Homemade silent air compressor

Hello to all,

I must admit that I have a passion for silent air compressors, simply because you can use them anytime you want without disturbing your neighbors! I built my first compressor 11 years ago using a truck’s brake air tank. Until today I've made 5 silent compressors and I have a 6th one under construction (unknown when it will be finished).

The following video shows the construction of the 5th compressor I’ve made that is actually my first serious built when I started my YouTube channel 6 years ago.

I don’t want to tire you with pictures here (except the necessary ones) because the whole video is actually a slide show with all the info about the built; at the end of the video you will see some photos from the other 4 compressors, but since the time of the video is short I will put these pictures below so you take closer look. I would like to show you more from my previous builds but unfortunately I have only these pictures.

Attachment 27713 Attachment 27714 Attachment 27715 Attachment 27716 Attachment 27717

https://www.youtube.com/watch?v=fCW9d5Lx_Qk&t=6s


These are the previous 4 compressors I've made.
Attachment 27719 Attachment 27721 Attachment 27721 Attachment 27723 Attachment 27724 Attachment 27725 Attachment 27726 Attachment 27727 Attachment 27728 Attachment 27729

I have also put one more video showing the basic maintenance of the compressor as well as the replacement of a defective part (non-return valve). I hope that this video will show you a better view of the compressor.

https://www.youtube.com/watch?v=BsJMUXdGS9o

All the best
Dimitris

Would it be possible to buy one of your silent compressors?

How long do the refrigeration compressors last pumping air? What kind of lube do you use in the compressor, and how do you check levels etc.?
They would be perfect for airbrushing or using a pencil die grinder. My shop is plumed for air with the tank and compressor outside in it's own little outhouse. I also have a little pancake compressor for jobs away from the shop. Trouble is, when those guys run everybody hears it...this would be a great addition :)

I am trying to put the pressure and volume in perspective for me. Is .33 cfm at 80 psi about right?

I am retired teacher, we used to explore with pneumatics and building automation type devices in class. I built a compressor in the late 80's to run those pneumatic devices and air brushes etc. in my classroom. That compressor is still working. These days it will run my finish nailer as fast as I can cut and fit trim pieces.

I got my compressor from a dehumidifer I picked up along the road on trash day. I get them all the time. I have NEVER found one with a bad compressor. They stop working because the evaporator coils get FILLED with dust from the houses, and they no longer function so people throw them away.

A couple of things I did to ensure longevity is to draw the incoming air through an oil bath air filter. Just a peanut butter jar with oil and a piece of foam filter from a lawn mower type engine. I put an oil separator on the outlet side, between the compressor and the tank. If no oil comes out when you first start the compressor, add little oil until it spits some out. After that keep the separator drained. Read on the appliance where you get your compressor what kind of refrigerant is uses. Then get oil compatible with that.

I used empty "fat boy" propane bottles for the air tank. You can safely remove the center valve core with a home made tool, like you would use for regular valve stem on a tire. It just needs to be longer to reach down into the hole. You have to use a small pick tool to remove the o'ring and small metal collar to access the core. Then fill the bottle with oil to be be sure all of the propane is out. Then drill and tap the hole for 1/8" NPT. Then you can plumb the bottles together with common pipe fittings. My system has 3, just because that is what had around at the time. Each bottle also has its own little pressure relief valve.

The inlet and outlet tubes on most compressors are 1/4" copper tubing, some are steel. I connected to them using a flaring tool. But could just as easily use compression fittings.

Keep in mind that these little compressors are capable of pumping in excess of 500 PSI, be sure you put a safety pressure release valve in your system.

Thank you very much for your kind offer Flintlock, unfortunately I can't help you for two reasons; first I don't have any of these compressors (they have been sold), except the one you saw on the video that is in used in my shop and second even if I had one available the shipping cost would be extremely high because I live in Greece!

Cheers
Dimitris

Excellent maintenance video, Dimitris and perfect timing for you to display your precision handy work and meticulous attention to detail! Hopefully you can finish your dual compressor one day soon as that would be of interest here also.

Thanks for sharing this timely build with us.

PJ

Hi Sleykin
As you well said it this type of air compressor is perfect for using an airbrush, a pencil grinder or for a small pneumatic engraver for stone setting or any other art work, this will answers your first question; with proper maintenance they can last for many years because they are made to support tools with low air consumption. Now, the main disadvantage of a fridge compressor is that its motor runs at high rpm transferring motion to a small cylinder inside the housing that increases temperature, meaning that the motor must not work continuously; thankfully all fridge compressors have a thermal switch for protection but it is wise not to reach this limit. The working time of compressor like this is depending on the power of its motor; the motor must stop down equal time with the time of its continuous run.

The rule of thumb is:
A 135 Watt motor must not exceed 15 min. continuous run, after this time must cool down for 15 min. A 280-340W 20 min run - 20 min stop, a 735W 30 min run - 30 min stop

As for lubrication, I use the recommended coolant oil from the manufacturer.
Attachment 27756 Attachment 27757

Now checking the oil level is a bit problematic, because fridge compressors haven’t the glass checking window; so the only option is to use a syringe with a hose for sucking the oil from inside the housing and check the quantity and the color of the oil in a measure pot; luckily all reputable manufacturers state the proper oil quantity on the motor’s label.
Fresh oil has transparent pale yellow color, when the color become dark yellow (but still transparent) it's recommended to changed it.
Attachment 27758
Remember that always small quantities of oil will transferred to the air tank through the cylinder, so it wise to check it every 15-20 hours of total work.

