Air in pump stariner bakset

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
So I've been doing lots of reading and have a problem with my pump sucking air when I close off 2 of the 3 skimmers.

Background:
  • moved into house in December
  • Age of pool unknown. County says 2003, but from looks more like '83
  • Had Leslie's rebuild the 2-HP Northstar pump (it was way too loud and was not fully priming)
    • I did replace lid t-seal first, that didn't help
    • Had them replace any serviceable parts (o-rings, etc), including pump union o-rings.
    • After service the sound level respectable, now fully primes = no air
  • In terms of the plumbing, I have 3 supply lines from ground/pool - I believe they are 1.5" underground supply/return.
    • I've replaced seals/rings on Jandy 2-way valve (closest to pump) -- spa/pump suction
    • replaced o-rings on Hayward 2 way valve for the 1 skimmer basket line (call it 3rd basket)
    • Other supply is pool, shared skimmer supply for baskets 1 and 2
  • I'm confident I also replaced seals on the Hayward 2-way valve (closes skimmer basket, farthest from pump)

Problem, to get the appropriate suction to get any vacuum action I need to close off 2 of the 3 skimmer baskets. When I do, the pump loses prime/sucks air. I can get about 15 minutes of vacuum time if I close 1, restrict 2, and vacuum with 3rd.

I've used the smoke test to try and find any leaks. Fittings look old, re-plumbed before - sleeved 2" fittings on established 1.5" pvc, etc.

I'm thinking it's just too much based on some of the pump sizing threads I've read. Ie. the 2HP pump on 1.5" lines is just oversized.

edit: best I can tell the filter and pump are not original to build of pool.
 
Last edited:

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
Just some reference stuff I was reading on pump sizing:
Re: What size sand filter do I need for my pool?
A few simple calculations can be utilized to properly size a sand filter.

Volume divided by desired turn over (in hours), divided by 60. (60 mins)

Lets say for instance you want a 4 hour turnover

Pool = 8600 Gal, divided by four, divided by sixty = 35.8 gpm This would be your target flow rate to achieve your 4 hour turn over.

An easy way to further calculate your GPM into required square ft of filtration area is...

15 gpm per sq ft, divided by 38.5 = 2.38 sq ft or required filter area for 4 hour turn over.
https://www.troublefreepool.com/threads/38545-What-size-sand-filter-do-I-need-for-my-pool


Re: Need help choosing correct filter size
JasonLion
Normally you look at the size of the pool and estimate the number of GPM you want to aim for. Then you pick a pump that is close to that number of GPM for the kind of plumbing setup you have. Your pump is larger than I would recommend for a pool without a spa or any water features. Further you don't normally want to pair a 1 1/2 HP pump with 1.5" plumbing. It will work, but it puts more stain on everything in the system and wastes a substantial amount of electricity.

The filter must be large enough to handle the GPM coming from the pump. Unfortunately, while it is fairly easy to guess at GPM, it can be quite tricky to figure it out with any precision. I would guess that your current pump might be putting out 80 GPM (very approximate). The FNSP36 is rated at 72 GPM, so it would be marginal in that situation. It would very likely work, they always leave some margin on the ratings, but it would be slightly inefficient and could be prone to tearing the grids if the pump is actually moving more water than that. (All assuming I'm not way off on the GPM.)

Second, it is a good idea to get a filter that is larger than the minimum required. Larger filters mean longer times between backwashing/cleaning the filter, slightly better filtering, and a higher overall efficiency.

Mas985
Filters tend to work better with lower flow rates and lower pressure so a smaller pump is better for at least that. And unless you need high flow rates for a spa, waterfall, etc, I would go with as small a pump as you can. I now have a 1/2 HP on a 20k pool and use it for a suction cleaner and even a decent spa spillover. Skimming is reduced slightly but you will find that you really don't lose that much flow with a lower HP pump. I use to have a full rated 1 HP pump and the 1/2 HP flow rate is only about 20% less than the 1 HP but the energy use of the 1/2 HP is close to 1/2 of the 1 HP.
https://www.troublefreepool.com/threads/18402-Need-help-choosing-correct-filter-size


Y-not
Re: Is it that big, Pentair quad DE 60?
According to this chart from mas985's "Hydraulics 101" post, of which you are to double all but the sand filter square footage, your friend's DE filter is 3x the recommendation. So he's more than covered.


