# Designing a Quiet Air Compressor



## vederstein (Oct 22, 2022)

Now that the Dancer Engine is complete, I'm starting to think about my next big project: I'm going to attempt to build a quiet air compressor.  I have some ideas, but first of all, one of the goals is to minimize the air pulses (chuffing) coming out of the pump.

Note that this is pure engineering at this point.  Once I have some spreadsheet models to help guide me in the right direction, I'll get into the design process.  At this stage I'm only doing an engineering analysis.

I've created three spreadsheets, modelling an air pump with 2, 3, and 4 cylinders.  This analysis is just to see the optimal number of cylinders to produce an even airflow without an excessive number of cylinder.  I modeled the output with some flow cutoff ±15° to ensure no crossing of ports between the piston inlet and outlet.

Let's take two cylinders, 180° out of phase.  The air pulses are very pronounced.  The average flow is 0.60, but the range goes from zero up to one.









Now let's look at three cylinders, 120° out of phase.  The average flow is 0.92 with a pulse range of .29:







Now let's look at four cylinders with a 90° phase angle.  The average flow is 1.22 with a pulse range of .45:







Given this analysis, I'm only looking for the smoothest airflow with the lease number of cylinders.  Based on this, my air compressor pump will have three cylinders.  I suspected this to be the answer, but now I have the analysis to back it up.

This is very early in the design process.  This isn't really even design yet.  It's actually engineering.  This _is_ what mechanical engineering looks like.

That's enough for now.

...Ved.


----------



## johnmcc69 (Oct 22, 2022)

Nice! Ambitious project!

 Like you said, it's all about the engineering.

 I'm following...good luck!

 john


----------



## vederstein (Oct 23, 2022)

Next up in the design process is to figure out what I can expect from a motor selection.  I want the pump to have the ability for an output pressure of 120psi.

I want to use a commonly available compressor duty motor that runs at a relatively low speed.  Also, I don't want to exceed most US single phase circuits.  That leaves me with a 1½hp motor @ 1725 rpm.

At that speed and power, the average motor torque is 54.8 in-lb.

Knowing there's going to be frictional and other efficiency losses, I assumed a 15% efficiency loss.  Also in every slider crank, the worst case position is when the connecting rod is 90 degrees to the crankshaft:




With these data points, I can play with the bore and calculate the stroke to match up with the tooling I have available and what seems reasonable to me in a design.  The design parameters are as follows:

*Number of Cylinders: 3
Cylinder Bore: .625"
Cylinder Stroke: 1"*

Each cylinder stroke will have a compression ratio of 8.3:1.

Calculating Pump CFM is not straight forward because the hardware store's air compressors specifications are complete bullshit.  On a 120V/1ph/60Hz/15amp house circuit you can get a maximum of 1,800 watts which equals 2.4 hp.  Go to the hardware store.  You'll find ratings that just don't make any sense.  How the hell can a compressor running off 120V house power be 4 horsepower!?!?  It's total marketing bullshit.

Anyways, using the ideal gas law (Pv=nRT) I calculated that the pump will output .91 cfm @ 120 psi.  Another way to think of it is that the pump will compress .332 moles of air from atmospheric pressure to 120 psi per minute.

This calculation results in an air inlet consumption of 8.1cfm.

If you've made it this far.  I thank you.  I know this post is a bit dry.  No fancy renderings or videos, just a bunch of numbers.  But again.  This is what engineering is.

Attached is the working spreadsheet (OpenOffice .ods format) with all these calculations.  If you study it, let me know if I've screwed up somewhere.  But the numbers seem reasonable and that's one way to check if the calcs are correct.

Thanks,

...Ved.


----------



## ddmckee54 (Oct 28, 2022)

Ved:

Yup, it's marketing BS alright.  I believe that in order to get the most IMPRESSIVE numbers they'll use the motor's current values at startup to calculate the HP.  A motor typically pulls 6 times its' normal full load amps during the split second that it's not turning.  Now I ask ya, doesn't 4Hp sound a LOT more impressive than the 2/3Hp it actually is?

