Hot rod compressor

[Robbyrockett2]

Ok, So this is not really an airbrush compressor but, I often have to do some paint on site. Which severely limits my spray gun choices because i'm stuck with a portable compressor (two if i can reach different circuits)
I'm kind of thinking of trying to sort of hot rod a compressor. Basically take a belt drive, drop the cutoff switch to like 60psi and change the drive ratio to 1:1 or something thereabouts. My thinking is that since the compressor no longer needs to push to 150-175psi or even 90 for that matter. It doesnt need all that torque but could just push at speed.

The machine simply gets less efficient the higher the pressure it must pump to. So I think id be gaining by increasing the output volume at a lower pressure.

So in theory, If I double the rpm where I did have 6 cfm at 40psi I can now push something close to 12 ( minus a little motor strain since 40 is now like 90 to the motor.....So 10cfm (since I get 5.2 at 90)

It would make this compressor not good for a whole lot other than painting but Idk

Thoughts?

 

[Robbyrockett2]

I may just go gas powered, but this idea crossed my mind.

 

[Vladimir]

I thought about the issue for maybe in future I's need such. My thought were about kinda this

Increasing RPM more likely you'll end up with burned cylinders and very fast parts death.
As I remember from a book on compressors, for normal work max RPM are about 1400. All those coaxial compressors run at crazy speed for normal work.
Look at the speeds the belt driven compressor work at.
I work on building big compressor for the studio and going to use it at 900 RPM (or 800, don't remember for sure). It will produce the volume I'll need with HVLP gun, so I will not be raising the RPM. My compressor head is 2 stage.

 

[SiRoxx]

Way out of my wheel house, but... Would you be able to change to gear ratio to keep the RPM down? Or is that what you meant by drive ratio? Saying out loud, I think it is.

 

[Robbyrockett2]

Way out of my wheel house, but... Would you be able to change to gear ratio to keep the RPM down? Or is that what you meant by drive ratio? Saying out loud, I think it is.

Well yeah I could change the gear ratio to whatever I want but how would slowing one down help to get more volume?

I thought about the issue for maybe in future I's need such. My thought were about kinda this

Increasing RPM more likely you'll end up with burned cylinders and very fast parts death.
As I remember from a book on compressors, for normal work max RPM are about 1400. All those coaxial compressors run at crazy speed for normal work.
Look at the speeds the belt driven compressor work at.
I work on building big compressor for the studio and going to use it at 900 RPM (or 800, don't remember for sure). It will produce the volume I'll need with HVLP gun, so I will not be raising the RPM. My compressor head is 2 stage.

Thats what I meant by "gas powered", Which is most likely what I'll have to end up doing Is just buy one of them . They already run 17-18cfm ,theyd be fine
I have all the air I could ever need at the shop. It's when I have to go to a site im looking at.

Yeah most like to run 1200, But direct drives run 3400. Yeah they don't last as long.

It would be Ideal to put a pump with a larger cylinder , or simply a second pump would work fine im sure since that would raise the volume and I wouldnt need a larger motor simply because It would never have to push much over 50psi.

 

[SiRoxx]

Well yeah I could change the gear ratio to whatever I want but how would slowing one down help to get more volume?


Thats what I meant by "gas powered", Which is most likely what I'll have to end up doing Is just buy one of them . They already run 17-18cfm ,theyd be fine
I have all the air I could ever need at the shop. It's when I have to go to a site im looking at.

Yeah most like to run 1200, But direct drives run 3400. Yeah they don't last as long.

Ideally putting a pump with a larger cylinder , or simply a second pump would work fine im sure since that would raise the volume and I wouldnt need a larger motor simply because It would never have to push much over 50psi.

I was thinking of it more from the longevity of the equipment than higher volume. But it was a shot in the dark more than anything. Adding a second pump seems like a good plan.


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[Robbyrockett2]

Heat comes from a drastic and fast increase in pressure, thats how a diesel engine works.
I wonder though, If the heat would still build quickly when it's only increasing 50psi instead of 150, in a fraction of a second. you need a bit over 200 to effectively ignite diesel.
Which is why 175psi compressors use two stages. If you tried to go to 175 in a single stage ,after it warmed up, if any oil was in the cylinder it would be likely to ignite it.
Also why 3400rpm direct drives are oil-less

 

[Robbyrockett2]

I was thinking of it more from the longevity of the equipment than higher volume. But it was a shot in the dark more than anything. Adding a second pump seems like a good plan.


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I kinda figured. which would be a good plan if that were the goal.

 

[SiRoxx]

I kinda figured. which would be a good plan if that were the goal.

Sure. I think there’s something I’m not getting in how the system works. If I imagine it like bicycle gearing, I was thinking one side could be slowed while running the other at higher rpm to increase output. But as I said, it’s a bit of a way out my wheel house [emoji3].


