Home made compressor

[Rick]

I'm after a new compressor for my new workshop, being single phase i'm struggling to get anything decent.

I currently have a Vtwin 3hp compressor with a 100l tank.

I was thinking about buying another 1 or 2 compressors the same and having a big auxiliary tank they all feed into. To make the tank I thought about using some 300mm pipe, 3-4 meters would give me 200-300 litres extra.

A rough calculation and my compressor seems to be about 4cfm-5cfm at 90psi. Rather than the claimed 12cfm.

I think with 12cfm and 300-400litres i'll have plenty of air.

I'm just wondering if something like this, would be better.

http://www.machinemart.co.uk/shop/p...ump/path/air-compressor-pumps-pumpmotor-units

But i've a feeling it'll only have the same output at higher pressures.

I've got a healthy power supply to run 3 x 3hp motors, but obviously I cannot buy a 9hp compressor because i'm single phase.

I did think about buying a pump like this. and using 2 x 3hp motors with 1 belt on each to power it. But I think starting would be a problem.

http://www.machinemart.co.uk/shop/p...ump/path/air-compressor-pumps-pumpmotor-units

A couple of things I was wondering.

1. I know compressor tanks are relatively thick, but only to stop them rusting. If i use stainless steel to make the tank. 2mm should be plenty thick enough.
Has anybody made the own tanks? Without using propane bottles or something similar.
Has anybody made square tanks out of sheet metal? I'd imagine you'd need to make it very thick and brace it to deal with the pressures so it doesn't bow.

2. Am I better using 2-3 compressors, or 1 large pump with 2 motors. I like the idea of having 2-3 compressors with a large tank because if something goes wrong I still have air. I can also set them to come on at slightly different times to limit the surge.

 

[rtbcomp]

Not sure about the practicallity of making your own tanks, but I'd bet a pound to a penny it would be cheaper and easier to buy a couple of big compresssors ready to go than buy the bits to make one. You would be better off warranty-wise too.

You would also have to get the tank certified, which could cost as much as buying one!

You could connect the tanks together via valves so if you want to do a quick job with a small amount of air you don't have to fill a big tank, and you could isolate a machine if you need to remove it for maintenance.

To make them switch at different times simply set the operating pressures slightly differently.

 

[pedrobedro]

When compressors were expensive I built a little one from a lorry brake tank. All the parts needed will make it dearer than buying one now.

 

[Shox Dr]

With the greatest of respect, if you are even considering building a Square or rectangular tank then you clearly know nothing about the dangers. And would suggest you need to read up more before you go ahead.

 

[syborg]

building tanks is a dodgy job.

unless its keep outside in an explosion proof cage.

we do alot of insurance inspections at work on huge receivers some 1000 litres plus...

although their safe working pressure may high, their tested pressure is way way higher.

its all about the pressure vessel regs. i toyed with the idea of building a pressure vessle from a 45kg gas bottle, which is probably safer as they are rated and tested.

its just a case of getting the correct fittings as gas bottles seem to use a really odd imperial coarse thread type, some sort of npt or bspt.

if a receiver goes bang you will end up deaf at the least, plus the flying shards of jagged steel and fittings will tear u in half in a split second.

so if ya gonna make one try using 2 45kg bottles or more with non return valves fitted if u want to use them independantly.

i didnt tell u this,lol

peace

syborg

 

[Rick]

With the greatest of respect, if you are even considering building a Square or rectangular tank then you clearly know nothing about the dangers. And would suggest you need to read up more before you go ahead.

I asked if anybody had done it, I wanted to know the thickness of material used, a cylindrical tank could obviously be MUCH thinner. The rectangular tank would bow. With 10 bar you obviously get 10kg per square CM.

Not sure about the practicallity of making your own tanks, but I'd bet a pound to a penny it would be cheaper and easier to buy a couple of big compresssors ready to go than buy the bits to make one. You would be better off warranty-wise too.

You would also have to get the tank certified, which could cost as much as buying one!

You could connect the tanks together via valves so if you want to do a quick job with a small amount of air you don't have to fill a big tank, and you could isolate a machine if you need to remove it for maintenance.