The big players in air compressors are not above that game either.  Several years ago, we installed a 4000 CFM compressor, not gonna name names.  The compressor had an 845Hp, 480V 3 phase motor, with a FLA of 900 and a service factor of 1.15.  We finally got it running, and that was a struggle in itself.  The motor, if started across the line, would pull 5400 amps for about 25 seconds.  This would trip the main breakers in the sub-station.  We about crapped when we measured the motor's running current at 1050 amps.  We thought we had a brand new, bum motor so we called a motor company to come check it out.  It was just hunkey-dorree, but when we put it all back together it was still pulling 1050 amps.

I got to looking at the performance curves of the motor/compressor and found out that we were spot on the curves.  In order to get the 4000 CFM at our ambient temperature, our motor had to crank out 900Hp or about 108% of its' rated value.  This was still within the motor's 1.15 service factor, so the manufacturer was happy.  They could SAY that their compressor would crank out 4000 CFM using an 845 Hp motor - that was ALL true.  It's just that the motor wasn't loaded to 845Hp when the 4000 CFM was produced.  We've rebuilt that motor 2-3 times since we installed it.

Nope, not JUST the hardware store guys.

Don


----------



## Toymaker (Oct 29, 2022)

As you noted in your first post, the more cylinders you have, the smoother the output airflow will be.  A secondary benefit of lots of smaller cylinders is lower noise level as it becomes harder to hear individual cylinder pulses.  With that in mind, I built a small home-shop air compressor using an automotive Air Conditioner (AC) compressor which uses a wobble plate to drive 10 cylinders.  Here's the thread: *Shop Air Compressor using Auto AC Compressor*
I use a small 1/3 HP motor with a couple a reduction pulleys and the system is very quiet; what noise you hear doesn't sound at all like a typical air compressor.

Thanks to the automotive industry, there are quite a few different AC compressors and designs to choose from.  The Denso 10S15C I used is one of the smallest units made, so if you need more air flow, just choose a larger compressor. All automotive AC compressors will typically exceed 200 psi, so no worries getting to your 120psi design pressure.


----------



## Richard Hed (Oct 29, 2022)

vederstein said:


> Next up in the design process is to figure out what I can expect from a motor selection.  I want the pump to have the ability for an output pressure of 120psi.
> 
> I want to use a commonly available compressor duty motor that runs at a relatively low speed.  Also, I don't want to exceed most US single phase circuits.  That leaves me with a 1½hp motor @ 1725 rpm.
> 
> ...


I bought a table saw in the Philippines.  The claim on the package was 3 HP.  The wattage was 1800watts.  LOL.  I called the sales people on it, but frankly, they were just too uneducated to know a thing about a horsepower in watts.  In Asia, one must look VERHY carefully at all claimjs.  Of course, in Rome it was called 'caveat emptor', let the buyer beware.  Truthfully it is everywhere, but when advertisers are allowed to openly lie?


----------



## Steamchick (Oct 29, 2022)

The same with "200Amp" Weld sets! - And "Lifetime guarantees", mean "the lifetime of the battery" - not you or I! And they don't tell you that is only 100 re-charge cycles.
K2


----------



## Richard Hed (Oct 29, 2022)

Steamchick said:


> The same with "200Amp" Weld sets! - And "Lifetime guarantees", mean "the lifetime of the battery" - not you or I! And they don't tell you that is only 100 re-charge cycles.
> K2


What's a 200 amp weld sets?


----------



## Toymaker (Oct 29, 2022)

Richard Hed said:


> What's a 200 amp weld sets?



My TIG-200P, which I purchased thru AliExpress, is rated 20 to 190 Amps; whether that's input or output is unclear, but the power outlets in my house in Thailand, where I live, are 220VAC (single phase) and my breakers are 40 amp. The unit works just fine in my house without blowing the 40 amp breakers, so I've always assumed that the 200 amp rating is for the output and that it likely uses a step-down transformer to lower the voltage and raise the current.  This is unit I have: *TIG Welder*

Maybe K2 can further clarify the meaning of the 200 amp?


