What limits the speed of an air compressor?

[matthewsx]

FWIW, I'm about to hook up my little dual tank Hitachi compressor to a 30 gal tank that will live in the rafters of my little shop. Not worried about how quickly it charges or how loud it is at this point.

Why?

My dad's old craftsman 20 gal compressor still works fine and I don't really need anything more.

But I have the parts


John

 

[strantor]

Well, I think you're on the right track for a rabbithole project. It's clear that you intend to modify the shape of the tank pressure-time graph by adding power to the system using a VFD while the system is under low-pressure load, then returning to stockish power levels at the top. You are exploiting an efficiency by changing how the motor is putting out it's power that isn't done in an analog scenario. You've got a complete idea, and kudos for breaking out the parts and trying it out. I won't judge if the juice isn't worth the squeeze, as long as you learn something.

Well you have that knack for brevity that I lack. That's a beautiful summary of something that would (did) take me several pages to explain. Thanks for the encouragement.

 

[strantor]

I wasn't trying to say that it couldn't or shouldn't be done, I was thinking that there must be a down side that would make it impractical. With that said, new innovations can come from projects like this, Go for it!
Richard

I'm sure there is a down side, I will find out what it is. Maybe there's a workaround for it.

 

[strantor]

FWIW, I'm about to hook up my little dual tank Hitachi compressor to a 30 gal tank that will live in the rafters of my little shop. Not worried about how quickly it charges or how loud it is at this point.

Why?

My dad's old craftsman 20 gal compressor still works fine and I don't really need anything more.

But I have the parts


John

I'm glad you said that. It runs parallel to a question that came up last night while I dreamed sweet compressor dreams. Why is the compressor always mounted on top of the tank? This makes it top heavy. In my case, putting a 5HP head and 3HP motor, either of which easily weighing double what my existing 2hp compressor+motor weighs, is going to make my 26gal craftsman compressor very top heavy. I would rather mount the motor & compressor at ground level and place the tank on top. But nobody else does that. I've never once seen a compressor configured that way. Why?

I assume it's the condensation that would surely happen along a long vertical air line from the compressor on bottom to the air entry on top, especially when the compressor switches off. That water would trickle down and maybe into the cylinders where (maybe?) It would create a hydro-lock situation and blow head gaskets?

Would it be ok if there were a cooler and a water trap between compressor and tank? Would it be ok in your situation, considering you aren't going from a compressor head directly to an overhead tank, but rather from a tank to another overhead tank?

 

[matthewsx]

I'm not sure of the engineering but I suspect either something like you say, or it might just be easier. In my case I'll just be running a hose from the regulator into the extra storage tank I have. The small compressor will live underneath the table where my mill/drill is.

I don't have any experience with coolers or water traps but I'm sure copper tubing will provide some of what you need.

John

 

[talvare]

I'm glad you said that. It runs parallel to a question that came up last night while I dreamed sweet compressor dreams. Why is the compressor always mounted on top of the tank? This makes it top heavy. In my case, putting a 5HP head and 3HP motor, either of which easily weighing double what my existing 2hp compressor+motor weighs, is going to make my 26gal craftsman compressor very top heavy. I would rather mount the motor & compressor at ground level and place the tank on top. But nobody else does that. I've never once seen a compressor configured that way. Why?

I assume it's the condensation that would surely happen along a long vertical air line from the compressor on bottom to the air entry on top, especially when the compressor switches off. That water would trickle down and maybe into the cylinders where (maybe?) It would create a hydro-lock situation and blow head gaskets?

Would it be ok if there were a cooler and a water trap between compressor and tank? Would it be ok in your situation, considering you aren't going from a compressor head directly to an overhead tank, but rather from a tank to another overhead tank?

I have worked on compressed air systems in industrial environments where the air storage tanks were above the compressors, some times several stories above the compressors with inter-connected storage tanks. These systems work just fine but you do have to insure that the plumbing takes into account the accumulation/draining of condensate.

Ted

 

[Reddinr]

From my experience compressor speed is limited to about 60 MPH. A few years ago I was helping a friend move a large, tall compressor he bought at a yard sale. He tied it in and we took off in his pickup. About half way home there was a tire chunk in the road, then a curve. The combination broke the compressor loose and it went flying over the side, down a bank and into a tree. Must have been 60 MPH, limited by a tree. ..

 

[pontiac428]

I second @Reddinr 's assertion. Back in the '90s I moved a lot. I had my big vertical compressor strapped upright like a motorbike in the bed of my trusty ol' stepside. Similarly, I hit a bump, took a corner, and saw my compressor drop through the weakened, rotted bed planks hidden under a sheet of plywood. Definitely would have been worse had I been doing over the established compressor speed of 60 mph.

 

[tq60]

Supercharge...

An old vacuum cleaner pump can be used as a supercharger.

Air filter on suction side and pressure side to air intake.

Did that with an old gas station pump and greatly reduced fill time.

Place a meter on moter current and add cut out switch to turn off it it causes issue with higher pressure.

Was 2 stage made into 3 stage...

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[epanzella]

The problem with driving a reciprocating motor over speed is that it, uh, reciprocates. Piston speed goes up but the piston still has to reverse direction twice for every stroke. The load and impact imparted to the main and rod bearings go up exponentially as the RPM goes up. Would it throw a rod or sieze? I dunno but I would bet the farm that the life of the compressor head would be drastically reduced. It sounds like you need a bigger compressor. Failing that, increase the storage capacity of you existing machine. This will give you more intermittent output but it won't help with continuous operation.