Great Article About High Pressure Air Filtration
Ran into an article that covers in detail what we are crudely trying to emulate in the air gun world.
The pressure maintenance valve is an interesting bit that is absent in the “little” airgun compressors
like the Airmax Extreme.
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Thought about the PMV and finally understand why it can be a problem if there isn’t one. It is easiest to understand if you first consider what happens when an empty tank is filled without a PMV. As the tank goes from 0 to 4500 psi, the pressure inside the mechanical water separator and filter are just a little higher than in the tank. That means the “wringing out” of water by the mechanical separator removes only the water vapor that can be squeezed out to the extent of the current pressure. The early portions of the fill are at low pressure, hence the water separator is nowhere near as effective as at the end of the filling cycle. The first half or so of the fill isn’t very effectively dried. Also, the molecular sieve filter material isn’t as effective at low pressure.
Add a PMV that forces the water separator & filter to pressurize to 2,000 psi before anything exits the compressor and you force the water separator to “wring” out the water from basically the start of the fill. Also, the high pressure lets the molecular sieve work more efficiently. The overall amount of water getting into the tank is thus lessened.
The PMV valve of an Alpha filter essentially adds a PMV to a compressor that lacks a PMV. There still needs to be a water separator before the PMV, but even an Airmax Extreme has a water separator. Dive grade compressors have a PMV already.
A super slow compressor has another mechanism for removing water vapor from the compressed air — thermal cooling. If the compressor is slow enough for the compressed air to approach ambient temperature, the temperature change itself will cause water to condense out to its saturation point for the pressure and temperature. If cooled, compressed air is fed into a water separator, the separator becomes more efficient. The air will still be at saturation for the ambient temperature, but frank liquid water would be less likely. The gotcha here is the saturated air still goes into the tank. It is at full saturation at the elevated pressure. You don’t have liquid water, but saturated water vapor in the tank. That won’t be visible if one opens the tank. You’d have to chill the tank to get the water vapor to be visible water. A final stage air drier is still needed to scrub out the last bit of water vapor.