Will a two-speed motor work with an older pump?

[stualden]

If my pump curves (UltraFlow pre-94) don't show results for the low speed of a two-speed pump, does that imply that it won't work (or at least not well), or just that two-speed motors weren't common back then (1991)?

I understand that I will have to size the motor correctly. But I'm wondering whether there was something about the impeller design that precludes the use of a two-speed motor (running at the lower speed). Thanks.

[thepoolman1]

Just installed one last week on an Ultra-Flow. Works great. If the pump is current or only recently discontinued, this is a good way to save money on a 2-speed pump, no matter the brand. Make sure to size the motor correctly to the impeller. Since the Ultra-Flow is no longer made but parts are still available, it wouldn't hurt to get a new impeller and wear ring while doing the job just to make sure and for best performance.

[stualden]

Thanks poolman. What would I need to know to determine the right horsepower and the right impeller for the new two-speed motor?

The pump right now seems to be sized correctly for the pool; the motor is a 1 hp (with a service factor of 1.0 according to the label). I need to check again but I believe it has the 1 hp Ultraflow impeller as well.

Thanks again.

[stualden]

Any suggestions on this? Is there some rule of thumb on the "equivalent horsepower" for the low speed of a two-speed motor?

[mas985]

If you keep the same impeller, you must match the braking HP as close as possible to the existing motor. Otherwise the load could be too high or too low. So your old pump has a BHP of 1 and most high efficiency motors have service factors above 1.6 so you will probably need a 3/4 HP motor with a 1.6 SF (1.2 BHP).

Also, motors are rated at high speed so match based on that. Low speed HP is about 1/8 of the high speed but it depends on several factors and really is not that important. Important factors for two speed pumps are low speed flow is 1/2 of high speed and head is 1/4 of high speed, approximately.

Have said all of that, I don't quite see why you are not replacing the entire pump. Pre-94 pump parts are probably almost worn out so you will be replacing more than the motor soon. I would highly recommend replacing the entire pump as it will save you money in the long run with your electric bills. My guess is you will pay off the new pump with electic savings in less than a year anyway.

[stualden]

Thank you, that was very helpful.

You suggestion is good - I will look into getting a new high-efficiency pump for the pool and use the old pump as a spare for the spa jets.

I thought I was trying to save money (and time - a new pump means I'll have to re-plumb as well) but when the electricity is factored in, I can see how a new pump makes more sense.