[PSUBS-MAILIST] Pressure Test Chamber

Thu Jun 22 08:11:38 EDT 2017

A typical pressure test in one of my pressure chambers (hyd cyl)  goes as follows.  I connect a short hose from the chamber to a penetrator in Gamma's hull, then I remove the Hp braided hose that goes to the forward MBT and connect to the hull penetrator.  I close the valve to the HP tank to isolate the compressor.  I open the valve that sends air to the forward MBT and turn on the compressor.  I pump air to reach desired pressure and close the valve and turn off the pump.  This takes mere seconds since there is so little air volume.  I am inside the sub where it is nice and safe and the chamber is between the sub and exterior wall of the shop.  I also never pump my HP tank to full pressure in one shot, I worry that the compressor gets hot, so I fill in two or three stages.   My compressor  is out of a US military aircraft, I figure if it is safe enough to be in an airplane it is safe in my sub.   I hope ;-)When I test ports, I take air from a tank and place the chamber on the other side of the shop wall, but that is much lower pressure.Hank 

    On Thursday, June 22, 2017 4:24 AM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Hugh,Thanks a bunch for the detailed explanation - that makes good sense for the SCUBA compressor example and I hadn't considered adiabatic heating.  
I should perhaps have qualified what I was getting at - that I always like to reconcile my empirical experience with the theory behind it, because the "real world" interactions that are often counterintuitive to the theory.  I'm also an engineer and I find it's the combination of background knowledge and empirical experience that makes an expert.  My background is in cryogenic and industrial gas systems which are strictly oil free, but I'm still a little surprised I've never even come across this concept.  I also do things with SCUBA compressors, which is where those examples come from.
Really interesting to hear about your HP seats spontaneously combusting!  Do you think that's from reaching heat of ignition on the seats?
On a big compressor the final stage sections may get up to 200bar+ in a matter of 10 seconds or so as a matter of normal operation.  I guess this still counts as "slow compression".
What are your thoughts on reconciling the diesel engine example?  I would think they spontaneously combust the fuel/air mix by pressure at similar pressure, and the fuel will have a much lower flashpoint than the oil.  Surely that would be fast compression?
Cheers,Steve

On Thu, Jun 22, 2017 at 2:10 PM, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Thanks Hugh,great example. I can imagine the sonic boom travelling up the valley &your wife running out of the house!I  was at Global dive recently getting them to look at the sloppy thread onmy pressure transmitters that fit on to my first stage regulator. I might run them past you for a second opinion if that is ok.Thanks for the offer of the 40,000 psi tester. I thought my lights mightimplode around 2000psi but for my use they only need to stand 500psi.Cheers Alan

Sent from my iPad
On 22/06/2017, at 11:15 AM, Hugh Fulton via Personal_Submersibles <personal_submersibles at psubs. org> wrote:

Alan,We have a pressure tester that goes up to 40,000 psi.  If you need to do a high pressure test we can assist. We had an explosion with a 1” line that was pressurised with 3,500 psi air but there was oil left in the line after hydrotesting with oil.The explosion blew out the side of the shed  and reached an estimated 25,000 psi in the pipes which ended up looking like Spaghetti. I had explained in detail to the guy who did the fitting of the pipes that everything had to be taken apart after the hydrotest and cleaned using solvent, then soapy water etc. as well as telling him stories of explosions.The guy, an aircraft engineer, did not do it properly and left oil in a branch tube, and I did not do a check on it.  Very lucky my son did not get killed as he opened the valve  doing tests.  These things do not just go pop when they fail and this forum needs to hear of these dangers.  The explosion was heard all round Clevedon. That was our first accident of that nature in 40 years of high pressure involvement. We only use water now for testing and make sure there is no air present.  We did have another incident when we hired out our tester to another company who tested a tank to 1500 psi and the sight glass was held in with a very fine thread.  The sight glass went through the roof iron along with the fittings and we never found the parts.  The inspector had looked in the sight glass about 20 seconds before it let go.  If you are using tube fittings always disassemble after swaging and check the ferrules are in the right way and that a proper joint has been achieved.  There are some fittings which are copies and not up to the job.  We had issues with “DK-lok” (from Korea) with NPT threads where the taper was ½ the required taper but the thread gauge said it was OK. They were also not full form threads.   Also had some fittings called “Tubefit”  from I don’t know where and they were poor copies of “Swagelok”.  We use SSP fittings out of USA which are fully interchangeable with Swagelok but in my opinion they are better quality.   Air from a scuba tank over water is OK but make sure you have a concrete wall between you and the thing to be tested.  Also you should have an excess flow valve in the line.  You can get those from  Swagelok etc.Hugh   From: Personal_Submersibles [mailto:personal_submersibles- bounces at psubs.org] On Behalf Of Alan via Personal_Submersibles
Sent: Wednesday, 21 June 2017 5:58 PM
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Pressure Test Chamber Thanks Greg & Hugh,there was a bit of doubt in my mind about it so mentioned myintended process. I have just googled accumulators in hydraulic systems& the danger of high pressure air! Yikes just as well I've got you guyslooking out for me.What about air from the scuba tank pressurising water?I can get all the air out of the test chamber apart from the air inthe line pressurising it!Other than that I have done some previous tests with the water blaster& may have to suffice with it's pressure!Cheers Alan Sent from my iPad
On 21/06/2017, at 3:33 PM, james cottrell via Personal_Submersibles <personal_submersibles at psubs. org> wrote:
Alan, Pressure testing that high needs to be done with liquid not gas. High pressure air is VERY dangerous. A pressure washer pump using water would be a safer choice. Greg From: Alan via Personal_Submersibles <personal_submersibles at psubs. org>
To: personal_submersibles at psubs. org 
Sent: Tuesday, June 20, 2017 9:01 PM
Subject: [PSUBS-MAILIST] Pressure Test Chamber I am making a plastic container to fill with water & stand inside mypressure chamber. There is a gap between the wall of the container& the chamber which I intend to fill with oil. There will be about aninch of air at the top of the chamber & I'm using a scuba tank topressurise the unit up to 3000psi.Will car engine oil do to fill the gap between my plastic container &the chamber wall, or do I need to go with a hydraulic fluid.Am using the plastic container to keep water from rusting my testchamber. (Aussie Steve's idea)Cheers Alan Sent from my iPad______________________________ _________________Personal_Submersibles mailing listPersonal_Submersibles at psubs. orghttp://www.psubs.org/mailman/ listinfo.cgi/personal_ submersibles  
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