Wobble Plate Air Compressor

[Toymaker]

UPDATE:

Finally received the 3:1 reduction pulleys and timing belt from China. Once installed I realized I would need a belt tensioner to keep the belt from slipping over the smaller pulley. For the moment, I will keep using the air accumulator (shinny polished steel ball in background) to further smooth the airflow into the burner's siphon type fuel nozzle; I already have it, so why not use it . The fuel nozzle only needs 4 to 6 psi and my little air compressor can deliver up to 10 psi, so I have lots of over-capacity. BTW, the belt tensioner spring was salvaged from an empty shampoo bottle,...works great and it's even stainless steel .

 

[dazz]

Hi
Nice work.
You should try it without the accumulator. I suspect you won't need it.

 

[Bentwings]

Hi
Nice work.
You should try it without the accumulator. I suspect you won't need it.

Amazon has the flanged idler pulleys you need on set had about 10 of them with bearings I think it was under 20$ They looked like they would be a perfect color match. You have done a nice job on yhiscproject

 

[Toymaker]

Amazon has the flanged idler pulleys you need on set had about 10 of them with bearings I think it was under 20$ They looked like they would be a perfect color match. You have done a nice job on this project

I had waited nearly 2 months for the timing belt & pulleys to arrive so when I powered the compressor up the first few times and realized I needed a belt tensioner I was more than a little disappointed at the prospect of having to wait another 2 months for an idler pulley to be shipped to me.
It was my very strong desire to just finish this project (lack of patience?) that prompted me to make my own idler pully. I already had spare bearings from a previous project and plenty of steel and aluminum stock for all the pulley and lever arm; so in less than a day, I had made and assembled all the pieces.

I truly love my retired life here in the tropics of Thailand,....BUT,....the time it takes to acquire even the simplest parts, (because most everything must be shipped in from China), can be very frustrating. I probably need to practice my Buddhism a bit more,...take a few deep breaths, sit back, relax, meditate...... but,.... making chips in my small shop is sooooo much more satisfying

 

[Toymaker]

Hi
Nice work.
You should try it without the accumulator. I suspect you won't need it.

You were right. My analog air pressure gauge needle shows the air flow both with & without the accumulator to be very smooth.

 

[Toymaker]

Here's a very short clip of the swashplate compressor running at nearly 14 psi into the 2mm fuel nozzle. This is well above the nominal 4 to 6 psi rating of the fuel nozzle. I don't have a sound level meter so I can only guess at the db noise level, perhaps 40-ish db. Note that the cell phone camera & mic were only inches away while I recorded.

 

[Steamchick]

Hi Toymaker.
What wattage and speed is the motor?
I suspect your guess at 40dBA is half of what you really have. But really I have no idea from the recording. Is the air intake directly open to atmosphere? - Probably 80dBA just from the "Pop" of air rushing-in when the intake valve opens on each cylinder?
All I could hear was compressor noise, not motor noise. And that could be 50 or 60dBA...? - Or more?
As you have the receiver, I should retain it as the fuel injection needs a really stable air supply. Will you fit a reduction air pressure regulator between the receiver and fuel control (AIr nozzle/Jet?)?
How hot does the compressor become after say 10 minutes of running? The physics of Gas laws ensure compressors always get hot...!! (Adiabatic compression heat losses).
K2

 

[Toymaker]

Hi Toymaker.
What wattage and speed is the motor?
I suspect your guess at 40dBA is half of what you really have. But really I have no idea from the recording. Is the air intake directly open to atmosphere? - Probably 80dBA just from the "Pop" of air rushing-in when the intake valve opens on each cylinder?
All I could hear was compressor noise, not motor noise. And that could be 50 or 60dBA...? - Or more?
As you have the receiver, I should retain it as the fuel injection needs a really stable air supply. Will you fit a reduction air pressure regulator between the receiver and fuel control (AIr nozzle/Jet?)?
How hot does the compressor become after say 10 minutes of running? The physics of Gas laws ensure compressors always get hot...!! (Adiabatic compression heat losses).
K2

The DC motor is driven by a 36 volt PWM DC source, which allows for very good motor speed control. Calculated motor speed in the video for the almost 14 psi output is just under 2000 rpm. I've never bothered to measure the Amps or calculate the Watts.

Measured Performance connected to 2mm Fuel Nozzle:
(Note: RPM is for the compressor, the motor is 3X the rpm shown below)

​ PSI​ RPM​ 15​ 700​ 14​ 660​ 13​ 630​ 12​ 610​ 11​ 585​ 10​ 560​ 9​ 510​ 8​ 480​ 7​ 430​ 6​ 410​ 5​ 335​ 4​ 320​ 3​ 270​

I probably should have been more specific concerning my guessed db level. The recording was made with my cell phone positioned about 12" from the compressor, and at that distance, you're probably right about an 80 db level. My 40 db "guess-tment" has the listener standing a more respectable distance away from the compressor,...about 10 ft or so, which is roughly my location when I'm videoing the burner in operation.

There's no need for an air pressure regulator. One of the main reasons I chose the swash plate design was that it allows me to have 10 pistons, resulting in 10 pressure pulses per revolution equating to very smooth air flow straight out of the compressor. Also, when I was trying to using a single diaphragm type compressor, I built a small air accumulator in an attempt to smooth the air flow to a usable state. I still have that accumulator and I'm still using it with the swash plate compressor,...I have super smooth air flow into the fuel nozzle.

After 10 minutes of continuous operation, the compressor gets hot enough that I wouldn't want to leave my hand on it for more than a fraction of a second,...but it's not so hot that it burns the skin the instant you touch it.

