Sizing a new pump

[lstinthot]

I am planning on replacing my pump this year.

I was reading through sizing a pool pump. We have 1.5" piping coming from pool to the equipment. I generally run the two skimmers and send the water back to the main drain. Looks like my piping is limiting me to around 88 gpm. I have a 60 sq ft DE filter that says it is ideal to have 90 GPM, so these numbers kinda work out. A clean filter will show 20 pounds discharge pressure and the pump sits about 10 feet above the pool deck.

I will need a good self priming pump. We currently are running a 2 HP pump. Looking at the charts I believe I could use a 1.5 HP pump. I was thinking the suction side was worth about 30 ft of head between the piping run and elevation gain. Did not actually measure the suction. This gives a total of 50 ft of head with a clean filter.

I was looking into two speed pumps. Can I realize any advantage by running a two speed pump?

The lower flow rates will not turn the pool over as often as the charts recommend. I pretty much have to run in fast speed to get the turnover.

I am also looking into getting rid of the pool cleaner that requires the booster and get one that can run off the main pump. Our current cleaner does not move around very good.

Thank you,
Mike

[mas985]

First there are couple things to be aware of.

1) There is no physical limit to the flow rate in pipes. The numbers that you often see are recommendations and not absolute limits.

2) The flow rates posted on filters are maximums, not minimums and in most cases, filters do better at lower flow rate.

3) Forget everything you learned about turnover. It just doesn't mater. You can run your pump as short as you like as long as you get enough chlorine in the pool. I currently run my pump only 4 hours per day and more than half of that is on low speed so far less than one turn per day. Every pool is different but most pools can get away with less than 4 hours per day.

As for pump size, you did not mention any water features so there is really no limit on how small you can go. I have a 1/2 HP pump on a 20k pool as an example. Smaller pumps will filter water better and cost a lot less to run. However given the pump height relative to the pool, you might stick with at least a 3/4 HP. As long as you have priming valves or check valves on the pump, you should be ok.

As for two speed pumps, yes they can save quite a bit in operating costs so that is something I would highly recommend.

[lstinthot]

No water features on pool. We put a check valve in last year. It still takes some time for the pump to prime, like there might be a minor leak on the suction side of the pump. I am going to take the Nature 2 filter housing out of the discharge along with the propane heater we do not use. This should lower the discharge pressure some and hopefully tighten up the closed loop.

What are people's favorite 2 speed pumps?


Thanks again.

[mas985]

There is very little discharge pressure when priming. Just look at your filter pressure gauge as the pump is priming. So changing that probably won't help much.

The pump you have now is probably pretty typical of a high head pump so that is about as good as it gets for priming lift. I don't think another pump is going to be better. Most residential pumps have a max lift around 8' and even that is pushing it so the valves are critical when priming but may not always work well at 10'.

I would fix the priming issue before moving to a different pump because that is not likely to fix the problem.

Is the equipment pad elevated or does it sit on ground level?

Does the pump basket drain when the pump is off?

[lstinthot]

The pump basket does empty when the pump is off. I am limping this pump along right now. It is so load you can hardly talk standing near it and I blew the lid off at the end of last season with a bad valve line up blowing the lines out. It will need bearings, new lid and plumbing work, so I figured I would get a newer efficient model that uses less power.

We have a check valve on the suction side and on the discharge side of the pump. The valves are new. The plumbing is new on the suction side of the pump as well.

I was thinking of removing the extra equipment on the discharge side to help lower discharge pressure thinking that would allow me to run a smaller pump.

I currently am running a superflow by pentair. Is it worth rebuilding this pump? It has run many of times with loss of prime. Currently does not leak when it gets a good prime, which it can do with in 2 minutes.

Thanks

[mas985]

In your signature, you have UltraFlow but in your post you said SuperFlo. Those are two very different pumps so it makes a difference. Which one do you have? If you don't know for sure, post a picture.

Also, your pump should not lose prime when off so something is leaking air into the plumbing. Most likely it is the pump lid.

[lstinthot]

Good catch on the pump. It is an Ultraflow.

The basket stayed full this morning after I shut it off last night. There is a lot of gurgling going on after we stop the pump. There is a minor leak on the discharge of the pump, I was waiting to fix it and fix it when I changed the pump. Is it better to fix it now, make sure the system is tight and working before bringing in a new pump? I know the pump lid is no good, it seals when holding it there when I start the pump but the ears to hold the lid down are all broken so when it stops it pops up and I put it back on the pump.

[mas985]

The UltraFlow is a high head pump so priming is probably as good as it gets with this pump. You can either replace the entire pump or just the motor. It usually makes more sense to just replace the motor if the wet end is in good condition and you don't need to change any plumbing. But since you have to change the plumbing anyway, it may make more sense to replace the entire pump. Either way is fine, it is basically an economic decision.

However, when looking at a replacement, you need to focus on max head because that is the only thing you can go on for priming ability. The higher the pump head, the larger the impeller and more effective the pump will be at priming. However, in most pump lines, the max head is the same for the various HP ratings so you can lower the HP to save some on electricity costs.

