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Air compressors in series?
Air compressors in series?
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Old 10th August 2018, 06:33 AM   #11
Dave Zan is offline Dave Zan  Australia
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Join Date: Nov 2010
Quote:
Originally Posted by Trollet View Post
So 2 in paralell is propably better...
Quote:
Originally Posted by jsantoro View Post
Run them in parallel, NOT series. You need volume...
You both miss my point.
For any specific volume & pressure it is more effective to have two compressors in series, where each can be optimized for it's particular pressure, rather than add the output of two compressors in parallel where they are both inefficient.
The physics is that air compression is not a linear process.

Quote:
...that would deliver the 20CFM at 125 PSI I needed.
That about what I had in mind, what power and price?

Quote:
Originally Posted by BillWojo View Post
..requires a LOT of air and usually around 80PSI.
80 psi is a bit low, 100 psi is about 50% faster and seems to be the de facto standard for professional sandblasters.
Jsantoro's 125 seems a bit excessive, perhaps nominal pressure at the compressor rather than actual pressure at the blaster.

Quote:
...we turn on both compressors. Even than, frequent breaks to let the compressors recover is to be expected...
Yes, just my point, more efficiency means less heat, less stress on the compressors, less interruptions and better work flow, not just smaller power bill.

Best wishes
David

Last edited by Dave Zan; 10th August 2018 at 06:55 AM.
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Old 10th August 2018, 06:53 AM   #12
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by Pano View Post
..with an old VW engine. It worked. It was loud.
Yes, a local farmer reminded me of the old VW compressor too.
Noisy, smelly, too much maintenance, V8 even more so.
3 phase induction motors are so trouble free.

Quote:
Originally Posted by Refugee1 View Post
...perhaps just hire a diesel unit for a day or so once a year.
Even more sensible would be to skip the hired diesel and just take it to a professional who already has one and pay him to do it.
But it's nice to have the set up when you want to do a job.

Best wishes
David
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Old 10th August 2018, 07:21 AM   #13
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by PRR View Post
While CFM drops with output pressure, not by much on a healthy piston machine
This prompted me to pull out my compressor's spec. sheet and do the numbers.
CFM drops by about half at 100 psi.
And if I only pump to say 50 psi then I can run the compressor faster.
At 40% more revs I have about twice the volume at half the pressure and the motor will actually be less loaded because compression is a bit more efficient.
Have to check the red-line for the compressor but ~1200 rpm looks reasonable.

Quote:
..The [second] machine's torque is already sized for the rated exhaust pressure...
Peak torque won't increase because that's set by the peak pressure, and I can increase the torque from the motor, just alter the pulley ratio of the belt drive.
So I don't need different size pistons like a normal 2 step compressor where they run on the same crankshaft and revs.

Now I've done some numbers this actually starts to look practical!

Best wishes
David
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Old 10th August 2018, 07:29 AM   #14
Mark Whitney is online now Mark Whitney  Netherlands
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If this was a PSU would you be looking to increase the voltage or the current capabilitie? And, would additional capacitors help here?
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Old 10th August 2018, 04:53 PM   #15
jsantoro is offline jsantoro  United States
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yes 125PSI nominal adjust to whatever you'd like.

5HP 2-stage $1800 US
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Old Yesterday, 05:02 AM   #16
Dave Zan is offline Dave Zan  Australia
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Join Date: Nov 2010
Quote:
Originally Posted by jsantoro View Post
5HP...$1800 US
Thanks, that's about what I expected for both power and price, more expensive in Australia.

Quote:
Originally Posted by Mark Whitney View Post
If this was a PSU...And, would additional capacitors help here?
It's not quite equivalent to a PSU, there's adiabatic compression that doesn't match any obvious circuit behavior, at least not in a way very clear to me.
"Additional capacitors" is more tank volume and won't help - the problem is sustained output, a sandblaster uses a lot of air, practically non stop.

I've had a think and now incline to use my V4 as the final step, it is rated for >100 psi, as is the tank.
Just consider the other compressor as away to increase the mass flow, almost like forced induction on an internal combustion motor.
Not a turbo but 'boosted V4' sounds cool, 1/3 of a Rolls Royce Merlin
Maybe I need to study car hop-up or aircraft books, the physics of the pre-compressor would be the same as a blower.

Best wishes
David

Last edited by Dave Zan; Yesterday at 05:12 AM.
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