Pump strainer basket "cycling"??

[Vettepilot]

On this pool system, the owner, my brother-in-law, suspected an underground leak from pool strainer to pump inlet, so he installed an above ground, direct line from the pool to the input/suction side of the pump. This line, which goes about 3' under the water at the end of the pool closest to the pump, bypassed the underground plumbing, the Jandy valves, etc. He still had problems with the pump sometimes losing prime, so he installed a "Foot Valve." (A one-way valve at the end of the suction line, under water.) This somewhat odd system has worked fine for him for almost 2 years.

Recently though, I heard the system making odd noises one day, and investigated. What it is doing, is "cycling" for lack of a better term. It will draw the strainer basket by the pump full of water, then suck most of it out.

You see just a somewhat slow flow of water into the basket for, say, 20 to 30 seconds. Then rather suddenly, the basket will finally fill all the way with water. Then whoosh, it sucks it all out and sends it through the filter. Then the process starts again.

It would seem like it might be fighting a restriction on the suction/intake side, or an air leak. But since the intake plumbing is dead simple, (an above ground, single line with no valves), I don't think so. The only possible restriction, would be that one-way "foot valve." So I removed it. No change. I back flushed the filter, checked the pump strainer and basket, and re-primed the system, several times. No change. I pulled the pump apart, and checked for debris in the impeller, etc. Nothing. Pump pressure is zero. I assume because it can't build pressure cycling/struggling as it is.

Suck strainer dry, fill basket, suck dry again, repeat. Over and over. Strange! Flow into basket is steady, and uninterrupted, but slow. I would say by about half or slightly less. The basket doesn't just slowly fill. It draws water, and draws water, without filling the basket. Then rather suddenly, the basket fills all the way up, but within seconds it empties it out.

??? Where do I go from here? I do virtually all my own maintenance, (on literally everything), but this has me stumped at this point.

Oh, I replaced all the filter elements with new, and re-charged with DE on this system about 6 months ago.

Vettepilot

[Denniswiseman]

It's a suction side air leak
Check your pump basket "O" ring and lubricate with silicon grease
Check your unions
Check the pipe to the pump or replace

[Teapot1]

Seconded.
Stop building the pad above the waterline, it just uses more power to draw the Water and cost more money.
Flooded pump is best and more reliable.

[Vettepilot]

Strainer basket cover and gasket are fairly new, and are clean and well greased.

What's a good way to check for a suction leak? What's the "shaving cream method" I've heard mentioned?

More info. Could this be caused by the pump needing rebuilt/resealed? I suspected he ran it without properly priming it before. His answer: "Oh, I never prime it, eventually it starts pumping., but sometimes it takes quite a while." !!!

Vettepilot

[Vettepilot]

Seconded.
Stop building the pad above the waterline, it just uses more power to draw the Water and cost more money.
Flooded pump is best and more reliable.

Oh I entirely agree. However, this is the Arizona desert. Digging deeper than the 1 inch of dust/sand/gravel on the surface generally requires dynamite!!

;~)

Vettepilot

[Teapot1]

I get it, they dug the hole for the pool though. Sadly many pool builders just don't seem to think/learn.

Onto your pump, usually the bearings are away from the wet end so not a problem but over heating could cause damage to the bearing housing so I wouldn't leave anything out, noise is usually associated with bearing and seal failure. Any non return valve downstream?

[Vettepilot]

Well, the motor sounds fine; no bearing noise. But I wondered if the bushing or seals in the pump itself might be unhappy, having run unprimed.

Yes, there's a large one-way valve between the pump and the filter.

Vettepilot

[Teapot1]

Have you checked the one way valve carefully, diaphragm hardening, biofilm build up?

The seal is ceramic, usually so can take a fair bit of abuse. There is often a hole in the bottom of the pump at the dry seal end just in front of the motor, this drips water as an indicator of leaks passed the seal.

[Vettepilot]

Yeah, that would be tough to check. The whole system, including that ouput one-way valve, is glued together 2" PVC.

Back to suction leak. What's a good way to look for/find one, and also, what's the "shaving cream" method of leak detection I've seen mentioned??

Thanks!
Vettepilot

[Teapot1]

https://youtu.be/k4UAocX6DHI

[Vettepilot]

https://youtu.be/k4UAocX6DHI

Well, I tried numerous ways, but I can't get to the video you tried to link me to...

I worked some more on that pool yesterday. It seemed to be pumping a touch better than before, but was still "cycling". I gave it a much more thorough than normal backflush, and checked every single suction side fitting with shaving cream. No leaks. I tightened the four bolts holding the strainer assy. to the pump. I cleaned the pump strainer basket and lid real well, inspected/cleaned the gasket, greased it up good, and put that all back together. I then primed it well and fired it up.

It still would not keep the basket full, but overall flow seemed a touch better. I decided to try a much needed pool vacuum. Nope!! I barely covered any area at all, and the system all but stopped flowing. It was only some "dust" I was vacuuming up; virtually no debri. A good backflush got it flowing somewhat, but it's much worse than it was previously as far as overall flow rate.

This has me thinking of a clogged filter problem. But the pressure oscillates at 1 or 2 lbs. Is there a scenario by which the filter could be clogged, but not show excess pressure??? (Since I see the gauge move, I don't think the gauge is blocked.)

The filter elements were all changed for new in June on this diatomaceous earth filter, but we live in a dirty, dusty, windy area....

Please help??

Thanks,
Vettepilot

[Denniswiseman]

You definately have a suction side air leak which is confirmed when you try to vacuum as it puts an extra load on the pump suction
A clogged filter wouldn't cause a suction side air leak, in fact it would make it less
It would be worth running a temporary new line to check out the existing line

[Teapot1]

Can you get the line pressure tested by a plumber or worst case a pool company, I say worst case becausee most pool companies wouldn't know how hahaha

[Vettepilot]

It would pull enough vacuum that the strainer basket lid would be tough to get off. I sealed suction line and pressure tested to 25 lbs, and it held.

Disconnected the output and fired it up. Almost no flow.

Tore it all down and am re-building pump. It was worn out. Excessive running without prime, and plus I suspect a lot of grit going through pump caused this I believe. Owner is kind of a "ding dong"... I've been here before.

Vettepilot

[Teapot1]

Thats at least proved the suction line so good luck with the pump and please let us know what you find.