why are direct drive compressors loud?

[pondy]

can any body tell me, always seen people mention it but after searching Google I am unable to come up with an answer. may be a simple answer or stupid question but I cant see how linking the motor and pump with a belt effects the noise over putting the motor right onto the pump?

I have the bellow compressor, had it for over a year, spot on for my needs but its noisy

http://www.ebay.co.uk/itm/New-Rhyas...Air_Tools_and_Compressors&hash=item5af3cb1fe8

the motor and pump are isolated with the plastic/rubber pads. I read that that the noise is from the intake? and you can add a hose an put a filter on the end to isolate the intake? was thinking of trying this on my compressor, with the right fittings on the head, run 2 large hoses with filters on the end away some were else in the garage, is this going to improve things?

 

[shenion]

The belt absorbs some of the vibration; mainly the AC hum in the torque of the motor.

Direct drive = cheap. So, the pump/motor are not balanced and shake like crazy. I picked up a 1.5HP direct-drive pump motor and bolted it to my old 20 gallon tank. It literally walked across the floor it shook so bad.

 

[Daz1968]

Direct drive compressors run faster than belt driven.

 

[MattF]

I read that that the noise is from the intake? and you can add a hose an put a filter on the end to isolate the intake? was thinking of trying this on my compressor, with the right fittings on the head, run 2 large hoses with filters on the end away some were else in the garage, is this going to improve things?

There's some noise from an intake. Nothing earth shattering though. If you want to kill noise, isolate the motor/head unit from the cylinder completely. That'd likely be the best single change you could make.

 

[normspanners]

There's some noise from an intake. Nothing earth shattering though. If you want to kill noise, isolate the motor/head unit from the cylinder completely. That'd likely be the best single change you could make.

Exactly right I fitted a new pump to mine I used twice the size, but half the speed, direct drive unit, light enough for it still to be portable, I rubber mounted the pump on the tank on exhaust mounts, it is now less than half the noise it used to be.
PS I used a coil of copper pipe from the pump then a hydraulic hose to the Check valve.

 

[shenion]

On the 20 gal tank I put the cheap direct drive unit on, I cut up an old mousepad into squares and drilled a hole in. Stacked several layer under the motor and a few more under a washer on the bolt. It no longer walked around the garage and was quieter.

 

[mylesdw]

I think it's mainly to do with the revs they run at. A cheap 2 pole synchronous motor runs at nearly 3000 rpm and directly driving a compressor at that speed makes it pretty loud. By contrast my compressor has a four pole motor, spinning at under 1500 and belt drives the compressor at at least 3:1 reduction so 500 rpm instead of 3000.

 

[Wallace]

Using the motor direct there is less torque available so the compressors need to be a smaller capacity (smaller bores and shorter strokes) relying on the rpm to achieve similar cfm outputs to the belt drive.