Does water velocity depend on pump HP?

[mas985]

I'm cleaning the connections and about to unscrew the motor from the impeller case to turn it and oil the bearing first.

Pump motors use closed bearings so you can't "oil" them nor should you try.

Is the MaxFlow low speed pretty much the same as setting a new VS pump on low and running it 24/7, or would the MaxFlow Dual Speed run faster on Low than the variable?

A VS can run much slower and lower power than a two speed. Also, check your local power company for rebates on VS pumps which can make it more affordable.

A two speed will save on energy but a VS will save a bit more. The VS just costs a lot more up front compared to a free two speed so the break even is likely to be longer than the life of the VS pump.

 

[Pool Clown]

Granted, if the plumbing was not designed properly and the pump goes into cavitation, then this is an issue. But in most cases, this is not an issue so the relationship of RPM to GPM should always hold.



I agree with the first part but not the second. Why run a pump as long as you can when you may not need to? I would reword that as "Run the pump as low a RPM as you can, for as short a run time as you can get away with".

Maybe bad wording... If you run the pump at a low RPM, you would need to have an extended run time to achieve your target turnover (if any).

 

[mas985]

Maybe bad wording... If you run the pump at a low RPM, you would need to have an extended run time to achieve your target turnover (if any).

That is exactly my point. Turnover does not matter. We have been preaching that on this forum for many years now and the run time report in my sig supports this. After about 2 hours of run time, they saw no difference in water quality for dozens of different types of pools. Many on this site now run on very short run times with very high water quality.

 

[Pool Clown]

That is exactly my point. Turnover does not matter. We have been preaching that on this forum for many years now and the run time report in my sig supports this. After about 2 hours of run time, they saw no difference in water quality for dozens of different types of pools. Many on this site now run on very short run times with very high water quality.

Then we must agree to disagree. Your customers are happy, so are mine...

I won't tell my customers to run their pump for only 3.5 hours a day in the summer time. What i will do is, if they are interested, is have them take my recommendations (run time and/or speed) as a "jumping off point". Tell them to then start making small adjustments in the direction of saving energy until they see a difference in clarity, then go back a little. I believe that is the best advice.

Because if you tell them to follow a template based on a dated report from a different climate zone, and it doesn't work, he will be coming to you for answers, not the author. And to be fair, if a customer tells me he does 3 hours or 4 hours, or even 2 hours with crystal water, i will honestly tell him to "keep doing what you're doing, it's working". I'm not resistant pool operation that works. But that's just it, what works for Tom, may not work for Sam. Because Sam is not as attentive to his pool as Tom. Therefore, trying to get my customers to follow that report could very well be problematic.

Take care Mark, and have a good holiday.
Robert

 

[mas985]

On this forum there are many people from not only all over the US but also all over the world following these guidelines with much success. So we are not just taking a single report as our only source of information. That is the great thing about forums, you quickly determine what works and what doesn't for wide variety of conditions.

There is really nothing magical about a turnover and is not correlated to water quality at all. The problem is that it is an extremely conservative recommendation that forces people to waste energy for no real good reason.

But if you read the Pool School article on pump run time, we suggest something similar to what you did. Start off with more than enough run time for any pool and back off if you can or increase if you need to.

Pool School - Determine Pump Run Time


This might interest you as well as it shows that the distribution of chlorine happens very quickly and doesn't require much in the way of run time at all. So the 4 hours we recommend as a starting point is 4x the time it took to distribute the dye.

Circulation Dye Test

 

[peterl1365]

Peter, That's the reason I thought of using that old Hayward 2 speed pump, because it has a low speed. Am I wrong there? I'm thinking if it's strong enough to run my spa I'm in. Also what does VF mean, variable flow? I was planning on running 2" pipes. Do your 2.5" pipes come down to 1 1/2" through the pool wall, and then through 1 " directional eye inlets? This is a curiosity I am running into. Do you run your VS all the time or part of the day?
Repairman

Yes, VF is variable flow. Pentair sells both types, with the VF being a higher cost. The difference is that the VF model somehow measures flowrate and adjusts the pump speed to maintain your flow setting as the backpressure builds up in the filter. I have the VS because it was ~$300 cheaper at the time. Don't know what the difference is now.

I really don't know if a 2-speed is strong enough to run a spa at low-speed because I don't have a spa. The multiple factors make it challenging to make that determination, as you're finding. Pump HP, pipe size, length of runs, even the number of elbow fittings will affect your ultimate flow rates. A VS/VF pump will let you dial in an optimum speed regardless of how all the factors add up.

Additionally, you could change that speed depending on your mood. A slow-to-moderate flow for just soaking or a very fast flow for massage jets.

Even without a spa, I use three different speeds. I have a low speed of around 1200 rpm for slow filtering most of the day. I run it up to ~2000 rpm for the pool vacuum for about an hour in the mornings. And in the late afternoon, I run it at about 2200 rpm for 45-60 minutes for skimming (we tend to get some afternoon winds as the temperature cools off around 4-5pm, so this cleans up most of the debris before it sinks to the bottom). The pump is ALWAYS running in VS mode since the top speed is ~3450 RPM.

And yes, the 2.5 inch pipes do taper down to standard inlet fittings, but there's still a benefit to having the larger pipe runs. I'm not familiar with the calculations, but here's a link that calculates volumetric flow rates versus pipe diameter (assuming constant linear velocity).

http://www.1728.org/flowrate.htm

Basically, with all else being equal, a 2.5" pipe will flow about 40-50% more water than a 2" pipe. This is primarily due to reduced boundary layer friction losses. I can't quantify how much it helps, but I'm quite certain it doesn't hurt.