pipe sizing, reducers, runs, etc..

[coryp]

i recently had my pool completely redone. it's a small pool, about 13k, with a spa. i got a 2 speed 2hp hayward with the intention of always using the low for the pool and the high for the spa.

while i rarely use the pump on high for the pool, i occasionally flip it on for some quick skimming action if i need it.

for the most part, the plumbing is per the hayward site, 2.5/2.0, but i noticed that the pipe is necked down to 2.0" at the connection to the pump inlet and at the skimmer. is this a fairly common practice? i realize that the long runs of 2.5 are still of benefit, i'm just how detrimental (if at all) the reducing is.

i kindof started looking into this after i noticed tiny bubbles occasionally and started searching. one item i saw was the skimmer, (pentair admiral s20) that only has 2" port and a sticker that says max 60 gpm... it also has an equalizer valve that diverts water from the mains, which looks incredibly restrictive...

anyway, for now i'm trying to rule out cavitation, though i'm pretty certain that even at 2" pipe, i shouldn't be getting any cavitation bubbles at low speed. which i seem to be getting at about 6 hours into my 8 hour filter cycle...

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thanks for looking

 

[mas985]

i recently had my pool completely redone. it's a small pool, about 13k, with a spa. i got a 2 speed 2hp hayward with the intention of always using the low for the pool and the high for the spa.

while i rarely use the pump on high for the pool, i occasionally flip it on for some quick skimming action if i need it.

for the most part, the plumbing is per the hayward site, 2.5/2.0, but i noticed that the pipe is necked down to 2.0" at the connection to the pump inlet and at the skimmer. is this a fairly common practice? i realize that the long runs of 2.5 are still of benefit, i'm just how detrimental (if at all) the reducing is.

You really don't have too much choice. Most pumps and skimmers come in 2" size although at least on the pump side, they usually accept 2 1/2" couplings. The head loss in such a short section is really insignificant so I wouldn't worry about it.

i kindof started looking into this after i noticed tiny bubbles occasionally and started searching. one item i saw was the skimmer, (pentair admiral s20) that only has 2" port and a sticker that says max 60 gpm... it also has an equalizer valve that diverts water from the mains, which looks incredibly restrictive...

Flow rate max should not be of too much concern as long as that is not the only suction port. If you have a main drain or other skimmer, it should be fine. Even if you don't, it is very unlikely that exceeding 60 GPM would cause a problem.

anyway, for now i'm trying to rule out cavitation, though i'm pretty certain that even at 2" pipe, i shouldn't be getting any cavitation bubbles at low speed. which i seem to be getting at about 6 hours into my 8 hour filter cycle...
thanks for looking

Cavitation is probably not very likely and usually does not cause bubbles in the returns. When a pump cavitates, the bubbles will usually collapse on the pressure side of the pump so no bubbles will be seen.

Causes of bubbles in the returns could be a SWG or if you don't have a SWG, a suction side leak adding air to the plumbing. Usually, air will collect in the filter but sometimes there is enough to get pushed out the return side.

 

[coryp]

Flow rate max should not be of too much concern as long as that is not the only suction port. If you have a main drain or other skimmer, it should be fine. Even if you don't, it is very unlikely that exceeding 60 GPM would cause a problem.

Cavitation is probably not very likely and usually does not cause bubbles in the returns. When a pump cavitates, the bubbles will usually collapse on the pressure side of the pump so no bubbles will be seen.

Causes of bubbles in the returns could be a SWG or if you don't have a SWG, a suction side leak adding air to the plumbing. Usually, air will collect in the filter but sometimes there is enough to get pushed out the return side.

well, i only have one skimmer and the floor drain is only tee'd into the skimmer as shown in the photo. i guess as long as the "equalizer valve" doesn't cut it down too much it's kindof like going 2" out to the mains from the skimmer on at the worst...

so i ran into a few tells as i was diagnosing, but nothing completely conclusive.

fist i do have a swcg. and the bubbles are pretty small.
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they seem to occur at low speed, both after comming down off of the 3 min high speed prime and then again on their own after about 6 hours of the 8 hour low speed filter cycle.

the only thing that led me to think it was more suction leak or cavitaion was that i could see tiny bubbles in my pump basket and over time (on low) the basket gets low... probably about 2" or so from the top after 8 hours.

originally i was certian that the cleaner 3 way valve was leaking (see pic in above post) based on the following matrix of observed conditions...

