Compressed Air Power Tools

air flow;speed, moisture, duh.

ok thanks..........i'm new to this mechanical engineering stuff.....

nice........now i have a better understanding of the topic compressors.......thanks Drew

I am in pre-engineering myself, looking forward to getting into some of the more intense math and engineering classes in the next few semesters.

We went over the gas laws in chemistry. I know I am not 100% correct in my statement so keep watching as the experts chime in.

My area of expertise is Bulk fuel storage, issue, transfer, filtration and analysis with some expertise in cryogenic oxygen and nitrogen.

How far along are you in your engineering path?

here in trinidad the process flow of Obtaining a degree is very different........well I'm into this engineering for about three years now but i started off as a machinist......not really into the plant technology nor the Maintenance until 11 months ago....i have Exams in three weeks time so I'm gathering all the information i can get my hands on......

this site for me is the best because just hearing others' opinions on questions helps me better understand mechanical engineering

More improtantly than the duh, airflow, water, etc. is the fact that when you throttle water it freezes.

Yeah, the story is true. The sub was the Thresher. She was lost when she suffered a primary power failure and was unable to blow her ballast tanks when the compressed air in the pressure flasks froze on screens in the flow lines when rapidly released for the emergency ascent.

If you've got that much water in the compressed air that the tools are freezing up you need to get a water separator into the line. The moisture going into the tools is going to rust the part up very quickly.

You probably want to install an oiler into the compressed air line as well.

Having link issues...Please stand by.

Not unverified at all.

USS THRESHER (SSN 593) - sunk with all hands April 9, 1963. This catastrophe resulted in significant design changes in all US Navy submarines.

See link below for more info.

http://en.wikipedia.org/wiki/USS_Thresher_(SSN-593)

Punk113,

Years ago we had a neat tool that used air pressure to cool or heat, depending on which fixture was installed on it, to narrow down temperature related electronic assembly failures to a specific component.

Kuduk

I presume you are referring to one or another variation of the Hilsch Vortex Tube. Commercial versions are sold by Exair, Vortec, and, surely others.

DK,

The Vortec site is good.

It was a handy handtool.

The hot or cold air was applied to an attached adaptor that was put in contact with the component. This prevented Electrostatic charge from building up on ESD sensitive components.

Later we went to a controlled electronic heating device and handheld liquid nitrogen dispensers.

Kuduk

Most of the answers are near the mark, but lacking a little in accuracy/clarity. This won't be the full thing either as thermodynamics is too long ago for me to do the full monty easily- BUT

The change in internal energy of a gas depends on the work done on it or by it, and that is where the PV = NRT and P1V1/T1 = P2V2/T2 laws come in - they relate to internal energy.

In a compressed air tool the air does some work on an impeller and then exhausts to air, but I think you are going to get a similar result if its air just expanding through a nozzle. One author correctly provided the idea of PV/T showing the temperature drops but this was a little messy for two reasons.

First is that the air is ultimately at air temperature after expansion with P1V1 = P2V2 and this would be what is called an isothermal process. Of course in reality the air takes a little time to come into equilibrium in its new expanded state and per the PV/T equations must be at a lower temperature than ambient until that equilibrium occurs. The same can be said as it passes though the air tool or nozzle of whatever at each point at ever decreasing pressure on the way through. A no heat gain process is called an adiabatic process and would give the greatest temperature drop for a given gas.

Second very important point is that you should always take care with the units you choose to use. I don't recommend atmopheres unless you know what you are doing. BUT IN THIS CASE when using PV/T formulae you should use absolute temperatures - so going from 50 deg C to 25 deg C does not give a halving of volume for a given pressure. Its only a fraction of about (273+25)/(273+50)

You are correct! I made the same mistake on my homework, trying to use C when I needed K.

First is that the air is ultimately at air temperature after expansion with P1V1 = P2V2 and this would be what is called an isothermal process.

I am not sure how you mean this. If you take one liter of an ideal gas compressed at 2 atm and release it to a container who's volume will expand but stay at at 1 atm the temperature will decrease right?

Of course in reality the air takes a little time to come into equilibrium in its new expanded state and per the PV/T equations must be at a lower temperature than ambient until that equilibrium occurs.

How can it be a isometric process if the temp is lower until equilibrium?

(I am not questioning your information, I know I have lots more to learn when I get to thermodynamics)

Drew

I was trying to show what was happening from another perspective. Yes if you expand air from one box into another it will be cooler. Then heat will start to leak in and it will return to (presumably) ambient. If the second box and the nozzle were well insulted then in the first instance straight after expansion the new pressure and temperature would be calculated as an adiabatic process (and the gas would be colder than otherwise). After a long time when the temperature has returned to normal/ambient then the pressure would be calculated as if it were an isothermal process.

Hi Punk

Good that you asked this question. The answers given here were a potential missing link in some research I am doing. Now that I have more information and can understand how dangerous consequences can be avoided. I will not be hit by surprise, like those poor blokes on that submarine.

Drew:

Every time I think I have learned something about a subject all I really learn is how much more I have to learn!

I could not have said it better and I suppose it stays that way for the rest of our lives, at least I hope so, Ky.

The process here is casued by Joule Thompson effect. Under such throttling process, the enthalpy remains constant but the temperature drops due to JT effect. It is basically the departure of the gas from ideal behaviour and the extent of cooling will differ from gas to gas dependin upon it JT coeffcient.

Dear Mr.punk113

In simple terms – air gets heated during compression and temp. rise depends upon the compressed air pressure. Generally the compression is adiabatic compression which p x v^1.4 = constant.

While the expanded air is released either through a tool or to atmospheric air the temperature of air falls down – which is the reverse effect of compression.

While the temp. drops, the moisture in air and the humity in air also gets cooled and some times falls below zero Deg.C hence ice formation takes place. If the compressed air air is cooled to ambient temp. the ice formation will be more while expanding of compressed air.

DHAYANANDHAN.S