Compressor rating question

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Indeed, a pity! But that is pretty large. Assuming you had the space, and the proper electrical service to handle it, it would be an excellent choice, for it would handle most anything you might desire to run, including a nice blast cabinet, but it presents some serious issues for home use. I'm not up to speed on how things are wired in the UK, but here in the States, it would be a tough one to run without 3 phase power. Running it on diesel could prove to be a serious nuisance, and would be quite expensive as well. I agree----you should seek something smaller, 5 horse max, in my opinion.

Unfortunately, I'm not familiar with the shark saw of which you speak, so I don't have an opinion, but I can't imagine you couldn't run a die grinder, at least intermittently, with a 2 horse compressor. Frankly, I would think that your choices begin with a 2 horse compressor, and get more reasonable as they approach a 5 horse, so you're likely on the right track. Perhaps someone with a 2 horse could chime in and relate their experiences.

Harold

Sorry, forgot the link. This is the 2 hp compressor I was looking at:

I've just had a nasty thought about it though. The seller says it has a

2850 rpm 2 hp motor. Is there any chance a 1 hp 1425 rpm motor could have been replaced with a 2850 rpm 2 hp motor to increase the output? I've never seen a compressor with a 2850 rpm motor before. Apparently this machine is 2 cylinder and each cylinder is 2" bore by 2" stroke. Also the receiver looks a little rusty, but the machine is cheap. Might want to get a hydro test on it?

I'll think about the big Broomwade compressor. I have no problem with a

5 kW welding set in our workshop, so I might get away with a 10 hp compressor. It would have to have a small receiver though. Will think it over. Fortunately I'm not in a hurry...

By the way, the saws are made by

and are cheap because the fire service are selling loads. They need 5 3/4 cfm at 75-90 psi.

Best wishes,

Chris

Thinking about it again this morning I think I'll pass on this one too. Looks a bit too dodgy even for me!

Chris

Thinking about it again this morning I reckon I'll pass on this one too. It looks just a bit too dodgy, even for me!

Chris

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You certainly have a good point. I looked to see if the driven pulley was evident in the picture, and it isn't. Makes one think it very well could have been replaced with a smaller one, or it has, indeed, had a faster motor installed. I have no idea how you would know unless you could find a like compressor, or literature pertaining to it.

A hydro would probably be a good idea for any pressure vessel that is old, although I'm not following my own thoughts. I have never pressure tested my tank, and it's over 35 years old now. Shame on me! They are known to fail catastrophically, although not routinely.

Finding the appropriate motor would be my only concern under that circumstance. You'd never regret having the large compressor, of that I'm quite sure.

Armed with that information, I can't imagine a 2 horse wouldn't power it well, although the compressor may have to work almost full time. My 5 horse is rated @ 19+ CFM @ 175 PSI. Assuming it would produce 2/5 of the output mine does, it would be well within specs. Still, overall, you'd be happier with the larger head, long term. Besides, if you like to restore old things, you'd really enjoy a blast cabinet. It's one of the better ways to remove rust or old paint. I use mine routinely for such things. I've owned a blast cabinet for something like 35 years and wouldn't be without one. I use either glass beads, or aluminum oxide, each of which does an outstanding job, depending on what I'm trying to accomplish.

Nice looking saw, by the way. Very much like the Milwaukee Sawzall, only it's electric instead of air.

Harold

I'm cheering for the 10 horse unit, Chris, if you think you can make it work.

Harold

You can always run a large pump more slowly with a smaller motor pulley or maybe a jackshaft. Larger pumps running more slowly tend to be more efficient, providing that friction and leaks aren't excessive.

The 41 CFM is probably displacement, the 32 CFM delivered SCFM at rated pressure. This could be a nice unit with a 3 to 5 HP motor.

5 hp 220-volt single-phase motors are readily available. Even with 3 HP I think you'd have puhlenty of air with the Broom & Wade.

Lower speed operation is also usually quieter.

A 2850 RPM compressor will drive you bonkers with its noise.

Absolutely! One of the things I really hated about my first compressor was the fact that it ran fast and was terribly noisy.. It was more noisy at

3/4 hp than the 5 horse Quincy. Slow is definitely better.

Harold

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

experiences.

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:

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

Just another quick question. On the Bristol compressor I spotted on eBay I see a pipe leading from the crankcase to the cylinder.

Anyone know what this is for? Is it for pressure lubrication or does it mean the compressor is double-acting? Just curious.

Best wishes,

Chris

something to do with the shutoff, mine has the same

No, that looks like a s>I think unfortunately 7 hp is pushing it from our single phase supply.

A 240V single-phase 45A service in the UK would translate to a bit smaller than the USA small residence service for a old house, where you get 120/240V at 50 to 70 amps or so. Definitely NOT enough to run any sort of home shop equipment from at the same time there are residence-type loads being run.

Let the Missus ;-) start doing a few loads of laundry (washer, dryer, iron), start lunch (toaster) and run the air conditioning, and when the 5-HP motor for the air compressor kicks on out in the garage you are going to pop the Main.

You might have to break down and do a service upgrade on your house, or if you are renting you might have to find a new house with a more modern service. Or talk the landlord of your existing rental house into doing the service upgrade, and you figure out an equitable split of the electrician's bill with him - you get the extra power to use while you are living there, and it is an improvement that will raise the property value.

(I'd make sure the lease has enough time to run that you get your investment back through usage, or agree on a pro-rated buy-out of your part of the investment if he wants to terminate a lease or a month-to-month rental agreement before three to five years pass.)

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Harold,

My cabinet isn't real large----20" deep and 31" wide. It has a small gun with a carbide nozzle, which I recommend highly. Ceramic nozzles have a very short life span, especially when blasting with aluminum oxide. Much better life with glass beads, however. This small cabinet keeps my 5 horse compressor running almost continually when I have my regulator set at approximately 100 PSI. (For your convenience, the compressor is rated @

19+CFM @ 175 PSI). Using that as a guide, I'd suggest you not go under a serious 4 horse compressor unless you don't mind blasting for a while, then allowing your tank to recharge. You'd likely use air faster than you could provide it. Search your soul well and decide how large you can possibly accommodate, and make sure you can buy a single phase motor to power it. Large single phase motors can be a serious problem, both in current demand, and in availability. You reach a point where 3 phase becomes almost mandatory.

Harold

I can't imagine it's for a double action, but I can't see a good reason for it, either. Smaller hydraulic lines typically run to unloading valves, but I can't see how this one would work in that capacity, although it could have some strange internal porting. I'd be interested in learning what purpose it serves.

Harold

To clarify, the 45 A supply is for the workshop only. However, the 45 A is drawn from a 100 A supply in the house.

Best wishes,

Chris

Thanks for the information. I reckon 4 hp is the most I can power from my supply. I'm tempted by that Bristol compressor on eBay. It's cheap and the seller seems pretty knowledgeable. He said he bought it with the intention of fitting a single phase motor, but never found a suitable motor. Apparently he tried a 3/4 hp motor but it wasn't big enough. The receiver is 150 litres, so I'm guessing it might need a 2 hp motor? In terms of dimensions I don't want anything much larger than this, but maybe I should keep searching for a vertical machine. Will keep thinking...

Thanks for the help,

Chris

thinking...

Don't confuse receiver size with horsepower requirements, Chris. What matters is the power it takes to spin the compressor at a given speed. Receiver size dictates how long the compressor will run to build turn-off pressure, nothing else. By cautious when making your choice.

Harold