DIY Compressor

[btreize]

Hello everyone.
I just joined in here and have read everything i could during the past weeks. I am not new to airbrushing but after some years, i am getting back to this hobby.
So long that i could not find back one of my cheapo airbrush Or just an excuse to get a new one.

Ok now i ordered a Paasche Talon set and a Neo for Iwata CN to get back slowly into the addiction. They should be here by next week or so. by the time they arrive, i am trying to set up a silent compressor that i can use at night from a compressor that i removed form an old fridge. All check and rewired as the original wiring were old, but they did work well. All connectors cleaned and check. Compressor is running, very silent and oil checked too.
Now from my existing gears, i have an oiled-piston compressor with a 24lts receiver that works with no problem and just serviced it too. (trying to do a max of thing so i can start straight when the ABs comes in heyhey)
I want to hook the silent compressor on the existing setup and silver brazed new fitting on the fridge compressor. It will work and fill the tank (slowly though). Issue here is that it cannot past the 40psi in filling it.
I guess the CFM is low on it and it cannot go past this when pressure is getting that high in the receiver. So question is, even with a low CFM compressor and a working check valve (one way), will the compressor continues to fill a tank when pressure is getting higher on the other side of the valve? or it will slow the compressor due to so much high pressure?

I watched many videos and read many tutorials on doing this, and all seemed simple, i have everything on hand but it just does not work as it should. Or as i expected

I thank anyone in advance that can chime in and tried this before.

Bryan

 

[Pingi]

Do you have a check valve between compressor and tank ? Because mine DIY compressor fills tank to a 100 psi with no problem at all.

 

[btreize]

Pingi,
Yes i have a check valve on the line from the compressor to the tank. As i wrote before, in this setup i am just replacing the working piston compressor to the silent fridge one.
I think here that the fridge one is too weak to fill the tank and stand the pressure that applies on the check valve form the other side. But as i read everywhere, it might have a slow and verrryyyy low CFM but can have high pressure.

 

[Stranger375]

Not sure about all your setup and how strong your fridge compressor is, but i do have a ready bought Silent Air compressor that is using a fridge type.
It fills up the tank up to 6 bar and then shuts off and will kick on when it drops to 4 bars again. The fridge compressors can get a pretty high pressure,
but they do not like to start against a pressure again. That´s why you need to have a valve that will let the pressure out of the line to the tank.
Means you have a valve that will only let the air flow in one direction into the tank and not back anymore. And then also a valve that is in the line after
the compressor and in front of the other valve. So the idea is that everytime the compressor shuts off, the valve pops open and you hear the air coming
out of the short line between compressor and the tank. Now when the compressor needs to come on again, there is no pressure that he has to work against
before running up. If you dont have that valve and it has to run up against 4 bar or so, it can happen that it just wont start up correctly. There are alot of
plans in the internet how to connect all the valves and the electrics for that.
Good luck with your project.

 

[btreize]

Stranger,

I see your point here and i do have a non-returning valve on the line already. But the piston compressor will have a unloader valve that will evacuate the pressure on the line coming from it when the compressor stops at desired pressure (set by the pressure switch). Yes you are right and you hear a pssst coming from it when the compressor stops. This means the line is clear for when it starts again it will not have any pressure to fight against to fill the tank.
Now in my case the fridge compressor does not have enough CFM for the unloader valve to work and it will escape air from it. So i bypassed it and it does fill the tank and the one-way (non-returning) valve does work OK. But it will not fill it pass the 40psi or so. Do you have any picture of the valve you are talking of so i can see if there's any difference with mine?
Thanks
B

 

[Stranger375]

Hi again im sorry i dont have a picture of the valves that i seen in a plan sometime ago when i also wanted to build my own silent compressor. You just made me to have a closer look at my bought one
and indeed there is just a simple unloader valve integrated in the pressure switch that kicks in when the pressure switch turns off the compressor. In my case the compressor fillls up to almost 90 psi when the switch shuts off.
My compressor has a CFM of 0.7 ( 17 Litres) , so that is also not that much though.
I also just had a look again at the plans of a self made compressor that i found in a german forum, and they used a pressure switch that has the evacuation valve built in already, i guess i mistaken that as a seperated electrical
valve when i was reading it back then.
To be honest i would even suggest to build a compltete own silent compressor with your fridge compressor. You could get a smaller pressure switch and a little tank and then build it up completly new
without connecting it to the big one. I had a small oil less airbrush compressor that has a pressure switch that will shut off at around 60 psi and coming on at 30 psi again. Alot of people are using those
for their home made silent compressors. A small tank can also be made out of old fire extinguishers or you get a one that was ment for airbrushing, they are usualy not that expensive.
But not sure if the compressor will get past the 40 psi with a smaller tank though :S , there would be a option to use 2 fridge compressors parallel for that case and then you have plenty power.
What also is a good option if you can get your hands on a working compressor from a old freezer, since they also have more power.

