Homemade silent air compressor

[justinsane]

I don't understand the "heat exchanger on the input line to cool the input air" what are you cooling it with?
Inlet is ambient air so you can't cool it with an air cooler as it is already that temp.
It might be 3 phase.
Larger receiver tank would be good as long as it could be filled with in the current run time limit. And of course the tank(good if it's propane) the PRV and the components would all have to be rated for 200 psi or greater.

[hemmjo]

.... Would there be an advantage to putting the heat exchanger on the input line to cool the input air?....

Would be better to put it on the output, between the compressor and the storage tank, with a water separator between the heat exchanger and the tank.

.... A big propane tank at 200PSI would run stuff for a long time before it needed to be filled again.

How big a tank are you taking about? 20#, 50# 100#? I find 20# tanks all the time on trash day. Depending on where you live, people put the old style tanks out for the trash, but the trash companies will not take them. I always stop and get them, use whatever propane is left, then take them to exchange for a new style tank. Just saying that it a good source for tanks. (It makes my wife furious, but, I would stop to pick up $50, why not a $50 tank)

Just BE SURE you follow proper procedures for removing ALL of the propane!!!!!

Be safe out there

[Sleykin]

Brain fart I guess. I know that the Jun-air compressors are cooled by the oil in the system. The motors run in a dielectric oil for cooling. They make about as much noise as a refrigerator and they gang compressors together to get more airflow. The insides look very much like the old York A/C compressors, only much smaller.
Products - JUN-AIR
I had one for awhile and it was a nice portable for working inside, but the tank rotted out and the compressor cap and starter was blown. Parts are not easy to find at reasonable prices.

[Sleykin]

I was mostly just thinking about up-sizing the idea. I have a large 60 gallon compressor that runs everything I need and a pancake compressor for odd jobs I don't want to drag the hose to. Shop is plumbed for air with the big guy outside in it's own little outhouse.

[Dimitris Polychronis]

This concept is pretty good in that the compressor is really quiet.

However, I watched this entire video to see what all was included.

I am by trade an air compressor service technician (12 years) and DOE Qualified Air Master (10 years) as well as being universal certified refrigeration tech (20 years).

Of the maintenance operations you performed in this video, the only ones I would recommend are the oil check/top off and the filter element change(however certainly not after only 10 hours of operation unless it was contaminated, in which case you've got bigger problems).

The tank should be mounted vertically and a drain of some type placed at the bottom, be it a float drain, an auto drain or just a ball valve that you use to drain the tank after each use.

Also I would increase the size of the tank to store more air and consider using a compressor that is designed for a refrigerant other than 134a so you can increase the tank pressure without over amping. 407c or 404a could give you significant pressure increase if you use a tank, and all the other components(PRV regulator tubing etc) rated for 250 psi you can store more usable compressed air.

Also if you need more than one (substantially different) pressure output I would recommend multiple regulators rather than repeatedly adjusting the single unit.

I would never recommend disassembling a regulator unless it is not working properly(on that note I wouldn't disassemble any of the unit unless it isn't working properly.

Based on the life expectancy of the compressor the other components will likely out live it with no maintenance at all.


All of that said, to which I hope you don't take offence, I like the idea and may some day build one.
If I do I'll most certainly attempt to add oil separation, to both retain the oil in the unit reducing maintenance as well as prevent the oil from contaminating the air system. I would also at least broach the topic of cooling so as to extend the duty cycle and the life expectancy. Though not sure how at this time.

Thanks for the comment justinsane, please accept my apologies for the delayed reply. I don't feel offended at all; contrary your expert knowledge is welcomed, after all that’s the meaning of the forum.

It is important to say that what you saw in the maintenance video it hasn’t the meaning of showing some kind of expert knowledge; I made it mainly as a simple guide for all of us that we are amateurs and DIYers. Speaking for myself, the lack of expert knowledge as well as the limited budget makes me extra careful in everything I make so to use it for as much time as possible without problems.

I agree with you about the maintenance operations, the oil check and the filter is the most important, however as I said above all the other operations need to be taken as a simple guide, unfortunately I didn’t explained it on the video and that’s was a mistake!
Now, as for the 10 hours of checking the oil it is because I have seen from my other projects that the compressors losing a small amount of oil (the compressed air moves oil to the tank) and since the compressor at the time of making the had only 10 hours of work I wanted to see how much oil needed to add, since fridge compressors haven’t an oil checking window as well to have it as reference point for later maintenance-oil refill.

It will be very helpful for me if you can tell an estimate time for checking the oil?

As for the construction of this compressor, I proceeded by copying similar units that are commercially available; for the compressor unit I hadn’t the slightest idea about the differences between the types that uses 134a, 407c or 404a refrigerant, I just asked the supplier an affordable unit close to 300Watts (the lack of knowledge I said before).

I really appreciate your expert opinion-suggestions, are very helpful for me! I'm sure your expert knowledge will also appreciated from many others here that like to make their own silent compressor!

Best wishes
Dimitris

[justinsane]

Just to elaborate r134a (like its predecessor r12) is a lower pressure refrigerant, meaning that both the high side and low side operate at lower pressures than say r22 for the older school or modern r407c or 404a.


134a compressor will see 68 psi at 20°C or 68°F whereas 407c is 113 psi and 404a is 143 psi so if we were to assume that they are all expected to runt he same high side temperature that would mean the 407c and 404a units would expect a substantially higher pressure. When I work on 134a refrigerated dryers the high pressure shutdown is typically lower than the fan cycling switch for the 407c/404a units. In other words the 134a unit is shutting down on high pressure at a lower pressure than the 407c/404a unit is even turning on the condenser fan.
Again what you gain in pressure you will loose in CFM but in an intermittent use scenario storing the air might be a better solution than making it as needed "realtime".
By that I mean that the compressor can run, make/store the air and shut down while you don't need it and when you do need it, it is there.
If you use the lower pressure unit you will be quickly limited to the amount of air that the compressor can make which in all of these cases is not very much.

[NeiljohnUK]

Brain fart I guess. I know that the Jun-air compressors are cooled by the oil in the system. The motors run in a dielectric oil for cooling. They make about as much noise as a refrigerator and they gang compressors together to get more airflow. The insides look very much like the old York A/C compressors, only much smaller.
Products - JUN-AIR
I had one for awhile and it was a nice portable for working inside, but the tank rotted out and the compressor cap and starter was blown. Parts are not easy to find at reasonable prices.

I refurb our jun-air units at work, and part of the process is tumbling with stainless steel bolts to remove internal tank corrosion, as moist air soon becomes condensation in the tank, once done the tank gets rinsed and dried, then coated with high zinc primer, then over that goes chlorinated rubber paint which resists the carry-over oil that solvents the original internal paint. Once thats dried I perform a HYDRAULIC pressure test, never test with air/gas as a failure wouldn't do anything or anyone close by much good, before reassembly. The main compressor problem is the reed valve block suffers with corrosion from moist air, and usually needs careful cleaning and a new gasket made. The last one I serviced was being thrown away by an academic as it "wasn't working", the tank was FULL of condensate and the filter too having never been drained in 10 YEARS, after a prolonged tumble and all the rest it's back on the spares shelf ready to go when needed (we have quite a few around the labs), cost of repair, my time say £400 and some paint, the replacement cost the academic £1,500 (with discounts) so it was worth the effort to achieve a spare unit.