To avoid the inconvenience of buying compressed "air" cleaners and scavenging quarters for refilling tires, I'd like to get a pump that can do 72 PSI (vapor pressure of difluoroethane minus atmosphere pressure) at ~2 liters/minute for dusting, and 35 PSI @ ~40 L/minute for filling tires (I calculated to pressurize a 33L tire @30 PSI to 35 PSI, 10.4L of uncompressed air is needed, and I'd like to do this in 15s). The dilemma is that I can't seem to find any portable pump that can operate at both these 2 points.
I have one of those 12V portable pumps that can go up to 250 PSI, but the time it takes to fill a single tire is painfully slow (and loud). The problem is that at a low pressure of like 30 PSI, the flow is pretty much the same (I measured about 6 L/minute with a balloon) as at a higher pressure like 80 PSI. In other words, the motor isn't delivering it's full power at low pressures. This is just like the limited power band on diesel and gasoline engines.
Are there pumps that have a wide power band that would meet my requirement?
Or do pumps in general have limited operating points? Here's the impression I got:
(top - high pressure, low flow)
- centrifugal pumps
- axial pumps / propellers
(bottom - low pressure, high flow)
One idea is to make a piston pump with a large bore volume coupled to an electric motor with a constant power curve (torque = power / RPM). That way, it can operate at both high flow, low pressure (high RPM, low torque on the motor), and low flow, high pressure. But I don't think a constant power motor exist, so you'll end up needing a transmission, which will make it complicated.