Vacuum gauge on pump suction side reading zero. Problem?

[kjones6160]

I have installed a Pentair Intellifo model 011028 variable speed pump and am trying to calculate the total dynamic head for my system in order to determine the GPM flow rate at various RPM speeds. Pool was pre-existing when I bought the home so I have no information regarding all of the underground piping in order to determine the total length of all of the pipes. Pool has a Caretaker99 5 zone system with 1-1/2 inch returns. I read this Inyo Pools article about using two gauges using the pump's drain plugs, one on the suction side (strainer basket drain) and one on the pressure side (pump impeller housing drain) to calculate TDH using a formula that utilizes the two gauge readings (vacuum side in inHg, pressure side in PSI). I'm using two of these combination -30 Hg/30 PSI gauges .

Now for my problem....The vacuum gauge reads zero for all speeds except the maximum 3110 rpm speed, and then the needle barely reads -1 on the gauge. Is there a problem if the suction line has no vacuum? I have very good return flow to the pool because the Caretaker pop up heads are all functioning properly as well as the water features. I'm getting a range of pressure readings from around 5 psi @1000 rpm to 30+ psi @3110 rpm.

So my question is..... What would be causing a zero vacuum reading on the suction side of the pump, and is that really an issue? Should I try a different vacuum gauge with a more precise range than -30 to 0?

My overall goal is to develop a custom pump performance profile based upon real-time data for my specific pool installation. With the pump's RPM readings and calculated TDH at various speeds I can determine the pump's GPM flow rates at various RPM which will allow me to create the necessary pump programming schedules. The only wildcard here is determining the TDH for my pool. Any suggestions?

 

[Bperry]

I have installed a Pentair Intellifo model 011028 variable speed pump and am trying to calculate the total dynamic head for my system in order to determine the GPM flow rate at various RPM speeds. Pool was pre-existing when I bought the home so I have no information regarding all of the underground piping in order to determine the total length of all of the pipes. Pool has a Caretaker99 5 zone system with 1-1/2 inch returns. I read this Inyo Pools article about using two gauges using the pump's drain plugs, one on the suction side (strainer basket drain) and one on the pressure side (pump impeller housing drain) to calculate TDH using a formula that utilizes the two gauge readings (vacuum side in inHg, pressure side in PSI). I'm using two of these combination -30 Hg/30 PSI gauges .

Now for my problem....The vacuum gauge reads zero for all speeds except the maximum 3110 rpm speed, and then the needle barely reads -1 on the gauge. Is there a problem if the suction line has no vacuum? I have very good return flow to the pool because the Caretaker pop up heads are all functioning properly as well as the water features. I'm getting a range of pressure readings from around 5 psi @1000 rpm to 30+ psi @3110 rpm.

So my question is..... What would be causing a zero vacuum reading on the suction side of the pump, and is that really an issue? Should I try a different vacuum gauge with a more precise range than -30 to 0?

My overall goal is to develop a custom pump performance profile based upon real-time data for my specific pool installation. With the pump's RPM readings and calculated TDH at various speeds I can determine the pump's GPM flow rates at various RPM which will allow me to create the necessary pump programming schedules. The only wildcard here is determining the TDH for my pool. Any suggestions?

Only logical reason for reading 0 (other than a bad gauge) would be that it’s 0. Haha.

I guess it depends on what your trying to achieve by doing all that. None of that information is necessary to operating your pool, but If it’s just for fun, I guess you need a lower range gauge. If water is flowing, you have a vacuum (or negative pressure) being created otherwise water wouldn’t be moving.

 

[kjones6160]

Only logical reason for reading 0 (other than a bad gauge) would be that it’s 0. Haha.

I guess it depends on what your trying to achieve by doing all that. None of that information is necessary to operating your pool, but If it’s just for fun, I guess you need a lower range gauge. If water is flowing, you have a vacuum (or negative pressure) being created otherwise water wouldn’t be moving.

Update - Instead of using a combination pressure/vacuum gauge I replaced it with a vacuum gauge with 0-30 more sensitive scale and was able to collect my suction side readings at the lower speeds. So now I was able to set up my variable speed programming for a 24-hour runtime. Doing the calculations allowed me to see I was not running the pool system to its optimal performance. Running the pump in manual mode behind a mechanical timer for an 8 hour daily duration cycle works but negates the efficiency of the VSP. Instead of running at higher speed of 2800 RPM for 8 hours I programmed the pump to run at three different lower speeds and run it 24x7...it actually consumes less kWh per day running at much lower speeds all day versus higher speed for 8 hours then off for 16 hours based on my cost per killowatt hour from my electric bill. I'm achieving a turnover rate of 2.8 times per day at the lower speeds and longer run time, which I think is just about right. I was also able to "tune" my SWG to generate a supply of chlorine around the clock by running the pump at a minimum setting of 1100 RPM to create sufficient flow through the SWG's in-line flow sensor. I believe I'll see better residual chlorine readings and better water chemistry overall by not letting the pool sit stagnant for 16 hours a day...and am also cutting the pump's daily power consumption by at least one third. Variable speed pumps are definitely worth the investment in the long run, but only if one takes the time to do the math for your specific pool's configuration and then develop the necessary programming schedule(s) to achieve the best performance possible.

 

[PoolStored]

I'm curious, why is this important?

I run my pump 24/7 at the lowest speed necessary to run the SWCG, and keep my pool at a level that I get sufficient skimming action at that pump speed. Constant chlorine and skimming. What else are you trying to achieve?

 

[Bperry]

Update - Instead of using a combination pressure/vacuum gauge I replaced it with a vacuum gauge with 0-30 more sensitive scale and was able to collect my suction side readings at the lower speeds. So now I was able to set up my variable speed programming for a 24-hour runtime. Doing the calculations allowed me to see I was not running the pool system to its optimal performance. Running the pump in manual mode behind a mechanical timer for an 8 hour daily duration cycle works but negates the efficiency of the VSP. Instead of running at higher speed of 2800 RPM for 8 hours I programmed the pump to run at three different lower speeds and run it 24x7...it actually consumes less kWh per day running at much lower speeds all day versus higher speed for 8 hours then off for 16 hours based on my cost per killowatt hour from my electric bill. I'm achieving a turnover rate of 2.8 times per day at the lower speeds and longer run time, which I think is just about right. I was also able to "tune" my SWG to generate a supply of chlorine around the clock by running the pump at a minimum setting of 1100 RPM to create sufficient flow through the SWG's in-line flow sensor. I believe I'll see better residual chlorine readings and better water chemistry overall by not letting the pool sit stagnant for 16 hours a day...and am also cutting the pump's daily power consumption by at least one third. Variable speed pumps are definitely worth the investment in the long run, but only if one takes the time to do the math for your specific pool's configuration and then develop the necessary programming schedule(s) to achieve the best performance possible.

If it helps any, I also run my pump 24x7 at low speed to just to get good skimming and it’s quite a bit cheaper (and quieter) than my old single speed pump. Make sure you take into account the skimmer performance as well. If your SWG can generate at a low enough output level it sounds like you have a decent setup.