Skimmer basket shot up like a rocket

Hi - I am new to the forum. We have a 24ft above ground pool w/hayward sand filter & pump and just opened. We have had for 4 years. I have been having a problem when turning my pump off AND when try to vaccum the pool. The pump will drain of all water when trying to vaccum. When turning off the pump the skimmer shoots up in the air like a rocket. When we opened our pool (we always cover with winter cover as we live in wisconsin) it was pretty darn clean - just a little green. We treated and now the water is crystal clear and tests fine. I did inspect the vac hose...it did have a crack on the end that you attach to the skimmer. I have replaced that. I just went out this morning to inspect the hoses (all new) to see if there was a leak or a crack. I found a crack in the actual skimmer - the bottom. Would this be the cause of the air pressure shooting that skimmer basket up like a rocket? Do I buy a new skimmer and hook it all up and should be good? Please help I am so frustrated.

Just some starter questions:

What size and type pump and filter do you have?

Do you have a low drain on the pool as well?

Do you have a ball valve in line with the skimmer that allows you to decrease the vacuum there?

Is your water high enough in the skimmer?

Are you filling the vacuum hose from the return to blow out all the air in it?

Welcome to the forum. You'll need to answer Carls questions but what I'm thinking is the crack is letting air into the system. Because you're letting air in the filter isn't being purged of air fast enough. Normally if you get a little air in such as when you connect a vacuum hose that still has air in it, that little bit of air will quickly be purged from the system. Water is not compressable. With a solid water charge, no air, when you turn the pump off the flow just stops. Now consider a large volume of air in the top of the filter. Air is compressable so you have this big bubble sitting in the filter at whatever your pressure is. Say 15 psi or maybe more. Now you shut the pump off and that bubble wants to expand to 0 psi. It's going to push water out two places. Out the return jet and back thru the pump and skimmer. Now consider the filter sand is moderating or attenuating the flow out the return so the path of least resistance is back toward the skimmer. Most of the energy stored in that compressed bubble exits the skimmer. Poof. That's the only way I can explain a violent blowback.

A giveaway sign would be bubbles in the system that you would see out the return and in the pump basket. You may also see a spurt of water out the pump basket lid when the pump is turned off depending on how that is sealed.

Hope this helps.
Al

Wow - first of all thanks for the responses....I have to leave so I wanted to quick post a response.

pump is a hayward 1.5 HP motor w/a sand filter (above ground pool - 24ft round)
low drain on pool? I don't understand.....

Do you have a ball valve in line with the skimmer that allows you to decrease the vacuum there?,....NO

Water is high enough in the skimmer - it is a little over 1/2 way up the skimmer

Hose is filled w/water from the return before hooked to skimmer.

Filter is at a constant 12 psi (except for when it is turned off - we did buy a new gauge this year as I broke the old one :( )

When I turn off the pump...yes...the skimmer basket shoots up and lots of air bubbles come up and then little ones keep coming. I think there is also air bubble shooting out the return.

I am running to the pool place (45 min away..ouch) to buy a new skimmer. I think poconos had a great explanation and I actually understood it....thank....will update after the new skimmer is attached...after we drain....ugh i want to swim!!!

Well - the new skimmer is in and works like a charm. Vaccum works great too! Thanks for the replies - I truly appreciate it.

Glad to hear all is well again. thanks for letting us know.
Enjoy your pool.
Al