making a gas-powered quincy 5120 compressor

[396foxRN]

Hey guys, I am looking to start a discussion on methods to power a 5120 V4 Quincy air compressor. I bought two of them at an auction last week for next to nothing. I am trying to figure a way to make one of them run off of a gas engine, possibly on a trailer or dolly to permit it to be portable.

As I make custom EFI harnesses for Ford/Dodge engines, I plan to use one of those makes as the power source, as they are cheap, more than stout enough, and I can easily wire it up myself.

Short of running the compressor loaded/unloaded and always rotating with the gas engine, I am looking at ideas that would allow the engine to run continuously, but only run/rotate the compressor when pressure is needed, but be fully automatic. I have thought of a few ways to do this, including centrifugal clutches, or using the manual or automatic transmission from the gas motor.

The centrifugal clutch sounds, in theory, to be the simplest idea. Once pressure is reached in the tank, I could use the pressure switch to signal the engine computer to reduce the engine rpm to idle, effectively idling the gas engine, and stopping all power to the compressor, allowing it to fully stop rotation. When pressure drops, the pressure switch could tell the computer to raise engine rpm, and start turning the compressor again. My question is where my centrifugal clutch ignorance comes into play.....Do I size the centrifugal clutch to the approximately 25hp need of the compressor, or do I size it to the approximately 100ish hp of the gas engine? Obviously, I would want the gas engine to run wherever that engines peak torque is. I see a number of old ONAN 4.9L Ford generators, and have a 4.9L Ford 4x4, and these are torquey motors that peak at 2000rpm, so lets use that as a basis for discussion. Pulley ratios would also have to be sorted out secondarily.

Other backyard-mechanic methods could include the truck transmission as well. It seems it would be easy to use the pressure switch of the tank to operate a cylinder valve that would engage-disengage a hydraulic vehicle's manual transmission clutch assembly......or to use the cylinder valve or maybe even an electronic transfer case switch/motor to switch an automatic transmission back and forth between first gear and neutral as needed. Either of these methods would also require wiring the gas motor to increase rpm as the compressor is activated.

Another idea is an electronic clutch, similar to the type used on automotive air conditioner compressors. This seems about as simple a concept as the centrifugal clutch to make work, the problem is that I dont see many options for electro-magnetic clutches that would handle the power needed here. Clearly, it would have to be able to handle at least 25hp.


I am leaning toward the centrifugal clutch as it seems the easiest concept, as the pressure switch of the compressor would only have to activate a means to increase engine rpm, and the increased engine rpm would automatically, and relatively gently, engage the compressor crankshaft. Once pressure is reached in the tank, the pressure switch shuts off the signal to the computer, and the gas engine returns to idle.


I know pages could be written on these topics. What do you guys think of these different methods, or any additional ones you may come up with?


Thanks!

 

[cvairwerks]

Whole lots less monkety-motion to just run it in unloader mode and run the motor steady-state. Good coverage guards for the drive system and it should be pretty bulletproof.

 

[WhoWhatNow]

^ ^ What he said. No need to reinvent the wheel.

https://www.rolair.com/blog/piloted-unloader-valve/

 

[theoldwizard1]

Fancier gas powered units go to idle when the head is unloaded.

 

[396foxRN]

I know that the easy way out is to run both the gas engine and the compressor continuously, and just let the valve unloaders take care of cutting the valves in and out.........but, that's not what I was asking. I see no point in running the compressor crank/pistons continuously and bleeding off the compression, when I could come up with another means that would simply shut off the compressor completely instead. Running the compressor in bleed-off mode is wasteful and unnecessarily adding wear to the cylinders/rings while also increasing fuel demand.

I love the challenge of making something work; I am just asking for help on ideas where you guys may have more knowledge than I. So, assuming I want to go with the pressure met/compressor shuts off completely idea......what inputs do you guys have? I see several online listings for centrifugal clutches that kick in at 1800-ish rpm, with hp ratings from 24-140ish. My brain, limited as it is, tells me that a 25hp compressor and a 100hp gas engine would need a 25hp rated centrifugal clutch, as that is all the demand that will be placed upon it. Maybe I am wrong, but I am sure one of you out there knows those things inside and out. I am just an ex-history teacher/ex-semi driver/ ex-warehouseman/current nurse who loves to tinker with things.

