VS Motor Upgrade - Now what ...

... do I do about Filter PSI? I don't know how low is too low.

Last week (Thursday, July 9, 2020), I replaced the 0.75 HP single speed motor on Hayward Super Pump with a V-Green 165 Variable Speed motor. Also replaced the impeller with the 1.5 HP part number. I have scanned the forum and the tutorials on equipment to find information on how the VS might behave with the rest of the system. I found posts about flow rates, turnovers, skimmer operation, spa and feature operation, but I do not recall seeing information on Low DE filter PSI. Now I'm trying to figure out my minimum RPM operation so I can start to see those massive kWh savings!

With the SS motor, clean DE filter startup pressure over the years has consistently been about 6.5 PSI on the Hayward "eye test" gauge. I had (what I believed to be) good flow through the skimmer and decent return at the eyeballs. I typically run the single suction valve set 50% skim, 50% bottom.

The V-Green VS motor primes at 2600 RPM for 3 minutes. First startup was approximately 6 PSI (old gauge). I thought I was doing fine. Began to play with speeds. Tried Speed 1 at 1600 RPM: PSI=0, skimmer didn't seem to be flowing. Changed Speed 1 to 2100 RPM: PSI=0, skimmer looked to be moving very slowly, champagne bubbles out of the returns. Tapped on the gauge, PSI read about 3.5 (time to replace gauge, ordered new Glycerin Filled one from TFTestkits). Installed the new gauge and redid the pump inlet and filter outlet connections with TFE tape and lube yesterday, no more return bubbles at 2100 RPM.

Current Filter PSI (new gauge):
2600 RPM (Prime) = 7
2350 RPM = 6
2100 RPM = 4

There are many references to maximum specifications, but how do I find a minimum pump speed and know that there is sufficient flow through the filter?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,524
Laughlin, NV
There is no minimum flow through a filter. The filter works fine at any flowrate up to its maximum.

With a VS pump - this is my standard response to a new owner.
So the first reason to run your pump is to either create your chlorine (with a SWCG), or to distribute the liquid chlorine you add each day. As I do not see a SWCG in your signature, you must be adding liquid chlorine every day. So the pump needs to run about an hour after you add the chlorine.

Second reason to run the pump is to skim the surface. The RPM needed for that depends on your pool. I would suggest starting at 1800 rpm and 4-6 hours and see if that keeps the pool clean. Adjust as necessary (rpm and time) to achieve your desires.
 
I believe I have seen those recommendations in other posts. I just got concerned when I saw the PSI drop as the speed was slowed down. I'll continue experimenting with slower speeds.

Do you think I made the correct decision to change the impeller to more closely match the HP of the motor?

Thanks, Marty.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,524
Laughlin, NV
Do you think I made the correct decision to change the impeller to more closely match the HP of the motor?
Sure. It makes use of the full range of the motor.

You should check your filter pressure at prime speed. So that once it increases 25% over clean pressure at prime speed, it is time to clean the filter.
 
I did. Fresh DE was charged just before the motor change and the new Prime PSI = 7, which is essentially the same as it was with the old 0.75 HP, and old gauge. But I may need to recharge DE after testing speed variations and re-verify PSI on the new gauge... But at the time of the change, both motors read the same on the old gauge.