Time to replace sand filter?

[Johnbednarski]

Hello experts, I would appreciate any troubleshooting advice or suggestions you may have about my puzzle. I’m into my 3rd year owning an in ground pool from my parents’ property, installed 1990’s. Water flow when pump is energized is failing as follows.

Water flow: skimmer —-> gravity drain to 2 year old Hayward 1HP pump —> multiport valve —> Sand filter —> Chlorine puck cylinder —> return jet.

The multiport valve and sand filter are original 1990s vintage. I replaced the spider gasket last season. I did this because I could hear a foreign noise from the multiport valve, as if there were sand knocking about when under flow. Changing the spider gasket did not make any difference. I still hear this noise. While the multiport value was off the filter, I rinsed out the sand according to TFP video. I repeated this process this season.

My issue is that when the pump is energized, it is very slow to prime. Once primed, water flow seems normal (except for the multiport noise). I see bubbles in the return line.

When power it turned off to the pump, there is a significant “pressure exhaust” sound from the system and water releases backstream to the skimmer, lifting off the skimmer cover.

The multiport valve settings do seem to work as expected, i.e. filter, backwash, rinse, waste all seem to work as expected.

As I mentioned the pump is below grade of the skimmer. When open to air, water drains naturally from pool to pump, if open to air. but when closed to air, water will flow only when the pump is on, as expected. The problem is that when energized, the water does NOT flow, or hardly at all, for several minutes. The problem has become worse and I won’t allow the pump to work on timer anymore, for fear of burning out the motor for lack of water flow.

My guess is there is something in the multiport valve or filter that is resistant to water flow. I see no obvious obstruction and the sand seemed “normal” but dirty when I cleaned it this year. I wondered if the seal between the multiport valve and the sand filter pipe is leaky. I can disassemble this for a third time but I”m not sure what to look for. To test my theory, I tried running the system on “recirculate,” thinking that any issue with sand filter would be bypassed and system would run normal. Unfortunately, it seemed to make no difference. Still fails to prime as expected.

Since the filter and multiport valve are > 20 years old I’m fine with replacing them. I just wanted to get some reassurance from you that this is the right move, or if there is anything else I should try to be sure. Apologize for the lengthy post. Let me know what other info I can provide. Thanks so much for any comments or suggestions// John Bednarski

 

[sktn77a]

I'm surprized you pump has difficulty priming if it is below the water level. Bubbles from the returns suggests a suction side leak but that still shouldn't produce significant primimg issues given the pumps below water level location. Can you just get a replacement MPV (instead of replacing the entire filter)? That would eliminate one possible cause.

 

[jblizzle]

Yeah, I am confused by this one as well.

All the signs of a suction side leak, air building up in the filter, then when the pump turns off the air expands and pushes the water backward through the skimmer.

But, I don't understand how the pump can prime if it is below the water level, perhaps you are using the term prime incorrectly? I think in reality you are just not seeing flow (which is not prime) Prime is if your pump is full of air and has to clear it to get the water up from the pool to the pump.

Could it be that the filter is so clogged up that it is not allowing flow, which then causes the pump to pull more of a vacuum and pull air into the system?

Are you sure you put the multi-port valve back on at the correct clocking? There is usually one tab near one of the screws that should align with a similar tab on the bottom half.

 

[borjis]

I had the skimmer lid blow off quite violently right after a not so good pool company repair guy had just worked on the plumbing!
It's called "water hammer" and can be very dangerous.

Turned out to be a suction side leak.

 

[Johnbednarski]

Thanks to all of you for your thoughtful and rapid answers. Much appreciated!

Yes, I could change out the MPV and see if that fixes the problem. Since you all share my puzzlement, I’m glad you understand why I struggle to put together the symptoms to figure out what to try.

The comments about “prime” got me thinking here. Let me give more detail. With the system shut down, I peer into the clear cover of the pump. You’ll remember that if this were open to air, water will drain from the skimmer to this container by gravity.

Anyway, with the system closed and off, and while watching the pump chamber, I turn on the power. As we know, a closed system shouldn’t show anything in the chamber as it is full of water and hopefully no bubbles, right?

Well, instead of that, the pump sounds “different.” While watching this chamber, after several seconds of pump running, I see the beginnings of a trickle of water entering the chamber from the skimmer. This trickle tells me that, rather than full of water, the chamber was dry. Dry! This doesn’t make sense, as it should be full of water between power cycles, right?

The slow trickle would slowly increase, and evantually, the chamber would fill and the water flow approaches normal.

LIke I said originally, if I now turn off the power, the system appears to exhaust pressure, sometimes popping off the skimmer cover.

Not until your comment about “prime” did it hit me: The pump water chamber should not ever be dry between cycles, but evidence is that it is dry. I know this to be true, actually. Recently, before turning on the power, I can unscrew one of the tabs holding the water chamber to the pump. When I do this, the system is open to air, it “hisses,” and I see water draining into the chamber by gravity. I can then tighten the cover and turn on the power, which helps to get water flowing as it should. this is why I wont use the timer, as I have to get water into the pump first.

I’m sorry to have left out this key detail originally. Thanks for asking the right questions to add this detail. Does this extra info help to guide us towards a root cause? Thanks so much // John Bednarski

 

[jblizzle]

Sounds like your filter is full of air. When you run the pump it starts to compress this air and start to flow. When you turn off the pump, the air expands and pushes the water out of the pump?