 

[cvairwerks]

A compressor running in unloader mode takes very little hp to run, as you are not making any air pressure, only oil pressure. As to the additional wear, I wouldn't worry about it. That unit is probably rated at 20,000 hours, at full load, between overhauls. Unless you are going to run it in a production shop two shifts a day, you will probably never put enough wear on it to require an overhaul.

 

[396foxRN]

regardless, I only want to consider ideas that shut the compressor off when pressure is met. thanks

 

[A_Pmech]

Start the engine only when there is a demand for air.

 

[American Locomotive]

As mentioned, there's a reason why every single commercial engine driven compressor just unloads the compressor and idles down the engine when pressure demands are met. Cylinder/ring wear is minimal while unloaded. The compressor will see far more bearing wear from constantly starting/stopping (no oil pressure on startup), then it would from idling. It'd take maybe 1/2HP at most to spin the compressor over unloaded - negligible compared to the amount of power required to keep the engine itself idling. Remember unloaded is not the same as "bleeding off". In the unloaded state, the valves are held open so the piston is just pumping the same air in/out without any actual flow happening.

You would size your clutch for the load, and varying engine speed could engage/disengage it. That's still far more complicated and probably more wasteful (cost wise, and slipping wise) than just unloading the compressor. A simpler solution would be to just shut the whole thing down when you hit target air pressure, but you'll be subjecting the whole thing to a lot of bearing and starter wear doing that.

The bigger problem is going to be regulating engine speed. The factory electronics are not going to do it - especially if they're cable throttle engines. You need a constant-speed governor control that adds throttle as engine load increases. The idle air valve cable-throttle EFI engines will not flow enough air to do such a thing, and later engines with electronic throttle bodies don't have any software provisions for that type of governor control.

You'd have to roll your own electronic governor control system.

 

[larry_g]

Start the engine only when there is a demand for air.

Absolutely this if you want min wear and max economy. Think golf cart. Run to pressure, open the unloader, after a given time shut down the engine. When there is a call for air, start the engine with unloader open and close the unloader either with oil pressure or a minimum rpm on the pump. No mechanical clutches to wear out or excess mechanical monkey motion. Get fancy and control the motor RPM with a differential pressure sensor, the further off set pressure the tank is the higher you rev the engine.

That said, size your unit for the job you need to do. If the load doesn't require near 25 hp worth of air then use an appropriate sized compressor.

lg
no neat sig line

 

[396foxRN]

OK.....lets just assume that henceforth, I want to go with the continually running engine and on-off compressor. I am thinking centrifugal clutch. lets debate the pros and cons.

Also up for debate, are the truck manual/automatic transmissions being shifted back and forth between gears and neutral as needed to drive the compressor. And, an electromagnetic clutch to connect the gas engine and compressor as needed.

I appreciate any inputs to help achieve this. Thanks!


Doug

 

[American Locomotive]

Using a transmission is just going to add considerable size and weight while reducing efficiency considerably.

Look into riding and commercial lawn mowers. They typically have magnetic clutches and 20-30hp engines.

 

[matt_i]

I'd look into a forklift transmission, used of course. They are torque converter but very simple, just a clutch or band apply & release. Should be easy to do with basic electric/hydraulic controls as that machine is also a 12v machine. There are probably some existing electrical interlocks such as parking brake (etc) that you can repurpose to be run by the pressure switch inhibit. Would be good to have a "digital throttle" meaning full-closed and also a governor-working position for load compensation. Imo not good to raise up the ERPM (or leave it at a high level) and then try to snap a band closed.

I'm familiar with Hyster, there are old 250-L6 GM packages and more modern 4.3L V6 GM packages as well that are fully integrated. The propane fuel system is nice in that it doesn't have issues with fuel gum, but a TBI or an SFI fuel injection engine app would be able to get around that pretty well too.

