request assessment of suction side plumbing

[ramblinwreck001]

Hi folks. Just had a local pro install some new equipment (pump, filter, booster) and in the process he re-did my suction side plumbing. New equipment is working well, but in the process he changed the configuration of the suction side plumbing and I have questions about it.

Here is what I started with, i.e. before equipment install. This setup worked OK, except the system is a pain to prime if the pump shuts off because this equipment is uphill from my pool/spa.


And here is what I have now after the equipment install:


The two main changes are:
* Addition of a check valve before pump, helps with subsequent re-priming.
* Now only one Jandy valve needs to be moved to switch between pool and spa mode (simplify future automation...), whereas before I potentially had to move 3 valves to do the switch.

Now, my questions:

1. Does this look like an OK installation? I'm no fluid dynamics expert, but I observe there are many more 90-degree bends than there were before, and I know this can't be good for flow. But maybe this is not unusual for this type of equipment? Can someone give me an objective assessment of this setup?
2. I'm getting major cavitation if I try to pull from main drain only (I.e. spa and skimmer suction off). I can pull from the main drain successfully only if the skimmer line is also open. I can't help but think this is related to #1. In my original setup on the main drain line there was only a single 90 degree bend from the ground to the pump. Now there are four, one of which is a "T" fitting.

Installer is coming out tomorrow to take care of some unrelated leaks downstream of the pump, and I've already mentioned the cavitation issue and plan to discuss tomorrow, but I'd like to get some opinions about this before that chat.

Chris

 

[JJ_Tex]

Certainly not my area of expertise, but giving my 2 cents and a bit of a bump to get more eyes on it.

1. Not a terrible setup, but seems like moving the pump closer to the filter would let you kill the 2 90's after the pool/spa jandy valve.
2. In the picture your drain is almost fully closed. When you close off the skimmer, I assume you are opening up the drain all the way?

 

[ramblinwreck001]

Certainly not my area of expertise, but giving my 2 cents and a bit of a bump to get more eyes on it.

1. Not a terrible setup, but seems like moving the pump closer to the filter would let you kill the 2 90's after the pool/spa jandy valve.
2. In the picture your drain is almost fully closed. When you close off the skimmer, I assume you are opening up the drain all the way?

Thanks @JJ_Tex for the reply. It is not evident from this particular photo, but the pump and filter can't really be any closer, unfortunately. The filter drain is nearly touching the back-end of the pump motor as it is. The previous setup avoided this by placing the pump AND filter further to the left, however, half the filter was hanging off the edge of the pad. I don't know what they were thinking when they built this!!!

And for #2, the answer is yes, I.e. drain is wide open when I close the skimmer. I acknowledge that is not a configuration I intend to use much (if ever), but I noticed it when testing out the valves and assumed it should work. What you see in the photo is my intended valve setting for normal pool mode operation (I.e. mostly pulling from the skimmer, with a little flow through the drain). I expect this is how they will be set most of the time.

To be more clear on the valve setting where there is a problem, the progression looks like this:

1. Start with the valves in the position shown in the photo (skimmer fully open, drain barely open). This works fine. NOTE: Also works if skimmer fully open and drain fully closed, as expected.

2. Slowly open up the drain valve while the skimmer valve remains open, stopping when both valves are fully open and therefore pulling from skimmer and drain together. This also works fine.

3. Slowly close off the skimmer valve while the drain valve remains fully open. After closing the skimmer valve a bit, I start to get what seems to be turbulence/cavitation (visible through the clear cover on the check valve just before the pump basket), then the pump basket goes empty and the pump loses prime, at which point I reset the valves to re-prime which happens quickly..

 

[DavidArmenB]

Cant speak about the cavitation but he made the plumbing better than it was before, imo. You now only need to move one valve to switch from pool to spa mode as opposed to three valves. This is the proper/standard way. Also makes valve automation very easy if desired.

 

[Jimrahbe]

001,

The 90's will not make any noticeable difference in the overall operation of your system...

The check valve in front of your pump is a crutch and not a fix. It does allow your pump to not drain back into the pool when the pump is off, but it does not address the leak that is causing this to happen.

It sounds to me like you main drain is not working at all.. If you open the main drain 100% and close your skimmer 100% I suspect that your pump will not prime, or if it does, it won't run for long before all the water is gone.

