gain in the flowrate with multiport removed?

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Diver

Diver

0
May 5, 2011
480
South of Boston
This might be a little unorthodox and the post might be a little too long, so please bear with me 
I have a Hayward Pro-Grid DE4820 filter with a 1.5” multiport valve, which is second most restrictive combo according to a table from mas985’s outstanding “Hydraulics 101” post:

Hydraulics 101 - Have you lost your head?



I also have a 2 speed SuperPump - I replaced the original motor to a similar 2 speed. Here is the flow vs. head chart for my pump on high speed (curve SP2607x10):


After a few weeks of filtering, my system numbers are like these (high speed):

Pressure gauge on the filter: 11psi
Vacuum gauge at the pump wet end: 6”Hg
Head (calculated): ~43’
Flow rate according to the chart above: ~50GPM
Assumed flow rate on low: 20-25GPM (?)
Flow rate from the flowmeter is about the same 50GPM, so it seems that the numbers I have are right.

I can get a maximum flow rate of about 60 GPM, but that’s freshly coated, with all return jet fittings removed, so it’s not realistic. Looking at the filter efficiency table, it seems that for 50 GPM the head loss for my filter/multiport combo is 15.3’ or about 35% of the overall system head. The head loss for filter without a multiport for 50GPM is about 8.1 or almost half of the loss of the combo! So the multiport is pretty much as restrictive as the filter itself.

What I can’t calculate is what my flow rate would with the numbers mentioned above if I remove the multiport out of the picture. I can’t simply deduct 7.2’ of the head loss for multiport at 50 GPM from the overall system head loss. Reducing the head loss will increase the flow rate which will in turn raise the head loss for the rest of the system. I would think I could see a jump in the flow rate to about 65GPM, but it’s a guess and if someone could help me with more intelligent number I would appreciate it!

Here is a little bit more info why I’m curious about it. I’m a 4th year pool owner. After reading pretty much the entire TFP site over the winter of 2010-2011 I was ready for the pool season and it was a breeze! But I like to tinker with things so I replaced an aging motor on the original superpump with a 2 speed. Since then I seem to have some problems with low speed filtering that manifest themselves as green algae spots here and there and occasional haziness. With adequate chlorine levels for given CYA none the less.

For a while I thought it was a solar cover that got waterlogged and that stays in the pool 5 days out of 7, but now more and more I believe it was lack of proper circulation/mixing. Especially since I made a mistake of short filter times and removal of all the return jet fittings. I thought I’d help the flow rate since the cover was constantly on and no skimming was taking place anyway. It did help with the flow rate , but it severely impeded the mixing.

The filter time is increased now, ½” fish eye fittings are on, but the green spots here and there still tell me that I could use better mixing. Even if for some reason that’s not the case, better flow rate is good any way.

Currently I’m hard-plumbing waste port of my multiport to a drain pipe so I could do backwashing without using flexible hose that is PIA. I’m also hard-plumbing drain port of my filter to the same drain pipe with a ball valve – this will allow me to rinse the DE grids in-place during maintenance and drain the water out of the filter at the end of the season.

While I was planning this work I start to realize that waste port on my multiport might not as important anymore .With this plumbing in place and with some additional full port ball valves in front of the filter I can get rid of the multiport and still perform all the basic operations required for DE filter with some small exceptions:

- The waste function would send the water into the filter, bypassing the grids and to the drain port. Should be ok, I think.
- Rinse operation would not work w/o additional T at the filter output. But looking thru posts on the forum, lack of this operation doesn't seem to be a big deal.

I have a inline 3” tablet feeder (Rainbow 320) that was working very well for my on high speed. My starting CYA is low and my swimming season is short, so I could use some tables for quite a while without dramatic CYA raise. But on the low speed there is not enough flow thru the feeder even with top feeding position, dosing valve removed completely and tubing swapped for a large diameter. I’d like to use the feeder so maybe with increased flow I would be able to do it again.

Thanks for reading!
 
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I guess you could use a series of valves in place of a multiport. I don't recall if mas985 talks about the push-pull type of valves, but I bet those have much lower head loss. It might just be easier (cheaper?) to get one of those.
 
