4 replies to this topic

[AlexRM]

Hi all,

 

I am looking for some guidelines or calculations for sizing pneumatic air lines.  We have a 7 bar air supply with more-than-adequate volumetric capacity.  We will be using the air supply to actuate a valve at approximately 100m distance from the air supply.  So, initially the valve and pneumatic line will be at atmospheric pressure and will pressurise to 7 bar when the air supply is opened.  It will fall from 7 bar to atmospheric pressure when the vent is opened (the vent will be near the air supply).  

 

Over a distance of 100m I would expect the pressurisation and depressurisation to take some time, but I am not sure how to calculate what this time will be.  I am also not sure what effect the diameter of the pneumatic line should have - a larger diameter means a larger volume to pressurize, but less friction losses.  I'm not sure how to characterise friction losses - is something like Darcy-Weisbach even valid for an unsteady-system?

 

Is there any standard method for characterising delays in pneumatic systems and determining the line size required?

 

Cheers,

Alex 

[sgkim]

Hi Alex,

 

There are lots of different systems in pneumatic conveying such as -- i) dilute phase conveying, ii)dense phase conveying, iii) pulse phase conveying, iv)vacuum conveying, etc.  So the line size would be depend upon the system you selected.  You would rather refer to the text books dealing with the subject <pneumatic conveying design>.

 

~Stefano

[AlexRM]

Stefano,

Thanks for your reply.  However I am not interested in pneumatic transport/conveying, I am looking for pneumatic actuation.  eg. using air to close a valve.  Sorry if this was not clear.  If anyone can recommend a text that would be appreciated, I've had a look myself but have not found the information I need. 

Cheers

[breizh]

Hi ,

You may find pointer in this forum :

http://www.eng-tips.....cfm?qid=157377

 

Breizh

[sgkim]

Hi Alex,

You will have to supply the air required during the pneumatic conveying, that's why the air rate is to be calculated.  To calculate the size of the on-off pressurizing valve is not so simple as you might think.

 

Flow through the valve nozzle is usually composed of two time zones - one for constant(critical) flow and the other for variable flow.  The former is due to the limit of sonic velocity and the latter is based on the variation of differential pressure through the nozzle.  

 

Total time required, supply pressure, built-up pressure, system volume, is required for such calculation. But you'd better relocate the air supply valve just to the vicinity of the pneumatic conveying line; which can save the compressed air consumption.    

 

~Stefano