Thanks,

Jim R.

 

[ramblinwreck001]

Cant speak about the cavitation but he made the plumbing better than it was before, imo. You now only need to move one valve to switch from pool to spa mode as opposed to three valves. This is the proper/standard way. Also makes valve automation very easy if desired.

Thanks, this is a relief to hear. And spa/pool automation is in the future plans because right now my spillover runs 24/7 and I know that is exacerbating fast pH rise which I'm experiencing now. I'd like to be able to switch the spillover on for 30 minutes twice a day to circulate the spa without having to run it nonstop.

The 90's will not make any noticeable difference in the overall operation of your system...

Thanks.

The check valve in front of your pump is a crutch and not a fix. It does allow your pump to not drain back into the pool when the pump is off, but it does not address the leak that is causing this to happen.

Can you elaborate on this, please? My equipment pad sits about 6 feet above the surface of the pool water. I was led to believe it's normal (without a check valve) for gravity to take the water in the pipes back down to the pool if/when the pump is stopped. Is this not the case? The check valve seems to have made a noticeable improvement on my ability to quickly re-prime after stopping the pump. But I'm interested to hear more about this, if there are other things I still need to address.

It sounds to me like you main drain is not working at all.. If you open the main drain 100% and close your skimmer 100% I suspect that your pump will not prime, or if it does, it won't run for long before all the water is gone.

You may be right about this. If I open drain 100% and close skimmer 100% it will not prime, as you say.

The only way I can operate the system with the drain valve open 100% is if the skimmer is also open 100% (I.e. step #2 in the sequence in post #3). It just occurred to me that in this scenario, just because the drain valve is open doesn't mean it's actually pulling from the drain, it could just be pulling from the skimmer since that valve is also open. So that would also fit the clogged drain theory..

I've been searching/scouring this forum to see if I could find folks with similar issues, and stumbled across this older post which sounds suspiciously similar to what I'm experiencing, and that issue was ultimately found to be due to a clogged main drain, also consistent...

 

[Jimrahbe]

001,

In theory, when the pump is off, there is a vacuum that prevents the water in the pump from flowing back into the pool. Kind of like when you pull a straw out of a glass of water with your thumb over the open end of the straw. The higher the pool is above the pool the harder this becomes. It is much easier to install a check valve than it is to find a leak... When the pool was new, did the pump prime like it should??

Main drains are not really needed. No one uses a main 'drain' to actually drain a pool.. There are thousands and thousands of pools out there that either have no main drain at all, or don't have an operating main drain. It makes very little difference. I have two rent house pools that do not have operating main drains and they work just fine.

I would not spend five minutes trying to 'fix' your main drain problem. It may not be clogged at all, it could be a broken pipe, so that when you try to suck water from the main drain, you are actually sucking air, causing the pump to quickly run out of water.

I suggest that you just shut the main drain valve completely off. It might even fix your pump prime issue..

Thanks,

Jim R.

 

[ramblinwreck001]

In theory, when the pump is off, there is a vacuum that prevents the water in the pump from flowing back into the pool. Kind of like when you pull a straw out of a glass of water with your thumb over the open end of the straw. The higher the pool is above the pool the harder this becomes.

Thanks. Thinking about your straw analogy, the thumb over the open end of the straw would be analogous to a leak on the pressure side of the pump (e.g. filter leaking air), but thinking more I guess a leak anywhere in the line would also allow it to drain down eventually..

It is much easier to install a check valve than it is to find a leak... When the pool was new, did the pump prime like it should??

Don't know. Pool was built approx 20 years ago, and we just bought the house, so I'm sort of flying blind trying to figure it all out. The previous owner told me to expect having a hard time with priming, suggested using the bucket method to get some water into the lines before priming. I did do that a few times and seemed to work OK, just a pain. VSP runs 24/7 so don't really expect to have to re-prime unless we lose power or I'm working on the system.

The only info I have about the prior status of the main drain operation is what the inspector put in his report before we closed:

"Bottom Drain - Good - Working I noticed two Bottom Drain covers to comply with Federal Safety Regulations. Both drains had good suction to the pump and were not showing signs of leaking at the time. "

So ostensibly the drain was working, at least partially, when we took ownership last month.

