Quiet Small Engine

[Bailes1992]

Hi All,

I'm looking to build a supplementary gas-powered air compressor.

I have a small 24 litre 1.5HP compressor which puts out ~6.5cfm. It's enough to run an impact for a few seconds, small air brushing, pumping up tyres etc etc. However, sometimes when using the impact for repeated tough bolts or spraying stonechip/underseal etc it is running constantly and can't keep up.

I have acquired 3x 15KG Butane bottles which I have purged with water loaded with Bilt Hamber Atom-Mac to stop any corrosion and planning on mounting them upside down in a rack at the back of my shed which is at the end of my garden to increase my air storage capacity. It'll be burying a 1/2" air hose in a duct up to my garage where it will T into the existing pipework in my garage. They'll be guarded with mesh and ply-wood to ensure some protection if one does split or break.

I've also acquired an old air compressor pump. It's 4hp/18cfm and needs to spin at ~1500rpm. While perfectly do-able with an electric motor and easier being that I'm an electrician, I have a love for engines and would love to run this with a small OPE engine.

I need the engine to be reasonably quiet because when I'm spraying or using grinders etc I can be using them all day. I've seen devices that will operate the throttle/governor to reduce the engine speed once the system is up to pressure which I plan on using.

BUT... is there any truly quiet 5-6.5hp OPE engines out there? Or am I better off buying a cheap Chineese copy and investing in some sound deadening? Maybe boxing it in (providing it with adequate airflow of course) with some sound deadening foam/egg crates?

 

[wag123]

This is far more complicated than you think. Stick with an electric motor.

 

[csandste]

Originally Posted by wag123
This is far more complicated than you think. Stick with an electric motor.


Yeah, but that wouldn't be as much fun, would it?

 

[Bailes1992]

Originally Posted by csandste
Originally Posted by wag123
This is far more complicated than you think. Stick with an electric motor.


Yeah, but that wouldn't be as much fun, would it?



This guy gets it! ^^^

 

[Tman220]

First of all, a 5-6.5 hp gas engine would be overworked on a 18cfm air compressor. The air compressors available with gas engines with that CFM rating have 9-10 HP engines.

My suggestion, if you want something as quiet as possible is to look at an engine even larger than that, (probably a twin) and size the pulleys so that you can achieve as low of an RPM possible with whatever engine you are using. Sounds like a project I would like too. If it were me I'd use a 16-18 hp vanguard Vtwin and I would shoot for keeping the engine turning under 2500 RPM. With a good muffler the setup, could be reasonably quiet.

 

[wag123]

Don't forget about the necessary and correct throttle control valve and unloader pilot/check valves.

 

[meep]

I'll bite, too.

Any excuse for a twin OPE engine, I'd be all over, but conversely you could just as easily run a smaller, say a 212CC predator and just run smaller pulleys and run it at less RPM. I too like the relaxed RPM idea - 2500 when on-load sounds ideal to me. Single lung, out back, surrounded by a fire-proof sound-deadening enclosure (brick?) seems ideal. Make it a 2-bay and keep a genset next door.

The fuel burn for a twin lung engine while idling between cycles might be off-putting.

You NEED to have water drains on your homemade tanks. The risks from long term rust/degradation in that stuff scares the **** out of me. And you need to make sure you have adequate over-pressure blow-offs installed.

 

[j_mac]

I have a solution I came up with to deaden gasoline (petrol for you dear sir) engine sounds emanating from the carburetor air intake. I was looking for a way to quieten a Goped stand up scooter with a 2-cycle engine. Now, on 2 strokes people will be amazed to learn that almost ALL of the noise comes from the INTAKE side. Those box mufflers with their tiny exit holes are extremely effective at reducing the racket coming from the exhaust ports, but the manufacturers pretty much just let the air filter/intake be. But on a 2-stroke I'd say 95% of the sound comes from the intake. This is because the intake and exhaust ports are open at the same time and the sound escapes backward out of the system.
Now, a 4 cycle suffers from a similar problem. They've done a fabulous job deadening the exhaust on 4 stroke small engines but a great deal of the sound comes from the intake too for similar reasons as a 2 stroke, with the added clatter of the intake valve slamming and resonating.
Also, an air compressor cylinder has the same problem with sound resonating back out the intake tract and into the surrounding air.
What I can propose to you is a way to deaden the sounds coming from the intake on the gas engine AND the compressor cylinder(s.)
This is what I used:
https://www.amazon.com/Maxpower-334...mp;psc=1&refRID=BQ96HXCFMMRQE9F66S34
Not the exact muffler but it was this type, maybe even identical to this one, but mine was a gold color...
After experimenting I found that attaching one of these mufflers, BACKWARDS, to the carburetor intake that it would ELIMINATE the sound coming from the engine. The Goped scooter which normally made a typical 2-cycle buzz was rendered almost completely silent. This was the ONLY modification done to the scooter! I really just stumbled onto this, but it worked incredibly effectively. I was SHOCKED how effective it was and that the cooling fan and cylinder fins did not contribute hardly any sound at all.
I would imagine adding these mufflers to the gas engine and compressor intakes that you will be amazed just how much noise it will eliminate.
You might experiment with different sizes of this type of muffler, but I would size the opening on the threaded end to a similar size of the diameter of the carburetor inlet.
To be sure, the muffler end with the threads is where the ambient air rushes in and the other end (opposite the threaded portion) faces the carb. I'd just be sure the opening in the ends of the carb is just slightly larger than the carburetor's venturi.
Do this and you might not need any sound deadening material and the inherent poor airflow and heat dissipation associated with it.

