Flow Rate Help

[d088]

Hello everyone. I am hoping someone here can help me out. I am a volunteer with a non-profit organization which operates a community pool and we have been having some problems. We have consistent problems with the pump motor burning out every 2-3 years and it seized-up again a few days ago. I started looking for a new motor today and began thinking about if the existing motor is the right size for our application. Here are some of the system specs:

Volume: 135,000 gal (In-ground Rectangle pool, 70' long by 40' wide, avg depth of 7')

Motor: 3 phase, 7.5 hp, 320 GPM

Plumbing - Intake: 3 pipes @ 3" each

Plumbing - Pot to Filters: 1 @ 6"

Plumbing to Filters: 3 @ 2" each

Filters: 3 sand (unknown flow rate or size)

Plumbing - Return: 1 @ 6"

Questions:

1. In calculating the Turnover, we currently have a turnover rate of approximately 7 hours, if we are achieving the full potential of the motor. This seems awfully long for a commercial application.

2. The limiting factor seems to be the filter plumbing of 3 pipes at 2 inches each (225 GPM). Am I correct?

3. Could the filter pipe sizing cause enough strain on the motor to decrease the life to 2-3 years, or is this lifespan normal?

Any help would be GREATLY appreciated since this organization cannot afford to continually replace a $3,000 motor.

[poolbuilderLA]

Most states only require a min. turnover rate that is 3 time total volume in a 24 hour period. As for the 2" plumbing what is the pressure on the filters?

Hello everyone. I am hoping someone here can help me out. I am a volunteer with a non-profit organization which operates a community pool and we have been having some problems. We have consistent problems with the pump motor burning out every 2-3 years and it seized-up again a few days ago. I started looking for a new motor today and began thinking about if the existing motor is the right size for our application. Here are some of the system specs:

Volume: 135,000 gal (In-ground Rectangle pool, 70' long by 40' wide, avg depth of 7')

Motor: 3 phase, 7.5 hp, 320 GPM

Plumbing - Intake: 3 pipes @ 3" each

Plumbing - Pot to Filters: 1 @ 6"

Plumbing to Filters: 3 @ 2" each

Filters: 3 sand (unknown flow rate or size)

Plumbing - Return: 1 @ 6"

Questions:

1. In calculating the Turnover, we currently have a turnover rate of approximately 7 hours, if we are achieving the full potential of the motor. This seems awfully long for a commercial application.

2. The limiting factor seems to be the filter plumbing of 3 pipes at 2 inches each (225 GPM). Am I correct?

3. Could the filter pipe sizing cause enough strain on the motor to decrease the life to 2-3 years, or is this lifespan normal?

Any help would be GREATLY appreciated since this organization cannot afford to continually replace a $3,000 motor.

[d088]

The typical pressure range is 10-15 psi.

[Doctor Hot Tub]

Questions:

1. In calculating the Turnover, we currently have a turnover rate of approximately 7 hours, if we are achieving the full potential of the motor. This seems awfully long for a commercial application.

2. The limiting factor seems to be the filter plumbing of 3 pipes at 2 inches each (225 GPM). Am I correct?

3. Could the filter pipe sizing cause enough strain on the motor to decrease the life to 2-3 years, or is this lifespan normal?

Any help would be GREATLY appreciated since this organization cannot afford to continually replace a $3,000 motor.

Should be more then enough pump. Crazy question but are you storing your chlorine close to the pump or any other chemicals in that pump room? Chlorine fumes will corrode all metal. Is the water properly balanced? I ask because if your seals keep leaking then the water is going to take that pumps windings out.

[d088]

Great points that I hadn't thought about - thank you!

We do store the chlorine immediately adjacent to the motor, so we can change that easily. It is kept in closed containers, but while working with the chlorine the dust does drift onto the motor. It's an open air shed, so we never considered the chemicals as a possible problem.

I pulled the motor this morning and brought it to a shop to be diagnosed. Hopefully they can give me some possible causes of the failure. They felt that the motor should last 4-6 years running continuously, not 2-3. The seals on the impeller all looked good with no leaks, but the impeller itself was pretty worn.

[Pool Clown]

!. How and where do you introduce the Dry Cl to the pool? The dry Cl by itself in a open air "shed" would not be as corrosive to the motor as if you were putting it into crocks and filling them with water then metering that solution into the pool via injector. Please tell me your not introducing it at the pump.

