Downsized my pump this weekend

[MikeInTN]

Hello all!

I downsized my pump this past weekend. I went from a 2HP Hayward Power-FLo LX to a 1HP Hayward Power-Flo LX, and the 1HP pump seems to be moving more water, strange as that sounds. Anyone with any theories as to why??

I also replaced the pressure gauge on the filter, changed carts in the filter, and plumbed in a drain line w/ a ball valve for draining the filter. All in all, a productive pool weekend!

 

[Poolsean]

Plumbing? If you have 1.5", the 2 hp will have more restriction due to the higher velocity of water through the pipes. Max flow rate through 2" pvc is about 100 gpm. Max through 1.5" pvc is about 70 gpm. Pushing too much water = backpressure (restriction).

Clean filter? Replacing your filter would have aleviated backpressure from a dirty and clogged filter element.

Can't see anything else that may have contributed to the better flow.

 

[mas985]

First, there is no such thing as max flow rates for PVC pipe. The specifications are simply recommendations not absolute limits. There is no limit to flow rate however, as flow rate increase pressure in the pipes increase but PVC has a 600 psi limit so it would take a very large flow rate to exceed that.

Theoretically, it is not possible for a 2HP pump to have lower flow rates than a 1 HP pump given the same plumbing conditions. Assuming two perfectly working pumps, conservation of energy must apply, more energy in = more energy out. However, the 2 HP pump impeller may of had a problem reducing the normal flow rate.

It could also be the new cartridges. Filter pressure can have a significant effect on flow rates as well.

 

[nocaster]

Could the impeller have been cavitating as it was trying to draw more water than the inlet would allow?

 

[MikeInTN]

You're probably correct on both accounts. I do have 1.5" plumbing to the pump, and the old filter was pretty filthy. The filter pressure with a clean filter is the same for both pumps, though, and this pump still seems like it has more suction. Could've been something wrong with the old pump too, now that I think about it.

Thanks for answering, kind sir!

Mike

 

[mas985]

Could the impeller have been cavitating as it was trying to draw more water than the inlet would allow?

That's possible but very noticable as well. There probably would have been a lot of air in the pump basket as well as very noisy.

 

[MikeInTN]

The old pump was fairly noisy, but had no air in the pump basket.

 

[Poolsean]

Mark,

I disagree with your statement:
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First, there is no such thing as max flow rates for PVC pipe. The specifications are simply recommendations not absolute limits. There is no limit to flow rate however, as flow rate increase pressure in the pipes increase but PVC has a 600 psi limit so it would take a very large flow rate to exceed that.
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There is a maximum velocity "recommendation" for pvc pipe before which the excessive flow becomes detrimental to the hydraulics of your system. South Florida Building Codes are 10 ft/second discharge and 6 ft/sec suction side. Actually, sound hydraulic practices vary between 7 - 10 ft/sec on the discharge side and 5 - 7 ft/sec on the suction side. In either case, excessive flow will cause excessive restriction and poor hydraulics.
So while you are correct in that there is no such thing as max flow rate for pvc pipes, there are sound hydraulic practices for maximum recommended flow rates through different diameter schedule 40 pipes.

http://www.co.kern.ca.us/eh/pdfs/Pools/ ... VCPipe.pdf

HAVING said all that, as Mike in TN has stated that the clean filter pressure was the same for both pump, it probably had more to do with the filter element itself, and/or suction on the inlet side (which goes back to the "recommended" max velocity of pipe).

 

[nocaster]

When my pump cavitates it sounds like a hundred BB's rolling around in a plastic 5 gallon bucket. It usually happens when I'm vacuuming and the head gets stuck to the bottom. It is quite noisy and also detrimental to good water flow.

 

[mas985]

Sean,

As I said in my reply, those are recommendations only not hard limits. My only point was that the water does not stop moving faster just because you hit those limits and yes, according to those who created the limits, the pipe might be damaged.

However, many pools operate well above those limits without ill effects. Any pool with 1.5" plumbing and high efficiency pump is operating above those limits and probably has done so for several years without anything happening.

Have you ever heard of plumbing wearing out or damaged with excessive flow? I haven't. Yet I have modeled several pools where the flow rates do exceed those limits but the owners have not experienced any damage. With all of the oversized pumps on pools across the country, I would have expected at least one to show up.

HAVING said all that, as Mike in TN has stated that the clean filter pressure was the same for both pump, it probably had more to do with the filter element itself, and/or suction on the inlet side (which goes back to the "recommended" max velocity of pipe).

He also changed the guage so I am not sure you can actually go by that. But if it were correct that the pressure was the same, it is more likely that the impeller was damaged on the old pump so it was moving water closer to the new pump. In any plumbing system, the head loss goes up with flow rates. If the filter pressure is the same between pumps, the head loss is the same and thus the flow rates are the same. In order for the flow rates to be the same, the old pump must have been damaged.

 

[MikeInTN]

Sean,
He also changed the guage so I am not sure you can actually go by that. But if it were correct that the pressure was the same, it is more likely that the impeller was damaged on the old pump so it was moving water closer to the new pump. In any plumbing system, the head loss goes up with flow rates. If the filter pressure is the same between pumps, the head loss is the same and thus the flow rates are the same. In order for the flow rates to be the same, the old pump must have been damaged.

The gauge I replaced was one that I'd installed at the first of the season, but had already gotten so much condensation under the lens that I decided to replace it again with a better quality gauge. Both gauges read 10 psi with a clean cartridge, so I'm betting there was something wrong with my old pump.