Pump motor dying - upgrade needed?

[ezpool]

I just inherited an 18K gallon in-ground gunite - our
first pool. The pool looks great thanks to the info
on this forum! The problem is that I think the pump
motor is dying. The in-pool jets aren't pushing much
water and the pump makes quite a racket. So I've
about decided to get a new motor (rebuild is ~$100
I've heard vs. ~$160 for a new one). My quandary is
what size motor to get. The original pool install
(1984) used a 1.5 hp Sta-Rite XL-VII pump (no specs
available). Then in 1994, this was replaced with a
Sta-Rite P4E6E-151L 1hp pump (high service factor).
Should I stick with a 1hp motor or try to fit a 1.5hp
motor on this pump? I've read that sizing a pump to
a pool is a bit of black magic - any way to estimate
what I need or should I just assume that whoever
switched from 1.5hp to 1hp knew what they were doing?

Some stats:
18K gunite w/ attached spa
Sta-Rite S7D75 DE filter (37sq ft)
two skimmers in pool
two main drains (one in pool & one in spa)
seven jets total (3 in pool & 4 in spa)
one "cleaning" jet (to attach my Ray-Vac)

Thanks in advance!

[mas985]

If the pump has to run the spa jets, then you may want to go with at least a 1.5 HP full rated pump. How are your current jets, too weak?

Given the size of the pool, spa jets and cleaner, you may want to consider a two speed pump. That way you have the higher speed for the jets and you can use the lower speed for circulation.

[ezpool]

The pump does indeed run both the pool and spa jets though I typically set the valve to reduce the spa jets so they're only pushing enough water to keep the spa from draining. Even with the low setting on the spa jets, the pool jets are pretty weak. Regarding the two-speed pump, is it possible to install a new two speed motor on my existing one-speed pump? I have an older Sta-Rite Max-E-Glas II - P4E6E-151L 1hp model:
http://www.swimming-pool-pump.com/PD...las_manual.pdf

Thanks!

[mas985]

Yes,

You should be able to replace just the motor but you need to pick a motor similar in braking HP to your existing one otherwise you will need to change the impeller as well. You can get both the motor and impeller from poolplaza but shop around.

http://www.poolplaza.com/C-MaxEGlas-II-Parts.html

[ezpool]

Thanks for the info. I now realize that I forgot to mention that the original pool install had a heater which was un-plumbed at some point in the past. I imagine that might be the reason they switched from a 1.5 hp pump to a 1hp pump. So since I'm considering:
1. Adding a new heater at some point in the future, and
2. Adding a SWCG next year
I'm thinking that I need to bite the bullet and buy a new 2-speed 1.5hp motor and the appropriate impeller. The only problem now is parting with all of the money that will cost!

One concern I have is that I don't want to over-power the filter. Right now
my clean filter pressure is about 18-20psi. Judging by another post, that roughly equates to a 64 head (3.2 *filter pressure). Would increasing the motor HP by 50% be a problem if I won't have a heater in-place for a year or so?

[mas985]

A SWCG should not change your pressure by more than 2 PSI but depending on the heater and how it is plumbed can add quite a bit. If you put in a flow bypass with an adjustable ball valve you can set the flow through the heater to be just enough to activate the internal flow switch while bypassing most of the water.

If you take your lowest pressure today which is 18 PSI, you could be running with head as low as 55 feet. This is pretty close to 74 GPM which is the limit of your filter today. Given that you are so close to your filter limit, I would say that a 1.5 HP will probably push you over your filter limit. Without more accurate head measurements, it would be risky.

[ezpool]

Well, the new two-speed motor is finally installed. I went with the 1HP motor and things are working fine. I had no problems installing it - disassembly and reassembly took a few hours but I was double- and triple-checking everything each step of the way. I *really* like the sound (or lack thereof) of the motor on low speed.

[mas985]

Glad to hear things went well. Just curious as to what your filter pressure is on low and high speed now with the new motor.

[ezpool]

Sorry for the long-delayed response - my multiport valve was leaking too much so I had the pool covered for a few weeks while waiting on a part. But it's open again now and the filter pressure is reading:

7psi on low speed
18psi on high speed