Pentair IntellifloFX pumps fighting each other in series?

[poolguy03]

I just installed two Pentair IntellifloFX VSF pumps, replacing two old single speed, 2HP pumps. So far they have been working great, but I have noticed that when I have both running for my spa (they share the same suction line and work in parallel), one of the pumps will cut its wattage from 2200 watts at 3450rpm, to about 1700 watts but still saying 3450 rpm. The other will stay at 2200 watts at 3450 RPM. The flow meter on the pump also shows a big difference between the two, with the one at 2200 watts showing around 65gpm, and the one that cuts its wattage down at around 40gpm.

My old setup with the single speed pumps had an external flow meter and each pump was pushing around 50gpm. So both setups output around 100gpm but now they are not equally split as they were before with the 2hp single speed pumps, even though in both scenarios the pumps are identical. If i turn off the spa, the pump that cuts its wattage down will go back up to 2200 watts at 3450rpm. What could be the cause of this, and will it damage the pumps?

I should also add that in my single speed pump setup, it would consume around 5Kw to run the spa jets. With the intellifloXF's it only consumes around 3.9Kw with the same output (maybe a bit more as the jets seem a bit stronger).

For clarification, the suction line they share is a mirror image "Y", but the outputs are not mirror image. One pump (the "main" pump that filters the pool) goes through the filter and normally returns to the pool. The other pump returns directly to the spa. In spa mode, the main pump has a jandy valve that switches to return to the spa. In this mode they eventually share a common return point to the spa.

 

[ajw22]

Are the IntellifloXF pumps controlled by automation or their own control panel?

Is the pump speed set in RPM or GPM?

 

[poolguy03]

Are the IntellifloXF pumps controlled by automation or their own control panel?

Is the pump speed set in RPM or GPM?

Own controllers, each set to "SPEED" in the menu.

 

[ajw22]

Let's see what @mas985 has to say about the shared suction line.

 

[mas985]

Generally, running two pumps off the same suction line will only causes problems. The only exception is maybe when the suction line is sized properly for both pumps running at the same time which almost never happens.

What size is the suction line? Anything less than 3" is too small and ideally should be 4" for that sized pump. Your spa users could be at risk of entrapment if the water velocity in the suction lines exceeds 6 ft/sec.

When sharing the same suction and both pumps are running, the combined flow rate is significantly higher and the result is much higher head loss in the suction line which could potentially cause cavitation but at a minimum will cause a reduction in flow rate and power of both pumps.

It is a bit odd that only one of two pumps is affected as both pumps should experience a reduction in flow rate and power which makes me think something else is going on.

Also the flow rate you are reporting appears to be much higher than that reported by Energy Star for nearly the same wattage levels. Here are the Energy Star numbers for each plumbing curve:

Curve-B: 44 GPM @ 2138 Watts
Curve-A: 74 GPM @ 2545 Watts
Curve-C: 101 GPM @ 2837 Watts

Your wattage numbers are close to Curve-B which is representative of extremely high head loss plumbing. 1700 Watts is well below the wattage of Curve-B and indicates a situation close to dead head.

What type of flow meters are you using (e.g. FlowVis, Blue White)?

What does the pump internal GPM display show?

Do the external flow meters match the pump GPM display?

Have you checked the maximum flow rate settings for each pump?

Was anything else replaced at the same time as the pumps?

Are there check valves on the outlet or inlets of both pumps?

Describe in detail the plumbing after each pump. Pipe size, distance to the pool/spa, number of spa jets and nozzle size, other equipment.

Post a picture of all the plumbing on the equipment pad.

 

[poolguy03]

Generally, running two pumps off the same suction line will only causes problems. The only exception is maybe when the suction line is sized properly for both pumps running at the same time which almost never happens.

What size is the suction line? Anything less than 3" is too small and ideally should be 4" for that sized pump. Your spa users could be at risk of entrapment if the water velocity in the suction lines exceeds 6 ft/sec.

When sharing the same suction and both pumps are running, the combined flow rate is significantly higher and the result is much higher head loss in the suction line which could potentially cause cavitation but at a minimum will cause a reduction in flow rate and power of both pumps.

It is a bit odd that only one of two pumps is affected as both pumps should experience a reduction in flow rate and power which makes me think something else is going on.

Also the flow rate you are reporting appears to be much higher than that reported by Energy Star for nearly the same wattage levels. Here are the Energy Star numbers for each plumbing curve:

Curve-B: 44 GPM @ 2138 Watts
Curve-A: 74 GPM @ 2545 Watts
Curve-C: 101 GPM @ 2837 Watts

Your wattage numbers are close to Curve-B which is representative of extremely high head loss plumbing. 1700 Watts is well below the wattage of Curve-B and indicates a situation close to dead head.

What type of flow meters are you using (e.g. FlowVis, Blue White)?

What does the pump internal GPM display show?

Do the external flow meters match the pump GPM display?

Have you checked the maximum flow rate settings for each pump?

Was anything else replaced at the same time as the pumps?

Are there check valves on the outlet or inlets of both pumps?

Describe in detail the plumbing after each pump. Pipe size, distance to the pool/spa, number of spa jets and nozzle size, other equipment.

Post a picture of all the plumbing on the equipment pad.

When in spa mode, the suction line is 3 inches that then breaks off using a T, into two 2 inch inlets. After that, the main pump outlet is 2 inches and goes through a 580 sqft cartridge filter, then through a chlorine generator, then into a 3 inch pipe that goes to the spa jets.

The other pump that is only ever used when the spa is in use, has an inlet from the other output of the T (3 inches down to 2 inches). It then output through a 2 inch pipe, and then makes its way to the same 3 inch spa return that the main pump returns to in spa mode (jandy valves direct the main pump to the 3 inch spa return when in spa mode or the 2 inch pool floor jets when in pool mode). So basically, it goes 3 inch suction that breaks off into two 2 inch lines, then each pump has 2 inch lines that meet back at a 3 inch return line. Only the spa pump has a check valve as the spa pump would never be on without the main pump on. This is how the system has ran since installed, and I only replaced the pumps, no other plumbing.

The spa is on the larger side with 12 Waterway Roto Deluxe jets and the gpm numbers I quoted above were the readings from the intelliflo controllers. The mechanical flow meter (blue white) reads slightly higher than the intelliflo number.

 

[poolguy03]

UPDATE: I was able to get both pumps to output the exact same gpm, with exact same psi readings, with exact same wattage readings. When the spa pumps' heater bypass is enabled, it creates the above scenario I originally posted about. When I disable the bypass and let the spa pump flow through the heater core, it makes the pumps match in flow and power draw. I assume this is due to the spa pump having much less restriction when the heater bypass is enabled than the main pump, which always flows through the cartridge filter.

 

[mas985]

What is the flow rate with only one pump running? Are you really getting that much more total flow to the spa jets with both pumps running?

There may be a better way to configure your spa so it only needs one pump to run by using strategically placed bypasses and it may provide better flow rates than your current configuration. Something like this: