PRE COMPRESSION DESICCANT

Not really. The ambient air pressure doesn't compress the moisture out of the incoming air enough for a desiccant filter to work properly. Desiccant filters are usually used after air is compressed because compression increases the humidity level. The moisture in the air is literally squeezed out during compression which makes water separators and high pressure filters effective.

Yes (but not for the compressors sake as much as for the output air quality) and I run a pre dryer on my AV Compressor as well as a post 13X zeolite filter to remove residual moisture and oil vapor! As a matter of fact AV sells an input filter kit for their compressor. YMMV!

Thurmond

I’m with Humdinger on this one. Compressed air has 30x the moisture in it that uncompressed air has. So as you can see, you get minimal benefit from the pre compression dryer. Those are normally used for breathing air to remove toxins, or for shop compressors that only compress the amount of air 5x or 6x. 

I agree with what humdinger and centercut say, but would add that 30x 3% RH air is way better than 30x 50% RH air, so I have a Campbell-Hausfield inlet dryer on mine (you have to have a way to pressurize the inlet enough to make the inlet dryer effective). If nothing else, you don't have to regenerate/change your zeolite/silica high-side dessicant as often.

Also in my case I'm going to feed the inlet with 45 psi from a shop compressor, so the inlet filter will remove the water and oil from that before it hits the YH 1st stage - basically going to try and run it like a booster pump.

Compressing air does not increase moisture, what it does is increase the temperature at which it condenses. Moisture is actually measured in grains per pound of air, whereas relative humidity is the percentage of moisture that air contains at a given temperature before reaching saturation (dewpoint), at which it condenses to liquid. Therefore the same number of grains of moisture will yield different relative humidity based on the air temperature. It can be plotted on a pychrometric chart:

This is the way I look at it. You will always get water out of your HP air compressor. Even if your relative humidity is low. Water is basically incompressible. Air is obviously compressible. So if I take Air at normal pressure of 14.7 psi, and compress it to 4500 psi, I am compressing the air about 310 times. Hence 310 or so Bar, since each bar is one atmosphere. So now you have, as a percentage of air, about 310 times more water per volume than you did when you started, since the air compressed but the water didn’t. Make sense? That’s why we periodically vent off water that precipitates out of the air at the HP outlet and also use an air dryer to remove most of the water that hasn’t precipitated. For obvious reasons you don’t want to put humid air in your air tank or air gun. 

Mike's explanation is nice and intuitive I think. Water doesn't compress, air does. We all agree that drying on the high pressure side is way more efficient than drying on the inlet side alone. But look at the psychro chart... if you start with 20% RH air at 25C, your inlet air has about 4 grams of water per kilogram of dry air, but if your inlet air is at 80% RH at 25C then you have about 16 grams of water per kilgram of dry air. That is 4 times more water that will need to be removed on the high pressure side, hence my comment earlier about drying the inlet to extend the time between dessicant changes on the high pressure side. Drying on both ends is certainly better than drying on just the high side (but only if you can dry the low pressure side effectively - just sticking some dessicant on the inlet at 1 atmosphere of pressure won't do anything meaningful). If you have to choose to do one thing, then put your dryer on the high pressure side.

I'm going to try running the YH as a booster this weekend with 45 psi air on the inlet - lots of reasons why I think that might work well, but certainly increasing the efficiency of air drying is one of them (as is prolonging motor life, shorter fill times or ability to fill larger tanks, ability to run the YH longer and at lower temps since it doesn't have to work as hard to go from 450psi to 4500 psi, etc). Hopefully the first stage outlet can handle 450psi since it runs a 10:1 compression ratio.

Makes sense to boost the inlet pressure. Let us know how it works?

"prfssrlee"Mike's explanation is nice and intuitive I think. Water doesn't compress, air does. We all agree that drying on the high pressure side is way more efficient than drying on the inlet side alone. But look at the psychro chart... if you start with 20% RH air at 25C, your inlet air has about 4 grams of water per kilogram of dry air, but if your inlet air is at 80% RH at 25C then you have about 16 grams of water per kilgram of dry air. That is 4 times more water that will need to be removed on the high pressure side, hence my comment earlier about drying the inlet to extend the time between dessicant changes on the high pressure side. Drying on both ends is certainly better than drying on just the high side (but only if you can dry the low pressure side effectively - just sticking some dessicant on the inlet at 1 atmosphere of pressure won't do anything meaningful). If you have to choose to do one thing, then put your dryer on the high pressure side.
I'm going to try running the YH as a booster this weekend with 45 psi air on the inlet - lots of reasons why I think that might work well, but certainly increasing the efficiency of air drying is one of them (as is prolonging motor life, shorter fill times or ability to fill larger tanks, ability to run the YH longer and at lower temps since it doesn't have to work as hard to go from 450psi to 4500 psi, etc). Hopefully the first stage outlet can handle 450psi since it runs a 10:1 compression ratio.

Click to expand...

If you plan on raising your first stage pressure, you will probably have to replace or block the blowoff safety valve. I think that they are set pretty low. Mine trips sometimes after the unit auto-stops. It will be interesting to see if it does infact increase efficiency but I would be cautious about subjecting it to more stress than it is designed for. These things don't appear to be over engineered.

Hi Ian - Yes, good point about the blowoff valve letting go. I plan on regulating the inlet pressure - maybe start at 20psi then try 25psi, etc. But at some point the blowoff valve will open. I can just replace it with an M10 plug or maybe just remove the entire cyclone for the experiment ("base" model arrangement). Then it's just a steel tube from 1st to 2nd stage, and that tube has a 310 bar working pressure (fittings rated that high as well). Yes, that's probably the way to go for this 1st trial. Glad you pointed that out!

