Thread: 1 or 2 stage compressor

My understanding is that multi stage is just for getting high pressures using a but less power and $.

BTW I am skeptical of the claimed 389 L/min (11.9 CFM) figure for the single stage unit.
For a 3HP powered compressor to do that, that is close to 100% efficiency in operation which just doesn't happen.
I'd be more likely to believe the 10.2 CFM for the other compressor.

For a 3HP motor to generate 11.9CFM it has to be operating above 3HP - this is quite possible as most motors can operate above their nominally rated HP but how long it can do that for is another question.

You cannot really tell what their real performance is until you time their recharge times yourself.

Originally Posted by BobL

BTW I am skeptical of the claimed 389 L/min (11.9 CFM) figure for the single stage unit.
For a 3HP powered compressor to do that, that is close to 100% efficiency in operation which just doesn't happen.

You cannot really tell what their real performance is until you time their recharge times yourself.

I have to agree with you, but this is why I compared the two from the same manufacturer - I am a little sceptical about the 10.2 also. I wouldn't mind betting that its closer to 9 - 9.5 at best.

I actually wondering if I need to build a manifold and use two 10 amp ~ 7 cfm compressors to do the job for hvlp and the a/h ram.

I have a single stage two piston compressor that was made in 92, its being repainted at the moment, its had the motor replaced with a 1400rpm motor not the 2800rpm for noise reasons after the first motor died. Its run a plasma cutter no problems

Opelblues2 what brand is the compressor and are you happy with it (noise aside)?

Originally Posted by SPF

I actually wondering if I need to build a manifold and use two 10 amp ~ 7 cfm compressors to do the job for hvlp and the a/h ram.

You have to be careful when doing this if they are just connected to each others tanks.
It will be near impossible to get the pressure switches on each compressor to switch on at the same time as one will always trigger slightly before the other and it will then do 90% of the work.
Now you are asking one compressor to recharge double its original volume so the compressor will need to run for longer every time it recharges ad get much hotter than usual and long term it will suffer more wear and tear.
The only time the two compressors will run is when the pressure drop below both triggers.

A better arrangement will be to trigger both compressors from one pressure switch.
However its not advisable to use a 15A pressure switch to do this as the total current through the switch would be greater than this.
20A total pressure switches are usually for 3P machines but for a 20A switch each phase would usually current limited to ~6.7A per phase which is no good for a 20A SP.

I ran into the same problem with my 4HP (4 cylinder - 2 twin stage) compressor which I converted from 3P to SP.
It was originally a 3P compressor with a 3P pressure switch with 6.7A per phase.
To get 20A per phase on a 3P switch I found it would cost as much as a cheap compressor
I looked around for a 20A SP pressure switch but could not find one.
In the end I used as HD a 15A pressure switch as I could find.
I have an an ammeter on my compressor controller and can see the current doesn't go above 16.7A so I'm just hoping it will be OK.

If it fails I will rig up a circuit so that the pressure switch controls a 30A relay.
This system will also work for you

BobL, that's some great info, thanks for posting it.

it was a Ingersoll Rand 2.5 HP 100lt tank with a Italian made pump, it was mounted on the work trailer when I was still welding, it now mounted on the door of the container and I can swing the door around to the side to cut the noise down
It came in handy when I had jobs a the grain loaders in Gladstone, no power tools or flame to be used. its been used to paint two cars, and at the moment it been pulled apart for a rebuilt, I'm heading over to Compak on Monday to pick new gaskets. I have one of their battery chargers that is 45 years old and still goes

Does anyone own either of these Pilot models, or any others? Anything good or bad to say about them?

Don't own either of them, but have nothing bad to say about Pilot. A quality product with good backup.

Regards your calculations, Pilot conform to Protocol 2000 for specifying compressor performance. The FAD is calculated from the time taken to cycle from 600kPa to 800kPa. This is averaged over 3 tests, conducted indoors at 15-30°C and elevation between sea level and 300m. The formula used is FAD = twice the receiver volume in litres divided by the time taken to recharge from 600kPa to 800kPa in minutes and decimal minutes. That gives the litres per min rate, which you can divide by 28.3 to get CFM.

Originally Posted by richmond68

Don't own either of them, but have nothing bad to say about Pilot. A quality product with good backup.

Regards your calculations, Pilot conform to Protocol 2000 for specifying compressor performance. The FAD is calculated from the time taken to cycle from 600kPa to 800kPa. This is averaged over 3 tests, conducted indoors at 15-30°C and elevation between sea level and 300m. The formula used is FAD = twice the receiver volume in litres divided by the time taken to recharge from 600kPa to 800kPa in minutes and decimal minutes. That gives the litres per min rate, which you can divide by 28.3 to get CFM.

Rischmond68 thanks for your reply. I ended up buying the 2 stage Pilot compressor. My observations so far:
1. Time to fill varies. From cold it takes about the time I initially calculated, but once its warm, then it takes about 30 seconds less. My assumption is that the cylinders seal better once warmed up.
2. The noise level is much better than the single stage alternative, the machine just seems to plug along, and I can stand next to it and have a conversation with someone (just). I have used an app to calculate dB at 1 meter and it gives a reading of 76 dB. I have no idea whether this is close to the actual figure or not, but I did some test readings on other machinery with stated dB figures and it was within 3% of the stated number each time.
3. I live in a humid area and the compressor produces very little condensate in the tank. I have also built a 15M 3/4" copper aftercooler with fan cooling to remove as much water as possible, however, to date I have not run the compressor long enough to get any water in the aftercooler drop points, or in the filter/regulators that are mounted post aftercooler. No moisture comes through the hoses to the tools.
3. The build quality is good.
4. Despite my preference to buy a locally made product and seeking out products on this basis (and the marketing material saying that the tank was built in Australia) the new short tanks on this model are built in asia - I can't recall where ATM. This annoyed me.
5. The compressor starts up just a fraction earlier than shown in my calculations above (for both 40 and 90psi), but it seems to kick in at closer to 120psi tank pressure. When using my die grinder at mid flow rate the compressor will switch on and catch up and stop, despite continued use. At full speed, the compressor operates continuously.
6. Despite the 160psi stated cut-out, mine is set to 153 - I haven't investigated adjusting this yet.
7. Using a blow gun at 130+ psi is very effective at removing mud wasp nests from machinery.

Once I have used it for a decent spray job and a couple of other specific tasks, I'll post a review.

[Edit] I'll use the FAD calculation above, and provide a number with my review.

I should add that the protocol 2000 makes no allowance for humidity levels, which does affect compressor performance. I do have formulas to calculate FAD taking humidity into account, somewhere. But I've got more chance of finding Harold Holt than where I put them!

if you are painting you might want to add a post filter, a pre filter and a dryer to your compressor line.

Originally Posted by Albert

if you are painting you might want to add a post filter, a pre filter and a dryer to your compressor line.

Albert, if I was doing an automotive job in a booth, then I agree. But for work (industrial coatings) in uncontrolled atmospheric conditions I don't see the need. I have designed the fan cooled aftercooler to reduce the temperature of the air as much as possible while going through a 15m long 3/4 inch copper dropper. I haven't tested the temperature reduction thoroughly yet, but the air is dry even when running for 10 mins continuously after a day of intermittent use (compressor is warm), and the air and tools feel cool regardless of how long they are used. I haven't put an oil filter on yet, but that will go on before any spraying is done.