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  1. #1
    Join Date
    Nov 2007
    Location
    Perth
    Posts
    44

    Arrow *QUIET* air compressor

    I've got an odd job :

    We have a large (~800L) glass tank used as part of a commercial display. It has bubbles of air forced out of a perforated tube at the bottom.

    This job was previously done by a piston style aquarium air pump (located some way away). Sadly we've found these pumps quite expensive (in the $100's when we first bought it), loud (vibrates) and unreliable (constantly changing flapper valves and seals). It only does two 10 hour shifts a week!

    I tried our cheapo direct drive 2HP / 40L air compressor (normally for dusting / spraying / nail gun) at 15 psi and its great. It charges for around a minute and cycles every 3-4 minutes.

    The only downside is its still pretty loud.

    And now the questions :

    * Are the belt drive really that much quieter?
    * All the noise come from the air filter intake - I see some companies supplier "silencer" intake filters - are these really worth it?

    My gut feel is to buy slightly larger 2.5HP belt drive (sadly Bunnings don't do belt drives but SuperCheap, Repco and all the local air tools shops do) with a bigger tank and try that.

    Any comments or suggestions?

    Cheers, Antony.

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  3. #2
    Join Date
    May 2003
    Location
    Perth WA
    Posts
    3,784

    Default

    The belt drive still wont be as quiet as the aquarium pump. The only way to make a compressor quiet is to make a sound hood. No need to go to extremes as a simple MDF box or even cardboard box over the unit will make a big difference. If you want to get fussy carpet the box and this will help a little but I think the MDF will do the job you want. Just watch for heat build up but it should be OK.

    If you want to test the intake silencer idea then just make a small box out of polystyrene packing and cover the inlet (air cleaner). Make sure the inlet is at right angle to the intake of the air cleaner. Sound waves don't like turning around corners. This will give you an indicator to how much noise can be removed.
    Cheers,
    Rod

  4. #3
    Join Date
    Sep 2007
    Location
    Finland
    Posts
    360

    Default

    Hi,

    How about these, aquarium air pump offers collected from Oz eBay: http://www.e-aquarium.com.au/buy/air-products/air-pump

    *************

    Jun-Air compressors are the most reliable and the most silent there is. They are one of the most expensive ones too, but worth every cent if reliability with low sound level is an issue. Medical care units like them as much as precision airbrushers, not to mention ordinary nailgunners like me, too .

    kippis,

    sumu

  5. #4
    Join Date
    Nov 2004
    Location
    Santpoort-Zuid, Netherlands
    Age
    67
    Posts
    462

    Default

    Sumu is right, for my illustrator's jobs i regularly used airbrushes (now it's all digital) and the Jun-Air compressors are the most silent ones around. In a studio we used one, but at home i had a smaller and cheaper Italian Sil-Air. They are all operated on the principle of the fridge compressor. Relying on the working parts of a household appliance sounds a miserable solution, but is in fact rather brilliant.

    The motor hangs in springs inside the total enclosure. It has its direct drive little piston and butterfly valves in top. The piston intake draws from the enclosure volume, the piston outlet has a copper tube (wound like a spring to enable it to absorb motion from the spring hung motor) that leads to the outside. The motor even hangs in an oil bath. The stator windings are cooled by this oil, their heat is transfered by the oil to the metal housing. There is spatter lubrication going on inside and there are holes and canals drilled in the axle all the way up to the piston rod and top bearing, to provide some sort of pumped oil lubrication like the principle used in combustion engines.

    Because of this very good and intense lubrication system, a fridge compressor only needs sleeve bearings. Often the steel axle runs just in simple cast iron bearing surfaces, without any bronze bushes or sintered alloys in between. Still, a fridge compressor runs many thousands of hours in its lifespan years , without an oil refill or any other maintenance. This is because the system is a sealed and closed loop, no dust and dirt can enter because there is just the coolant gas running round and round. Soiling of the oil only comes about from within, from tiny worn-off particles from bearings or piston and cylinder surfaces.

    This principle also works very well for compressing air, but the air must be sucked into the enclosure and blown into the tank, it is no longer a sealed and closed circuit. Moisture and chemical traces in the air can cause erosion and dust and very fine gritty parts can cause soiling and a higher degree of wear. That's why fridge compressors for quiet little air compressors have a good intake filter and an enclosure lid that can be opened for inside inspection. They also have the need for regular oil level checks, since oil is lost through evaporation into the airflow. The soiling of oil by intake air can cause lubrication problems through clogging and residu can accumulate in the oilbath. Therefore, a silent fridge type air compressor needs oil changes like the large types with visible cylinders do.

