterate, on a Wednesday I turned off the old pump - bearing was going out so pump was making too much noise, pump frame/impeller/etc were shot so I decided to replace the whole
instead of making repairs. Other than the noise, the old pump was working fine, no issues with water flow. The next day I started work on swapping out the old pump with the new, which basically was
rewiring and reattaching input and output lines to the new pump. As I said on original post, I checked all connections for leakage in case I had knocked something loose during switch over.

 

[Lbray812]

Silly question. Did you check to see if your skimmer doors are down while the pump is running? Sometimes mine gets stuck and not enough water is making It into the basket.

all valves are open?

 

[dlukin]

Silly question. Did you check to see if your skimmer doors are down while the pump is running? Sometimes mine gets stuck and not enough water is making It into the basket.

all valves are open?

I don't have a weir door on the skimmer, water level is at the 3/4 mark on the skimmer opening.
I get same suction results (low rate of water) regardless of valve setting (skimmer + main open, skimmer only open, main only open).

My pool is @23000 gals, I'm using 48gal/min for 8hr turnover rate, estimating 60ft TDH (really just rough estimate of feet of 1 1/2" line to main drain, not including joints/values/etc)
I'm beginning to suspect the new 1hp pump is underpowered for my requirements. Rough calculation of required flow is near the limits of the pump (as shown on INYO power curve chart for the pump).
I'm puzzled as to how an old 3/4hp pump can outperform this new 1hp pump (I can't find any documentation for the Sta-Rite pump so don't know what the power curve is for it with the Centurion motor).

 

[1poolman1]

I don't have a weir door on the skimmer, water level is at the 3/4 mark on the skimmer opening.
I get same suction results (low rate of water) regardless of valve setting (skimmer + main open, skimmer only open, main only open).

My pool is @23000 gals, I'm using 48gal/min for 8hr turnover rate, estimating 60ft TDH (really just rough estimate of feet of 1 1/2" line to main drain, not including joints/values/etc)
I'm beginning to suspect the new 1hp pump is underpowered for my requirements. Rough calculation of required flow is near the limits of the pump (as shown on INYO power curve chart for the pump).
I'm puzzled as to how an old 3/4hp pump can outperform this new 1hp pump (I can't find any documentation for the Sta-Rite pump so don't know what the power curve is for it with the Centurion motor).

Which Sta-Rite pump? Depending on model, a .5hp pump could easily outperform a 1hp pump. The horsepower rating of a pump is, first of all, how much power it can consume to move water. After that, the design of the pump will determine how much water will be moved for that energy usage.