To make them switch at different times simply set the operating pressures slightly differently.

I thought about buying a couple of big compressors. But you don't really get above 100litres and single phase.

Thats said, would i need more than 300litres total if i've got at least 12cfm of pumps.

building tanks is a dodgy job.

unless its keep outside in an explosion proof cage.

we do alot of insurance inspections at work on huge receivers some 1000 litres plus...

although their safe working pressure may high, their tested pressure is way way higher.

its all about the pressure vessel regs. i toyed with the idea of building a pressure vessle from a 45kg gas bottle, which is probably safer as they are rated and tested.

its just a case of getting the correct fittings as gas bottles seem to use a really odd imperial coarse thread type, some sort of npt or bspt.

if a receiver goes bang you will end up deaf at the least, plus the flying shards of jagged steel and fittings will tear u in half in a split second.

so if ya gonna make one try using 2 45kg bottles or more with non return valves fitted if u want to use them independantly.

i didnt tell u this,lol

peace

syborg

The tanks will be outside. Well enclosed but not in the main work area. I'd rather do nothing "dodgy" the pipe I had in mind is pressure tested and comes certified to 25,500psi. But it would obviously have the ends welded on by me.

Thanks for the help.

I'm actually thinking, 2-3 tanks piped together will be enough. The only other thing is the outlet from the tank, which seemed to be small and probably fairly restrictive. But I could upgrade this i'm sure.

 

[rtbcomp]

I have a Clarke 14 cfm single phase 150 litre tank, add two of these to your 100 litres that will give you 400 litres, I can't really see any need for anything bigger unless you fill them up on off-peak electricity.

I wouldn't worry too much about the outlet size on the tank, you'll have 3 in parallel. The one on mine is about 2 inches diameter.

 

[rtbcomp]

......
its just a case of getting the correct fittings as gas bottles seem to use a really odd imperial coarse thread type, some sort of npt or bspt.

........
syborg

Blue butane bottles are a weird size, it's a BSP thread but somewhere between 3/8 and 1/2. The best bet is to remove the valve, run a drill down it and solder a piece of pipe in.

Red propane bottles have a 1/2 bsp tapping so it's easier.

If you do use gas cylinders mutilate them by cutting the valve guard off or something so they will never get refilled, otherwise you could end up with a gas/air mixture inside.

Also mount them upsidedown so any moisture will get expelled, saves fitting a drain cock.

 

[Rick]

I have a Clarke 14 cfm single phase 150 litre tank, add two of these to your 100 litres that will give you 400 litres, I can't really see any need for anything bigger unless you fill them up on off-peak electricity.

I wouldn't worry too much about the outlet size on the tank, you'll have 3 in parallel. The one on mine is about 2 inches diameter.

I was going to buy all 3 the same just to make it easier for spares, and so the strain is the same on them.

I was just thinking the bigger the better on the tank. I've spent so long getting annoyed with the air pressure dropping off I wanted to go overkill.

 

[rtbcomp]

I was going to buy all 3 the same just to make it easier for spares, and so the strain is the same on them.

I was just thinking the bigger the better on the tank. I've spent so long getting annoyed with the air pressure dropping off I wanted to go overkill.

Sound policies.

Receiver size is always a trade-off, with a big tank it will take longer for the pressure to drop but then again it will take longer to recuperate.

If you have 3 x 14 = 42cfm I think you'll be covered for mosts tasks!

 

[brightspark]

u havent said what u are running of it and the air consumption required .it must be sumething large as u can run a 3mm nozzle of a 28cfm pump no bother ??

 

[Rick]

Sound policies.

Receiver size is always a trade-off, with a big tank it will take longer for the pressure to drop but then again it will take longer to recuperate.

If you have 3 x 14 = 42cfm I think you'll be covered for mosts tasks!

I did a quick calculation though, baised on the time it takes my compressor to gain 1 bar of pressure at 90psi. and mine was more like 4-5cfm at this pressure. still though, with double or tripple what I have now like you say I should be fine.

I guess the first thing is to try it then I can always add a tank with whatever means afterwards.

