blueman writes:

blueman writes:

I have a low-end Harbor Freight 8 gallon air compressor that has many
times over earned its $100 cost.

However, there are times when I would like to have a larger air supply
tank such as when I am blowing out my irrigation system. Of course the
steady-state is limited by the compressor motor to about 4-5 CFM@90 psi.

But I was wondering whether I could extend at least the initial volume
by adding an additional tank.

Harbor Freight for example sells an 11 gallon portable air tank
(http://www.harborfreight.com/11-gall...ank-65595.html)
for about $38. It is rated up to 125 psi (same as my compressor) and
comes with a gauge and a tire-type fitting.

I was thinking that I could re-plumb to NPT and attach it to the drain
hole on my compressor tank (with a T-fitting and ball valve to still
allow drainage).

This would then give me effectively 19 gallons of initial air supply.

Of course, I would need to be careful about duty cycle since filling up
19 gallons vs. 8 gallons would be like doing 2 1/2 continuous fills of
my original tank.

But assuming that I am careful about duty cycle is this a reasonable way
to temporarily extend the initial air supply for occassional uses where
I need to get the advantages of a larger tank?

(Note that it seems that several of the Harbor Freight compressors use
the same HP motor with similar CFM ratings for a range of tank sizes --
probably because the HP is ultimately limited by the 110V 15A supply
circuit)

Thanks!

Now that a new Harbor Freight has opened up about 9 miles, I went to the
store and bought the tank for $37, an 8 ft 3/8" 200psi hose on sale for
$4 and a couple of fittings for a few bucks. And I used a 20% coupon on
the entire purchase...

So for less than $40 total, I have it all working beautifully.

The setup now looks like:


Portable tank------- Tee --- 3/8" hose -- Female quick connect
| |
Gauge Ball valve
& pressure release
(included)

(Note: I added the ball valve to allow for easy emptying rather than
having to exert constant pressure on the built in release


Compressor ---- Drain --- Ball valve --- Male quick connect



When I want to fill the external tank, I quick connect from the tank to
the drain, open the ball valve on the compressor drain and close the
ball valve on the tank.

Then if I want to use the combined volume, I just attach my hoses and
tools to the normal regulator side of my compressor and get a combined
19 gallon volume

If I want to use the portable tank remotely, I just disconnect the quick
connect and then connect hoses and tools to the female quick connect on
the portable tank (I may add an inline regulator later).

If I want to drain both tanks, then I disconnect the quick connect and
open the ball valves on both the compressor tank and the portable tank.


Thanks for all the helpful comments that gave me the confidence to go
ahead with my plan.

Now I just have to wait a few weeks until it's time to blow out my
irrigation system.

Also, as a few others have mentioned, it will be good for high volume,
relatively limited time operations like HVLP spraying.

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.