Hello,
I have many variables, but am not sure of how they relate or where to
begin.
I need to pressurize a cylindrical chamber to either 50, 100, or 150
psi using a blower to supply the air and a pressure release valve to
regulate and maintain the pressure of the chamber. I'm looking for any
guidance in how to determine the approximate incoming airflow needed to
generate a constant internal pressure of 50-150 psi, and from that how
powerful the blower motor needs to be (cfm, rpm, hp, etc) to provide
that volume of air and overcome any backpressure.
If you could point me in the right direction, I would be most
appreciative.
My best,
David
If you are talking about taking atmospheric air and pumping up to 50+ psi with a "blower" that's a pretty stout requirement. Unless your thing of a centrifugal blower like a turbocharger spinning at 100,000+ rpm, this is way above the pressure ration you can get out of a "blower" ---------- Ed Ruf Lifetime AMA# 344007 ( snipped-for-privacy@EdwardG.Ruf.com)
Dear davidrowyn:
Use a compressor. Size for the airflow requirement. It is common to switch it off, or throttle its inlet, to operate in a range of pressures. Also common is a receiver tank with drain apparatus to release moisture.
What are you trying to operate with the air? Will it/they (the thing being operated) require lubrication? Will it/they require filtration?
We need to know where the air will go. We need to know something that will specify (or allow derivation of) the airflow rate. To quote Johhny 5 "Need Input!"
David A. Smith
When you mention a blower, I'm assuming you're thinking of some kind of fan (either centrifugal or axial)? Commercially available fans, such as those intended for ventilation, cooling or even wind tunnels, will struggle to produce a pressure of more than 1/10 of an atmosphere, or 1.45 psi. The maximum attainable pressure using a fan can be calculated using the Bernoulli equation. See the following site for more details:
The problem with fans is that air can escape backwards through them. For this application you'll be better off with a compressor, which won't allow air to escape backwards through it. Compressors are often termed "positive displacement" devices as they convey a fixed volume of gas from the inlet to the outlet with every revolution of the shaft. And because air can't escape backwards through them, you can raise the pressure in your vessel until either the compressor's motor stalls or the vessel explodes.
Compressors are widely used for powering industrial tools and consequently aren't that expensive. Most industrial air supplies are rated at 150 psi, so one of these compressors would be ideal. You'll probably need a non-return valve between your compressor and the vessel and an outlet valve to vent air to the atmosphere. A safety valve is a must, as is a pressure test performed on your vessel using water. A vessel exploding at 150 psi could be nasty!
Best wishes,
Chris Tidy
The air flow rate needed depends on the cylinders leakage rate. If there were none, no air flow would be needed at all.....
Brian Whatcott Altus, OK
Some idea of the size of the chamber ?
why do you need any flow... how does the air get out once it's pressurised.
Is this a paper exercise, or do we need to know where it's to be made ( pressure equipment regulations vary with country )
At this pressure you are going to need a multi stage turbine.. but a compressor is most likely to be better suited to the job.. any particular reason for using a blower ?
you know, when someone asks about how to pressurize a vessel to 150 psi using a blower, I get real nervous about exploding vessels. And so the advice is not to the means, but more to the idea that pressure vessels are strictly regulated because when rookies build them, they more than not eventually blow up.
Take a simple 12 inch dia tank - at 150 psi, you are just about to 8 and a half ton pushing that end off. The welds split because of the end plate diaphragming and the forces cycling - not to mention tiny cracks from pressurized porosities splitting welds.
In built-up sections, the air gets under the seal, and that 8 1/2 ton 12 inch diameter just went to 11 1/2 ton.
so when someone lacks the expertise to build the original device, I have to believe they might not have all needed to keep people alive and well, and thus they should get an engineer specifically expert in vessel design to assist.
just a thought.
"they should get an engineer specifically expert in vessel design to assist.
just a thought. "
yeah, sounds like a good idea.......................
Hello again,
Firstly, thank you everyone who took the time to respond. At this point, I'm just throwing out project details -- we're not looking to actaully make something for quite some time. I say this for those of you with safety questions.
Secondly, my original post used 50-150psi, though upon review it seems that the internal pressure of the chamber only needs to be 15-50psi. Also, a compressor seems to be the way to go now -- due to Christopher and Ed's remarks on the limitations of blowers.
My only follow up question(s) at this point are what follows:
The chamber must remain pressurized, and yet have constant airflow through it -- hence the compressor at the inlet and a pressure release valve(s) at the output. To pressurize to 50psi (at the maximum) a cylindrical chamber with dimensions of say 9"d x 18"h and maintain this pressure for ten minutes or so, what type of compressor would be needed? What if the temperature of the compressed air needed to be significantly higher or lower than room temperature?
My best, David
Dear davidrowyn:
You've got two requirements that remain undefined: 1) How fast do you need the chamber to go from 0 psig to "max" psig? 2) How much air flow is flowing through it? ... once this is known, the compressor requirement will fall out. Likely a Gast or Thomas compressor from the Grainger catalog will do just fine.
Note that it is common to specify airflow as "standard cubic feet per minute" or some such. Depending on how you will quantify/control this (rotameter, thermal mass flow) will be one issue.
The air from the compressor will be 30 - 60 F deg above ambient temperature, but has very little heat capacity. If it is a process requirement to have a "constant" temperature; you'd better plan on heating, cooling, control of same, and insulation.
And I encourgage you to have a vessel designed for safety. The State of Texas has a Board of Professional Registration (or whatever name they go by) in Austin. They can provide you with a list of Professional Engineers that are certified in Texas. If you will have the inattentive operating this system, it would be best toi keep the insurance companies (and your lawyers) happy. Start Here: URL:
David A. Smith

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