Harbor Freight has a 4-day sale going. One of the sale items is this, for $49.95 with coupon, one per customer:
formatting link
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.