    But the spring suspension and the perfectly lubricated sleeve bearings make for a very silent running. The Jun-Air compressors can be seen as a heavy duty version with much more yield. Whereas a small fridge has a motor ranging from 90 to 135 Watts and large storage type freezers have motors of 180 to 250 Watts, the Jun-Air compressors have motors upwards from 340 watts, often in twin-motor configuration. They are superb and very durable.

    greetings

    gerhard

  6. #5
    Join Date
    Nov 2004
    Location
    Santpoort-Zuid, Netherlands
    Age
    67
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    462

    Default

    back with some pics

  7. #6
    Join Date
    Nov 2007
    Location
    Perth
    Posts
    44

    Talking

    There's no Australian distributor of Jun Air that I can find. I'll keep searching / watching eBay.

    Given I can get a 2.5HP air compressor and put it in a silenced box (I've got a stack of anticon about) all for less than $200 its pretty hard to resist as an option.

    Cheers, Antony.

  8. #7
    Join Date
    Nov 2004
    Location
    Santpoort-Zuid, Netherlands
    Age
    67
    Posts
    462

    Default

    hi Antony,

    yes, that can't be beat; the smallest Jun-Air compressor costs about twice as much.

    The silencing of machines begins with the machine itself, the custom built enclosure comes after that. With a belt drive external cylinder compressor, only the silencing of the air intake pays off . The standard intake filters are very cheap and simple and often far too small. By changing this for a better type, some improvement can already be had. Special silenced intake filters are sold, these will shave off a few deciBels of the total noise level.

    The rest of the compressor system is hard to silence. The motor noise is the total of fan noise, bearing noise, mains frequency hum and rotor bar whirr, all of which are hard to make more silent without disturbing their function. The belt drive is relatively quiet (provided it's a smooth V-shaped and not a toothed belt). Far more noise comes from the piston system (bearing play in big end and piston side bearings, play in piston rings) and from the valves (butterfly valves which, although reasonably quiet, can be heard nonetheless). Budget compressors are more rattly from new than the expensive long lasting cast iron German or Swiss ones are, even a total taking apart and rebuilding will offer hardly any results. So a silencing of the air intake is the only effort worthwhile.

    Please note that a hood type silencing box seems attractive because of simplicity and price, but it traps hot air inside. This reminds me of a printing shop's roller washer i once changed the motor of. This machine was a sort of washing basin combined with a system of wheels and brushes. The basin was filled with a solvent and soiled rollers from the printing press were laid on the drive wheels. The motor was switched on and the rollers were spun quickly around in the solvent and along the stationary brushes. You let this thing run for some 15 minutes and even the toughest dried up printing ink residue was effectively removed from the rollers.

    The original motor was burned because of overheating, which we didn't understand since the load was very light. The replacement motor also burned, within a few months. The system ran friction free, we couldn't find any obvious cause. But the motor was mounted underneath a hood, which was totally closed from above to prevent solvent from the basin spilling onto it and catching fire. We didn't suspect this hood to be the cause, since it had a totally opened bottom. When looking underneath, the motor was entirely visible. But still, the motor proved to recycle its own cooling air. This air was trapped underneath the hood (warm air rises) and no cooler air was allowed in to mix with it. So even in an almost half opened enclosure, the motor still burned because of lack of cooling air. We made a sort of suction trunk for the motor fan through which it drew air from some distance below the hood's rim and it ran cool ever since. That simple.

    A compressor generates a lot of heat, the piston system may generate 5 to 10 times as much as the motor. Should you provide for a total compressor enclosure, the 1 minute duty cycles and 3 minute pause in between will heat up the air inside quickly. The sound damping is also an excellent heat insulator and the heat rise during the up-time will not cool down enough during the down times. Within 15 minutes the heat inside will mount to 50 degrees Centigrade or more, which will eventually damage the compressor motor. When the choice exists between an oil-free or an oil filled compressor, go for the oil filled one. Oil-less compressor use teflon cylinder wall coatings or piston rings made from similar low-friction and heat resistant subtances, which are known to fail sooner under extreme circumstances than conventional oil-lubricated systems do.

    The making of a quality sound damping box that also allows proper air circulation will be a challenge, like it is to make a good loudspeaker enclosure. Professional makers of silenced compressors and generator sets make use of labyrinth systems, through which passing of air is possible, but in which sound waves reflect against arrays of sound absorbing baffles. The link below guides you to a Atlas Copco product leaflet PDF, in which some cutaway views of such silencing hoods are displayed.

    www.classzero.com/doc/SF1-15.pdf

    Success and greetings!

    gerhard

  9. #8
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    7,696

    Default

    A long length of air line and park the compressor somewhere else.
    CHRIS

  10. #9
    Join Date
    Nov 2004
    Location
    Santpoort-Zuid, Netherlands
    Age
    67
    Posts
    462

    Default

    Haha, brilliant! That's the trouble with me, i could have thought of that but instead i write some stupid 5000 words about it

  11. #10
    Join Date
    Mar 2005
    Location
    Melbourne, VIC
    Posts
    64

    Default

    Check out today's trading post - trading-post.com.au
    There's one being sold in Victoria today (2nd hand).

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