DE filters pack a lot of filtration per SQft.
https://www.troublefreepool.com/threads/63468-Is-it-that-big-Pentair-quad-DE-60
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Hello and welcome to TFP! :wave: Just to help everyone reading your thread .. about this statement:
have a problem with my pump sucking air when I close off 2 of the 3 skimmers
Does the prime issue happen when you close the "same" 2 of 3 skimmers, (which might indicate one bad line), or is it any random 2 of 3 skimmers (more of a pressure thing)?

Hopefully we can put of TFP heads together and get you some help. Nice to have you with us.
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
Hello and welcome to TFP! :wave: Just to help everyone reading your thread .. about this statement: Does the prime issue happen when you close the "same" 2 of 3 skimmers, (which might indicate one bad line), or is it any random 2 of 3 skimmers (more of a pressure thing)?

Hopefully we can put of TFP heads together and get you some help. Nice to have you with us.


Me too, good question. It's any 2 of the 3 that are closed off. So, I can close 1&2, or 2&3, or 1&3 and get the same result. But If only 1 is closed off, no problems. It isn't until the second basket is restricted or closed that I begin to lose prime. The problem here is I dont have adequate suction to vacuum. It would take literally all day, maybe 3 with such a size pool.

- - - Updated - - -

I am not sure there is a question here??
It's a problem not a question, and I cant figure out next steps. Is the pump oversized? Is it a bad seal between joints?

I have not pressure tested yet. I'm trying to stabilize the pool chemistry. I've fired all pool companies and bought my own test kit, and right now am using bleach and MA.

Point is, I want to first minimize down time to stabilize the water. Fighting algae too, but right now its in check.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Okay, then it could very-well be more of a hydraulics issue. We'll watch progress on this thread, but if you don't receive anything solid after a day or two, you might consider PM'ing "mas985" who, as you may know from your cut & pastes above, is one of TFP's hydraulics experts. There are a few others, but "mas" (Mark) seems to watch for such posts quite often.

In the meantime, while you appear to have done a lot of work already, I'll simply paste the TFP Pool School - Suction Side Air Leaks for you to review if you haven't already. Others might ask about some of those basic before getting too deep into other areas of your plumbing.
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
Yeah, I was thinking cavitation, but I don't hear the rocks. Also, I don't believe I have a leak. Water levels stay constant - but there is an unrelated filler valve that leaks that I need to also fix. [hose Bib tapped to pool leaks a little, so possibly loss = leak)
 

Flying Tivo

Well-known member
Jan 24, 2017
602
Monterrey, NL, Mexico
By the looks of the filter on your picture, I would have you look into disassembly of the filter and
checking the o-ring. I know its more related to the suction side, but with equipment this old
its easier to check.

Felipe
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
I've torn down the filter twice since this problem started. Surprisingly everything is in good shape. Some of the elements are new. But I cleaned and lubed all o rings. I didnt double check any missing parts though.
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
Also wanted to add the skimmer baskets are probably in need of replacement. But I don't think that's the source of my leak, if that's what it actually is.
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
Would running water over the joints really show any results?

How could I get that kind of flow rate?
Pressure test and look for bubbles?
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Would running water over the joints really show any results?
Sometimes - if someone can do that while you're watching the pump basket. There are various tricks (smoke, water, shaving cream, even plastic wrap). I kind of like the plastic wrap one myself. Pressure test can be valuable for those that have a way to make the connections and do it safely.

Perhaps tomorrow shoot a quick PM over to mas985 to take a peek at your thread here. He's our hydraulics expert, and it may be something related to the pump's ability to adequately pull from those lines.
 

