Adding external air tank to existing air compressor to give equivalent bigger tank

[Swingman]

Be sure to report back and let us know how much difference it made.

[tiredofspam]

[blueman]

Interesting. I use my shop vac in blower mode to go through 20-30ft of

2" PVC to reach & blow out the gutters on my 3rd floor roof. It works well.

I guess the question would be what type of pressure could a shop vac push through 100-150 feet of 1" pvc irrigation tubing. Also the sprinkler heads & rotors along with the backflow preventer all require a certain minimal pressure to operate plus you need enough force to flush out the water.

Sort of the opposite problem of a compressor where you have plenty of pressure but lack volume; here you have plenty of volume but may lack pressure...

[Steve Barker]

Absolutely reasonable thing to do. My son does exactly this when he blows out his irrigation system. A "T" and some extra couplers then

3/8" hose from the extra tank to the blow point.

[blueman]

Well, I actually connected it to the tank directly (via the drain hole) so it goes before the regulator and insures both tanks are filled to full pressure...

[Ray]

Thanks for the input. I am half considering buying the 6CFM HF $129 compressor so I can do it myself and don't have to hassle with the air compressor people. My configuration is different from yours. I have

9 sprinkler heads on a zone. The 3 heads at the end of the run are about 10 feet below the other 6 heads. The first two blasts of air will clear the higher up 6 heads. After that the blasts loose the pressure in the clear heads and I can't seem to build the pressure on the 3 low heads. I vacuumed the lower heads and got just over a cup of water. I am not sure that this would cause much damage. I am in my 70's so I am not sure how much longer I will be up to this.

Any further insight would be appreciated.

This year the price was up to $25. There are also a lot of people doing lawn aeration for $25. That seems like a lot more work than a blowout. Times are tough and a lot of people looking to make a few bucks.

[chaniarts]

put a drain at the lowest end.

[blueman]

OK - I used the above setup to blow out my sprinkler on Friday in advance of the upcoming October Noreaters snowstorm...

To maximize air delivery, I ended up using a 1/2 inch 25ft hose from my compressor to the water faucet with the hose pressurized to full tank pressure (115psi) and a regulator just before the faucet set at about

55psi (not my regular static water pressure is about 80-90 psi).

It all worked fine though surprisingly I didn't notice a major increase in the amount of time that the heads stayed open before falling back due to decreased pressure. In fact, as soon as I opened the valve the pressure almost immediately dropped off from the static psi of about 55 to approximately 20 psi. It then took about 30 seconds before the tank pressure dropped to ~80 psi and the compressor kicked in again. (note that the pressure lasted longer the first time through each zone when there was still water in the pipes).

So it seems like the 1/2inch air hose and 1/4 inch fittings (at both ends) were insufficient to supply enough pressure to maintain 55 psi through the irrigation system. I guess this makes sense since the irrigation system itself has 1" diameter pipes and the heads probably let through a lot more air than the 10 gallon/minute of water that it does when driven by water.

So, it still had no problem clearing all the zones (one-by-one) of water down to a slight mist. But I'm not sure the added tank made much of a difference. Still, for ~$40, it seems like a good addition to my stem that I can use for multiple uses in the future.

[Larry Jaques]

I'm betting on the regulator being your bottleneck. If you're running

90psi normally, the 115 shouldn't be a problem, as it won't be that high for long.

It might have been more evident at the full rate, without the regulator. You could always fill and try it again to see.

-- Inside every older person is a younger person wondering WTF happened.

[blueman]

It's a cheap regulator (Harbor freight). So if I understand you correctly, you are suggesting that the regulator limits the volume significantly and may be the problem here?

I was hesitant to run it higher than 60 since people always warn against using high air pressures in pvc pipe. Is high air pressure any more damaging (in the non pipe burst case) to irrigation control valves, irrigation heads, and backflow preventors then an equivalent water pressure? (I would think not but just checking)

But you are right that it won't be at that pressure long since as soon as the irrigation valve opens, the pressure will definitely drop even before the tank runs out just simply due to the resistance of the hose & fittings. Actually, the compressor while rated at 115 psi, the pressure switch shuts off closer to 100 psi.

Note: my water supply is at 90psi static and drops maybe to 80-85 with faucets open.

Still, I am a bit hesitant to put that pressure in the irrigation pvc pipe and fittings...

[Larry Jaques]

I'm saying A) that you probably don't need the regulator at all and B) that they absolutely can have a secondary function as a flow reducer. First, run it all the way up to full pressure and check the run time. Then eliminate it and see if your flow changes. I'm betting that it will.

90% of it is underground and you already use 90psi water, so the difference is minimal. I'd wear eye protection in any case.

OK, then don't. If you don't feel it's safe, don't do it. That's your option, and don't let anyone tell you differrent.

I wouldn't hesitate on my own system, but it's drip irrigation and I open the far end of the 1/2" poly anyway.

-- Knowledge speaks, but wisdom listens. -- Jimi Hendrix

[Ray]

Most of the commercial blow out people use 100 PSI. If you are concerned most air compressors have built in pressure regulators and you can dial it down. 2 regulators will reduce air flow.