I'm looking into replacing the single speed 1hp pump motor I have with a two speed. The pump is a Pentair Whisperflow WFE-4. The motor was replaced prior to us buying the house, but here are the details (and please pardon my book):
A.O. Century Centurion B2841 Square Flanged Full Rated
The pool is about 14,000 gallons with a roughly 500 gallon attached spa. The pump runs both pool and spa through a Sta-Rite PTM135 cart. filter. The plumbing (as far as I can tell without digging up part of the yard) is 2" from the pool drain/skimmer (drain/skimmer are plumbed together) as well as 2" from the spa drain. There are 2 returns to the pool and 3 to the spa, all at 1-1/2". Again, this is what I see above ground. Equipment is about 12' from the pool.
Now I beleive I could do a 1:1 swap of the motor and call it a day, but here's a wrench in the works. If I run both the pool and spa suction valves full open and pool and spa return valves full open, the water level in the spa will slowly decrease (I estimate about 1 hour until it would be completely empty, though I've never tested that). Basically it's pulling water out of the spa faster than it can replace it. There does not seem to be a flow problem. All three spa jets have equal pressure. If I run the pump only for the spa, it obviously doesn't drain the spa, but pressure on the filter goes up by about 5-6psi. I have no leaks that I'm aware of (no water loss other than evaporation). What I have to do is either run with the both (pool/spa) return valves fully open and partially close the suction side spa valve to restrict the drain (this is what I usually do) or run with the pool return valve partially closed to restrict flow to the pool (I don't do this as I fear I don't get adequate circulation in the pool).
Okay, onto my questions; If, instead of a 1hp, I buy a 1-1/2hp two-speed motor, do you think it...
1) would have enough oomph, at either speed, to have both suction and return valves for pool and spa fully open?
2) would overwhelm and subsequently damage the filter and/or return plumbing?
Normal pressure on the filter is:
17psi when both pool and spa are running (spa suction restricted at valve)
19psi when only to pool
23psi when only to spa
Eventually (next year hopefully) I want to move the equipment pad, replace the cart. filter with a DE and buy a 1hp VS pump for the pool and reuse the current one for the spa. With the two speed motor I estimate saving, on average, $40-50/month in electricity costs (location is Camarillo, CA), so the ROI should be less than a year. I'll be doing the work myself, so no additional costs other than the cost the motor, tax and shipping.
I also wouldn't mind the more powerful pump, if possible, just to get a little better massaging action on the spa jets. The returns in my brother-in-law's spa will almost peel your skin off. I really enjoyed that...
The replacement motors I have in mind are (not necessarily from this site... still shopping):
Thank you in advance for any help or advice.