Nothing wrong with them, they do what they should, just without the added functionality that is often nice.
I find it hard to believe that removing the valve would cause enough of a flow rate change to suddenly prevent your algae issues. Do you run the pump on high each day for a short period of time? How often do you brush?
 
jblizzle said:
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thanks for your help. i adjusted my original post.

- - - Updated - - -

jblizzle said:
Nothing wrong with them, they do what they should, just without the added functionality that is often nice.
I find it hard to believe that removing the valve would cause enough of a flow rate change to suddenly prevent your algae issues. Do you run the pump on high each day for a short period of time? How often do you brush?
Click to expand...

i have a switch that will either allow me to run pump on high or low. the timer just switches it on. so i only run it on low.

i use the robotic cleaner on the weekend and that's about it. if i brush the green spots when i see them, they go away without causing much trouble. so i could just brush it every other day or so, but i would like a more automatic solution. when i was running on high all the time i had zero problems.
 
my CYA is about 30ppm and yesterday when i saw some green spots my FC was 7.5ppm and it was coming down from the shocking level.

on high speed with this level of CYA I maintained FC in around 3-4ppm with occasional dips down to 2.5 without any problem.
 
Why would you want to remove the multi-port valve???? The flow rate will go up, but the electrical usage will also go up and the system will end up using more electricity to move the same amount of water.
 
JasonLion said:
The flow rate will go up, but the electrical usage will also go up and the system will end up using more electricity to move the same amount of water.
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it wouldn't be the same amount of water. it will be more water at higher rate. i would also have an option:

- run the pump for shorter period of time with the same turnover saving on electricity or
- run with higher flow rate achieving better mixing/circulation. yes, this will result in higher power usage but it might help my situation.
 

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it wouldn't be the same amount of water. it will be more water at higher rate.
Click to expand...
Which uses more energy. Watts increases with flow rate so the only way to compensate is to run the pump less. But my guess is that you could do that anyway and save more energy.

The cleanliness of a pool depends less on flow rate and more on run time. So you may find that either way you will need the same run time which means that running without the multi-port will cost more in energy than running with it. The only time that it really makes sense to reduce head loss in plumbing is if you have a VS. Then you can definitely benefit from it. But even then it has to be significant before it makes a substantial difference.
 
You misunderstand how electricity gets used when running a pump. The flow rate goes up, but the electrical usage goes up more than proportionately, so the amount of electricity used per unit of water goes up. You do indeed run the pump for a shorter time to move the same amount of water, but you end up using more total electricity. Think of it this way, the higher flow rate causes more friction in the pipes, which increases the total amount of energy required.

As for "better mixing/circulation", you do get more mixing/circulation, but it really doesn't take very much mixing/circulation to keep a pool. It is kind of like having 40 times as much as you need vs 41 times as much. Yes, 41 is a larger number than 40, but it isn't different in any way that is going to make a difference. Higher flow rates also result in less effective filtering.
 
One correction - If you are moving along the head curve (left to right) then the energy factor (EF=gallons/watt-hr) actually increases with flow rate increase so the energy use does not go up as much as flow rate does but it still goes up. However, if the flow rate increases via RPM, then the energy factor decreases.

But I agree that the extra flow rate doesn't buy you as much as one would expect.
 
I was writing the response to Jason, but it looks like Mark beat me to it. If increase in flow rate was always a bad thing, we would all "upgrade" to 1/2" piping all around and save on money :) or plug the returns a little bit :)

The disproportional raise of the energy consumption to the flow rate is correct for any given system, but if you modify the system by removing some dead head it's not longer the same system.

So it sounds like I should leave it as is and possibly try to increase the run time.

Thank you for contributing to this topic, guys!

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JasonLion said:
Higher flow rates also result in less effective filtering.
Click to expand...

I would run the pump on low, it would still be significantly lower rate compared to high speed. My goal was to increase the rate for low speed filtering, not on high. Maybe I wasn't very clear in my original post and confused someone.
 
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