Hayward Pump Size

[Hilton]

I've got some confusion that I'm hoping someone can help me clear up. I have a pool for which the original engineering data sheet specifies 44 US GPM @ 76 ft. TDH. I presume the TDH figure is correct, since this is the original engineering. The original pump model is unspecified, but would be of little concern anyway. The current pump is a Hayward Super Pump 1 HP, fairly new.

Now the thing is, Hayward's data for a 1 HP Super Pump doesn't even HAVE a value for a TDH of 76 ft - it drops off completely past 60 ft.
(see brochure: http://www.hayward-pool.com/pdf/literat ... mp10_4.pdf or http://www.hayward-pool.com/prd/In-Grou ... 002__I.htm / Specs tab ).

What's the problem? I have an actual flow rate of 58 GPM, which is way above spec and likely to get me in trouble with the health authority (large increase in water velocity creating a suction hazard). By Hayward's spec sheets, I should have something akin near zero with the installed pump.

What is going on???

A little more information: The pool is 18,200 gallons, sucks from a pair of main drains (via one line) and two skimmers (each with their own line). There are four returns. The filter is a Hayward S-244T capable of up to 63 GPM.

 

[Bama Rambler]

76 feet of head is a lot of head. I seriously doubt that pool has anywhere near that much head. If you can get suction and discharge pressures you can tell what the head is with the setup you have now. If that's a commercial pool it should have an SVRS anyway and the additional suction force won't affect the safety of the pool. If the main drains are plumbed together like they should be it's not a concern anyway.

 

[mas985]

It would be very unlikely that the plumbing/pump had an operating point at 44 US GPM @ 76 ft. If you can give me the following, I can tell the approximate operating point:

Plumbing Questions:
Pump Make/Model
Height of pump relative to the pool water level
Diameter and number of individual suction pipes from the equipment to the pool
Diameter and number of individual return pipes from the equipment to the pool
Diameter and number of return eyeballs
Filter type and backwash valve model if known
Filter PSI reading at the desired valve settings and pump's highest speed setting.
Optional: Pump suction reading (in-hg) - not necessary but improves accuracy
Heater - yes or no
Pool/Spa Valve - yes or no
Check Valves - Number and locations

 

[Hilton]

Yes, there are two main drains plumbed together. No, there is no SVRS as it is not required (yet) in Canada. Local health authority allows a maximum water velocity through a drain of 1.5 feet per second. The original design was 0.91 with drain covers that had 3.8 square inches of free opening. I do not know what the current drain covers provide - and there are two different covers, to boot! I think one may be original (20 years old); the other is a domed type with large perimeter holes and a solid top. Everything is Jacuzzi brand if that narrows it down.

I've tried talking to the local health authority's engineer, but he won't help me unless I drain the pool and get the drain cover model numbers. Ugh. Is there a site or a forum thread that will assist me in calculating water velocity through the drains without involving the health authority? I can estimate the free opening of the covers based on similar models...


mas985:
Hayward SP2607X10A (1hp). Floor where pump sits is about 8" over water level. 1.5" connections on pump suction and return ends.
Three 2" suction pipes, connected one each to two skimmers (with 1.5" ports) and one to both main drains.
One 2" return pipe (which reduces to 1.5" briefly at the heater and the salt generator cell).
Four 1/2" diameter returns.
Hayward Pro Series High Rate Sand Filter Model S-244T (3.14 square feet surface area; 63 US GPM maximum filtration/backwash rate).
Suction valves are kept fully open; single speed pump; filter operates at roughly 17psi.
Vacuum gauge has been broken for years and I never saw a need to replace it, sorry.
Heater yes. Pool/spa valve no. The spa and the other pool have their own equipment.
Check valves - none visible anywhere.