I would think the 3: or 4:1 pinion ratio in the differential would be exorcised. That's a reduction you don't need imo. Replacing either a 1750 or 3450 rpm electric motor would be something you could do from a sheave (v belt) drive.

Just a thought.

 

[396foxRN]

Thanks for the suggestions!

mowers seem to max out around 18hp from what I see online, and most look to be 1-2 ribbed pullies. a forklift clutch/trans, from quick online searches, look heavy and expensive.

what are some additional items you guys can think of, with a centrifugal clutch, a 25+hp drive engine, and 3+ pulley use? I see some online, but they are universal, new, $500-ish pieces. What might I find a used one on, hopefully with about a 10" pulley?

Thanks!

 

[American Locomotive]

Reefer units.

 

[396foxRN]

Reefer units.

thats right where my online research has had me looking!

I had no idea, or I would have bid on the beat-up thermoking refer unit at the same auction where I had bought the 5120's.

The motor and clutch from such a unit would probably be enough to run a 5120.

What other junkyard/used ideas can you guys think of?

Thanks!

 

[chrism0107]

A centrifugal clutch requires the ability to control the engine rpm how do you intend to control that accurately for demand when needed. I have a alternative a timer that shuts the engine off after say 10 minutes of continuous time at a specific pressure but restarts when the pressure drops below say 95 psi. But this would require a electric start motor

 

[396foxRN]

initially, I am thinking of using the tank pressure on-off switch to turn on-off a solenoid on the throttle lever that would kick up the rpm when the pressure switch determines the tank needs more air, and return the motor to idle when pressure is met and shuts off the tank switch. similar to the way older cars with carbs would kick up the idle when the a/c compressor switched on.

I'm keeping an eye out for decent 4.9L and 4.0L Fords right now, as they both make great torque at low rpm.

 

[396foxRN]

The thought occurred to me today that I could use a pulley/flywheel of about the same size as the compressor uses, adapted to the flywheel of the gas engine, and run them at a 1:1 ratio, direct drive, with no clutch. I could then wire it up so that when pressure is reached in the tank, the gas engine shuts off entirely. easy to do, the challenge comes in getting it to restart as pressure drops, and repeat the cycle, just as an electric compressor would do. Here is how I would do that:

the pressure on-off switch at the tank is a 4 terminal set of contact points essentially. When setup electrically for 220 motors, there are two power in wires (from the house wiring), and 2 power out wires (to the motor that drives the compressor). When you turn it on, the tank is empty, and the contacts are closed, effectively connecting the two 'in' wires to the two 'out' wires, and allowing full home current through the switch and into the motor. When the set pressure is reached, the contacts pop open, effectively braking the circuit, and turning off the motor. What I would do is take two 12v feed wires from the power distribution box of the wiring harness, and run them to where the two home 'in' wires went on the switch, and then run the two 'out' wires back into the harness; one to the ignition 'run' wire, which does what you do when you turn your ignition switch one click forward, and it energizes the ASD/auto shutdown relay and the fuel pump relay. The second 'out' wire from the pressure switch, I would run through a vacuum or pressure switch, and then to the starter relay. This is effectively now doing what your car does when you go past the first click of the ignition switch and twist/hold the key until it starts. The vacuum or pressure switch could be one of two things: either a pressure switch plumbed into the oil pressure line, that breaks the power to the starter relay once the engine fires and makes oil pressure.......or a vacuum switch, that breaks the circuit to the starter relay once the engine fires and makes vacuum. Either one would be acting like the neutral safety switch, as far as the computer knows. It will crank the engine until it starts, makes vacuum or oil pressure, then it would shut the starter off, much as if you were cranking a hard to start car in neutral, then trying to shift to drive while cranking.

