Benchtop air compressors

[BobL]

Hummmm . . .

The 6.5L/min needs to be delivered at 90 pSI but these air requirement volumes for spray gun and tools etc are usually always converted back to atmospheric pressure volumes so I agree with John that he will have about a minute worth of spraying before the compressor needs to recharge.

Same with FAD and recharge.

The questions that need to be asked is how reliable are the 65 L/min on the gun and the FAD. Most manufacturers overstate their FAD and it will degrade with time/wear so you may start out with 60% but you may end up closer to 100%

[ian]

Hummmm . . .

The 65L/min needs to be delivered at 90 pSI but these air requirement volumes for spray gun and tools etc are usually always converted back to atmospheric pressure volumes so I agree with John that he will have about a minute worth of spraying before the compressor needs to recharge.

scratching head...

although a 36 litre tank at 115 psi may contain the equivalent of 300 or so litres at atmosphere, I understood that only the air that is at or above 90 psi is usable. (90 psi being the pressure required to operate the gun).
This volume is not very great.

[BobL]

scratching head...

although a 36 litre tank at 115 psi may contain the equivalent of 300 or so litres at atmosphere, I understood that only the air that is at or above 90 psi is usable. (90 psi being the pressure required to operate the gun).
This volume is not very great.

yep, that's right usable air (converted back to atmosphere) before going to recharge is 36*(115-90)/14.7 = 61 L

Recharge using 134 L/min should be ~30s but that FAD could be at 90PSI, so FAD will be less above that meaning longer recharge times

[John G]

Thanks Bob and Ian,
I will report back all the actual numbers vs the theoretical numbers once I have given it a run.
The machine is 2nd hand so I wont be running it until I've given it an overhaul, new oil etc and checked the tank for any damage etc.
So it may be a few weeks before I report back.

No idea what the actual FAD will be as I have no idea the state of the gaskets, valves etc.
The spec in the manual simply says "Delivery 134L/Min, Discharge Pressure 115PSI/8 Bar" and there is a big "134 FAD" sticker on the side.

In theory (if the FAD remains constant), the tank holds (36 x 115)/14.7 = 281L of air, which should fill in 281/134 = just over 2 minutes.
(As I've never used a compressor before this is quite an interesting investigation for me)

John.

[BobL]

Thanks Bob and Ian,
I will report back all the actual numbers vs the theoretical numbers once I have given it a run.
The machine is 2nd hand so I wont be running it until I've given it an overhaul, new oil etc and checked the tank for any damage etc.
So it may be a few weeks before I report back.

Let the compressor charge itself up several times so it gets hot and then get yourself a container of water and add a squirt of detergent to it and using a paint brush paint all the fittings with the liquid and see if you can spot any leaks you can tighten.

No idea what the actual FAD will be as I have no idea the state of the gaskets, valves etc.
The spec in the manual simply says "Delivery 134L/Min, Discharge Pressure 115PSI/8 Bar" and there is a big "134 FAD" sticker on the side.
In theory (if the FAD remains constant), the tank holds (36 x 115)/14.7 = 281L of air, which should fill in 281/134 = just over 2 minutes.
(As I've never used a compressor before this is quite an interesting investigation for me)

If it's real 134 L/m FAD @ 115psi then it should take less than 2minutes to recharge since a great charge rate will happen at the lower pressures.
If the compressor is in good condition t could be as little as half that time but most likely it will be between 1 and two minutes.
How many HP is the motor?

[ian]

Recharge using 134 L/min should be ~30s but that FAD could be at 90PSI, so FAD will be less above that meaning longer recharge times

Dr Google suggests that FAD is typically quoted as cylinder volume x number of piston strokes per minute -- i.e. it's measured at atmospheric pressure.
so 134 litres FAD would be around 22 litres at 90 psi

[John G]

Let the compressor charge itself up several times so it gets hot and then get yourself a container of water and add a squirt of detergent to it and using a paint brush paint all the fittings with the liquid and see if you can spot any leaks you can tighten.
...
How many HP is the motor?

It is 2.5hp motor direct drive. It is basically the same as this model (but not this brand).
First problem with changing the oil (if it even has any!) is the sump bolt isn't one with the oil level window, so I don't know how much oil to add. So I need to get one of those first to change the oil before I can even start. Also clean out the breather plug and a whole bunch of other stuff I am still learning about.