JamesW

TFP Expert
Mar 2, 2011
13,312
Try this:

Turn off pump. Close two skimmers. In the open skimmer, rig up an adaptor to connect a garden hose to the skimmer hole. Turn on garden hose to push water into pump basket, through the system and out the returns. This will pressurize the suction side enough that a leak should be evident. You could restrict the returns some to generate more pressure but not too much. Probably not more than 10 psi on filter. You don't want full house pressure on the system.

Make sure that the skimmer line being pressurized is not closed. Verify which valves go to which skimmers before beginning.

Also, something looks wrong with your multiport. Can you show a clear picture of the label?

What filter do you have?

When is the last time that the filter was broken down and cleaned?

I think that you might have the wrong multiport.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,375
Pleasanton, CA
Problem, to get the appropriate suction to get any vacuum action I need to close off 2 of the 3 skimmer baskets. When I do, the pump loses prime/sucks air. I can get about 15 minutes of vacuum time if I close 1, restrict 2, and vacuum with 3rd.
It sounds like you have the cleaner in the 3rd skimmer with the other two off. With a 2 HP pump that will suck air on even the tightest plumbing. Just too much suction. It sounds more like there could be an issue with the cleaner. You should not need to close off the skimmers that much to get the cleaner to work, especially with a 2 HP pump.

A couple of questions.

What is the filter pressure when all the skimmers are open?

What is the filter pressure when two skimmers are off and the 3rd has the cleaner?

What is the make/model of the cleaner?

I can get about 15 minutes of vacuum time if I close 1, restrict 2, and vacuum with 3rd.
What happens after 15 min?
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
It sounds like you have the cleaner in the 3rd skimmer with the other two off. With a 2 HP pump that will suck air on even the tightest plumbing. Just too much suction. It sounds more like there could be an issue with the cleaner. You should not need to close off the skimmers that much to get the cleaner to work, especially with a 2 HP pump.

A couple of questions.

What is the filter pressure when all the skimmers are open?

What is the filter pressure when two skimmers are off and the 3rd has the cleaner?

What is the make/model of the cleaner?

What happens after 15 min?
let me address something first. The cleaner in question started with a Hayward XL, but I gave up and used a regular flexible Weighted In-Ground Swimming Pool Vacuum Head.

The problem is repeated with NO vacuum. Closing 1, restricting 1, causes loss of prime. Close 2 and it's lost prime in less than 2 minutes.


I tested this after a filter cleaning: dismantling the filter and hose stream off DE from elements, add 7.5# of DE pressure is 20psi.

So, all 3 open 20 psi
I don't recall closed pressure.

With reatirctions, loss of prime at 15 minutes.
No restrictions, no air in pump. (Literally, no bubble at all).


I also also don't get much in the way of skimmer basket flow. Currently no floats things in baskets
 

Mycall9550

Well-known member
Apr 5, 2017
187
Houston
My gut tells me it's more physics than broken seals or joints sucking air. But it's nice to get some pointers. Anything to confirm.

It it would be nice to vacuum. I might just have to rig something up to vacuum off 2 skimmers.

- - - Updated - - -

At this point just normal light load debris. I'm sweeping 2x / week to keep algae down. Have a tigershark to get everything else 1x a week.

Im trying to keep the organics down. But I know I have pockets of algae in the rope line sockets. The old pressure side cleaner connection. And other crevices I'd like to vacuum those to waste.

- - - Updated - - -

So with a manual vac i have to crawl.

I cleaned my dads pool when I was younger. 12-16k gal w a 1hp DE. Single skimmer. So I know what to expect on his. I'm not getting it at my new home. I'd say rate to vacuum is like 1.5' per minute. It's daunting.
 

JamesW

TFP Expert
Mar 2, 2011
13,312
I suspect that you might have an underground suction leak. I would suggest that you have the lines pressure tested.

Do you have a main drain?
 

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