Hi all,
I'm looking for a threadable pressure port, the smallest possible.  The pressure sensing and "working" lines have very small diameters (~20 thou ").
I need the sense line to be 90 degrees to the "working" line   I'm wondering if I have to use something fairly large or is there something available in this size range?  

To clarify what I mean by "threadable", the ideal would be to have a threaded hole on the part in which the pressure line is drilled, and then screw in an insert to a more standard sense line size (80 thou " or ~2mm).

Thanks

plenty of methods to make your pressure tap, but more importantly you need to define what pressure you are actually trying to measure and at what mach no.

The pressure will be low (total and dynamic pressure measurements), my sensors are capable of 0-30psia  max.
I have found some threadable ports but they have M5 threads, that's too big. I was hoping for M3 (or similar imperial size) with 0.025" holes.

I found something:
http://www.beswick.com/products/product_details.php?pid=8

The flow-through size is a bit bigger than I hoped but I think it'll be OK.

that is not going to give you a valid pressure measurement unless your velocity is really low

is this for process piping


 

No it's for AOA probe use.

NACA report 1364 shows that small pressure ports are the most effective (0.020"-0.030" generally).  That's tiny, I know and unfortunately I won't be able to do it on my lathe, I'll need to use EDM drilling.

Unless you have experience otherwise, that using a small drill hole (1/16) would be acceptable?

???  It's not my field, but I don't get that conclusion from that report.  It seems to be talking about having smaller orifices on a relatively larger tube.  It mentions 25mil and 32mil as being better than 52mil.  It also seems to stress the importance of having good profiling of the orifice:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092348_1993092348.pdf

TTFN
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there are smaller drills for manual drilling but that is all it would be and not a proper pressure port

you might consider a tube insert rather than a drilled port

how do you plan to test your custom AOA/pitot measurement?






 

I never thought of using a tube insert, that's a really good idea.  I guess I would bond it in? Or simply heat the big tube, chill the small one and insert it with a small interference fit?

Testing: intially calibrated in freestream (ie: outside) and then in a wind tunnel.

sounds like you are just making a pitot rather than angle of attack probe, regardless, there are a number of methods to secure the tube depending on the temp range

for both measurements the edge effects of the port are important


 

I am doing both pitot and AOA in a single probe.  AOA will be measuring the pressure difference between the bottom and the top probes (known as a smart probe).
That's good information for the edge effects, I was just going to bevel the edges of the holes but I'll take a look at detailed information on this point.  
For the temp range, the probe will be unheated (limited to "sunny day" operation). so probably -20C to +55C (DO-160 CAT A2 for temp)

I still don't get why you need a separate tube.  The paper seems to suggest that a straight, unbeveled hole is all that's needed.

TTFN
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just buy an AOA probe, you are getting into a can of worms with a beveled port , but given that you were going to use a hose bib initially, maybe thats all you really need

sunny days -20C to 55C, famous last words, that's not enough, just get a heated probe that has been design and tested. ice crystals are very small but they can really make a mess



 

Any chance a modified carburetor jet might be of value? Small hole, threaded insert, etc...

pmrobert, another great idea, thanks!!