Main drains are not really needed. No one uses a main 'drain' to actually drain a pool.. There are thousands and thousands of pools out there that either have no main drain at all, or don't have an operating main drain. It makes very little difference. I have two rent house pools that do not have operating main drains and they work just fine.

I would not spend five minutes trying to 'fix' your main drain problem. It may not be clogged at all, it could be a broken pipe, so that when you try to suck water from the main drain, you are actually sucking air, causing the pump to quickly run out of water.

I suggest that you just shut the main drain valve completely off. It might even fix your pump prime issue..

Thanks. I had actually stumbled on some of your previous posts on precisely this topic but it is good for me to hear it again in this context. Are there no situations where I might ever want to use the main drain without the skimmers? What about draining the pool (if/when that becomes necessary)?

It will be hard for me to 'let this go', though, it's just my nature. I want the pool to work the way it was designed to, but I hear what you are saying and appreciate that info. I may try to do some inspection myself to see if I can find anything. Pool tech (who installed equipment) is also coming out Monday for few remaining items and I'll see what he has to say about it.

One possibly related thing is that the pool does have trees nearby, and I did notice a surprisingly large amount of twigs in the old pump basket (before removing old pump). I'm assuming those twigs didn't come through the skimmer baskets, can they get through the drain grate (where the holes look bigger than those on the pump basket)? If so, then I'll bet I've got a bunch of tree debris in my main drain line. I've been very diligent about maintenance since I took ownership, but I'm not sure how diligent the previous owners (or their hired pool service folks) were.

EDIT TO ADD: We did also just have a roof put on.. The roofers did cover the pool, mostly, but I did see some debris in the pool, but the Polaris seemed to pick it up quickly, running over the next day or two.

Chris

 

[Jimrahbe]

Chris,

It is your pool and you should do what you want... My advice about just closing the main drain is based upon the fact that you will not gain anything by having the drain working. If you just want it working, no matter the cost, or effort, then go for it...

I really doubt your pool 'inspector' actually tested the main drain... He probably assumed like you, that if the main drain and skimmer were both open, then they both must be working, which of course is not true.

You can have an air leak on the pressure side, that does not leak water when the pump is on...

If you have more time than sense, you can take the flapper out of the check valve and then with the main drain line closed, run the pump and then see if the water drains back into the pool when the pump off.

Like you, I run my pump 24/7, It works well for me as I have a SWCG and like making a little chlorine all the time, and I like skimming all the time. I also find that I like the look of my pool better when there is a little motion to the water.

Thanks,

Jim R.

 

[ramblinwreck001]

I've got an update with good news. The drain isn't clogged and I think my issue is caused by something else that I'll describe below. I welcome any feedback on this analysis..

Some context: I'm an engineer (unrelated field) which in times like these is an affliction because not knowing what was causing this issue was really bugging me and I wanted to get to the bottom of it. So I went back out to the equipment pad to play with it a bit more and I made some interesting discoveries.

First, I discovered that I absolutely can pull 100% from the main drain (no skimmer and no spa drain) if I return to the spa only rather than the pool, as shown here:

This confirms the main drain is working. I manually checked and confirmed there was no suction from skimmers or spa drain, and water was indeed being returned to spa only. So my main drain is working. Good.

The problems I described initially occur only when I try to return to pool+spa or pool only (which are more typical setups for me), like this:



Switching to either of these configurations causes cavitation in the pump, then the basket goes dry and the pump loses prime. So it seems the characteristics of the pump discharge path (backpressure, I assume) play a part in what happens here. Specifically, it works fine when there is more back pressure (return to spa only) and fails when there is too little back pressure (return to pool or return to pool+spa).

Referring back to this previous thread I referenced earlier, the original poster had similar issues to me, and I think @mas985 hit the nail on the head, quoted here:

Running a 2 HP pump on just the main drain line alone, especially a small pipe, can be problematic on it's own. I am not saying there isn't a blockage but just that the head loss alone could cause issues with the pump. This can be compounded by a low head loss return side.

Based on the description of your plumbing, it sounds like a setup that would be conducive to high suction head loss with low return head loss. That unbalance can cause problems with pumps, especially large pumps and I would expect the problems you are experiencing. The solution of course is not to run with just the main drain. Or if you do, close all but one of the return paths. That should help balance out the head loss.

