Pump Basics

[jordangregory]

I am trying to figure out if I have everything correct with my pump and filter.
I have a sand filter. 300 lbs of sand. Flow rate is 60gpm.
To my best estimate, I have about 20,000 gallons of water in my inground vinyl lined pool. I have two intakes (skimmer and then another intake on the side of the pool about 12-24 inched below the surface) and one input.
My pump is a 3/4 HP Hayward Superpump that states it is .75kw. As far as I know, it is only one speed.
My question is:
Is my filter and pump sized correctly? It seems that at times it sucks so hard that air gets pulled in the pump. I have checked for leaks over the summer season. I have found some and fixed them. When both intakes are open and the pressure on the filter is low after backwashing, I am fine. If I move to one intake or if pressure has gone up from a dirty filter, I see air being sucked in.
Do I need a smaller filter?
Do I need a less powerful superpump?
I have heard about these variable speed pumps or two speed pumps. Will this help? I don't know anything about these pumps at all.
Thanks for your help in advance.

 

[X-PertPool]

I usually sell a 1 hp super pump with a 300lbs sand filter so, nothing is over-sized or undersized. You might have more air-leaks, but a dirty filter will make it harder for the pump to draw water into itself and depending on how your pool is plumbed it might be normal that you are getting some air in the strainer basket if you are only running one intake (for example if you are vacuuming and running on full skimmer that's a lot of extra hose for the pump to suck water through; usually I'd keep it at 75% skimmer open and 25% Main drain open for vacuuming)

 

[Bama Rambler]

When both intakes are open and the pressure on the filter is low after backwashing, I am fine. If I move to one intake or if pressure has gone up from a dirty filter, I see air being sucked in.

That indicates that you have a suction side leak. It doesn't appear to be a bad one but the part about air leaking in when the filter pressure goes up bothers me.

Here's the scenarios I picture.
1) You have a suction side leak (maybe more than one). When you create more suction head by closing off a inlet you start sucking more air into the piping.

2) The other issue is that you have a suction side leak that is sealed off under normal suction pressure but whe the filter gets dirty the suction head goes down and the leak opens up allowing air to enter the plumbing. I'd suspect a slightly warped pump strainer lid for that. Or the most common suspects are things that have o-rings or gaskets on the suction side of the pump.

Good luck finding them.

 

[jordangregory]

Is there any problem with only have two returns? My piping is just 1.5 inch.

 

[Bama Rambler]

That shouldn't be a problem. Lot of people only have one return and 1½" piping. It may not be ideal but it will work.