----------



## Steamchick (Oct 29, 2022)

A weld set that can deliver 160 for a continuous weld (say 3 inches long!) Seems nowadays to be sold as a 200A machine, because the initial current can peak at 200A! Also, the service duty is often 5 mins welding per 15 mins cooling.... not good for anything but a few short welds. The thermal cut-out leaves you waiting for it to cool off....
That is advertising.....
K2


----------



## Richard Hed (Oct 29, 2022)

Toymaker said:


> My TIG-200P, which I purchased thru AliExpress, is rated 20 to 190 Amps; whether that's input or output is unclear, but the power outlets in my house in Thailand, where I live, are 220VAC (single phase) and my breakers are 40 amp. The unit works just fine in my house without blowing the 40 amp breakers, so I've always assumed that the 200 amp rating is for the output and that it likely uses a step-down transformer to lower the voltage and raise the current.  This is unit I have: *TIG Welder*
> 
> Maybe K2 can further clarify the meaning of the 200 amp?


As i understand it, step-down transformers are not used in the modern TIG welders, it is all done electronically.  That means there can be much greater control.  I have a transformer type TIG welder in which one has to strike the arc like a match.  It was one of the "new" ones made for small businesses back in 1980.  I got it for a Lincoln 250 welder.  The linconln is very nice, -- infinitely adjustable from 30 to 250 amps.  But the TIG welder is COMPLETELY basic.  I used it for a bit of practice then put it away as too difficult to use and control unless I absolutely HAD to use it which I never did need.  

However, last year I bought a newer model, controlled and run by electronic methods.--that is, the new type of TIG machine.  Many years ago, I learned to always check the % duty rating.  IMNSHO, one should always try to get 100% duty rating so there need be no down time.  If you are working professionally, this is a must.  If hobby work, not necessarily a must.  Also, this 100% refers to the higherst setting you can weld with.  If you are welding at 200 amps, then your machine has a 40% duty cycle.  If you are welding at a more likely setting of 40-120 amps, your duty cycle is longer, say something in the order of 60%..  If you are welding at 40 amps, your duty cycle is probably around 100%.  

Another thing:  since you are in the Land of the Thais, you are in a very hot country--that means the heat will not dissapate as rapidly as in a cooler environment which reduces your duty cycle.  Keep a fan on your machine and that will help.  

K2--Advertising?  Yes, FALSE advertising!  The Chinese have been known for centuries to give misrepresentations.  However, it really is the same everywhere.  In the US, false representation is often a illegal.  But a rat can squeeze thru any hole in which it can get it's ratty litltle head thru, so any rat in business will keep chewing till it absolutely breaks the law.  Unfortunately for the rats in business, they DO get a reputation, in this case, a "ratputation".  -- HA, I just invented a new word, it will now have to be placed in the Oxford Dictionary.  Will I be able to patent th word?  How about a  . . .


----------



## Toymaker (Oct 29, 2022)

vederstein said:


> Next up in the design process is to figure out what I can expect from a motor selection.  I want the pump to have the ability for an output pressure of 120psi.
> 
> I want to use a commonly available compressor duty motor that runs at a relatively low speed.  Also, I don't want to exceed most US single phase circuits.  That leaves me with a 1½hp motor @ 1725 rpm.
> 
> ...



Ved, reading through your two posts, I'm not sure if your primary end goal is simply to have a quiet compressor with smooth airflow, or if part of your goal is the satisfaction of designing and building your own compressor.  

If you just want a quiet compressor with smooth output air flow, the easiest choice is likely to use an Automotive Air Conditioner compressor,...(see  post #5).

If your goal includes the satisfaction of designing and building your own compressor from scratch, a swashplate compressor is a fairly simple build.  I designed and built a 10 cylinder scaled down unit which works very nicely, and because of the double-ended-piston design, you only need to drill and finish 5 holes in order to get 10 cylinders,... the thread for that build is here:  *Small Wobble Plate Compressor*.  

Since I only needed my compressor to develop about 10 psi, the only math I did for the design was to calculate expected output volume at various RPMs; at only 10 psi max, the compression load on the motor is smaller than the frictional loads.  
Since all the cylinders and pistons are contained within two halve of a cylindrical solid of metal, the process of  drilling, reaming, and honing all 10 cylinders was in practice reduced to making only 5 cylinders as the machining is done while both halves are bolted together.  

