Troubleshooting low flow, low psi, help!

[mas985]

Calibration was done at full speed WITHOUT cleaner attached. All the flow is going to skimmer. I have a simple set-up. Old pool. The main drain plumbs to the single skimmer (I have that closed off), and the skimmer goes straight into the pump, no valves. no heater, no solar. nothing really adjustable.

Then the flow rate numbers are meaningless when you put the cleaner on. Flow rates change with head loss.

I was hoping I could pick your brain on two fronts:
1. Measuring my return lines and guessing at the fittings, I get a return equivalent length of 135 Ft of 1.5 pipe, Suction equivalent length is 42 ft of 1.5 pipe.
On the return side, at 60 GPM, that translates into 27 ft of head, Adding 3 Ft for the sand filter (I read that is a good enough approximation), I get at an experimentally estimated 30 Ft of head for the return side. The Pump Spreadsheet calculates at 39.4 ft. Could the difference be evidence of a blockage? I haven't tried the drain king but a hose and shop vac have not helped.

From the picture above, the return head loss is 45' and the flow rate is 56 GPM. Why did you use 60 GPM? Also, did you include the fittings underground and the return eyeballs? Also, every filter has different head loss characteristics so you really can't use fixed value for that. It is also dependent on flow rates.

2. One thing I cannot understand is when the pump is on low speed, I can completely close off the suction line (with a plug in the skimmer), and it does not cause any air in the pump basket. Initially, I thought this confirmed that I did not have a suction air leak but now I am not sure. Shouldn't the basket evacuate?

At lower speeds, the pump cannot create as much suction as higher speeds so the pump lid can probably seal that very well. Also, a pump lid will have different sealing characteristic under different pressures. So you could have a leak on high and not on low or even visa versa.

 

[Hands]

I had a similar problem when I opened my pool a couple years ago. I was beating my head against the wall looking for a suction side leak or a blockage. It turned out to be a tear in one of the internal gaskets in the pump. The impeller could not develop pressure because of the tear. I bought a gasket kit and made it like new. Was a simple fix.

That is interesting, jimingreen, I'm fairly handy. Is it something that is DIY? What pump do you have? I saw that a gasket kit is available for my
pump fairly inexpensively. Will order that and keep testing till it shows up. Thanks!

 

[Hands]

Then the flow rate numbers are meaningless when you put the cleaner on. Flow rates change with head loss.

Yes, you are right. I could try attaching the cleaner with just 1 section of hose and calibrate that. Though I don't know how much head the cleaner will add. At this point, I just want to know for sure that my pump is in the ball park of its specs and not with a damaged O-ring as jimingreen suggested. I guess I really need a flow meter. I do have a pool pulse that came with my old Zodiac G3 suction cleaner, I could connect that up to a hose length and see what it does.

The manual says it needs 14-19 GPM which might give me a ball park on where I am. Otherwise, I guess I drain king it and open up the pump and see if it improves.

From the picture above, the return head loss is 45' and the flow rate is 56 GPM. Why did you use 60 GPM? Also, did you include the fittings underground and the return eyeballs? Also, every filter has different head loss characteristics so you really can't use fixed value for that. It is also dependent on flow rates.

Sorry about that, my psi is 12, which gives 61 GPM on the spreadsheet. That screengrab was from when I was playing around and trying to understand how things work. My mistake. Yes, I best guessed what fittings would be underground and removed the eyeballs. I was trying to reduce head to see if I could get the cleaner RPMs up. I matched my 3.14 sq.ft Hayward filter to a Pentair filter and came up with 2.5 that I rounded up to 3. I read somewhere (actually might have been you, Mas985!) that said that was acceptable.

Thanks for the info on pump lids. Very good to know. Appreciate your taking the time!

 

[mas985]

As long as you have a working pressure gauge, that is going to be the most accurate way to measure return head. The suction side is estimated from the configuration.

But I really don't think there is anything wrong with your system. It is just a limitation of the system design. It is very hard to get a suction side cleaner to work properly on low speed of most pumps. Even those with VS pumps find they have to run at higher RPMs to get the cleaner to work.

 

[Hands]

But I really don't think there is anything wrong with your system. It is just a limitation of the system design. It is very hard to get a suction side cleaner to work properly on low speed of most pumps. Even those with VS pumps find they have to run at higher RPMs to get the cleaner to work.

If that is the case, then that ends my investigation. I'm not sure it ever worked, so that would be par for the course. I guess its time to start researching robotics. Thanks for your help mas985!