Tom Miller wrote:
I've used Broomwade compressors in the past and found them very reliable.
If the price is good enough, you could replace the motor on the compressor
with one that is as big as you can power, then adjust the speed of the
compressor by selecting pulleys to load the motor fully. As long as you
have sufficient speed to pump the lubricating oil, it will last for ever at
the lower speed. ( It will also be quieter than a high speed compressor)
You might try getting onto Compair and ask them for the minimum speed and
horsepower requirements at that speed.

Tom

I gave CompAir a call and they were very helpful. They sent me a full
specification sheet for the BroomWade AC41 compressor. The minimum
acceptable speed is 460 rpm, whereas the normal speed is 710 rpm. Using
the table in the specification sheet I would need 5.3 hp to drive it at
460 rpm with a delivery pressure of 120 psi. This would give me 15.7
cfm. Probably I would need a 7 hp motor to be safe.

I think unfortunately 7 hp is pushing it from our single phase supply.
At the absolute maximum we can get 230 V 45 A. I know this is about 10
kW but I suspect the motor will overload the supply when starting. My 5
kW welding set makes the lights go dim in the house. I also spoke to a
helpful guy at a local compressor repair shop who thought I'd be pushing
my luck to drive this machine from a single phase supply. If I had a
three phase supply I'd jump at it because it would be a cheap way to get
a big compressor, but I think the only way I could power it here is with
a diesel engine. If I'm going to have a diesel compressor I might as
well buy a jackhammer compressor and have the convenience of being able
to tow it around. Unfortunately it seems just a bit too big!

I did spot this Bristol compressor on eBay which looks nice though, and
I've e-mailed the seller for a few more details:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=7980508669

This compressor is probably a more manageable size, but it's a pity it
isn't vertical.

I think I'm probably needing a compressor in the 2-4 hp range. Harold,
I'm interested in your suggestion about a blast cabinet. I probably
can't afford one now but would be interested in buying one in the
future. How much air does a small blast cabinet need? I've also always
wanted to have a go at hot riveting using an air hammer (hot riveted
benches and chassis look so nice), so you can see I'm thinking of more
uses for a compressor all the time. I also found an Ingersoll-Rand die
grinder which apparently consumes 43 cfm! This is probably extreme, but
I see your point about lots of air being useful.

Thanks for all the suggestions.

Best wishes,

Chris