2. What is the actual flow rate when the pump was running? You should be required to have a flow meter on the plumbing somewhere. Quote: "The limiting factor seems to be the filter plumbing of 3 pipes at 2 inches each (225 GPM). Am I correct?" I'm assuming this is a question and not a reading. Same with the flow rate on the pump. The flow rate listed on that pump is based on a certain amount of head on the pump. You may be achieving that, But probably not.

3. Can you tell me the effluent pressure (down stream of all filters)? You may or may not be required to have those pressure gauges.

[d088]

Pool Clown,

Please remember that we're talking about an entirely volunteer run non-profit with the only paid employees being lifeguards during the summer months.

1. We have an electronically controlled Chlorination system for day-to-day adjustment which uses a drum of chlorine tablets and another drum of acid. For manual additions, we typically add through a skimmer.

2. Sorry, no flow meter on the system.

3. Also, no effluent pressure gauges. Actually, the only gauges are the ones on the filters and the automated chlorinator readings...

[Pool Clown]

Well then, The best advice is to call a good pool tech once you get your motor back and running. Make sure he can measure what the motor is drawing in terms of amps. His reading should be within the limits on the service plate on the motor. You mentioned the equipment "shack", does this shack have a roof? I don't know where you are, but summers around here can play a part in the demise of a motor. If you have real hot days and that motor is in the sun all day, running, That could play a part for sure. If it is roofed, can the air circulate well around the motor? Heaters that don't have adequate ventilation can also contribute to high temps in the room.

Let us know what your motor guy finds.

[d088]

Pool Clown,

I truly appreciate the help. The shed is an 30x10x10 with both end open. The motor is about 5 feet from one end with as much circulation as it would ever be needed. I'm in the New Orleans area, so summers are low of 85 degrees high of 110. No heating equipment.

Unfortunately, a good pool tech is hard to come. We've tried all three of the big companies in our area, and I have known more than each of the idiots that they have sent out. (and that's not saying much - just that you had better have a good reason for your diagnosis) Seems they all want to sell something, and when I ask why they think we need it they never have a good answer. My favorite was the tech that came out and said the pipes under the slab needed to be replaced. He knew that by looking at the system while it was turned off... I asked him how he knew and he said because we had white pipes instead of black. I next asked how long he had been working on pools and he adamantly said, "for over 6 months!" I thought it was funny because we had just had a leak inspection done on the plumbing about a month earlier, and they only found a bad gasket on the pot.

That said, the motor is shot. Both housings are worn out and the windings had been over-heated. The motor tech said it must have been running rough for a couple of months to have that much wear on the housings. Makes sense since no one has been to the pool since summer, and the only way we knew there was a problem was the trouble light came on and a neighbor called me.

That brings me to my next question... Before I replace the motor with the same, how to do I calculate head feet of water? I want to make sure we are not over/under sized before dropping $1200 for a new motor. May not sound like much, but that's 1% of our annual budget and things are tight!

Thanks again!

Ben

[Pool Clown]

Now I'm thinking maybe something in the pump is unbalanced. But how? Bent stub shaft? I would have to think it would leak after a while, and I think the motor wouldn't last 2- 3 years. Warped or worn to thin impeller? I suppose that would cause a vibration. I would really like to get some pressure / Vacuum readings when It's all back together. You can Google "Feet of head" or "Head pressure". Here is my interpretation Feet of head is the amout of pipe in feet that the pump has to push the water through. Heres the thing, you have to add fittings. Fittings have an equivalent in feet. You'll have to do some homework here cuz I'm too old to commit that **** to memory. And unless you were there when they built the pool, You'll have to guess of the # of fittings underground. Lets start with press / vac guages. Even if you do figure out your head press, You really can't do anything about it at this point. I'm assuming your budget won't allow major re plumbing. There should be a plug at the pot of the pump, Vac. guage goes there. A pressure gauge somewhere downstream of the filter. And a flow meter. Install exactly how the instructions say.

[SDorje]

In addition to flow rate and chemical storage, I suspect adding chemicals directly into the skimmer could be a major factor in the pump/motor failure especially the worn impeller. If the impeller is badly worn, this will have a negative impact on your flow rate.

