Hi Bluechip, good news, there is nothing wrong with your pressure switch and you really do not want one with a narrow gap between on and off, whatever the price.
You see, that switch is not a pressure controller, and it is supposed to have a good range between on and off. It is the capacity controller for your compressor, and it's job is to match the capacity of your compressor to the consumption of what ever device you are using the air for. If you want a steady controlled pressure, you need a diaphragm operated pressure control valve on the outlet of your tank. Let me explain.
Your compressor is basically a fixed volumetric capacity device. Even if you added variable speed, you would only have a limited range of usable capacity. But your uses probably range from a tiny air brush to that sander. When you need less than the compressor capacity, you run the compressor in an on/off mode, which the pressure switch does very well, and results in the least power consumption for any given air consumption.
The tank on your compressor, and you really need one if you don't have one, has the task of storing excess air from the compressor when it is running, and supplying back that air when the compressor is off. Now air does not condense at the conditions in your compressor system, so the only way to store air is to let the the pressure rise. The more the pressure rises, the more air is stored, and you can use it for more time before the compressor cuts in again.
So the idea is to set that switch so the "on" point is a bit above the minimum pressure you need, then the tank will store air up to the "off" point, and the combination of the tank volume and pressure hopefully stores enough air to give your compressor the necessary cool down time before it has to start again. It should also allow the compressor to run long enough to ensure the lubrication is adequately distributed.
The air tank also damps the pulsations that a reciprocating compressor produces, but if there is not enough range between the on and off of the pressure switch, that is all it will do.
So providing the off setting is not so high that it lifts the safety valve, and the on setting is high enough for the minimum pressure required by any of your devices, the more range the better. And if you want a more steady pressure, say for an air brush, or to run your engines at constant speed, install a diaphragm type pressure control valve on the tank outlet. Preferably one with a coalescing type water separator included if you use an air brush, to stop water droplets spoiling your paint job. And relax, confident that that pressure switch is doing what it was intended to do.
MJM460