If you want to stick with Pentair, the Whisperflo is a good pump line but for priming reasons, I wouldn't go below 1 HP (full rated). So either the WFDS-4 or the WFDS-26 would be a good choice.

BTW, where is your location and how much do you pay for electricity? A VS may or may not be a good solution for you.

[lstinthot]

We pay about $.10 per KWhr. We were considering a Variable speed. Looks like it takes a long time to recoup the extra cost over a two speed pump.

[mas985]

At $0.10 /kwh, it would take a standard VS about 130 months of 4 hour operation/day to become more cost effective than a two speed . If you are willing to go with a lower cost VS such as the MaxFlo, it would take about half that time. But if you are in a lightning prone area, which is why I asked about your location, it is even worse (~50% longer) because you have to factor in the cost of surge protection.

[lstinthot]

We live in Central Virginia. We have a hurricane season.

[mas985]

You can use this map to determine your vulnerability.

http://www.vaisala.com/VaisalaImages/Product%20and%20services/NLDN%20CG%20Flash%20Density%20Miles%201997-2010.png


http://www.vaisala.com/VaisalaImages/Service/NLDN_210x170.jpg

[lstinthot]

Looks like we are in the 9-12 region.

[lstinthot]

Looks like these two pumps pull the same amps. The WFDS-4 is one HP and the WFDS-26 is 1.5 HP. The -4 costs about $75 more than the -26. Does it make sense they both have the same amp rating? Wouldn't make more sense to go with the 1.5 in my case then for the higher lift?

Thanks


The UltraFlow is a high head pump so priming is probably as good as it gets with this pump. You can either replace the entire pump or just the motor. It usually makes more sense to just replace the motor if the wet end is in good condition and you don't need to change any plumbing. But since you have to change the plumbing anyway, it may make more sense to replace the entire pump. Either way is fine, it is basically an economic decision.

However, when looking at a replacement, you need to focus on max head because that is the only thing you can go on for priming ability. The higher the pump head, the larger the impeller and more effective the pump will be at priming. However, in most pump lines, the max head is the same for the various HP ratings so you can lower the HP to save some on electricity costs.

If you want to stick with Pentair, the Whisperflo is a good pump line but for priming reasons, I wouldn't go below 1 HP (full rated). So either the WFDS-4 or the WFDS-26 would be a good choice.

BTW, where is your location and how much do you pay for electricity? A VS may or may not be a good solution for you.

[lstinthot]

Will these pumps move water on slow speed in my application? I am figuring 50 Ft of head, looks like slow speed graph tops out at 22 lbs.

[mas985]

Looks like these two pumps pull the same amps. The WFDS-4 is one HP and the WFDS-26 is 1.5 HP. The -4 costs about $75 more than the -26. Does it make sense they both have the same amp rating? Wouldn't make more sense to go with the 1.5 in my case then for the higher lift?The WFDS-26 is an up rated pump while the WFDS-4 a full rated pump but other than the label, they are identical in performance. So it doesn't matter which you get. One of the problems with pump ratings is that it causes confusion.



Will these pumps move water on slow speed in my application? I am figuring 50 Ft of head, looks like slow speed graph tops out at 22 lbs.Yes, they will still move the water on low speed. But head loss is dependent on flow rate so on low speed, head loss is about 1/4th that of high speed. If you indeed have 50' of head on high speed, on low speed you would have 12.5' of head. But you don't need to figure head loss to know that low speed is always around 1/2 the flow rate of high speed.

But because of the lift, you will need to always prime on full speed and then switch to low speed. The pump should not lose prime when shut off but if does, it will need to be started on high speed. If you get a two speed timer, that should solve any priming issues because you can always start the pump on high speed and then switch to low speed.

[lstinthot]

I installed the WFDS-26 today. Went pretty good. Took a little longer than expected to complete. The discharge pressure on high is 16# and maybe 2# on slow speed. Not sure what others are seeing for slow speed discharge pressure. I did change the piping on the return of the filter. It now comes out of the filter and goes back to the pool without going through the heater or clear water metal copper system. Very little water comes out of the vent when I open the vent on top of the filter in slow speed. I am returning to the bottom drain of the pool. We keep this lineup during the spring to help heat the pool. Have not tried going back to the return jets.
Pump is significantly quieter then the ultraflow 2HP even on high speed.

New filter elements will be in Friday.

[mas985]

Low speed will have lower pressure and theoretically should be about 3 PSI but gauges get inaccurate at low PSI. 1/2 the flow rate results 1/4 the head loss in the plumbing.

But is the pump basket staying full between pump runs?

[lstinthot]

The pump started up immediately the following day. Pump was full pressure came right up to 16# . Best it has ever done. I'm thinking slow speed could have started moving water from the start.

[mas985]

As long as the the pump doesn't lose prime after being off, you can start it on low speed if you want.

[lstinthot]

I plan on starting the pump in slow speed tomorrow to see how it does. We will add timer dogs once we are happy with the pump starting with no issues.