So, 2 12v power wires into the pressure switch, and two 12v wires out to the engine/computer. Both are hot to the computer/engine, and it cranks until it starts. Once it starts, one of the 12v out (the one that cranked the starter), then effectively gets shut off by the vacuum or pressure switch, shutting the starter off, while letting the engine continue to run at idle. Once pressure is reached in the tank, it all shuts down until the cycle restarts.

with equal size pullies on the compressor and the gas engine, the compressor will run at the rpm of the idling engine, or about 700ish rpm. Quincy recommends 400-900 rpm for the QR models, so this is right on target. With the unloader valve design of the Quincy, where motor strain on startup is reduced by the rotating assembly not pressurizing air until the oil pressure rises enough to close the valves, I figure the starter of the gas engine would barely notice the drag of the unloaded Quincy compressor. If the loaded compressor bogs the idle down to 600-ish, just raise the idle speed of the throttle body to compensate.

My harnesses already have self-integrated alternator/charging systems, so the whole thing would be self charging. And, I already have a very large aftercooler I plan to use, and could put the engine radiator on the backside of that, with the fan blowing air through the aftercooler, then through the radiator, then to atmosphere. Remove the a/c and p/s pumps from the engine and get a shorter serpentine belt, and it should be good to go. Run the exhaust outside, and make a small fuel system.


what problems or suggestions do you guys note on this? I'm eager to give it a try.

 

[JamesW]

Cub Cadet Tank lawn mower has a 27 hp Koler motor and runs an electric clutch to engage the belt drive to the hydraulic pump.

 

[American Locomotive]

You will not get very mich useable power at 700 RPM. Maybe 15-20HP, and that will be with the engine wide open. Oil pressure will be load and bearing loads high. That's a recipe for extreme wear. You will also have no "reserve" power doing that.

As I mentioned earlier, you still need a governor. Kicking the throttle with a solenoid will not work well, and the engine will slow down as tank pressure builds.

 

[Spareparts]

On the commercial compressors they have a spring loaded air cylinder on the carb hooked to the unloader valve. When the compressor is running the cylinder is retracted to open the throttle linkage and speeds the enging up and operates off the governer setting. When the unloader valve cycles it lets the air pressure to the cylinder bleed off and the internal spring in the cylinder pushes the throttle to a closed position allowing the engine to idle. When the unloader valve cycles it pressurizes the cylinder and and the engine soeeds up. A simple little air cylinder, small length of copper tubing, and a small tab attached to the throttle linkage going to the carb is all it will take. All the parts are redially available at any supplier of mobile air compressors, might even be available in kit form. The idea of an electro magnetic clutch off a commercial mower is very expensive $400 to $750.

 

[396foxRN]

You will not get very mich useable power at 700 RPM. Maybe 15-20HP, and that will be with the engine wide open. Oil pressure will be load and bearing loads high. That's a recipe for extreme wear. You will also have no "reserve" power doing that.

As I mentioned earlier, you still need a governor. Kicking the throttle with a solenoid will not work well, and the engine will slow down as tank pressure builds.

Maybe I am missing something. 15-20hp at 700 rpm with the engine running wide open? low oil pressure at 700rpm? no reserve power?

700 rpm and an engine running wide open are totally opposite parameters. If you're running at idle, you've got nowhere to go but up for reserve power. Engine oil psi should not be low on a healthy engine at idle.

I know that hp will be lower than advertised engine peak HP, as I will not be running it at peak rpm, but 15hp? I can't find a dyno chart online showing idle power ratings, but I imagine my 4.9L ford 4x4 that is advertised at 145hp @3400rpm and 265ft/lb torque @ 2000 rpm puts out more than 15hp at idle, and also does it at 40+psi oil pressure at idle on a 30 year old daily driver. Again, maybe I am missing something, but I cant imagine a 4.9L Ford at idle not being able to handle a 5120 Quincy compressor. Perhaps if I am trying to maintain a tank at 175psi tank, sure. Even in which case, why do you state that a simple pressure-dependent switch couldnt be used to manually raise the engine rpm to counter the resistance of the compressor at such a psi tank rating?