 

[Bailes1992]

Cheers Chaps,

I've ordered a cheap Honda GX200 Chinese clone. I think this is very similar to the Harbor Freight Predetor 212 you can get in the US. It cost me £76 delivered.

I'm tempted to buy an oil-bath type clutch as used in go karts so when the engine is dropped back off to idle it will not spin the compressor and return to a quieter idle. As I said in my opening post I plan to use a throttle control valve on the factory fitted governor and will be running the correct safety blow off valves and pressure unloaders on the system too.

I've got a few glass packs in my garage. I'm thinking about fitting one to the compressor exhaust (which will be piped to outside of the shed) and possibly fitting them on the intake of the engine and the compressor pump. I'd like to box it all in with sound proofing but I really need to look into airflow and cooling.

My plan is to mount the 3 tanks upside down with a header running below them with the tanks connected into the header. I'll put a drain on the bottom of the header to drain off any water. One side of the header will have the pipe out, running down the garden and into my garage and the other end will be connected to my engine/compressor setup.

 

[Bailes1992]

Just something else I find interesting...

At 2600rpm this engine makes 8.11lb-ft.

2600rpm x 8.11lb-ft / 5252 = 4.01hp.

The manufacturers data for the compressor pump says it required 4hp and 1500rpm to run effectively. I think I will have to have a good look at getting pulleys to run the engine at 2600rpm and meeting the compressors requirement at 1500rpm.

 

[Bailes1992]

All my plans seem to snowball out of control. I'm now looking at adding some kind of electric start/stop to the engine.

I could use basic pressure sensors and relays or even an Arduino. It would be pretty easy to setup I would have thought.

When the system pressure drops to 7bar, start up the engine and when it drops to 6bar/90psi increase the throttle until pressure hits 8bar and return to idle for 30s and shut off engine.

My Wife does the electronics bit, I'm going to have to talk to her. No doubt she will look at me and ask "And how much is all this going to cost?"

 

[meep]

nothing wrong with it, methinks you want the project more than the higher capacity. to clear your thinking, visualize your end goal, what you are really after, then re-scope the design / ask if this project really meets what you are after.

Electronic start-stop intelligence is overkill for this application, because all it does is offset fuel cost but adds maintenance complexity and more possibility for things to go wrong. Could be MUCH FUN, but also won't help you if it conks out in the middle of a project or burns out the starter when the tank goes dry.

That said, if you enjoy a shop that runs like a rube goldberg machine, go for it. I've dreamt of similar with such things as an electric hybrid bicycle, so I understand the allure.

Or simply run a 220V outlet and buy a nice, quiet, belt driven pump and enjoy the optimized tool size.

 

[Bailes1992]

Originally Posted by meep
nothing wrong with it, methinks you want the project more than the higher capacity. to clear your thinking, visualize your end goal, what you are really after, then re-scope the design / ask if this project really meets what you are after.

Electronic start-stop intelligence is overkill for this application, because all it does is offset fuel cost but adds maintenance complexity and more possibility for things to go wrong. Could be MUCH FUN, but also won't help you if it conks out in the middle of a project or burns out the starter when the tank goes dry.

That said, if you enjoy a shop that runs like a rube goldberg machine, go for it. I've dreamt of similar with such things as an electric hybrid bicycle, so I understand the allure.


Yeah, I think you're somewhat right.

I think 4HP pump designed to run at 1500rpm.

GX200 clone engine with a 2:1 ratio gearbox w/ oil bath centrifugal clutch.

1:1 Ratio Pullys (Pump will run at 1300rpm when the engine is at 2600rpm due to the above gearbox).

Air pressure throttle control.

Air unloader just incase.

Should be plenty for what I'm every going to do.

 

[j_mac]

Keep going with your idea! Some guys like to fish. Some like to play golf. Some like to gamble. And some like to exercise their brain and devise interesting that can help them do work and will ACTUALLY MAKE THEM HAPPY!
I once heard someone mention that when buying an expensive item, that it HAS to inspire PASSION. PASSION is an unknown quantity and a value cant be placed on it.
If your Rube Goldberg system puts a smile on your face, then go for it! I'm sure your wife can make the stop-start work with the Arduino and such, and you can do the hardware!
I'd love to see it completed and I would love to have a tutorial so I can make one myself, just like yours!
Take a look at the backwards muffler thing on the carb side. That, inside a glass pack would probably render the intake 99.999% silent. But beware. The Glass fibers will come out of the packing and will cause trouble more than likely. That backwards muffler thing might be the most amazing discovery of my life. I think adding one to the carb and to the cylinder(s) on the compressor will cut down on their sound by at least 90%. That scooter was almost silent.