 

[RebelAir]

Sounds like ya's all know what ya talking about but must admit I hate it when peeps play around with building bombs..Opps I mean home made compressors LOL..I'm a fitter by trade and seen and heard many horror storys in my trade of compressors blowing after adjustments, repairs and tinkering..Saying that though I know many peeps build these themselves and have no issues when done correctly, but it worrys me when peeps build a lot of this stuff out of salvage as realistically silent compressors ain't that expensive to buy, mine cost $120 of ebay...More saying this to those that may be reading this thread and who may not have such experiance or knowledge considering trying this themselves...But good luck on ya build and hope ya get it sorted.

So question is, even with a low CFM compressor and a working check valve (one way), will the compressor continues to fill a tank when pressure is getting higher on the other side of the valve? or it will slow the compressor due to so much high pressure?

No doubt the worst it will do is work its guts out and die, if the pressure build up is maxing the small fridge compressors capability's to push more in it will likely just overheat the unit, if it has overheat protection (Dunno much about fridge compressors) on it it will just stop until it cools, maybe a biggerfreezer compressor as suggested may indeed help push past that point..40 psi though is good enough for most needs, as long as the compressor can maintain that constant in the tank it should be enough to get ya going....

An alternative here is to consider a larger holding tank like a big gas bottle, fill this up with your large noisy compressor before everyone goes to bed and it will be enough air too keep you spraying for an hour or two without needing to re-pressurize and its not hard to set up the valves required for air in and out by using 2 hoses with individual ball valves going into a single line and of course a release valve just in case.Or even build a sound proof box for a normal compressor, store it out in the shed and run some hose to your paint area if it aint too far away.GL

 

[Jedi Weasel]

There is any problem applying fridge compressors, but you have to take safety measures to avoid explosion of the tank, because the fridge compressor don't stop until it gets it job done! Compressor brands like Bambi, Silentair, Werther, etc, do it without any problem. The important thing to do is applying a check valve between the line and the tank and the even more important is applying a pressure release valve to control the tank. For example, if you set the pressure switch for a maximum of 7 bar, and you have a pressure release valve regulated to 8 bar, if the pressure switch for some reason doesn't work, when the tank reaches the 8 bar, the pressure release valve will continually expel the air from the tank until it reaches a safety level. Another thing that is very important for homemade compressors is never do yourself the tank or the connections because you never have the optimum conditions to test it. Buy always tanks approved from factories and all the connections on a store. Be aware if you need to weld anything, a bad welding can origin a fracture spot, and with high pressures can be a begin of a serious accident. If you use two fridge compressors, always use equal compressors ( same brand and power, and with intern non return valves ). I did my compressor at home and it is running great.. I already shown a photo of it but I will put it again if you want to see anything in peculiar:
View attachment 5741

 

[Jedi Weasel]

Issue here is that it cannot past the 40psi in filling it.
I guess the CFM is low on it and it cannot go past this when pressure is getting that high in the receiver. So question is, even with a low CFM compressor and a working check valve (one way), will the compressor continues to fill a tank when pressure is getting higher on the other side of the valve? or it will slow the compressor due to so much high pressure?



Bryan

Do you know the compressor Power? 1/6hp..1/4hp.. 1/3hp ?? When you say.. " it cannot pass the 40psi" is due to Pressure switch engage or to low power on the compressor? Is the fridge compressor used? When the compressor hits the 40psi does it shut off.. or if it is not the case, it gets extremely hot?

 

[btreize]

Hello everyone. Even with no response, i have been reading the posts and they help me a lot.
Finally, i managed to get my DIY working. I got myself an empty fire extinguisher cylinder of 9lts in perfect shape and maximum it can hold is 160bar. It is waaaayy more than needed and it already have two in/out on it. One is a large 1" female and the other is 3/4" male. I got a 1/4" male fitting brazed on the large one and pressure tested it in the workshop where they fixed it. It will be used for the input. The 3/4" was easier to reduce for a 1/4" which will hold the other things.
I bought new accessories like the pressure switch (adjustable), check valve, safety valves and misc fittings.
Mounted everything and tested. It's alive Aaalive
Now i need to modify the unloader valve as the compressor's cfm is too low to hold it in close position and i risk heating up the compressor on cut it operation and it will have to run against the pressure in the hose when starting back. Do you use the unloader valve on these small units or just bypass it?
The receiver will fill to 8bar in 4-5 mins and kicks on again on 3bar. I am still trying to figure out a good balance for the pressure switch. (some help will be welcome on this)
The whole system is very very silent and with 15-30 mins of air at 30psi for working. I am quite happy with it. Will post a picture of it when all is finished and would like to thank everyone here for the help and support.
Any comment and ideas on setting up the pressure switch will be welcomed.
B

 

[ad fez]

this sounds awesome buddy, I have the same intention myself and also have an old fire extinguisher to use....I would be grateful of any plans/shopping lists, photos you could supply to enable me to make the same, as I am not very mechanically minded! ask the best and am glad you got this beauty working!