I’m not sure if y’all are exclusively speaking of stand alone compressors, but as far as boosters go, I use water filtration before and after the Altaros. 

Good topic and I was wondering the same thing. I have a desiccant chamber and a series of filters that I used on my Altaros booster but since I sold it it's not in use and I do have a AV now. I guess compressed to 145 or 150 and stripped of some moisture would be better than 14# intake and no moisture being stripped out. If beneficial, would a flexible rubber air hose plumb straight into the intake of the AV work? Fortunately here in SE New Mexico the air is pretty dry, normally in the 15-20% humidity range.
jimmy

Got around to doing the YH booster mode experiment this weekend. I filled a standard gold filter tube to 4500 psi, 1st starting from room pressure (0 psig or 15 psia), then feeding 10 psig (25 psia) to the inlet, then finally feeding 20 psig (35 psia) to the inlet. I stopped there because the 2nd stage tube reached 185C (365*F) during the 20 psi boost run. There is a 0.80 de-rating factor for ss tubes at 450 *F, so we were getting close enough to make me not go any higher. However, the experiment proved that boosting the inlet will speed up the fill time significantly. You can see the results in the graph attached. The base run took 3:30 to reach 4500 psi. The 10 psi boost run took 1:54 and the 20 psi boost run took just 1:17. The 1st stage compression ratio is 10:1, so it normally feeds 150 psi air to the 2nd stage. With a 20 psi boost, it is feeding 350 psi air to it - that stage is squeezing on alot more air and things really heat up. 

In summary, a 10 psi boost on the input decreases fill time to 4500 psi by about 45%, a 20 psi boost cuts fill time by a whopping 63%, but the 2nd stage temperatures get a bit worrisome. The water temp never got above 59C, but mine usually runs in the low 50s without boosting. I have a thermocouple attached to the 2nd stage tube, which is how I measured the significant jump in temperature of that tube. In normal (non-boost) operation, the tube will reach about 140-150C max.

Actually, the 10 psi boost works pretty nicely and almost cuts fill times in half.

Very interesting. Thanks for the information. +1 to you. 

Are the gains in fill speed times worth shortening the lifespan of the compressor? The increased pressure and temperature that the components within the compressor are being subjected to will stress the Yong Heng considerably beyond its design parameters and cause it to fail much faster than using it without a booster compressor. Is halving the fill times worth shortening the lifespan of the compressor? Just asking.

Humdinger- Sure that's the question and it's a tradeoff (probably not woth doing). I was just curious to see whether the YH would even tolerate being run as a booster pump. Turns out it can be done - but of course that doesn't mean it *should* be done.

I've been using my YH as an experimental testbed since I actually have a 6K nitrogen cylinder for refills. Once I got the nitro tank, the YH became a secondary backup for me because the local Fire Dept is also willing to fill my 6.8L tank. Figured just learn as much as possible and share the info - it might prove useful to others. So I've sized every fitting on it, measured the 1st stage compression ratio, monitored the temperatures of the steel tubes and motor housing with thermocouples during fills, installed the cyclone separator on a "base model", calibrated the gauge against a digital pressure transducer, etc. Also filled a 6.8L tank twice from empty and 4 times from 3000 to 4500, along with dozens of (50+) trial runs from empty to 4500 psi on the standard gold filter. It's been totally bomb-proof for me so far after some initial burn-in time.

I completely agree with you - it isn't marketed as a booster pump so it should not be used as one unless a person is willing to deal with whatever consequences might result from using in that manner (including safety concerns). On the other hand, if one is willing to deal with whatever happens, the parts are all available from cheap aliexpress.

Next I was thinking of using the boost to allow the pump to run slower. That is, use the boost to increase the lifespan of the compressor rather than speed up the fills. That's a bit tricky because this is a simple line-driven motor and shaft speed is fixed to line frequency. But somewhere in my lab I know I have a VFD which might do the trick. And as usual, if I get anything interesting, it'll show up in this forum.

Finally, an answer to something I was planning on doing, using my TUXING compressor as a booster pump, thanks prfssrlee.
However, the TUXING is different to the YH in that the interconnects are contained inside the coolant chamber so hopefully that will help keep the temperatures in check.

In looking at the construction of the first stage, the cylinder and piston with it's triple rings look to be fairly robust, my main concern is the crankshaft.
The piston wrist pin and crankshaft main bearing appear to have no needle bearings, which seems to be standard in these compressors.
Might be interesting to ream out the crankshaft ends to accept needle bearings, question is though, is there sufficient material to allow such a drastic mod?
Maybe a phosphor-bronze bearing at each end would work!
Greg.

Thanks again for your efforts with the Yong Hen. I have completed the project to install my home workshop 90 psi compressor as a booster pump to the first stage. I have regulated the 90 psi down to 5 psi to the YH 1st stage inlet. My goal is simply providing dryer air to the YH. This works very well if I allow time for my home compressor air tank to cool and condense the water vapor, but there is a noticeable increase in the saturization when the home compressor kicks on when the tank volume gets low.

I have ordered a refrigerated compressed air dryer and according to Uni Sim simulations I should be able to provide completely dry air to the YH after chilling the home compressor air to 39F. I expect this to greatly reduce the heat of compression in the YH as there will be little latent heat. With this setup it may be possible to increase the booster pump to 10psig.

Professor, are you able to verify? I do not know if you have a chiller but you did some previous verification of the skin temperatue of the 1st and 2nd stage outlet tubing and have ran tests at higher than 10 psig booster pump pressures with good results as far as regarding the YH robustness and the higher air volume.