# Case with pressure transducer

### Help Support The Rocketry Forum:

#### DannyB

Hi all! I'm not a machinist and do not have access to one, so I cannot build my own ex case with a pressure transducer, I currently only test with a load cell. I'm looking to buy, new or used, any reasonable sized case/closure with a pressure transducer built into it (would prefer 38mm or 54mm). Or, if anyone knows of a vendor or machinist for these that would be great. Thanks for any help!

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#### dhbarr

##### Amateur Professional
a) drill through the bottom of a tapped plugged forward or b) tap threads into the touch hole of a standard forward closure.

#### DannyB

Thanks dhbar, sounds pretty simple. So I should be looking for a closure with a transducer not a case. If it's that easy I may give it a go, don't want to ruin closures trying though and I've never tapped aluminum before.

#### dhbarr

##### Amateur Professional
Just practice drilling / tapping on some scrap, you'll be fine

#### jsdemar

##### Well-Known Member
Hi all! I'm not a machinist and do not have access to one, so I cannot build my own ex case with a pressure transducer, I currently only test with a load cell. I'm looking to buy, new or used, any reasonable sized case/closure with a pressure transducer built into it (would prefer 38mm or 54mm). Or, if anyone knows of a vendor or machinist for these that would be great. Thanks for any help!
What 38 or 54mm cases do you have? I've put pressure ports in forward closures of AMW/Loki motors (and an AT closure once).

If you send me the foward closure, I'll put a 1/8" NTP fitting in it (for free). I have some surplus (all stainless, high-end) pressure transducers that go to 1000 psi (1500 without damage). They require 28V and put out 0-5V. ($50). Or, you can find various used ones on Ebay for$50-\$100.

#### DannyB

John, that's incredibly nice of you. If you're up for it and it's not too much trouble I'll take you up on your offer. It will save me from buying the tools and learning to tap and thread. I really appreciate it, you're a good man John! I'll shoot you a pm. Thanks!

#### jsdemar

##### Well-Known Member
I have the tap and a lathe, so it takes very little time to put in the pressure fitting.

It's best to use motor hardware other than AT for testing. I recommend characterizing propellant with standard 38mm snap-ring hardware.
https://binderdesign.com/store/page11.html for example.
Or Loki's EX casing options.

The forward closure has more metal to tap into than the AT closure. Also, the snap-ring tends to fail first instead of the casing. The graphite nozzle can be used for multiple burns with good throat ID, and the liner/casting sets are cheaper.

#### crossfire

I don't know what a pressure transducer is for? Can you educate me?

#### DannyB

Hey crossfire, transducers are used in experimental motor testing to get a reading of the internal case pressure. They are used in conjunction with load cells, which produce the thrust curve. With these one can properly characterize a propellant. Without pressure the math simply can't be done.

#### dhbarr

##### Amateur Professional
AFAICT a 120fps infrared camera and some vibration sensors would help out as well.