-high speed, spa only: no bubbles in the bucket ever. i figured this eliminated leaks at the pump itself...

-high speed, skimmer only: tons of very tiny bubbles in the filter basket, though none collecting at the top of the pump basket, none visible in the returns.

-low speed, skimmer only: some tiny bubbles in the basket, collecting over time at the top of the basket. return bubbles as noted just below the bubble piture.

-low speed, cleaner only: just like low speed, skimmer only.

with all this info, i'm guessing it's got to be on of three things...

a, i have both a cavitaiton issue, which is causing the bubbles in the pump basket, and my swgc is spitting out the occasional tiny bubbles in the jets,

b, there is a suction leak on the pool side, probably by the 3 way valves

c, i guess it could still be at the pump. the spa could show no signs of bubbles as the suction side of the spa has less vacuum(negative pressure) than the pool side due to the configuration in the intakes in the spa, they are full 2.5" all the way... this seems valid as when i remove the "equalizer valve" from the skimmer when the pump is on high, i get a huge reduction in bubbles in the pump basket, almost to none at all.

i think the more info i get, the more i'm confusing myself...

thanks by the way for the good info,

cory

 

[coryp]

added all my pool construction pics to my sig if anyone is interested

 

[JCJR]

I also have a 2sp and on high, pump basket has no air. If I turn the pump to low the water stays the same. However, when the pump starts on low the water level in the pump is about 2 inches from the top (huge air bubble) and stays that way. I always thought that the pump does not build enough back pressure when it is on low but after reading your post, it looks like we have the same issue (or just normal).

 

[JasonLion]

The SWG will create small bubbles when the cell is active. Try turning off the SWG and see if the bubbles go away.

 

[mas985]

Coryp,

The air in the returns is likely to be the SWG. However, since you have air in the pump basket, it looks like you may have a small air leak in the suction side as well. This is pretty typical and is usually caused by the pump lid seal or a valve.

 

[coryp]

thanks for all the info guys, i'll run the swcg check in the next day or so and then do some quick high to off checks to look for drips.

would it be a safe guess that with 2" lines and my setup, that at low there shouldn't be any cavitation and that it's likely a small suction leak? i'm sure i can find it if i look long enough...

yet again, i can't say thanks enough for the info guys, as always, much appreciated.

i'll keep digging,

 

[mas985]

thanks for all the info guys, i'll run the swcg check in the next day or so and then do some quick high to off checks to look for drips.

would it be a safe guess that with 2" lines and my setup, that at low there shouldn't be any cavitation and that it's likely a small suction leak? i'm sure i can find it if i look long enough...

yet again, i can't say thanks enough for the info guys, as always, much appreciated.

i'll keep digging,

Again, I doubt you would have cavitation at high or low speed but even more unlikely at low. The suction pipe would need to be mostly blocked from flow and you would probably need to be at high speed to get it. Also, cavitation is very loud so usually you know when you have it.

See if you can find the air leak.

 

[muss08]

I was looking at your pictures and am wondering how far the pipe run is between the three way valve in front of your pump to the inlet of the pump. You say it is 2.5in pipe up to the pump inlet? Often times water traveling through the pipe at high speed will cause air bubbles when it hits a 90 (which is what your valve creates when one side is closed). However, when the water then moves to a straight piece of pipe the bubbles will disappear. If the straight piece of pipe between the three way valve and the pump inlet is too short then the bubbles will not have a chance to dissipate back into the water.

 

[coryp]

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it's a little hard to see, but there's about 7 or 8" of 2" from the last 3 way to the pump. i'ts necked down from 2.5".

unless it were turbulence from going through both 3 way valves, i don't think it would be that section of tube alone as when i switch to spa only, all of the bubbles in the bucket go away.