I hope this gives you a few more ideas and choices.


----------



## vederstein (Oct 30, 2022)

Toymaker said:


> I'm not sure if your primary end goal is simply to have a quiet compressor with smooth airflow, or if part of your goal is the satisfaction of designing and building your own compressor



I'd say my end goal is another project.

I already have an air compressor from California Air Tools and it's one of the quietest on the market.  My first compressor (circa 1998) was a "5hp" Craftsman direct drive.  It put out loads of air, but damn was it LOUD!  I'd guess around 90 dBa.  Several years ago I replaced it with my current unit from California Air Tools which runs around 65-70 dBa.  It's noticeable when it turns on but at least you don't need to leave the garage when it turn on.

I've had "quiet air compressor ideas" in my head for several years now.  Now It's time to see if those ideas can bear fruit.

Perhaps I _do_ want the satisfaction of designing my own compressor or at least (in)validating my ideas.

...Ved.


----------



## vederstein (Oct 30, 2022)

For a week or so, I've been working in the CAD system to flesh out the next, and what I think is the largest source of air compressor noise:  *Check Valves*.

A cheap, loud, single cylinder air compressor has two check valves.  One for and inlet on the cylinder's "suck" stroke and one for air exit on the "push" stroke.  Those valves can be balls, reeds, or whatever but they're slapping open and closed dozens a times a second.

The threshold of hearing is 20Hz at the low end and 20,000Hz at the high end.  The opening and closing "clicks" from the check valves are easily within the range of human hearing.

So, I want to eliminate check valves.  Better if I can eliminate valves altogether.

Many moons ago, I designed and built a 5 cylinder rotary steam engine.  This is one of the quietest engines I own.  I think that I can use this concept as a basis for my air compressor.  The valving is accomplished through the porting between the crankshaft and the engine block, not unlike a wobbler steam steam engine with the porting on the radius of the crankshaft.

There's two ways to look at this.  I can rotate the crankshaft and port through the block or I can rotate the block and port through the crankshaft.  If I rotate the crankshaft, I'll have an offset weight reciprocating at motor speed, 1725 rpm. or ~29 Hz which is in the range of human hearing.  If I rotate the block, the mass is higher, but the noise from the crankshaft throw will be eliminated.

 Therefore the block will be rotated and the porting is to be through the crankshaft.

I have a bit more CAD work to figure out, but I show that concept in a follow up post.

...Ved.


----------



## vederstein (Oct 30, 2022)

This short video is showing where the design for the air compressor is going....



P.S.:  I realized that my inlet air porting is faulty in the CAD rendering.  I'll need to think a bit more about it....


----------



## Toymaker (Oct 30, 2022)

vederstein said:


> For a week or so, I've been working in the CAD system to flesh out the next, and what I think is the largest source of air compressor noise:  *Check Valves*.
> 
> ...Ved.



I agree that some valve types are fairly noisy, but the reed valves used in auto A/C compressors are so quiet that I cannot hear them.   Now, at 72 years old, my hearing isn't as good as it once was, and hearing the compressor run for yourself will be far better than my written description, so with that in mind, here's a video with sound:  *Shop Air Compressor*.  During the video, I'm speaking at a low conversational level and you can easily hear my voice over the compressor noise.


----------



## vederstein (Oct 31, 2022)

Toymaker said:


> here's a video


Yup,  very quiet indeed.  It sounds like most remaining noise is from the motor.

Yet, the more I think about, I want the satisfaction of designing and building my own design.  This is more for validation of my ideas that anything else.

Thanks,

...Ved.


----------



## Toymaker (Oct 31, 2022)

vederstein said:


> Yup,  very quiet indeed.  It sounds like most remaining noise is from the motor.
> 
> Yet, the more I think about, I want the satisfaction of designing and building my own design.  This is more for validation of my ideas that anything else.
> 
> ...



