Valve between pump and filter.

[mas985]

My question is can I cause damage doing this to the pump or something else? Is this a good idea? I have also considered replacing the pump impeller, but with this setup I have a lot of control, like a variable speed pump. Thoughts?

Throttling valves are common in the water distribution industry and are not a problem for the pump or motor as long as there is some flow rate. A pump motor actually uses less energy and runs cooler when you restrict the flow (i.e. higher head loss). The down side is it is less efficient in terms of GPM/Watt-hr.

I have often wondered if you could use a simple rheostat to control the speed of the motor, like any other electric motor used in electronics. Heck, even my electric chain saw runs faster or slower depending on how far I pull the trigger.

However, that can potentially burn out an induction motor. Reducing the voltage on an induction motor increases current and slip so it does slow down the motor but at a higher current use so it can burn out the windings.

[swimdaddy]

That is interesting that the pump actually uses less energy and runs cooler with restricted flow. I do find that the filter, for what it is worth, does a better job with less flow. Its an intersting game I play, dropping the PSI with the control valve and then raising it some with DE. I think I learned this year that I probably backwash too much. I got in the habit of backwashing once a week but if the pool looks good and the PSI hasn't risen there is probably no reason to do it.

I have abandoned the idea of the rheostat or step down transformer, sounded good though.

The valve works really well, small movements change the PSI a lot, very fine control. Is there an ideal PSI to shoot for for efficient filtering? I don't know what my flow rate is, but the return jet is strong, kids can use a noodle to shoot water a good 15 feet. At fully open, 16psi, with DE 17psi, I have been throttling that down to 10 or 12psi.

[CarlD]

Mark knows more about pumps than I do, so his advice takes precedence over mine.

We've well-documented over the years what you have found: A sand filter filters better with less flow. Something about the dirt not being forced past the sand as easily. That's why I'd rather run it on Low (2spd pump) than High pretty much all the time. Thus a bigger sand filter does better for the same reason: More capacity for the same flow.