Is your multiport on the top or side of the filter?
If on the side, you should have an air relief valve on the top of the filter that should be opened when you first start the pump to prime and get all the air out of the system. Once water starts shooting out, close that valve. Then you should not be getting air in the system unless you have a leak somewhere.

 

[Johnbednarski]

I have a top-mounted multiport. There's a non-functional pressure gauge threaded onto the multiport. I can loosen or remove the gauge as a means to bleed any air, then put it back on again. Let's see where that gets me. Appreciate the suggestion. // John

 

[jblizzle]

Top mounted should not be able to trap air. Is the top of the multi-valve oriented correctly on the bottom half? Plumbing attached correctly?

Also get the gauge replaced as that would help diagnose too. The glycerin filled ones from tftestkits are a great upgrade for same cost at the cheap local gauges.

 

[Johnbednarski]

Good tip on the pressure gauge. The one I have now only lasted one season.

I think you’re on it here. I must’ve done something wrong with the multi port valve. I the valve isn’t seated properly onto the filter pipe, I wonder if a leak at that juncture coupd cause these symptoms. I can disassemble the valve from the filter and try again. I do think the remainder plumbing is connected as it should be, but clearly something is wrong somewhere.

 

[jblizzle]

Have you ever taken off the top of the multi-port valve to look at the spider gasket? I wasn't necessarily thinking about the entire multi-port being connected to the filter, but more so if the clocking on the upper half of the valve was misaligned with the lower half of the valve and that's not allowing proper water flow.

 

[Johnbednarski]

Got it. Yes, I first took apart the valve last season and replaced the spider gasket. I opened it up again this season, trying to understand the source of the rattling noise the water makes, as if there is some sand knocking about. The gasket looks seated properly and the valve functions appear to be correct, but the noise is unexplained and not normal.

 

[jblizzle]

Do you have some pictures of the multi-valve and your plumbing?

 

[jstephens1]

set your MPV to recirculate and see if behavior is different, this will bypass your filter and let you narrow down the problem. also not common fo the pump to be below the skimmer when you think the skimmer is 2 feet or more below the deck of the pool. that's how mine is anyways

 

[duraleigh]

So, if you open the pump basket lid, the pump basket fills to the top and would overflow if you let it, right?

1. Where does that water go when you turn on the pump?

2. How does the air that's now in the pump basket get in there?

 

[Johnbednarski]

Thank you all for your helpful suggestions and observations. As I was taking the pictures of my setup as suggested by jblizzle, I discovered that the shutoff valve upstream of the pump, which is threaded to the pump, was not tight. I realize why, now, why it was not tight. If it were spun to a tight fit (I have an upstream union that allows for this,), the handle of the shutoff is oriented downward, where it is near-impossible to operate in the confines of its installation within the pump shed. But when the valve handle is oriented to top, where it is accessible but loose, I figured this looseness is the source of my vacuum side bubbling. So, I rolled up my sleeves and got to work re-plumbing the upstream fittings, that lie between skimmer and pump. When I finished the job (handle tight and oriented "up" now) and turned on the pump, I STILL saw a large number of bubbles from the return line. Following my colorful language outburst I then went to the water-hose test against all the new plumbing I just did. While I wife watched the return line (not visible to me from the pump shed), I doused the new piping with running water. Still had bubbled. But, when getting the water flow onto the pump's clear basket cover area, the wife hollered "no more bubbles!"

The clear cover and its gasket looks fine. I then checked and discovered my pump's drain plug was loose enough that I could turn it by hand. How I missed this when I had the pump assembly on my work bench a few hours earlier is beyond me. anyway, I "gently" tightened the drain plug. No more bubbles and no more back-pressure. Hurray!

Here's the summary. I still have the knocking sound from the MPV and I think it needs to be replaced, as I have no more ideas about that. But that said, I think this MPV issue actually obscured the more acute issue here, which was a vacuum-side air leak. I'm pretty sure that the looseness of the valve, plus the loose drain plug, were both contributing to that issue.

I appreciate everyone "listening" to my woes and offering up suggestions that led me to fixing the problems. Much appreciated and thank you for your expertise! // John Bednarski

 

[jblizzle]

Great!

I think that air can make a fair bit of noise in the MPV as it passes through. Even with your fix and after all the air is purged, you are still hearing knocking?

 

[Johnbednarski]

Jason - great question. That's the crux of got me down the idea of the MPV being the problem. Meaning, the racket coming from the MPV was a "can't miss, something is wrong" sound, in the context of the bubbles and pressure popping off the skimmer.

Now that the suction side leak is corrected, the noise is much less apparent. So that's good. But there is still a noise, like a rattling. You'll remember that's the sound that led me to replacing the spider gasket last year, and taking the thing apart again this season. I swear it sounds like some kernels of sand swirling about within the valve. I've looked hard to find an object in the guts of the MPV but no luck there. Hmm - I wonder if this forum allows for sound file attachments? If it does, I'm pretty sure I could record the sound with my smart phone and upload.

 

[jblizzle]

Often people just put videos up and YouTube and post a link.

 

[Johnbednarski]

Cool idea. I use Microsoft OneDrive to store my photos and videos. I made a quickie video this morning of my setup and it includes the MPV rattling noise. Here is the URL link: 20190626_115314000_iOS.MOV

Thanks all // John Bednarski