Orientation - pump room is off one corner of the pool; pump is roughly 10 feet from the pool's edge as the ant crawls. Heater is roughly 24 feet away from the pump in exactly the opposite direction from the pool. Factor in the additional piping around the heater, the return pipe coming up into the pump room again to mount equipment (flowmeter, feeder, etc), etc and you've got about 80 feet of piping and about 20 elbows between the pump and the pool (return side). If everything runs straight, the suction side should have about 30 feet of piping from the main drains, 35 feet from skimmer 1, and 60 feet of piping from skimmer 2.

 

[mas985]

Ok, the pressure is a bit higher than I would expect but that could be due the backwash valve or dirty filter. But I matched the filter pressure anyway on the return side. The suction side, I used the layout you gave but that matters less because the head loss will be low due to the three parallel runs. Most of the head loss ends up on the return side anyway. Here is my estimate:

Operating point: 42 GPM @ 47.5 ft of head & ~1125 watts
Plumbing Head Curve: Head (ft) = 0.027 * GPM^2

There is a lot of head loss in the eyeballs because they are 1/2" (~7' of head). The exit velocity is about 17 ft/sec so I bet you get good circulation from those.

 

[Hilton]

That is normal pressure for most of the pools I operate - they mostly sit in the 15-20 psi range, and one at 25. I rarely see the pressure increase by much before a backwash is required - my flow rates can drop drastically before the pressure gauge moves more than 1-2 psi.
The particular pool in question had a sand change last summer.
You come up with 45gpm - my actual flow rate is 58 gpm. So...?

 

[mas985]

If the flow meter was installed incorrectly, it can easily give you the wrong answer. Depending on the type of meter, you may need enough straight pipe (e.g. 20" on the in flow and 8" on the out flow) for it to read correctly. Plus most cheaper meters have an accuracy of only +-10% of full scale so if it is a 100 GPM meter, the accuracy is +-10 GPM. BTW, what type of meter is installed?

However, if the filter pressure is wrong, then the answer I gave is incorrect. But let's work the problem both ways.

If you are truely getting 58 GPM, then the head loss must be only 36' of head based on the pump's head curve and your filter pressure should be around 10 PSI to match the head loss. This is why I said the filter pressure is higher than I would expect.

However, if you believe the filter pressure is correct, at a minimum, with 17 PSI pressure, the return head loss is:

17 * 2.31 + 4' = 43' (filter gauge is ~4' higher than the water level)

So if you assume there is only return head and 0 suction head, which is very unlikely, then the flow rate would be about 49 GPM.

So bottom line is that either the flow meter is incorrect or the filter gauge is incorrect. Does the filter gauge go to zero when the pump is shut off?

But I suspect it is actually both that are incorrect. If I just use the information you gave me without taking into account the filter gauge, I get an operating point that is 51 GPM @ 41' of head and 13 PSI filter pressure. So somewhere between what the flow meter measures and what the filter gauge suggests.

 

[Hilton]

Flowmeter is an acrylic block pitot... Blue-White F300-20 on a 2" pipe.
Flowmeter is smack in the middle of a 5' run of pipe. There is an inline feeder about a foot from it (within the 20" of straight pipe the flowmeter needs), but I doubt the little piece that sticks into the pipe creates enough turbulence to make a difference. I could try removing it and capping it, though. After the flowmeter is the required 8" of straight pipe, followed by a Zodiac SWG cell.

I have a similar result/problem with the hot tub on the same site, by the way. Design spec says 31gpm, and were running over 50gpm. And that flowmeter has nothing in the way - three feet of straight pipe before, one foot after.

The pressure gauge is new, and reads a couple psi lower than the old one. I had three new gauges (one for each pool at the site), and tried all 3 on one filter to ensure they all read the same (closest I can get for an accuracy test - if they all agree, they are probably right!)

 

[mas985]

Just to confirm, your pump model is the SP2607X10, correct? Are you sure the pump has not been modified in anyway (e.g. larger impeller and motor)?

If the pump model is correct and you feel that the pressure gauge is correct, then I think the flow meter must be incorrect. Have you tried to remove the flow meter and clean it out?