This is my first post on this forum - so please go easy
I have a 20,000 gallon pool with an Intelliflow VF as the main pump, driving a diatomacious earth (DE) filter.
The setup has been working great for over two years. The pool sweep is a Polaris 280, with a separate 2hp booster pump.
Recently, the pool sweep booster pump broke and I self-replaced it with a second Intelliflow VF, reasoning that it would save as much energy as the main pump. Yeah, I know, I should have done my homework BEFORE installing such a fancy pump as a booster, but hey, it's done...
However, the second Intelliflow VF, used purely as the pool sweep booster pump, has been quite a challenge to get just right. I'm hoping some of you experts can provide some good guidance.
Please keep in mind that I have owned a VF for over two years, have read the manual dozens of times, fundamentally understand how the VF works, and love it's flexibility and energy savings.
Here's the challenge:
1. The "booster pump" VF does not prime successfully. I have tried all variations of main pump on/off, main pump high pressure, low pressure, etc. I've fiddled with the "Maximum Priming Flow", high, medium, low, fiddled with the "Water Temperature" parameter, the backwash and vacuum flow rates, in fact, almost every parameter you can imagine, in almost any combination. My conclusion: The narrow feed lines of the Polaris does not allow a flow rate of 30 gallons per minute. (Effectively, too much "head")
To reach the above conclusion, I did the following experiment:
a. Set the "Maximum Priming Flow" parameter to its lowest possible value, i.e. 30 gallons per minute.
b. Partially open (unscrew) the pressure relief valve on the Polaris 280 entry port so that some water "blow by" and therefore flow is increased.
c. The booster VF now easily primes, and in Filter-Run mode, settles at 2200 RPM to reach the programmed target flow of 20 GPM.
d. Some smart people on the forum explained how RPM and flow rate are linear, so I conclude that to reach the PRIMING flow (of 30 GPM) I will need 30/20 * 2200 = 3300 RPM. This is achievable, as the maximum pump RPM is around 3500.
e. When I slowly close the pressure relief valve on the Polaris 280, the RPM count to maintain 20 GPM flow rises to 2900, and you can hear the pump working harder. In this state, I calculate that to reach the required minimum priming flow rate of 30 GPM, the pump would need 30/20 * 2900 = 4350 RPM, which is greater than the maximum pump RPM, so it's no surprise to me that the pump does not achieve prime.
Now, I can actually live with the pressure relief valve partially open (that's how it's set now), the Polaris 280 wheel turn rate is 30 RPM, which is what the manual specifies and it sweeps fine, but the extra flow of water is a waste of energy - the pumps draws about 900 Watt in this mode, but at least, it works.
However, in manual mode, with the blow-by valve closed, and manual speed setting, which overrides any priming requirements, the Polaris runs just fine on about 350 Watt, an almost 60% energy saving, which is why I am still pursuing this - the extra blow-by of water at the relief valve allows the pump to reach prime, but wastes a lot of energy!
The simplest solution I see is to somehow trick the pump to prime at a lower "Maximum Priming Flow" rate, for example 20GPM would work fine. I've tried several times to phone Pentair tech support, asking them if there is even a "backdoor" method to lower the "Maximum Priming Flow" to 20GPM, or even disable priming, but their answer has been "No way", probably since I'm a mere "consumer" (and therefore probably assumed to be an idiot).
Anyways, I'm hoping someone here knows a trick to convince the Intelliflow VF to prime at flow rates less than 30 GPM - or can suggest any other "trick" that would significantly lower the energy usage of the Intelliflow-VF-as-booster-pump application.