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[Robbyrockett2]

Sure. I think there’s something I’m not getting in how the system works. If I imagine it like bicycle gearing, I was thinking one side could be slowed while running the other at higher rpm to increase output. But as I said, it’s a bit of a way out my wheel house [emoji3].


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Oh I got ya, Kind of, yeah.
In terms of bike gears, if you go to the larger front gear or drive gear you increase speed at the wheel or driven gear.
But you need more torque, its harder to pedal. Youve slowed the pedal speed required to get the faster wheel speed.
If you go to a smaller front gear and pedal at the same rate, its easier but you move the wheel much slower.

In this case the electric motor turns at the same speed no matter what. So changing the gear ratio will only change how fast the pump is driven.

 

[SiRoxx]

Oh I got ya, Kind of, yeah.
In terms of bike gears, if you go to the larger front gear or drive gear you increase speed at the wheel or driven gear.
But you need more torque, its harder to pedal. Youve slowed the pedal speed required to get the faster wheel speed.
If you go to a smaller front gear and pedal at the same rate, its easier but you move the wheel much slower.

In this case the electric motor turns at the same speed no matter what. So changing the gear ratio will only change how fast the pump is driven.

Gotcha! Ok, I can see how my thought didn’t help LOL. But on the plus side, I’ve learnt something about compressors. [emoji3]


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[Robbyrockett2]

Gotcha! Ok, I can see how my thought didn’t help LOL. But on the plus side, I’ve learnt something about compressors. [emoji3]


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It actually got me thinking, so it helped some.
I may just have to try this and see. All there is to it is a belt and pulley swap. Maybe a spring change to get the cutoff switch to actually adjust down as far as I want. I would think I was crazy, but the demand for a portable high cfm/low-ish pressure compressor isn't real high or they would already be sold this way I imagine. All it could do really is paint and blow up tires.

 

[Mr.Micron]

I just built my own like this years ago, Back then it was put on my service truck when I ran a garage,
I used something like this one to start off with https://www.lowes.com/pd/Campbell-H...Electric-Horizontal-Air-Compressor/1000128209 then added a Onan twin 20 horse engine to it in place of the electric motor. I still use it from time to time on the farm if I happen to get a flat out in the field on the tractor.
Main thing is if you build it yourself find the quietest exhaust muffler you can .

 

[Robbyrockett2]

I just built my own like this years ago, Back then it was put on my service truck when I ran a garage,
I used something like this one to start off with https://www.lowes.com/pd/Campbell-H...Electric-Horizontal-Air-Compressor/1000128209 then added a Onan twin 20 horse engine to it in place of the electric motor. I still use it from time to time on the farm if I happen to get a flat out in the field on the tractor.
Main thing is if you build it yourself find the quietest exhaust muffler you can .

20HP twin, Holy crap thats a beast! seems like overkill for a compressor that size.

 

[Robbyrockett2]

Did you set some method to disengage it ,or or just put a bleed hole in it, or just fire it up and fill the tank and shut down?
I'm just curious, probably If I go gas I'll just buy a used one.
If I rig this HVLP electric....well idk we'll see if it works like I intend it to

 

[SiRoxx]

20HP twin, Holy crap thats a beast! seems like overkill for a compressor that size.

Being made by an American, I’m surprised it wasn’t a V8 LOL.


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[Mr.Micron]

Just ran it to fill the tank , It is an 80 gallon tank and would fill 2 tractor tire without having to start it back up.

 

[Mr.Micron]

Being made by an American, I’m surprised it wasn’t a V8 LOL.


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LOL Nah back in the 70's 20 hp on a compressor was over kill I think the one built with gas motors now only have 5 hp engines on them.
Hmm 454 powered compressor with a 100 gallon tank . I happen to have a couple of old 454's in the garage now ya got me thinking good thing it is way to cold for me to go start on it LOL

 

[Robbyrockett2]

Being made by an American, I’m surprised it wasn’t a V8 LOL.


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LOL Like Christopher titus once said: something like
We're America...we build drag cars that can do 300mph quarter miles in 5 seconds....for fun. We build giant monster trucks that could run over your house because....we can........., Piss us off and see what we build.

 

[Robbyrockett2]

LOL Nah back in the 70's 20 hp on a compressor was over kill I think the one built with gas motors now only have 5 hp engines on them.
Hmm 454 powered compressor with a 100 gallon tank . I happen to have a couple of old 454's in the garage now ya got me thinking good thing it is way to cold for me to go start on it LOL

Well see, use one to power it and the other as the compressor head, just need some dome tops and maybe a little filler in the combustion chamber. Hello 600cfm! no tank ever needed