 

[eil]

If your compressor is only giving you 4-5cfm at 90 psi when the claimed cfm (FAD) was supposed to be 12 (9-10 more realistically) it would appear to me to have some wear issues, Your idea of using two motors to power a pump would be a natural train of thought of doubling the power, but ask yourself if you have ever seen this kind of arrangement anywhere ?. probably not, and the reason is, as I'm led to believe is one motor would be the driver and the slower motor would be driven, which would in fact make it a generator even though both of your motors would state say 1450rpm doesn't mean both run spot on the rated rpm.

 

[shenion]

4-5 CFM seem low. My compressor is about 15CFM displacement (displacement is never specified here.) I get about 10CFM FAD.

From empty, it averaged near 13CFM (measure time to fill 60-gal tank.) It is over 20 years old.

A few months back, i noticed it was taking a long time to fill. Found the head bolts had worked loose. Tightened and it worked fine.

On a 3HP compressor you should be getting 7-8 CFM FAD>

 

[Rick]

4-5 CFM seem low. My compressor is about 15CFM displacement (displacement is never specified here.) I get about 10CFM FAD.

From empty, it averaged near 13CFM (measure time to fill 60-gal tank.) It is over 20 years old.

A few months back, i noticed it was taking a long time to fill. Found the head bolts had worked loose. Tightened and it worked fine.

On a 3HP compressor you should be getting 7-8 CFM FAD>

I'll double check, but on 1 quick test I did it seemed to be around the 4-5 mark.

 

[Rick]

Just seen this,

18cfm (probably more like 12) but 4hp and single phase, i've never seen a compressor/motor this big of a single supply.

Its a bit more than i'd want to spend to buy 2, but on its own it might do the job, or i could add the compressor I have now.

http://cgi.ebay.co.uk/CLARKE-AIR-CO.../110561739724?pt=UK_Air_Tools_and_Compressors


I've just tested the compressor we have now.

At 90psi-105psi its 8.2cfm.

at 105psi-120psi its 6.8cfm,

At 120 to 135psi its 4.8cfm.

I've changed the cutoff switch down to 120psi as it dies after 110psi as you can see. The motor doesn't slow down, i'm wondering if the reeds/rings are a little worn, allowing some blowby at higher pressures.

Its very happy at lower than 90psi and breezes 9-10cfm.

I don't really know where to look to buy a compressor of quality rather than a clarke or something. i know clarke say british made, but they are VERY similar to some of the chinese stuff about. So they either got copied or are British assembled.

Edit, oh look, somebodies thought of my idea before. haha.
http://cgi.ebay.co.uk/Compressor-SI.../180493572229?pt=UK_Air_Tools_and_Compressors

 

[rtbcomp]

I've had one of these for years and it's done a lot of work with no problems:-

http://www.machinemart.co.uk/shop/product/details/se16c150-air-compressor/path/professionalindustrial-air-compressors-elect

One important thing is to go for cast-iron cylinders.

 

[Rick]

I've had one of these for years and it's done a lot of work with no problems:-

http://www.machinemart.co.uk/shop/product/details/se16c150-air-compressor/path/professionalindustrial-air-compressors-elect

One important thing is to go for cast-iron cylinders.

Do you struggle for air? Could you sand blast with it? (sand blasting seems to be about the heaviest thing on air I do.

That compressor looks very similar but smaller than the 1 I linked. It doesn't say Cast iron cylinder on the 1 I linked on the machine mart site, but I presume it is, it looks to be cast. Although could be alluminium and sleeved, i'd doubt it though.

 

[rtbcomp]

I do blast with it, it will support a 3mm nozzle OK, but in practice I use it in parallel with a 2hp compressor and a bigger nozzle. It gets a bit tedious on modern paints.

If the cylinders are cast it will mention it in the ad. as that is a good selling point.

 

[Rick]

I do blast with it, it will support a 3mm nozzle OK, but in practice I use it in parallel with a 2hp compressor and a bigger nozzle. It gets a bit tedious on modern paints.

If the cylinders are cast it will mention it in the ad. as that is a good selling point.

It does mention it, just not on the key features bit.

None of the machine marts around here have it in stock though.

I'm going to use it in parrallel with my 3hp, so should be ok.

Thanks