Info on blowing lines w/compressor

[autoxer]

I tried to blow my lines with our shop-vac this year and failed to get that to work. Next step was to try a compressor. I'd been wanting an upgrade to my dinky little $50 compressor for other reasons anyway, but didn't want a behemoth, so ideally I wanted something that would work for the pool, but no bigger than necessary. Reading these forums I'd found several posts that hinted I'd need something pretty hefty.

Well, FWIW in case others want to know what might work for them, I borrowed and used a DeWalt (D55146) 4 1/2 gal (quite portable, not that big) rated for 5.2 SFCM@90psi from the pump basket drain and it barely even knew I was using it. I could take my time and never worry about running short on air. Based on what I experienced, I think anything over 3 SFCM would have still been overkill for our setup. I suspect most compressors would work, and almost wish I'd tried even my itty bitty one first, but I actually liked this size and may get one just like it for myself now that I know it works.

I blew dual MDs ~6.5-7' deep (after allowing for some water drained, + going "below" pool surface.) Connecting pipes are 2" and have probably around 40' linear run in addition to the depth.

It also blew a 2" waterfall line, exits ~+6' elevation relative to pump, probably 60' run, the vac return (probably the easiest to blow) and 3 (partially shared) return lines, probably 90-100' run.

The shop-vac took care of the skimmer previously but I'm sure this would have been fine.

Also FYI, 20lbs of pressure was plenty; it was hard to get the regulator on this one to set for less than that.

 

[gkruske]

That one would most definitely work. I used my consumer-grade Craftsman 16 gallon, 3 HP compressor, and will NOT be using it next year. The one thing it did well was blow the MD. As for the rest of the plumbing, a 40 PSI shot of air would last for less than a minute, then would have a very hard time recovering.

That DeWalt is a contractor grade compressor, for heavy duty use. It's a belt drive, so it will always be pumping the same amount of air, with a smaller tank to fill up. If it needed any recovery time, it would be negligible. Mine took about 4-5 minutes to recover. I am assuming that if I had been using the right equipment, I could have my lines blown and filled with antifreeze in under an hour. Instead, it took me about 4 hours, since I was waiting on my compressor.

I bought the biggest, baddest, ugliest shop vac for next year. 6.5 HP, so I'm hoping that will really jar things loose (water, not my fittings!).

The price seems to be right on that compressor too, just north of 300 bucks. A decent (decent for airing up tires, impact wrench, nailer, etc) Craftsman compressor, is just north of 200, so yeah, buy a good one.

I've got a pretty common plumbing setup, so I'm hoping this vac will work next year.

 

[DaveNJ]

I use a 26 gal, 5hp compressor (not oil less), and its worked well for me. I only run it at 25psi blowing out the lines. I had this unit before the pool for car work. I made a pvc pipe extension that screws into the skimmer. The pipe has a shutoff valve and air hose fitting. I can shut off the airflow without disconnecting anything.

 

[autoxer]

Smaller tank meaning less recovery time is a good point I hadn't really thought about and you're right. When I just let er blow for a bit to see what happened it recovered in probably less than a minute while still blowing air out of the returns :-D However, for someone sizing a compressor for their pool blowing needs I don't think it's really size (gals) or hp at all that one needs to look for, but Sustained CFM. It'll get the job done fine even if it's running continuously if it can maintain the pressure/volume while doing so (and it is "easier" on the compressor at lower pressure; you'll sometimes see diff SFCM specs at 90 and 40 psi).

Do you know the SFCM for your Craftsman? Based on the specs you gave I would have guessed at least 3 and thought you could just let yours blow continuously as well, but maybe it does take 4-5 to do that.

The "required" pressure is actually fairly easy to calculate and very low - it's simply the depth of your water. Roughly 10m of water is 1 atm of pressure, or about 15psi give or take. I believe that's fairly linear, so even a deep pool at 3m or ~9' only takes about 1/3 of that, or, about 5 psi.

Dave: I love the pvc extension pipe idea - I'll have to make one of those for next year!

 

[DaveNJ]

My SCFM is 6.6/5.8. I'll post a picture of the pipe setup.

 

[gkruske]

My SCFM is probably 4, or close to that. Doesn't do much, really. That type of compressor is made for tools that don't require continuous air flow, i.e. impact, nail gun, air ratchet, etc. I couldn't paint a car with it, for example.

The oil-less motors just really don't hack it, not enough moving parts, and really noisy.

I would crank my regulator to about 30 PSI, would get a good shot of 30 for about 45 seconds, compressor would kick on, create 30 PSI for about another 30 seconds, then drop like a bomb. It would to zero quickly, and not keep up. As mentioned, it did the MD just fine. I let that blow for 45 seconds, and figured that was good enough.

This is why you see the guys who blow out sprinkler lines with a trailered compressor. Those have no tanks....just a massive motor that is able to push large amounts of air.

So, yeah, you're on track. Smaller tank, big motor to produce big SCFM, and you'll have no issues, and small recovery time.