I'm sure that's a decision everyone on HMEM understands and supports, and looking over your past projects on YouTube, I'm sure that whatever you build, it will be awesome


----------



## davidyat (Oct 31, 2022)

*Ved and the others, I have to uncross my eyes after reading your engineering reports. Most of the time I just don't get it. Ved wanted me to learn some 3D CAD software and I bailed out when pretty much I couldn't even draw a straight line!!! I admire those who understand it. For me, just show me the plans so I can make some metal chips in my shop.
Grasshopper*


----------



## Asm109 (Oct 31, 2022)

There is a major difference between a compressor valve timing and an IC engine.
Engine timing needs don't change.
Compressor timing varies with the amount of pressure in the tank.
When the tank is at zero pressure, the valve is open for the entire stroke and all of the air goes into the tank.
When there is pressure in the tank. The air above the piston cannot go inside the tank until the pressure exceeds the tank pressure.
The reed check valves do a seamless job of meeting this requirement.


----------



## vederstein (Oct 31, 2022)

Asm109 said:


> Compressor timing varies with the amount of pressure in the tank



I agree with your assessment when working with check valves.  But think of an industrial scroll compressor.  That type of compressor has no valves.

In my proposed design, each cylinder inlet stroke takes in .31 cu-in of air which equals .0021 moles.  Those .0021 moles are then pushed into the air tank.  Prior to opening the cylinder to atmosphere again, the cylinder is isolated from the tank through the radial valving.

I guess I just don't see the difference other than the elimination of the check valves.  But I will lose some pumping efficiency due to the inevitable leakage between the high and low pressure air channels.  For this project, I'm willing to lose some efficiency for a quiet air compressor.

I need to take another look at my numbers though.  I'm not sure I got the massflow correct.

...Ved.


----------



## Charles Lamont (Nov 1, 2022)

I recently saw a video, perhaps on this forum, of a Stuart compressor running. The loudest noise it seemed to be making was a sort of plopping, slightly comical, which I put down to the inrush of air when the pistons uncovered the rather small inlet port.


----------



## Steamchick (Nov 1, 2022)

An observation on valve "pressure noise" and air column dynamics: 
To "compromise" for the inertia of columns of air, infernal combustion engines use overlap of valve timing - and even sonic wave reflection (as in 2-stroke expansion boxes, reverse megaphone 4 stroke exhausts, etc.) to push gases back into the combustion chamber thus increasing the mass of combustion charge in the cylinder.
Of course, compressors do not need to do that.  They work directly with pressure differences across valves. - Hence reed valves are very good - self adjusting for the varying pressure on the receiver side of the valve. Reed valves also have very low mass, short movement, and seal based on the air pressure across them. - Almost ideal for most small compressors. 
Pneumatic noise is the biggest cause for concern with compressors, usually intake noise as the "vacuum" in the cylinder opens to air, sucks air in then closes the reed valve rapidly. This rapid closure causes a very short period shock wave (positive pressure wave?) to be generated at the valve just prior to closure of the valve, when the mass of air column moving towards the valve then sees a "closed door" and builds the pressure wave further - which then travels at the speed of sound back up and out of the intake. Not "Valve" mechanical noise but Dynamic gas pressure shock wave noise created by the valve operation. A Helmholtz resonator adjacent to the intake valve can be tuned to the mass and frequency of the noise and make the compressor close to quiet. But it is added cost to an otherwise cheap and simple compressor, so no-one bothers!
Try modelling that on your existing compressor and making it quiet?
I considered doing it on my 90dB compressor until I realised the intake valve was a reed valve on the top of the piston, with air drawn through the piston (to cool it? or just design for "Cheap manufacturing"?).
But using a mechanically timed valve you should be able to tune the timing so the valve closes just when the pressure difference across the valve is zero - and thus reduce the initial "kick" for a valve that is closed by pressure difference. This does NOT eliminate the air-column shock wave when the valve closes though. A Helmholtz resonator does that.
Food for thought...?
K2


----------



## vederstein (Nov 1, 2022)

Steamchick said:


> An observation on valve "pressure noise" and air column dynamics



Is there some engineering subject that you don't know?!?!?!

