Pump sizing "feet of head" quandry?

Pool pumps, filters and the plumbing of swimming pools. Problems relating to the piping and pumping of the swimming pool water.

Pump sizing "feet of head" quandry?

Postby Pool User » Tue 29 May, 2007 10:18

Hi all...first post. Great forum!

I just bought a house with an older in-ground pool. It was a foreclosure/eviction so the previous owner stripped the house of everything not tied down, including the pump and filter multi-port valve (he did leave the filter however, too heavy to move I guess).

Anyway, I am having a hard time figuring out the correct size pump to buy. I have had two pools in the past, but both were above ground with hardly any pipe. This one is quite different. As best I can figure the pump is 60-65 feet from the pool (pipe is buried). Of course the rule of thumb is "replace the pump with the same size" but I have no idea what that size was and no local pool places have records of selling/installing at this house. Also I have read that oversizing is often worse than undersizing so I am not sure what to do.

Here are the specs:
  • Approx. 21,000 gallons.
  • 15' X 30' with deep end (average depth 5.5')
  • 60-65 feet of 1-1/2" PVC from pool to pump area (both directions).
  • There is no rise from the pool to the pump...in fact if anything the pump might even be almost a foot below the pool.
  • Hayward S244S 300lb Sand Filter (50psi Max)

I would like to add a heater in the future, so I am leaning toward the Hayward Super Pump 2610X15 which is a 1.5HP max rated pump (1.0/1.5).

Is this too small/big?

Sorry about the rambling post...and thanks for any advice!

Barry
Pool User
 

Perhaps 1.25 HP?

Postby DanO » Wed 30 May, 2007 23:27

I'm no expert, but your pool configuration sounds almost identical to mine, and I have a 1HP pump/motor. I don't have a heater, but I wouldn't think that would add enough extra pipe to warrant a 1.5HP motor. I do know that if you get something too powerful it will cause cavitation and that lowers the overall efficiency of your filter tremendously.

Good luck on your decision, and maybe someone else can throw in their $.02 as well...
DanO
 

Postby Backglass » Thu 31 May, 2007 07:56

Thanks Dan,

I am concerned about overpowering the filter as well. However when I look at pump specs, the flow curve drops off sharply at 60-70 feet of head. I guess my real question to the experts is "Does 65 feet of horizontal 1-1/2 pipe = 65 feet of head"? I know you can only suck so much water through 1-1/2 pipe as well.

I agree that a 1hp wil probably be fine, but my concern is that when I add a heater with four to six 90 degree turns, I might need those extra horses.

This whole head game is very confusing and the sizing charts from the pump manufacturers don't make it any easier!

Thanks for the reply.

Barry
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Calculating "head"

Postby DanOz » Thu 31 May, 2007 21:47

You are right, it is confusing. The number of feet of pipe that you have running from your pool to your pump inlet is NOT the same as "head". You can measure "total dynamic head" (in feet) by knowing what the vacuum (negative) pressure is coming into your pump, and by knowing what the positive pressure is going into your (clean) filter.

There is a great website that explains how to calculate total dynamic head, and also how to then determine what size pump you need. Here it is:

Good luck!
DanOz
 

Postby Backglass » Fri 01 Jun, 2007 08:29

Thanks Dan, I had seen that site before in my many "pump head" searches.

You answered the missing link though, about the horizontal pipe. Nowhere could I find an answer to that simple question! I don't have the means to take vacuum readings (who does?!) so I bit the bullet and and went with my gut and ordered the 10X15 Hayward super pump. I plan on adding a heater soon and maybe some other toys so I will have some headroom. Plus the filter is on the large size (24", 300lbs, 62gpm max) so it should be able to handle it.

Thanks for all your help!

Barry
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How to take the Vacuum Gauge pressure reading?

Postby Pool User » Tue 11 Dec, 2007 14:44

Can somebody tell me which vacuum gauge is necessary to measure the pressure coming into the pump? and exactly how to connect and take the vacuum pressure reading?

On my pool pump, there is a 1/2 inch threaded port(on the bottom of the pumps' skimmer basket), from where I assume some kind of vacuum gauge is to be inserted to get the actual vacuum pressure reading. I don't know where or how else I would take a vacuum pressure reading, but I hope someone here can tell me how.

Also, my pool is in-ground and the pump is in a pit below ground, where the pump sits at about the level of the deepest part of the pool, which is about 8 feet below surface level.

Please let me know how to take the vacuum pressure reading, so I can properly size my pools' pump. Thank you.
Pool User
 

Should I start a new thread for this question?

Postby Pool User » Wed 12 Dec, 2007 22:06

I'm not very familiar with how these questions get answered, but should I have started "A new thread" for this question?
Pool User
 

Can anybody help with this question?