I imagine torque ratings are more valid measurements in this application anyway. I see sources online selling Kubota 37hp diesel 3 cylinder powered 5120 compressors. The 37hp Kubota has a pretty flat torque 'curve' that doesn't vary much from 1500rpm to its 2700 rpm advertised rate of just over 100ft/lbs. Just for comparison, the 4.9L Ford is advertised at 265ft/lb at 2000 rpm. If you've ever driven a 4.9L Ford, you know their torque is pretty flat, and stout, from just off idle to just over 2500rpm...exactly why they were used in things like forklifts, UPS truck, tugs, generators, etc.

I do expect the motor to meet resistance and slow as the compressor struggles to pack more and more air into the same space. I figure though, that if it struggles to meet my needs at idle, an additional pressure switch could easily be added to activate a simple solenoid that kicks up the rpm. I dont understand how you figure such a device wont work. It's no different than your foot pushing the pedal to speed up.




I am not trying to start an argument here, I am trying to debate with you and others my options here, and discover some of the limitations before I find them by accident. Also, I am using the parameters of the 4.9L Ford just for debate purposes. I have not decided on what engine to use yet. I am very familiar with the 4.9L, as I am with Dodge 5.2/5.9 Magnums. I have a 5.9 Magnum (300ft/lb at 3200rpm) on a stand that I use to make/test/run custom EFI harnesses, so I may just use that engine for double duty. I've made 5.0HO Ford harnesses, so a 4.9L of the same era shouldn't be any surprise to me. I've also considered the 3.9L V6 Dodge Magnum (230ft/lb at 3200rpm) and the early OHV 4.0 Ford V6 motors. As far as low rpm/high torque ratios, the 4.9L Ford (265 ft/lb at 2000rpm) and 4.0L Ford (220ft/lb at 2400rpm) are at the top of the list, respectively. All of these engines are also cheap, plentiful, and easy to work on. The 4.0 Ford's physical size makes it appealing, as it's not a lot bigger in physical outer dimensions than the 5120 assembly, whereas the 4.9L is a long inline 6 cylinder. However, I am most familiar/comfortable with the Dodge EFI systems.

I'm kinda waiting to see what concerns come up through discussions here before I pick a donor engine.


Thanks!


Doug

 

[396foxRN]

You will not get very mich useable power at 700 RPM. Maybe 15-20HP, and that will be with the engine wide open. Oil pressure will be load and bearing loads high. That's a recipe for extreme wear. You will also have no "reserve" power doing that.

I was thinking that your no reserve power comment may be more on my 1:1 engine:compressor rpm pulley ratio, in which case I see some of your point, as the 5120 compressor is factory-recommended for a rpm range of 400-1050, per the QR manual. Increasing the motor rpm to compensate for pressure-related compressor resistance could put the compressor at the rpm limit quickly. Maybe a 1-0.75 ratio would be better (a 1000rpm engine and a 750rpm compressor ratio, for clarity), or perhaps even less

 

[Firebrick43]

The Amish around here have lister diesels running a shaft. Shaft is on a set of pillow blocks The biggest load is their milk chiller. They drive multiple things off the shaft. One guy has a chiller, air compressor, hydraulic pump to run drill press/lathe, and a DC welder. Each item has a slide under it attached to a small air cylinder.

All, except for the air compressor the cylinder moves the slide away from the shaft tensioning the belts engaging that item. The air compressor has springs that tension the belts and the air cylinder pushes the plate agaist the springs to disengage.

The compressor is done this way so it will engage if there is no air pressure. High horse items use a multi rib belt. The man says belt life is actually pretty good even though it set slightly in the sheaves groves when disengaged. Belts also consume less hp than many other options. Bimbo air cylinders are cheap and tension is easy to adjust by regulating air pressure.

 

[396foxRN]

the amish are using diesels and lathes? not surprised that they would come up with simple and effective means to do so though....

thanks for the inputs. thats another thing I had thought of, was possibly running the motor through a transfer case or something similar, leaving me options of hi-lo gearing and being able to switch between powering a compressor and something else, like if I wanted to add a generator head at some time. Love the ingenuity!


Doug