That sounds exactly like my system.

As one last experiment, I retried one of my problem configurations (I.e. return to pool only), but with one critical change: I slowed down the variable speed pump to "medium" speed (2400rpm), since my initial tests were done with my brand new 2.7HP pump running near max speed (3250rpm). Once I reduced pump speed to 2400rpm it worked like a charm!


I think this also fits the theory that this is a head loss / pressure imbalance issue, since the issue goes away when the pump is running less aggressively..

Does that logic hold water?

In practical terms, the solution is exactly what @Jimrahbe told me earlier (I.e. "don't do that"). I don't ever intend to pull solely from the main drain in normal operation and certainly not at high RPM. But at least now I think I understand the issue and I'll rest easier knowing I don't have a clogged drain waiting to cause problems for me in the future.

-Chris

 

[Jimrahbe]

Chris, @ramblinwreck001

I can't argue with anything you said... But..

It could still mean your main drain is partially clogged, or that it has an air leak.

When the pump is running at full speed there is a lot more suction than at lower speeds.

So, if the pipe is partially clogged, the pump can pump water out faster than it can suck water in.. unless there is some back pressure.. Also, if there is a small air leak in the main drain plumbing, then it would show up more at high speed than at a low speed.

Not that it matters much, now. Sounds like you got it under control.

I used to be a Repair Manager for several electronics manufacturing companies.. I worked with a number of great engineers over the years, and most of them had the same "affliction" that you have... It is what made them great engineers. They all had to know why..

Thanks,

Jim R.

 

[ramblinwreck001]

Thanks, Jim.
All valid points you raised and I'll keep them all in mind. I really appreciate you taking time to help me out here. I learned quite a few things working through this issue.
In fact, if it wasn't for folks like you on this wonderful forum I'd be totally lost right now. Bought a home with a pool last month and had zero prior pool care experience.
This forum has been a godsend.. Hopefully I'll be able to give back one day, but for now I'm 100% in content consumption mode.

 

[JoyfulNoise]

There is one situation where you might want to run the pump on the main drain alone and that would be to heat the pool. You would pull cold (more dense) water from the drain and return the heated (slightly less dense) water to the pool returns. This would be more efficient than returning water through the wall returns only to be sucked into the surface skimmer and thus creating a “blanket” of warm water sitting on top of the pool. A few hundred well executed cannonballs could mix the hot and cold water well but that requires a willing member of the Polar Bear Club to take the plunge …

 

[ramblinwreck001]

Apologies for resurrecting this old thread, but I just wanted to provide an update that the mystery main drain pump cavitation discussed in this thread has been solved.

I'll spare some details but short version is I had a pool tech out for an unrelated issue, and he 'blasted' (carefully) the pool main drain with CO2 in case there was any blockage in the drain line. When he did this, we noticed water getting ejected onto the pool deck from an opening in the deck I had never paid much attention to before today.

Pool tech referred to this as an "air break" and he said it was a safety feature for pools with one main drain (I have a split drain with two drain covers now, but I think the split drain was added in a 2020 replaster before I took ownership). Anyway, this pipe is connected to the main drain line and is also exposed to open air.

So under high pump suction, the standing water in this 'air break' pipe gets sucked out and the pump is able to gulp air from the opening in the deck, causing the cavitation I experience. Presumably, this is the same mechanism that would release someone if they had become stuck on the main drain (although I understand this is redundant now that I have two drain covers which performs a similar function).

So I think the mystery cavitation is solved, now. A new mystery is why wasn't that air break capped when they installed the split main drain covers, but the pool tech said it's not hurting anything the way it is, except maybe that it's another entry point for dust and debris to enter the drain line.

EDIT: For some reason unable to upload photo. Only way I could get it posted was to convert to PDF.

 

[JoyfulNoise]

We had a member once inadvertently cut the suction break line not knowing what it was connected to and it caused a huge leak because he cut it below the water line.

There’s no good option here without doing a lot of digging to find the line. Even then, if you cap it, it is a line that will always have stagnant water in it which is not great either. I would suggest capping it with a threaded cap so it can be opened up when needed.