New Harris 1HP Pump runs 5 psi lower than the ol' Sta-Rite 1 horse?

[Roguewave]

.
I believe I have solved it in Post #4...

Hello,

So the ol' Sta-Rite, though performing same as always, finally started making noise after 12 years of good service. So I found the Harris for $150 on Amazon with stellar reviews.

Hook up went smoothly and she runs quiet, but the pressure between pump and filter is about 5 lbs lower than the Sta-Rite and if I nearly close a valve after the filter to simulate the need for a backwash, the pressure builds up to maybe 25 lbs, whereas the Sta-Rite could climb over 30 if I let it go a little too long.

Filter is a Sta-Rite sand with a little DE

Inlets are 2 - 1 1/2".

Outlet is 2" to filter and on out... and then 1 1/2" in the ground to 2 nozzles. (Contractor put in the 1 1/2". I replumbed the everything above ground later to gain a little efficiency with all of those fittings after I installed the solar. It definitely helped.)

Pressure is 13.75 at the filter when clean (I have a pretty good gauge.)

Sta-Rite would run about 18.5 when clean.

Harris claims to be 1 horse, but the current rating is substantially lower of 5.8 max load. I was hoping it was just a more efficient motor, but...

It's wired for 220 and I verified the internal switch was preset for 220.

I checked the current draw. It checks out. It runs at more like 6.5, which tells me there isn't much of a load. When I apply pressure at the valve, I can get the current down to right about 5.8. So this seems to check out.

The output at the nozzles SEEMS... to be a hair less. And it seems noticeably less than before once I turn the solar on.

I called Harris. Only explanation is it could be defective.

I wouldn't mind terribly if it will still vacuum and I save money on power. I run the pump about 12 hours a day for solar in the morning and skimming 'til bedtime.

Any thoughts?

 

[mas985]

HP is a very poor way to size a pump because it only has a very loose relationship to actual "size" of the pump. But lower pressure is actually better for many reasons. This means the flow rate is lower which means the filter will actually work better. Plus as you found out, it also will draw less power. You should be happy on both counts.

But also, do not let the filter pressure rise much above 25% of the clean filter pressure or flow rate will decrease substantially.

 

[Roguewave]

HP is a very poor way to size a pump because it only has a very loose relationship to actual "size" of the pump. But lower pressure is actually better for many reasons. This means the flow rate is lower which means the filter will actually work better. Plus as you found out, it also will draw less power. You should be happy on both counts.

But also, do not let the filter pressure rise much above 25% of the clean filter pressure or flow rate will decrease substantially.

Thanks!

Yes, I rarely let the flow get down too low before backwashing.

I sized the pump by calculations based mainly on inlet sizes and outlet to a smaller degree. I used what knowledge I had plus the owner's manual I downloaded from Harris. 1 HP seemed the best option.

It just seems there is no other way to slice it, the pump puts out less flow than the Sta-Rite with the same motor specs. It therefore is either defective or the liquid end is not as stout as the old Dura Glas... perhaps by design. Unfortunately Harris doesn't provide a nice curve chart like Sta-Rite does. They only say max flow of 83 GPM and max head of 15'. Well... of course... that's impossible. At 14 lbs, it's already doing about 32' of head... and with a ton of flow.

I found the old Dura Glas manual. Specs show it was putting out about 70 GPM at 19 lbs. Since the sand isn't new, I would think it no surprise for the filter to allow a few gallons more. It's been doing a fantastic job with a little DE, so I have zero reason to change it out.

But yes... the 300# Sta-Rite filter has a GPM spec of 63. So the old pump had to be capable of more, but the filter wasn't allowing much more through, thus the increased pressure. Funny thing is... it's very possible that... both motors are chewing up similar power since current is related to flow, not pressure. I didn't test the current on the old one before I yanked it.

The filter is rated at 50 lbs. So it doesn't seem I was stressing it with the old pump.

 

[Roguewave]

I believe I have solved it.

The old motor had a SF (Service Factor) of 1.25 for a BHP of 1.25. An even older, boneyard motor I had shows a SF of 1.65, which, I believe is a little more the standard.

The new motor has a SF of 1 for a BHP of 1. It appears most would consider this an "uprated" motor. I think it's basically a 3/4 horse.

So guess what 3/4 or 75% of 19 psi is...

14.25. And my old one could have been running at more like 18.5. I don't recall the exact figure, but it's very close.

So now would you guess that I'm better off with this 3/4 horse for this system? I'm good with any potential power savings I MAY experience (not positive due to restricted flow of the old pump.)

 

[mas985]

Even THP does not tell the entire story. I can show you two pumps with the same THP but have radically different head curves so the performance is vastly different.

But a smaller size pump is not really a problem unless you are running high flow rate features (e.g. spas, waterfalls, etc). I run with a 1/2 HP two speed pump on low speed most of the time.

 

[Roguewave]

Even THP does not tell the entire story. I can show you two pumps with the same THP but have radically different head curves so the performance is vastly different.

But a smaller size pump is not really a problem unless you are running high flow rate features (e.g. spas, waterfalls, etc). I run with a 1/2 HP two speed pump on low speed most of the time.

Agreed. The liquid ends can certainly be of different designs. However, very interesting that 75% of 18.5 psi is just about exactly what the new pump does. Also, note that there is a chart on pg. 4 of the Harris manual that denotes a "Max Rate" and a "Full Rate." The Max is 1 and the Full is 3/4 horse. 0.75 and 0.55 KW respectively. So obviously zero fudge factor in their SF rating of 1.

http://www.poolsuppliessuperstore.com/Pdfs/152601-156578-156579-152716-152748-HPP-Pumps.pdf

And yes... I bought the pump based more on flow specs than horses. The 1 1/2 seemed overkill for the inlets and filter size. This pump may be just perfect since the filter is really the one in charge of the flow and there may be less crud forced through the media. Also... I may just save a few spins of the power meter.

Funny thing... I was thinking I may want to downgrade to a 3/4 before I bought this pump. But A., they didn't offer one and B., as mentioned, the 1 horse flow specs seemed just about right.

I was more concerned that I had a defective pump. In lieu of helping me troubleshoot, both the manufacturer and retailer were happy to let me test my theory with a replacement. Not sure I'll take them up on that now.