Postby remember » Mon 17 Dec, 2007 21:56

I forgot my username and password, but I was the "pool user" that posted the question about how to measure the vacuum pressure.

I still have not figured it out and I need to measure my system and get the right pool pump size asap. Please help me.
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Postby mr_clean » Tue 18 Dec, 2007 10:29

who told you that you need a vacuum gauge to replace pump?
what size pump do you have now?
1/2-hp pumps can have heaters with them, is your heater not close to pump?
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Postby remember » Tue 18 Dec, 2007 15:58

Thanks for responding. I thought my question was unanswerable.

To your first question, "who told you that you need a vacuum gauge to replace pump?"

- The answer to that is in post # 4, when "DanO" says,. . ."You can measure "total dynamic head" (in feet) by knowing what the vacuum (negative) pressure is coming into your pump. . ."

Thus I was going to follow DanOs' above instructions so I could get the suction/inlet head measurement and then add that to the pressure reading from the gauge on top of the filter(multiply by 2.31) and thus get the total head pressure. . . I think? Essentially, I want to calculate the "total head", so I can finally get the right pump.

At the moment, we have a 1 HP pump, called "WaterAce" which I got at Lowes, which is a replacement for a 1.5HP pump from the same manufacturer & store that I bought about 6 months ago to replace the original pool pump of what size I can only guess was 1.5 HP, but I'm not 100% sure. The 1.5 HP Waterace broke after such a short period of time, that I don't want the same to happen again. I am assuming that the 1.5 HP Waterace pump broke because of "cavitation"?, i.e. that the pump was too powerful for our pool system.

I should say that we only have 1.5 inch plumbing throughout the pool, but the pump and filter are located below ground in a big underground pit. The pump and filter sit at about the level of the deepest part of the pool, which is about 8 feet below the surface. Thus, I am pondering whether the suction/inlet vacuum pressure on the pump would have any reading at all? If most people have there pool pumps above ground, then the pump would have to suck the water up and out of the pool and thus cause the pump to lose power because of the addition to its total head pressure. But with us, the pump is below the pool and I am suspicious that, with this type of arrangement, we might not have any vacuum suction pressure at all and thus our total head may be quite low? But that is just another question I need to have answered. How do I find out what the total head of our pool is?

I have been comparing the flow charts from the "Waterace" pumps and the one I am intent on getting which is a Hayward Northstar. The flow rate for the 0.5 HP Northstar looks similar to the current 1 HP waterace pump I'm using. Thus, if I can save money on electricity, I will definitely try to. But again I need to make sure that I am using the right size pump. The 0.5 HP Hayward pump performance curve shows that at 40 Feet of Head, the pump can flow 60 gallons per minute.

The 1 HP Water Ace shows that at 40 Feet of Head, the pump can flow about 67 gallons per minute. Of course these flow rates vary significantly when you assume that there is 30 feet of Head or 50 feet of head. The 0.5 HP Northstar maxes at about 60 feet of head(at which point there is no flow), but the Waterace does not stop flowing until about 73 feet of head. But again, I have no idea how much head our pool has? Thus I am trying to figure out what our total head is. And I want to emphasize, that electricity consumption is very important(expensive). I would rather spend less on electricity than more, if it is safe, practical, viable and inconsequentially equal in all other ways.

At the moment, we do not have a heater, but it is something that we may definitely consider for the future, maybe in 3 months or maybe in 3 years. I really can't say for sure.

The main reason, I had my mind set on the Hayward Northstar is because of the largest 220 cubic inch size skimmer basket I could find, which made me think that I could go for longer periods of time without having to clean it. This was part of the fact that I was investigating a pool system that would allow us the maximum number of time spent away from the pool without having to be "attending" to the pool.

The reason for this is because,. . . it is in Palm Springs(one of the hottest places on earth in the summer) and we often can't stand to go there for at least 2 months in the summer, thus I was trying to find out if the extra large Northstar pool pump basket, plus some type of pool sweep or pool cleaning device, plus the installation of a salt system, would allow us to stay away from the pool in the unbearably hot summer months and have all the above mentioned tactics and devices keep the pool relatively clean and maintained during long periods of time that we would prefer not to have to spend here.

Well that is about all I can say for now. I hope you can give me all the right advice because I need it and I don't know where else to turn. Ultimately after I hopefully can decide which pump to get, I would like to do all the other things with the pool, like the cleaner and salt system and even a heater, but for now, we really need the right size pool pump so that it lasts a long time and also consumes as little electricity as possible. Aside from a few very low wattage consuming light bulbs around the property, our pump accounts for about $300 a month in electricity and I would like to get the smaller, more electrically efficient pumps if possible and if it is the right pump to do so with. So, please let me know anything and everything you can. Thanks for your time and help. I hope to hear how to solve this as soon as possible.
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