Compressor faulty, or am I stupid?

[not done it yet]

It might just be the way I'm reading this, but the statement above confuses me. You do know what CFM stands for right? And huge apologies if I've completely misread what you've said here, I likely have

Correct, CFM is rate and the other is an amount. People are often befuddled with kW and kWh because they don’t understand simple physics/physical units.

 

[Cook1e]

It might just be the way I'm reading this, but the statement above confuses me. You do know what CFM stands for right? And huge apologies if I've completely misread what you've said here, I likely have

"What you think you heard is not necessarily what I intended to mean" is one of my favourite quotes, though I don't know who said it first.

OK, here's how the conversation went...

Pigeon Droppings 2 said:
150l in 4.3 minutes? ..very roughly 35l per minute on average. Is that 1.25 CFM (Google!) or is my maths totally wrong. I really only think in metric if I'm honest!

My brain did something like "150 litres divided by 4.3 minutes is 35 lpm (1.25 CFM), but that's only if it stays at atmospheric pressure, which of course it doesn't, it goes to 125psi."

So I wrote:
I think 150l at 125psi will be a bit more than at atmospheric pressure. If the relationship's linear (a LONG time since I did O-level physics), it's about 10.4 CFM

I worked that out again just now, writing down each step in my reasoning:
If the pressure/volume relationship is a straight line (i.e. doubling the pressure is twice as much air) then 150 litres x (125psi/15psi) is 1,275 litres at atmospheric pressure (15psi-ish), so the 1.25 CFM would be 10.4 CFM, as it's pumped150 litres 8.3 times.

I hope that's a bit clearer...

Hotponyshoes calculated it better:
His 10.5cfm compressor should pump 297lpm. 125psi in the tank is 8.6 bar. 150l tank at 8.6 bar is 1290l. 1290 / 297 = 4.3 minutes to fill

 

[jimbo1962]

Are you any wiser after all that?

 

[jo1010]

Size of compressor is like size of a garage - get more than you need







And then double it
200l tank, 32amp (assuming 240v supply) as minimum - which means you can spray paint too if you don't go mad

 

[Cook1e]

Sorry for late response, been busy elsewhere and then I found a brake fluid leak, which took priority over polishing.

I reduced the pressure to 50psi, but the grinder stalled too easily. 70psi seems to be the best compromise and the job is now done.

I have learned more than I needed to

I have had the compressor for several years, mostly used for windy gun, tyres and a bit of HVLP spray gun, for ACF50 corrosion inhibitor mostly, occasionally paint. I've used it with the die grinder from time to time, but this is the first time in extended use.

I was really just worried that my compressor was ******** again (it failed a few years ago, faulty valve block), but I'm pleased to have determined that it's working to spec.

Thanks for all the information and help. I'm well used to manufacturers/vendors making exaggerated claims, but in the field of air power, they absolutely excel!

 

[Cook1e]

Size of compressor is like size of a garage - get more than you need

And then double it
200l tank, 32amp (assuming 240v supply) as minimum - which means you can spray paint too if you don't go mad

Sound advice, but only practical if funds, space and planning permission are conducive which, in my case, they aren't.

A massive garage/workshop with a 3-phase supply and I would rule the world!