All the best
Dimitris

Hi cmarlow,
Forgive me, but my knowledge doesn't reach so far. The only that I know is that cfm describes the flow and psi describes pressure and I haven't seen any calculation chart for these two. I'm sorry but I can't help you.

Cheers
Dimitris

Understand!! Thanks..

It is OK. Reading the comments from you and Hemmjo about these fridge compressors is giving me a fairly good idea of what they can do. I have a couple of small compressors that are good enough for spraying paint or running small tools, nothing big enough for heavier tools or jack hammers. I also have a couple of the small diaphragm type compressors for running airbrushes. Your posts make me think I should assemble a compressor like yours because I have all the pieces in a scrap pile so it would basically be zero cost.
Thank you again for this interesting post.

Hey hemmjo,

Thank you for the info, they are very helpful! As I wrote above, I have a 6th compressor under construction for-quite some time now; I was worried about longevity too, so I decided to use oil filters for the incoming air since the compressor will be inside my shop (the level of moistrure and dust in the shop is low)

Here is the oil filter
Attachment 27759

and these are the motors
Attachment 27760
Embraco aspera NJ6226Z 220V 1Hp

Attachment 27761
L’UNITE CAJ4517Z 220V 1.5Hp

Now as for protecting the tank from moisture carried from the pressurized air, I have thought to put a carbon filter between the motors outlet and the tank. Anyway these are some thoughts for now, will see how will goes when I'll start working the project again. Thanks again for the ideas!

All the best
Dimitris

Quote:

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Originally Posted by cmarlow

It is OK. Reading the comments from you and Hemmjo about these fridge compressors is giving me a fairly good idea of what they can do. I have a couple of small compressors that are good enough for spraying paint or running small tools, nothing big enough for heavier tools or jack hammers. I also have a couple of the small diaphragm type compressors for running airbrushes. Your posts make me think I should assemble a compressor like yours because I have all the pieces in a scrap pile so it would basically be zero cost.
Thank you again for this interesting post.

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I would like to see it when you finish it! It was my pleasure sharing it with all of you!

Best wishes
Dimitris

Quote:

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Originally Posted by PJs

Excellent maintenance video, Dimitris and perfect timing for you to display your precision handy work and meticulous attention to detail! Hopefully you can finish your dual compressor one day soon as that would be of interest here also.

Thanks for sharing this timely build with us.

PJ

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Thanks for your kind words PJ, I hope the same too! It's my pleasure sharing it with all of you!

Best wishes
Dimitris

Dimitris Polychronis,

I like your air compressor and would love to make one for my own small shop. My shop is in the basement and I have a small noisy oil-less compressor. Loud annoying sound is not welcome in the house so this would be a nice tool to have.

Quote:

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Originally Posted by old_toolmaker

Dimitris Polychronis,

I like your air compressor and would love to make one for my own small shop. My shop is in the basement and I have a small noisy oil-less compressor. Loud annoying sound is not welcome in the house so this would be a nice tool to have.

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Hey Dick,

Thank you very much, glad to hear that you like my compressor! I think that every shop needs to have a silent compressor; first the low noise is the big advantage especially if you have your shop in home and second for all the jobs that not need high volume of air. I would like to see your silent compressor when you finish it!

Cheers
Dimitris

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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.

While it is not gospel consider that a consumer grade single stage lubricated reciprocating compressor will make around 2-2.5 cfm per HP at 100 psi(let's use 2cfm/hp though this type of compressor may do better).

Since this is a positive displacement compressor there will be no gain in CFM by lowering the pressure. Power/Pressure/Flow form a triangle if you lower/raise the pressure but do not change the flow the power will be reduced/increased equal to the amount you changed the pressure, you can save energy by lowering the pressure but you can't get more air. You can however STORE more air in the tank if you raise the pressure, which will use some more energy(honestly energy savings are nearly irrelevant on this because of its size and expected time of use).

If the unit is 1/3 hp you can expect CFM=~(2*.33) or about .66 CFM at +/- 100psi which is not far from where the 134a compressor wants to be on the high side. You can check for a factual number when running the unit but it will likely be over amping not much past 150 psi(remember you're not cooling it like the refrigerant normally would on the suction line coming back at 35deg F).
This is why I would recommend going to a compressor designed for a different refrigerant which is intended to run higher head pressure. That way you can achieve higher tank pressure while not reaching max amps.

In any regard what air compressors make is heat, usable compressed air is a byproduct, about 85% of the energy you put in will become heat, only 15% will become usable compressed air.

What could I expect to get with a big outdoor unit that runs 404A? Like a 3 ton A/C . Would there be an advantage to putting the heat exchanger on the input line to cool the input air? I know it would have to run on 220 VAC, A big propane tank at 200PSI would run stuff for a long time before it needed to be filled again.

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.

Quote:

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Originally Posted by Sleykin

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

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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.

Quote:

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Originally Posted by Sleykin

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

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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

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 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.

Quote:

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Originally Posted by justinsane

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.

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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

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.

Quote:

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Originally Posted by 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.

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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.