coalescing filters are way better than dessicant of cotton filters.
Quote from: lennyk on October 15, 2022, 09:23:12 AMcoalescing filters are way better than dessicant of cotton filters.Sorry, but I have to disagree with this too . . .A coalescing filter is designed to "coalesce" - or to gather up - liquid water (or other material) droplets that are in the air charge. They are principally intended for situations where the air is going to be used almost immediately - think air powered tools and a shop compressor. These filters remove all the liquid water that is in the air charge before the air gets to the air tool through gravity, spinning and other such mechanical actions (some even use electrostatic forces too).But that usage is not what we are doing in our use of these compressors, by the very definition of the PCP use: we are Pre-Charging. Thus the air is being compressed for use later in time. That leads to the critical factor in all of this: The air charge typically starts out warm, and then cools down as it sits over time. Take this as a given, as it is true (I can explain more it needed though): the air coming out of the compressor (or out of any post-compression cotton or coalescing filter) will be at an RH (relative humidity) of 100% for that pressure and temperature. As it cools further, that "excess" water vapor absolutely will condense out into liquid water, as by definition the cooler air charge will not be able to hold as much vapor as it did when it was warmer - the charge becomes saturated, and liquid water results.Thus the critical factor is the temperature of the air charge as it enters the reservoir. These Yong Heng style compressors put out hot compressed air - if the compressor is showing temperatures of 50-60 degrees C, you can be sure the air is a lot warmer than that - after all, the heat in the compressor is coming from the air being compressed. If the metal of the compressor is that hot, it has absorbed the heat from the air charge, but of course it can't absorb all of it.Compressed air at "room temperature" and 3000 psi can hold less than about 0.1 gram of water as vapor per standard cubic meter of air (meaning the volume of air before compression), and about only half of that when further compressed to 4500 psi. As a reference, that cubic meter of air is about what gets compressed into a 30 minute tank to take it from 3000 to 4500 psi twice, and it even insanely dry desert air will start with over three grams of water as vapor in that cubic meter (and probably approaching 20 grams in very warm humid conditions).If the air coming out of the Yong Heng style compressor is at ~60C (and it probably is much warmer than that) it will hold about a gram of water as vapor in that same amount of compressed air. If compressing to 4500, it again will hold roughly half that. That leaves a lot of water vapor to condense out with every fill of the tank. Remember that one gram of water vapor can condense out to one gram of liquid water, and that one gram of liquid water has a volume of 1 cubic centimeter - so we talking about a good amount of potential liquid water - fill that 30 minute tank straight from a Yong Heng ten times and it could have about 5 cc of water in it already (if not more).I'll repeat is one more time: It is all about the temperature of the air charge as it enters the reservoir. That defines the amount of water vapor that has to be managed. Run the compressor for a very short time, like filling a small reservoir, and more of the heat will be absorbed by the compressor, thus less vapor will pass through. Run it longer, like when filling a tank, and the temperature will quickly rise and more vapor will pass. This is why a properly used hand pump has no issues - the air charge cools with the dwell time of each stroke, condensing out the water vapor in the base of the pump (take too many pump strokes and vapor will pass because the base gets hot).All that said, a coalescing filter can actually do some good - by absorbing more of the heat in the air charge, thus also condensing out water vapor. I like the idea of putting one in a bucket of ice water - but do know that this won't get the air charge all the way down to ambient in long fill sessions, given that the speeds these compressors run at and the density of the air under compression (ever notice that it takes a filled tank hours to cool down, even when filled in a bucket of chilled water at a dive shop?). With that in mind, a good coalescing filter might be better than a cotton filter - but not better than a good desiccant filter.If you really want to manage the water vapor in the air charge, an appropriately sized desiccant filter is the best way to go for most of us. After all, there really are only two ways to "dry the air" in the pre-charging manner that we use our pumps - actively absorb the water vapor in the air (with desiccants) or chill the charge to the final usage temperature before it gets to the reservoir (with chillers). The problem with chillers is that they increase the amount of air we need to compress before we even get air to the tank . . .
So cooling the air just before the tank does not do any good right, The air needs to be cooled before the water seperator (coalescing or dessicant) is this correct? Assuming one might want to intercool the charge.
Quote from: superchikn on October 15, 2022, 12:41:14 PMSo cooling the air just before the tank does not do any good right, The air needs to be cooled before the water seperator (coalescing or dessicant) is this correct? Assuming one might want to intercool the charge.Close . . . if you are using an appropriately sized desiccant filter, it does not matter where it is in the system - once the water vapor is removed from the air to a level under roughly 0.1 gram per standard cubic meter, there will never be enough vapor in that air to condense out later when it cools to ambient. That said, there is less vapor to manage in the air if it is cooled down before getting to the desiccant, so an intercooler would be better to place in front of the desiccant than after it, if only for the sake of having to dry out or replace the desiccant medium less often.When using a coalescing filter, you absolutely want to cool the charge as much as possible before it rather than after it.
Take this as a given, as it is true (I can explain more it needed though): the air coming out of the compressor (or out of any post-compression cotton or coalescing filter) will be at an RH (relative humidity) of 100% for that pressure and temperature.
I have recently heard of boosters, but still don't fully grasp the concept. Is that what the Tuxin does when it says it has one low pressure cylinder and a high pressure cylinder?