Anyways if I read your comments correctly, you're saying the inrush of air when the intake valve opens is the cause of the noise.  I can see that because it will take a certain pressure differential to counteract the spring tension on the valve.

As far as my compressor concept goes, I may have half of that issue resolved, being that the valving is based on the rotation of the cylinder body and not on a check valve.

When the piston completes its push stroke, there's a dwell between the cylinder being the cylinder being open to the receiver and open to atmosphere.  Once the cylinder is open to atmosphere, there will be an out rush of compressed air from the cylinder to the outside world.  If the entire cylinder volume + internal passageways is determined, it's possible to open the cylinder to atmosphere just when the pressure in the cylinder reaches atmosphere thus minimizing the an air out rush.

This would greatly decrease the efficiency of the compressor and may be a step too far.

I'll need to study this a bit more and determine the impact.

Thank you for the thoughts.

...Ved.


----------



## Bentwings (Nov 1, 2022)

Richard Hed said:


> very clever design . Our shop has probably the loudes compressor ever made  it’s almost like running a top fuel engine in the shop  you can clearly , loudly running even when table sawing  big wood  now on the other hand I have a California air compressor at home that you can barely hear running in the next room  it’s actually two cylinder but only runs about 2/2  normal speed the intake is nearly silent  using the air blower is far noisier    Running air to a couple of my steam turbines creates higher db noise I YHINK it’s the high frequency whine that dominates the noise level  I’d suggest some kind of baffled maybe with a foam or paper filter  air intake
> As i understand it, step-down transformers are not used in the modern TIG welders, it is all done electronically.  That means there can be much greater control.  I have a transformer type TIG welder in which one has to strike the arc like a match.  It was one of the "new" ones made for small businesses back in 1980.  I got it for a Lincoln 250 welder.  The linconln is very nice, -- infinitely adjustable from 30 to 250 amps.  But the TIG welder is COMPLETELY basic.  I used it for a bit of practice then put it away as too difficult to use and control unless I absolutely HAD to use it which I never did need.
> 
> However, last year I bought a newer model, controlled and run by electronic methods.--that is, the new type of TIG machine.  Many years ago, I learned to always check the % duty rating.  IMNSHO, one should always try to get 100% duty rating so there need be no down time.  If you are working professionally, this is a must.  If hobby work, not necessarily a must.  Also, this 100% refers to the higherst setting you can weld with.  If you are welding at 200 amps, then your machine has a 40% duty cycle.  If you are welding at a more likely setting of 40-120 amps, your duty cycle is longer, say something in the order of 60%..  If you are welding at 40 amps, your duty cycle is probably around 100%.
> ...


----------



## Steamchick (Nov 1, 2022)

Hi Ved.. "Is there some engineering subject that you don't know?!?!?!" - A hell of a lot!! 
But I have worked on car engine design (and had a few weeks training in the Japan Design office) - which covers a multitude of sins. The visible sins are discovered by mechanics the world over, especially all those who know better and are not constrained by Legislation, Sales and Manufacturing departments' limitations, customers, accountants, etc. - but those guys usually know a hell of a lot that I don't know. - So I listen to everyone... 
e.g. the design engineer will fit Helmholtz resonators, until the accountants (cost experts!), or aftermarket mechanics decide to remove them for some purpose. - After all, what is a bit more noise? - when the customer isn't happy with an "aged" car he'll buy a new one. - Which sounds quieter.. because it has the Helmholtz resonators that keep it quiet... Same with exhaust "silencers". To make after-market parts cheaper, the "luxury" bits of silencing are omitted as they were just there "to get the car through the homologation test" - and not "necessary" to the after-market customer. The fact you may lose 1% of fuel economy in the process or make the Ozone layer dissolve just a tad quicker, isn't seen by those accountants who make the bits cheaper!
And don't ask me about tyres. I am not an expert. But the tyre makers only sell (the best) 20% of their tyres to car makers, because the (Poorer quality) 80% go to after-market sales, where price is paramount... They will make a small loss on the 20% OEM just to get the brand name and size, etc. on the car as new. And the original performance required by the Designer is met by those 20%.... The rest are simply rejects, sold at a whacking profit - because they can. Ever tried a non-original branded tyre on your car and noticed the difference? - Hard to spot except the name. But 2~5% MORE fuel consumption, 3dB MORE noise, 5~10% GREATER stopping distance (You only measure that when you crash), etc. are factors that make those cheaper. (And I stress "More" for "less money").
But that's how the world is going around at the moment. 
It is my ambition to become a knowledgeable Engineer in many subjects, but so far succeeding poorly.... Which is why I read many of these threads! - Simply to learn.
Thanks for asking. 
K2


