I have a few questions before I buy a new pump..

[cruzmisl]

Hi All,
I currently have a 18x36 IG vinyl pool with a 1HP Sta-Rite Duraglas pump and a 300lb sand filter (likely changing to DE though). The plumbing of the pool is 1.5", I have 2 returns to the pool, 2 stair "spa" jets and a return to the spa that allows me to heat the spa or if I turn a valve allows spillover into the pool.

I have found lately that it takes FORVEVER and a day for the pump to prime. It's especially noticeable while vacuuming but once it's primed it seems to run fine. I don't have any leaks. I was thinking the pump is worn out (it's only 4 years old though) and was considering replacing it with a Hayward Northstar. I just don't know how big to buy it. I don't want a huge monster but I also want enough flow and a decent electricity bill. Any thoughts or tips?

Thanks!
J.

[mas985]

Is the pump at a much higher elevation than the pool? This would explain the slow priming. Also, check the impeller to see if it is worn or damaged. They cost less than $30 and can improve the performance considerably.

[cruzmisl]

No, the deck is level with the pool and the pump is mounted probably 30ft from the skimmer. The pump did run dry a few times (leak) and I think that took a toll on it. I wanted to get the Northstar to try and save some electricity and hopefully get more silent operation. Aside from that the housing of the pump gets so hot I can't even touch it. The pool company that installed it says it's normal:confused:

I was thinking since my total head is about 50 (filter pressure of 17psix2.31= 39.27 + 10 for an average suction since I can't measure it = 50) If this is correct then I am thinking the HAward 3/4 HP full rated would be adequate since it delivers 70 gpm at 50ft.

The 1/2 HP delivers 50GPM at 50 ft but that may be pushing it with the spa spillover and stair jets. Then again I have no idea what I am talking about:)

Any opinions?
Thanks,
J.

[mas985]

If your current pump is 1 HP uprate, then the 3/4 HP Full Rated Northstar may still be too big. When replacing a pump, it is a good idea to compare braking HP (BHP) of the pumps. The BHP for the full rated Northstar = 3/4 HP * 1.85 SF = 1.4 BHP.

As an alternative you may want to consider is a 3/4 or 1 HP two speed pump. That way you can run it on high for the spillover and jets but on low most of the time for circulation and save a ton of money on your power bills.

One other thing to note is that when you change to a pump with a lower BHP, the head will drop as well. So a 1/2 HP pump will have a head of closer to 32 feet. A good estimate is:

New Head = Old Head * (New BHP/ Old BHP) ^ (2/3)

[cruzmisl]

The BHP of the Sta-Rite currently installed is 1.25Bhp (1Hpx1.25sf). I like the idea of a 2 speed pump but have 110V running to that area and it would be a huge pita to run 220V there.

Would the 1/2hp be enough? I didn't understand your calculation.

Thanks!
J.

[mas985]

Pentair Whisperflow and other companies have 2 speed pumps that run on 115v so that should not be deciding factor. With the 2 speed, you can get a 3/4 HP full rated pump so that all your features and vacuum will work properly when needed and you can run it on slow speed for extra savings.

My point with the calculation was that with the 1/2 HP, your head loss will drop to about 40 feet (corrected for your actual current BHP). So the 1/2 HP pump would provide about 63 GPM. You need to compare this with your current GPM to see if it is significantly different. My guess is it is slightly less.

[cruzmisl]

According to my current pump specs with 50ft of total dynamic head it flows 60gpm. I was counting on a Hayward unit but will look at the Pentair. Hopefully they won't break the bank......