Harbor Freight has a 4-day sale going. One of the sale items is this,
for $49.95 with coupon, one per customer:
http://www.harborfreight.com/cpi/cta...emnumber=90168

It has a 1/4 hp motor and a 3-gallon tank. Easy one-hand carry, about
20 lb. Not exactly a Quincy two-stage, might last 100 hours of run
time, but I think it'll do what I want and the price was right.

The mission: air at the lake that takes about no space, is easy to
carry out of the shed and even out to the dock. Uses: inflating low
trailer tires when necessary, and inflating inner tubes to use
buoyancy as an aid to moving the shore station or getting the boat off
the shore station if the lake gets really low. I have some big truck
tubes for playing in the lake.

I don't recall the dimensions of our inner tubes, but I think I once
calculated that if completely submerged and inflated to 1.5 PSI they'd
each produce about 400 lb of buoyant lift at a depth of 3 feet.
(Water pressure is about 1/2 psi per ft of depth) If the depth is
greater than that I don't need to move anything. To produce 400 lb
of lift one must displace about 48 gallons of water. If the 3-gallon
tank is charged to 100 psi, that will expand to about 200 gallons at
1.5 PSI and same temperature so it should easily inflate two inner
tubes with one charge. It won't be isothermal expansion because the
lake temp is lower than ambient air temp, but it looks like there's
ample margin. And, I can always plug it in and run it for another 3
minutes.

I could just use an air tank, take it up to the Cenex station and
inflate it there. I did think about that. But the compressor at the
Cenex station isn't always in service and driving back and forth more
than once could get tedious. This little compressor is smaller
than my air bubbles made of old freon tanks, and I don't have to drive
it to town for it to be useful.

I've been waiting for a while to see a plausible 110-volt compressor
on sale for under $50. The 12-volt jobs struggle to inflate an air
mattress and can take 20 minutes to inflate a low tire if they last
that long. BTDT. This one charges its 3-gallon tank to 100 PSIG in
3 min, 14 seconds.