----------



## Steamchick (Nov 1, 2022)

Oh Ved, I leave it to you and other experts to filter out or correct my errors, wrong statements, Junk, Rubbish, simple B.S., etc. as I REALLY don't know what I am talking about half the time... - But I try to learn from some of my mistakes.
I cannot take offence from any corrections from you lot. - I simply enjoy all the expertise available here.
K2


----------



## Rocket Man (Nov 2, 2022)

Before I retired work had a 60 hp piston air compressor it was very quiet for a piston type compressor, it compressed air on both sides of the piston, top & bottom.  I'm not sure how efficiently is determined but it was very efficient for a piston pump compressor, we only serviced the valves about once every 10 years & ran good for 20 years and was still in good running condition.  Then the company was convinced an industrial scroll compressor will be more efficient and same money so the old compressor was replaced but left in place to be a back up compressor.  The new industrial scroll compressor was loud like an airplane jet engine.  No more piston stroke sounds just a jet engine sound.  I think most of the jet engine sound came from the high speed cooling fans.  The scroll compressor had to be serviced more often to make sure it has oil and cooling, etc. it also had safeties that turned it off if there is a problem.  WE had people that were trained to service the industrial scroll compressor.  The industrial scroll compressor self destructed after 1 year and was replaced the 2nd new industrial scroll compressor ran good for 6 years.


----------



## Steamchick (Nov 2, 2022)

In the 1960s I worked (Saturday mornings and holidays) as a school kid at an Engine Machine shop. They also serviced some large Broom Wade compressors for a Paper Mill. 10 inch dia pistons, 2 ft stroke, and the annual service was oil changes, then simply to clean valves and fit new carbon (3- piece) piston rings. They were about 20 years old? Like steam engines.. They were double acting with cross-heads. I machined the cross-head castings on the huge lathe in the workshop. Measured diameters with the large micrometer, checking from above and below as the large micrometer changed size depending on whether you offered it up or down the the job. True size was the mid-point of the 2 measurements. They lasted to the end of the Mill in the late 1980s. But I never saw them running to know the noise....
K2


----------



## Toymaker (Nov 2, 2022)

About 6 months ago, another forum member, dazz, suggested I look into building a Guided Rotor Compressor (GRC).  At that time, I had already finished building my wobble plate compressor and therefore had no need to build another, different compressor, which I had never heard of.

Ved, I know you want to do your own design, but since you're still in the design phase, you may want to consider using the GRC as a basis for that design.  I've not been able to find an animation showing how the various parts move so I can only guess at how the rotor moves around inside the outer case.  I suspect the yellow circles in the drawing below represent roller bearings,...but that's just a guess.   I also suspect that there are no moving valves, but rather only intake and outlet ports,....but again, I'm guessing.

Perhaps another forum member can supply more details about how the GRC works.  Where are the in and out ports, etc.


----------



## Steamchick (Nov 4, 2022)

This design is very similar in principle to the trochoidal oil pumps on the end of the crankshaft on most modern cars. Intake ports are oestrogen when the chamber expands, and outlet ports open when chambers are reducing volume. Disadvantages are the tight tolerances of clearances required (10 x tighter tolerances than regular home workshops). All the leak paths are difficult to seal for leak rate to LP from HP.
K2


----------



## vederstein (Nov 4, 2022)

Looks similar to a gerotor.  I designed a hydraulic pump once using one of these.  I was trying to get 1000psi.  Only when I started violating the recommended tolerances did it put out the required pressures.  Strangely, I had to put in more clearance than what was recommended by the gerotor manufacturer to go from about 750psi and make the full 1000psi.