DaveNJ has a shop compressor....he definitely has no problems with that one.

 

[Durk]

I have the same size/spec compressor as DaveNJ, although I blow at 20 psi and I do it from the pad. Air hose from the regulator connects to a garden hose bibb on the pump output pipe and I switch it on and off with the hose valve. I just think gkruske is asking for more air than he needs. 45 seconds is way longer than I ever blow. A few repeated shots of 5-10 seconds each at 20psi is all I do on skimmers. I have to do my returns "wet" as they are set much lower than I want to make my winter water line. So I drop to 5 psi so I don't keep blowing my plugs out as fast as I put them in. Main drains get one shot and I close them off about 5 seconds after the air starts bubbling up.

I think if you used lower pressure and shorter shots of air your Craftsman would do just fine.

 

[gkruske]

Durk, you're probably right. I think my issue was pretty simple....this was my first year closing, and I would never hear the end of it from the wife if I wound up with busted lines next spring! I got about as much info as I could here, and from what I recall the PB doing last season. He used a Mighty-Vac, and no way I was buying one of those.

I know there's no way to get all the water out of the lines, I just wanted to get as much as I could. And a lot of it is just my experience with that comp. from using it on other jobs.

 

[Durk]

I hear that. The first year I did it I was plenty nervous. Now I've done it five times and I'm less nervous and I've made a bunch of improvements to my technique. Both DaveNJ and I have ways to plumb the air compressor tight to the pool plumbing. You didn't say how you did the connection. I can tell you it makes a big difference in how effective your compressor is if you are not losing air anywhere except at the end of the pipe being blown out. Anyway, good luck next spring, I'm sure you'll be fine.

 

[gkruske]

Took the advice here and hooked directly up to the pump drain. Worked better than I thought.

My thought is next year, I'll do what a lot of people do here, and that's blow from the skimmer. I remember the PB doing this my first year.

As mentioned, I know I got the majority of the water out of the lines, and I've got 9 gallons of antifreeze in the lines......I have no idea where at in the lines, I just know it's in there! I found it for 1.99/gallon on sale at the farm supply, so I didn't feel bad about overkilling it a bit.

I'm in Missouri, and although it does get cold, it never stays horrible cold for very long. Weird weather here....

 

[polyvue]

I'm in Missouri, and although it does get cold, it never stays horrible cold for very long. Weird weather here....

I lived in Kansas City (Westport, near the Plaza) for a couple of years in the 1980s. Love the city, hated the (winter) weather.
Can remember several times when the temp stayed at or below -10°F for three or four days. Brrrrrrrrrr.

Just so no one will mistake this for a thread hijack, I'd like to state for the record that I think it's a good idea to blow out exposed pipes in temperate climates as part of winter closing. Whew! Going way out on a limb, here.

 

[jay_k]

I use a Rigid vac for everything except the main drain, slide or any other "lift" features where the shop vac can't develop enough pressure. For slides and other "lift" features, I use the vac after the compressor blows most of the water out. I find that the volume of air from a compressor doesn't move enough water to completely flush the lines. By using the vac after the compressor, I notice some additional water blowing out.

 

[gkruske]

I think this is my 'bingo'

 

[botanica37]

My compressor is Porter Cable, 2HP, 6 gal and it didn't do a good job of blowing the lines (thanks again, Durk, for all the advice). So I have been looking for a suitable (i.e. cheaper) alternative to the Mighty Vac and thought it might be useful to share what I found so far. I am somewhat unsure on what is more important: air flow or sealed pressure...:

Mighty Vac (Balboa water group) $320+
air flow 92 CFM
HP 2.75
13 amps 120 V
1.25 diam. hose
sealed pressure: unknown

Cyclone vac/blower (Air supply) $320 +
air flow 130 CFM
HP 3
sealed pressure: 160 inch.

alternatives:
Shop Vac 963-14 $142
air flow 183 CFM
HP 5.5
12 amps 120 V
2.5 diam. hose
sealed pressure: 59 inch.

Shop Vac 931-17-11
air flow 210 CFM
HP 6.5
12 amps 120 V
2.5 diam. hose
sealed pressure: 58 inch.

Shop Vac 963-12-27 - $130
air flow 145 CFM
HP 4.5
12 amps 120 V
1.25 diam. hose
sealed pressure: 55 inch.

Ridgid WD 1670 (1671) - $200
air flow 190 CFM
HP 6.5
12 amps 120
2.5 diam. hose
sealed pressure: unknown

 

[Bama Rambler]

I am somewhat unsure on what is more important: air flow or sealed pressure...:

They're actually equally important. You have to have enough flow to clear the lines and you have to have enough pressure to overcome the head in the lines. For an above ground pool as little as 50" could be enough but for an inground pool you could need 150" of pressure. Especially blowing the main drain. As you found out, an air compressor has plenty of pressure but can't sustain enough flow to blow them effectively unless it's a large unit.