 

[Stranger375]

The pressure switch of my bought Silent Air compressor is set to shut off at 6 bar and come on at 4 bar again. You should let it come on at 4 bar already since you then
always have enough pressure in your tank again for the airbrushing. If you also make it shut off at 6 bar instead of the 8 bar you might shorten the time alot that the
compressor is running to fill up the tank and it wont get that hot so fast.

 

[btreize]

Stranger, yes this is what was on the factory default setting but i found that 4 bars for airbrushing is OK and the compressor does have time to cool down completely before restarting. I read somewhere that those compressor are a 50/50 cycles, that is they run for 5 mins and must have 5 mins pause before restarting.
I am perhaps wrong here but when i will start working with it i will see if i can tweak it a bit more. Thank you for clarifying those points everyone.

Ad Fez, i don't have any pictures of it right now but i just finished the boxing for it today. Will assemble everything and take some shots after i painted it etc.
What do you have in hand right now?

 

[ad fez]

an empty fire extinguisher, and a direct jet compressor but want to get one from a fridge really for silenced air!.....unless you mean literally on which case I have my phone in hand! hehe

 

[Stranger375]

I dont know about the 50/50 though, but could be yes. Mine has just a 1.5L tank and it shuts off and starts up pretty often in a short ammount of time. Untill now it didnt have any problems.
And i know people in forums that are using such compressors already since 20 years and more. I guess unless you run them without oil they are hard to wreck . Oh almost forgot, mine has a
filter on the pipe where it sucks in the air, not sure if you also attached one but it is a good idea to do that so no dirt will come in the compressor.

 

[btreize]

Stranger, the filter is necessary i think as it avoid nasty things get sucked by the compressor.
I tweaked the unloader valve for it to work with the low cfm of the compressor. Installed another spring in it that aids it close the valve when the compressor start.The pressure switch lever will engage the pin and "pcchsssstttt" line and compressor pressure unloaded. I tried it several times and noticed that the compressor get less hot than before. It could be the high pressure working against it but now i can feel it starts smoothly and runs better. This will perhaps lengthen his life time.
Next step is to change the oil in the compressor. From all the test and sometimes running it without the filter, i think the oil need a change. Do you know guys what oil to you?
Can motor oil 10w30 be used here?

 

[Stranger375]

My Compressor came with a special compressor oil from a italian company, it is called Sincom/32E
Im not sure if a 10w30 mororoil works, but probably it does. You should do abit of a research in the
internet about that.

 

[AndreZA]

Okay I don't know how far you got with solving the problem but my compressor, same motor as you get on the GMC/Californai air compressors, has a solenoid valve instead of just a plain one one way valve. When the required pressure is reached, the motor cuts out and the valve shuts and releases the air build up in the tube. This is what it looks like.

 

[btreize]

AndreZA, this is a great gadget to have. Can it be purchased as a part?
Mine is working fine since i tweaked the unloader valve. I fill up the receiver to 100psi now withing 4 mins and it kicks in again when it drops to 35psi. This gibe me some good 30 mins of continuous painting..and silently

 

[mad scientist]

Stranger, the filter is necessary i think as it avoid nasty things get sucked by the compressor.
I tweaked the unloader valve for it to work with the low cfm of the compressor. Installed another spring in it that aids it close the valve when the compressor start.The pressure switch lever will engage the pin and "pcchsssstttt" line and compressor pressure unloaded. I tried it several times and noticed that the compressor get less hot than before. It could be the high pressure working against it but now i can feel it starts smoothly and runs better. This will perhaps lengthen his life time.
Next step is to change the oil in the compressor. From all the test and sometimes running it without the filter, i think the oil need a change. Do you know guys what oil to you?
Can motor oil 10w30 be used here?

Most fridge/freezer aircon compressors do ok with mineral oil, Shell Tellus 68AW works very well. Using the wrong kind of oil will lead to a rapid demise
If you know the name and model of the compressor, the manufacturers spec sheet will tell you how much oil it needs.

I figured i should post mine with the specs. I`ll be upgrading it to a twin unit later in the year.
Receiver: 24L, compressor: 3/4hp commercial (chiller), Output: 1.65cfm (46.7 lpm)
I have it set for 45-120psi, the tank takes exactly 2mins 37 secs to fill.