Where I reside (Northern California) the turnover rate is 6 hrs. for commercial pools. In your application this would be 375 GPM. I would reccomend a flow meter as this is required where I work and can tell you alot. Also install guages before the pump, after the pump and after the filter. You should calculate the Head of you system. Piping issues such as elbows, reducers, distance, size of pipe all affect flow. Finally, If you have a heater, check the heat exchanger and check valve for proper flow.

[ps558]

Pool Clown,

I truly appreciate the help. The shed is an 30x10x10 with both end open. The motor is about 5 feet from one end with as much circulation as it would ever be needed. I'm in the New Orleans area, so summers are low of 85 degrees high of 110. No heating equipment.

Unfortunately, a good pool tech is hard to come. We've tried all three of the big companies in our area, and I have known more than each of the idiots that they have sent out. (and that's not saying much - just that you had better have a good reason for your diagnosis) Seems they all want to sell something, and when I ask why they think we need it they never have a good answer. My favorite was the tech that came out and said the pipes under the slab needed to be replaced. He knew that by looking at the system while it was turned off... I asked him how he knew and he said because we had white pipes instead of black. I next asked how long he had been working on pools and he adamantly said, "for over 6 months!" I thought it was funny because we had just had a leak inspection done on the plumbing about a month earlier, and they only found a bad gasket on the pot.

That said, the motor is shot. Both housings are worn out and the windings had been over-heated. The motor tech said it must have been running rough for a couple of months to have that much wear on the housings. Makes sense since no one has been to the pool since summer, and the only way we knew there was a problem was the trouble light came on and a neighbor called me.

That brings me to my next question... Before I replace the motor with the same, how to do I calculate head feet of water? I want to make sure we are not over/under sized before dropping $1200 for a new motor. May not sound like much, but that's 1% of our annual budget and things are tight!

Thanks again!

Ben

You should try to make sure the impeller rating and motor rating can go together. A wrong impeller can really shorten a life of a motor. As stated before a check of voltage and amp draw should be done as well as correct wire size. Bad wires and connection can really be bad for a motor.

[Pool Clown]

I'm willing to bet the impeller Is correct, Being that a 7.5 Hp impeller isn't cheap, especially if it's bronze. I doubt if anyone has switched it, Given the intelligence of the service Co.s in the area as reported by Ben. Five Five Eight makes a good point that I missed, Wire size. That could add to the heat problem. If the wire size is borderline, large enough not to trip the breaker but small enough to "starve?" the motor of necessary current, or if there is something up with the connection to the motor, It would heat up. When you reinstall the motor, be sure that you have a good stripped piece of wire to connect with, and make sure it makes a good connection. I still want to know the amp draw and voltages on all tree phases when your back on line.

Good luck

[lonestar23]

Just to prop up a point thats already been made:

Your air is likely very humid. Storing chlorine in high humidity areas would knock out the bearings pretty quickly and cause corrosion on the electrical as well. Ive seen a few pumps knocked out by this alone, with an indignant customer yelling about crummy motors.

Putting chlorine into the skimmer might be knocking out the shaft seal in the pump.

If you ever see any water leaking from the pump (or wetness around the pump) I would consider replacing the shaft seal immediately.

[4serendipity]

Adding chemicals through the skimmer may have some effect of the life of pool equipment but it would appead that your pool motor is wearing out due to improper pipe sizes. Three 3" suction lines and a 7.5HP pump are certainly sufficient for your application. The 2" discharge from the pump to the filter is restricting the flow of the pump.

Restricting the flow of the pump will cause it to overwork, run hot, melt the windings and damage the impeller and seals. To solve this problem you need to address the mechanical balancing of the filtration configuarion. A three zone bypass to relieve the pump from forcing all of the water through the filters may help to decrease the strain on the pump motor.

Additionally the plumbing system should be installed as to create equal pressure in each line to the filter. Check the filter pressure guages to see the difference from one to the next. The difference in pressure between filters should not be more than a PSI or two.

You may also like to take note of the return lines and heater confiruration as these may also be contributing to an artificially increased hydrostatic head on the pump. Be sure zone valves and bypasses are not throttling back the flow. For three 3" suction lines I would expect to see 5 or 6 of 2" lines or 2 of 3" lines going back to the pool.

I hope this information is helpful.

S

PS- try HVAC and Plumbing companies to get a second opinion on your mechanical configuation if you feel that you are not getting the help you need from the pool companies.