						Gerotor - Wikipedia
					






					en.wikipedia.org


----------



## ajoeiam (Nov 5, 2022)

vederstein said:


> Looks similar to a gerotor.  I designed a hydraulic pump once using one of these.  I was trying to get 1000psi.  Only when I started violating the recommended tolerances did it put out the required pressures.  Strangely, I had to put in more clearance than what was recommended by the gerotor manufacturer to go from about 750psi and make the full 1000psi.
> 
> View attachment 142098
> 
> ...



I'd be  right curious as to how that pump was actually 'made'.


----------



## vederstein (Nov 5, 2022)

I designed that pump about 20 years ago and the company went bankrupt since then.  I don't have access to any of the design files anymore.

A quick search and the actual gerotor manufacturer was Nichols-Portland which is one of the many divisions of Parker-Hannifin.   I remember they published a design guide back then. Perhaps it's still available.

...Ved.


----------



## vederstein (Nov 5, 2022)

I worked a few more hours on the pump design.

The pistons are fairly simple, but being that the internals will be oiled via splash lubrication, I added some weep holes in the side of the piston so oil the cylinder walls between the piston.






I had to play around with the geometry to keep eliminate some interferences, but it's coming together.  I also fixed the inlet and outlet valve porting and I until I realize I screwed up somewhere.

I have the air intake on the radius of the pump.  The air outlet is out through the center of the crankshaft.






And now the standard computer rendered video:





Your browser is not able to display this video.





Until next post.

...Ved.


----------



## vederstein (Nov 13, 2022)

With the pump essentially figured out, it was time to mount it.  I want to use a 56C frame motor which is an industrial standard for face mounting of motor accessories.  I can direct drive the pump off the motor shaft and then support the crankshaft fast with some bracketry:










Your browser is not able to display this video.


----------



## vederstein (Nov 19, 2022)

I went ahead and made the drawings for this design.  Usually, I don't publish until I make the first one, but being that I'm sharing the entire design process, I'm posting draft drawing set.  I'll re-post the design files after I make the prototype, but the attached .zip file is what it looks like before I build it:


----------



## vederstein (Dec 29, 2022)

It's been over month since I've made any posts concerning this project.  As you can see in the following photo, I have been making some progress.  In the manufacturing stage, I've noticed a couple of design errors and/or manufacturability improvements.

The crankshaft really took some planning prior to making chips because the thread pattern in the end of the shaft must be "clocked" correctly to the radial ports.  Thus I created a jig (triangular part in the upper left of the photo) so I could put the threads in the end of the shaft then remove when resetting the mill, keep my orientation correct.

I screwed up one of the three pistons and I'll need to remake that component.

I guess that's it for now.

...Ved.


----------



## Bentwings (Dec 29, 2022)

I have a California ultra quiet air compressor actually the harbor freight knock off . While not high volume  itbis so quiet that you can sit right next to it and hardly Lear it run . My son has a larger on that is only slightly more noisy .  I YHINK these are two cylinder  but short stroke there aren’t any drawings of construction . Someone posted a video  on you tube of a disassembled one  they really don’t have reed valve. I think they are more automotive engine construction , can driven piper valves . I’m not sure  but even a big v 8 car engine doesn’t  make a lot of noise even cranking with a starter  with plugs removed. I would think a iston valve engine might be very quiet too as an alternate.  There is a certain amount of noise on the intake side but that is easily quieted by air cleaner


----------



## vederstein (Dec 29, 2022)

Th actual CAC model is made in China anyways.  I wonder if they're made in the same factoey.


----------



## Steamchick (Dec 30, 2022)

Bentwings suggests silencing of intake noise.... This is best achieved with a Helm Holt Resonator. When you know the volume of air per cylinder stroke/suck, and the frequency (from rpm) the calculations are simple and found on the web.
As revs and displacement are constant, a single resonator, correctly sized and positioned, will considerably reduce intake noise to "quiet"....

K2


----------

