How Loud is your Roots Blower

[turnpointdesign@rockisland.com]

I just finished piecing together a roots blower to a 5 hp single phase motor. When I turned it on the pump was incredibly noisy! I don't have a way to measure decibles, but it is painfull to get within 20 feet of it without hearing protection.
I was wondering if this is normal or if there is a problem with my pump? Right now the blower doesn't have a muffler on the exhaust side and has a filter on the intake side. The 5 hp motor is pulling 17 amps @ 241 V when running unencombered (1" mercury of vacuum) and is pulling up to 22 amps when I start to block off the intake (and the vacuum gets down to 15" mercury).
Is this much draw and noise normal? I may put a smaller pulley on the pump to decrease the rpm of the blower and thus the draw of the motor but what can I do about all the noise?

[ron brown]

Brandon,

Much of the noise of a "Gimmy" engine is the Roots blower pulling air through multiple filters. The exhaust is probably louder. IRRC, many Roots blowers have straight lobed impellers - which would be even louder.

A good muffler box might be built but will be expensive and might not properly quiten such a device.

Ron

[gerald_d]

"I may put a smaller pulley on the pump to decrease the rpm of the blower" If you want to decrease the speed, you need a smaller pulley on the motor.

[fleinbach]

Or a larger one on the blower

[brandon@blueotter.com]

Thanks Ron,
I have ordered a muffler for the exhaust (Grainger). The muffler is claimed to take 5 decibels off but that won't be enough. I am building a box with a few layers of soundboard inside and plywood outside. I wish I could afford the real soundproofing like what they make for the engine rooms of large powerboats.

The exhaust will be directed across the pump and motor before going through a series of baffles. The hard thing will be getting to the pump for cleaning the filter and changing the oil.... But I can't live with that much noise so I have to do what I can.

Has anyone measured the noise of their roots blower with a decibel meter? And what do most people do with these things?

[simon]

Brandon
keys to soundproofed boxes are as follows.
1. Heavy weight of walls and glass
2. Double walls and glass (or triple even better)
3. Ensure nothing is parallel to anything else in the room. Better a quadrangle than a square, better not regular shaped.
4. When double glazing, ensure one end of one glass is a few millimetres out of parallel with the other.

- Stuff I picked up at the BBC.

[brandon@blueotter.com]

Thanks Simon.
Some interesting advice... I never thought to make the walls unsquare. But it does make sense.
I have been really researching the noise problem with roots blowers and found that all of the commercial prebuilt roots systems have very large exhaust silencers to deaden the throbing/pulsing of the exhaust air. I found a company that makes them ($800) and had the idea that the noise coming from the roots blower is very similar to the noise that will come from an engine (minus the muffler). So I went to my automotive store and bought a large muffler ($38)and IT WORKS GREAT! Now the noise is bearable. It was about a 15 dbs reduction in noise! But I still need hearing protection to be around this So the next will be to mount this whole contraption into a soundproof closet that I built for my dust collection system... I am putting the door on it and baffling system in it today...
But the automotive muffler worked great, It is a "Sanford and Son" solution, and my wife laughed at me when she saw it, but it works.