Finally, each one of the 10 intake reed valves is located just behind a small white felt pad which functions as an air filter. So, yes, I suspect some of the pop-pop-pop noise you hear in the video could be coming from those valves. I also believe some of the squeaking sounds I hear are from the belt and pullies.

 

[Steamchick]

Hi Toymaker.
Of course, if the noise of the intake (Majority of the sound power I guess?) is a bother, you can make a simple airtight lid to form a plenum over all the intakes. This plenum can then have a relatively small pipe (maybe 5mm bore?) and not very long (10cm?), so it can have a tee part way along to a closed chamber acting as a Helmholtz resonator. When you decide the frequency (depends on the speed you are running) the sums to design an intake with resonator are pretty simple as you know the volume you suck into each cylinder.
Anyway I think you are well on the road to success!
Enjoy!
K2

 

[terryd]

Here's a very short clip of the swashplate compressor running at nearly 14 psi into the 2mm fuel nozzle. This is well above the nominal 4 to 6 psi rating of the fuel nozzle. I don't have a sound level meter so I can only guess at the db noise level, perhaps 40-ish db. Note that the cell phone camera & mic were only inches away while I recorded.

View attachment 144253

Hi Toymaker,
if you have a smartphone there are free or inexpensive apps for measuring sound levels in decibels. Even those that charge allow a free trial.
TerryD.

Edit: I just checked my db chart and 40db is a quiet whisper so I agree with K2 your assessment is way too low. 80db is loud singing and 90db would equate to a motorcycle. remember also that a decibel chart is logarythmic not linear so a relatively small increase in db levels equate to a larger increase in noise level especially at higher levels.
TD

 

[Toymaker]

Hi Toymaker,
if you have a smartphone there are free or inexpensive apps for measuring sound levels in decibels. Even those that charge allow a free trial.
TerryD.

Edit: I just checked my db chart and 40db is a quiet whisper so I agree with K2 your assessment is way too low. 80db is loud singing and 90db would equate to a motorcycle. remember also that a decibel chart is logarythmic not linear so a relatively small increase in db levels equate to a larger increase in noise level especially at higher levels.
TD

Thanks for the info about phone apps for measuring sound levels; most likely their results, even without any sort of calibration, would be more accurate than my "guess-tement".

Hmmm,...I'm pretty sure a heavy-metal singer (80db) could easily drown out the noise from my compressor, and I'm even more certain the compressor is much louder than a whisper (40db). So I Googled decibel charts to get a better idea of noise comparisons. I think my compressor is probably somewhere between, Piano Practice (65db) and a noisy restaurant (70db).

This has been an interesting discussion; without calibrated instruments, comparing or quantifying db levels is not easy.

 

[Steamchick]

Hi Again:
I was on one job where I needed to re-design a silencer for a cylinder of air with rapid opening valve at 28 bar pressure. 10" diameter and 5 in stroke. opening to atmosphere... Through a multi-chambered expansion box gave 127dBA at (If I remember correctly?) 100m range... Akin to a small cannon? But it was above the Regulation, so I designed a silencer system to change the "note" Frequency range) of the silencer, which changed the attenuation with distance (across fields) and we passed the test.
But I could only test this "in the factory" (it was almost daily practice to test a device anyway!).
At 1 m range I reduced the 135dBA peak with the old system to below 125dBA. Actually, stood at more than 10m range, with ear plugs, ear defenders and pinching nose, closed mouth and eyes, you could not detect any reduction of volume....
But when operated on-site in the middle of the country, it sounded more like a rifle shot at 1/4 mile, (Nearest road/public access) than the deep boom of the old design. (The old design was satisfactory at 21Bar operation pressure, but my equipment needed the 28Bar NWP = a bigger "Boom"!). At 1 mile it was barely detectable, compared to the old equipment sounding like a distant Shotgun report.
That illustrates to me how we perceive sound differently from the sound meter. Most sound meters measure a metered sound pressure level (dB) metering), then have an algorithm to convert to how we perceive sound with our "variable" meters - the ears (dBA conversion). We do not perceive a linear scale across frequencies. So it is hard to compare and estimate sound levels for even the best experts! But you can think of:
* 1 person talking = 70dBA,
* 2 people talking = 73dBA,
* 10 people all talking in a bar = 80dBA,
* 100 people in a works canteen, talking not eating = 90dBA (above permitted sound levels?),
* 1000 people shouting at a demo = 100dBA,
* 10,000 people cheering at a sports match 110dBA and
* 100,000 people shouting at the cup winning goal = 120dBA... or a racing motorcycle exhaust when at full throttle away from a standing start? (One of my noisy experiences, the guy at the back waving the green flag to the starter!)
* Formula 1 cars screaming off the start line = 130dBA (This can permanently damage ears in seconds), (I guess that speakers at pop concerts produce this level of noise to project to the dancers at the back of the crowd?).
* a fighter jet taking off using after burners 135~140dBA? or small cannon, if you get that close? - One is continuous, the other a single peak. 140dBA is double the "number" of 70dBA, but a million times more "sound power " - RMS power rating of the "noise" spectrum - or energy of a peak pulse. It depends on the recording device as to what it is measuring I think?).
The brain is off-the-scale beyond that!
* But NASA & co. make bigger noises at over 150dBA at source... when rockets lift off!
- Or at least that is my guess of the scale?
Terry, can you post your dBA scale to correct my ideas?
Ta,
K2

 

[The Ignoble Troll]

That's a really nice build!

If the heating gets to be an issue, a used rotary vane pump might suit your set up.

You can even find them already mounted to 36v motors for dirt cheap on ebay.

If you can hold it for 3 seconds before it hurts, it is only about 60°C

Awesome approach to a lack of readily available parts!