Tips on blowing out the main drain

Lindseyc123

Active member
Sep 11, 2019
30
MA
You guys are always more than a wealth of knowledge. First time closing pool. We blew out the returns and skimmer u til we saw a mist. We closed the skimmer line and opened main drain and put shop vac blower in. We don’t notice bubbles. Could this be that the blower isn’t strong enough? I’m needs to blow for a long time? Or perhaps we have some valve open or closed that’s not supposed to be? Please help I’m so scared to do it wrong. I must add at one point after blowing we took hose out and water then came out. So weird. We just aren’t seeing any bubbles as we expected to see. pic to show our set up.
 

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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
38,892
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
A Cyclone blower can blow out main drains when a shop vac cannot.

How deep is your pool?
 

JamesW

TFP Expert
Mar 2, 2011
32,445
Shop Vacs really are not made for pressure.

They are designed for airflow and some suction.

You can look up the performance of a shop vac in the specifications data page.

For example, this one can do 58", which is 4.8 feet.

If the main drain is 8 feet, and the shop vac can only do 4.8 feet, then it won't work.

Below is a chart for spa air blowers, which work in a similar way to a shop vac.

The air flow rate decreases as the back pressure increases.

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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
38,892
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
If you can get the water pushed below the frost line, then that is good enough.

The frost line for your area is around 3 feet.

You need to get water out of the pipe for around 30" underground. The problem you have is how to judge how deep of an air column int he pipe your shop vac can create.

You need to right tools for the job.

Frost_Line_Map.jpg
 

jester4

Active member
Sep 13, 2020
44
Erin, Ontario
Pool Size
36000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
I have an 8' drain and just blew it out using a small 4 gal air compressor. You don't need much PSI (about 30 max). Some say to install an air fitting in the pump body instead of the drain fitting and use it that way. I remove my pump and go from compressor to the pipe directly using home made adapter my neighbor made. Worked great.

Edit - I forgot to mention that I tried to use my blower as well before going air compressor route and could not budge it.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
38,892
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Interesting. I've only ever used an air compressor. Similar to jester, I only have a small compressor. No trouble getting bubbles to come from the drain. I blow everything right from the top of the DE filter tank.

Air compressor sometimes can and sometime can’t.

Depends on the compressor and your pool setup.

Air compressors sometime have too much pressure and not enough air volume for the job.
 
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