Hydraulic testing air tubes to 30,000 psi

[lloyd-ss]

=====edit=== 11/24/16 - increased the pressure in the subject line of the thread from 20,000psi to 30,000 psi, to reflect the test system capabilities.  Lloyd====

Seems like the trend in PCPs is heading to 4,500 psi reservoir pressure.  Thicker walled steel tubes or high strength titanium tubes are generally needed to safely contain the high pressure. Calculating the proper wall thickness is fairly straightforward, but how about actual testing to prove that your calcs were correct or that the purchased material meets its specs?
I've got some high pressure projects planned and I'd like to verify the safety of the tubes, but such testing is very expensive. I decided to try making a hydraulic multiplier to get hydraulic test pressure over 20,000 psi.

Here is a snapshot of the test rig, including a pic of it pressurized to 21,000 PSI. It is just the test rig, nothing is being tested except the test apparatus itself.
Details are coming.
Lloyd-ss

Low pressure side on the left, HP on the right.



4,200 psi input, 21.000output................... approx 5 to 1 pressure multiplication.


Pressure testing capability to over 21,000 psi.  I'll be trying with higher pressure
when I can take it outside for a few "confidence building" exercises.

[Back_Roads]

Eliminate the O  Rings and nothing will blow up ok way out of my league but very intriguing

[CraigH]

Good stuff, Lloyd!   Looking forward to the future details.

[Matt15]

Subscribing. 

[michaelthomas]

Hi Lloyd,

I use a company called Galiso in Montrose CO.  They manufacture the hydrotest equipment that most of the world uses.  They are not very expensive.  Usually costs me 50-75 dollars and they provide me with a lot of information such as volume cc of expansion, and volume after depressurization...which is useful in determining if the tube has surpassed its limits, but not actually failed.  You can also get a chart that shows where in the pressure curve the actual expansion is occurring. 

Mike

[Buldawg76]

Lloyd
This sounds like its going to be another of your very informative and interesting tests you do for all of our benefit here on the GTA. Looking forward to the testing of materials and the results that are sure to very in depth so we can receive non biased and accurate statistics and values that you discover.   

Mike

[Wayne52]

Very interesting

[Rob M]

Lloyd, how will this be duplicated on a larger scale?? I see the theory , but as is how would it fill even say a 12 gram co2 ?? ( unless theres a check valve we dont see.. VERY NICE WORK BTw

[rsterne]

Great work, Lloyd.... Looking forward to seeing you blow stuff up test components to failure.... *grin*....

Bob

[Motorhead]

"Hydro"stat sure makes me feel better than straight "Gas" testing ...... hydro upon failing go's WHUMP .... With a non volatile Gas being an explosion.
Indeed will be watching this thread for further developments.

[lloyd-ss]

Thanks for the interest guys.  I'll start with a few thoughts that I hope will answer the questions and comments, and also explain a little about my motivation for this project.   Bob Sterne has mentioned this a number of times, that there is a lot of good airgun information and knowledge in the airgunning community, but much of it is held close to the vest and not willingly shared.  Bob, and myself, and many, many other people on this forum have made a conscious effort of providing that information to anyone who is interested.  I really enjoy testing and development, in fact, more so than shooting.   I've said it many times, if I couldn't work on airguns, I wouldn't have them. A lot of my previous testing is on my Youtube channel "airgun lab."  I did some testing of aluminum air tubes for the P-Rod a few years ago, but was limited to 10,000 psi, which wasn't high enough for serious destructive testing.

Now that I am starting to work with titanium tubes, I wanted to be able to test them to verify that the performance of the tubes agreed with the calculations.  I guess I could have found somewhere to do the testing for me, but that is not my style.  I'd much rather design and build my own test rig, including the learning curve that goes with such an effort, and then have the testing capability in my shop.  I'll  be making some videos of pressure testing of various tubes and end attachments.  The methods might not be as sophisticated as a certified testing house, but the results will be just as valid and the procedures used will be appropriate.  I worked with a lot of very smart people during my 35 years as a manufacturing engineer, and I managed to pick up a little bit of info along the way, LOL.
But enough of the introduction; on to the test equipment.

This first picture shows the basic internals of the system.
Thereis a .740" dia low pressure input piston that drives a .312" dia high pressure output piston.  That gives about a 5.6 to 1 pressure multiplication.  The stroke length is 6.7", which limits the output volume to about 7.4 ccs. I'll explain how I get past the volume limitation in a minute.  With the multiplication ratio, 5,300 psi input from a hydraulic handpump will produce about 30,000 psi on the output side.
The LP piston has the o-rings right on the brass piston, and the o-rings for the HP side are stationary inside the cylinder coupler and the .312 dia polished rod slides thru the o-rings.  There is a .125" dia tell-tale rod attached to the LP piston so that location of the piston in relation to its travel limits can easily be seen.  This makes it easy to avoid trying to pump the pistons past the end of their travel.


This next picture shows the system pumped up to almost a full 30,000 psi (2,068 bar).  There is a pressure gauge on the low pressure side and one on the HP output.  The gauges show good correlation regarding the 5.6 to 1 pressure multiplication and also show if part of the system gets locked up, or starts leaking, or has trapped air. In this  picture, the output is about 29,500 psi and the input is about 5,500 psi. Not quite 5.6 to one, but the o-rings in the system tend to clamp up tighter as the pressure increases. Modifying the gland diameters by a few thou here and there might have eliminated some of the hysteresis, but I didn't think it was worth trying at the risk of possibly causing leaks in the system.


Here is how the system operates within the limits of the 7cc output of the HP side.
To set a tube up for test, it would be threaded directly into the female 1/8" NPT hole on the side of the HP manifold at the end of the test apparatus.  That port is labeled Hi Press Tap for connection to test piece. The tube would obviously need some sort of end fitting with the 1/8 pipe thread, and by so doing, the tube and end fittings can all be checked at the same time.

The first step in the filling process is that the input to the low press piston from the hyd hand pump is closed.  Also, the bleed for the LP side is cracked open.  The input from the handpump to the Hi Press piston is now OPENED.  Pumping is now done, which fills the high pressure side of the system with hyd oil directly from the hand pump.  There are bleeds in various places to allow the trapped air to be purged.  The hand pumping continues until the high pressure side and the tube to be tested are filled with oil and all the air is bled.
At this point, the HP side should be filled with oil, with no air, and pressurized to about 7,000 psi. Now, the input valve to the HP side is closed.  The bleed on the LP side is closed.  The input valve on the  low pressure side is now opened.  Now, when the hand pump is operated, it will only being trying to further compress the hyd oil in the HP side via the pressure from the large LP piston.  That is why the 7cc of HP oil is sufficient.   It only has to increase  the pressure from 7,000 psi to 30,000 psi.  Because the oil is already "pre-loaded", the pressure increase will use very little additional oil until failure of the test piece balloons its volume.

That's about all there is to it.  By far, the most difficult part of the testing is filling and bleeding the test part befre trying to pump it to full pressure.  But it seems to work well.  Luckily, for the destructive testing, the pressure only needs to be held for a few minutes, and there has been no indication of bleed-down in that time period. 

That's it for now!
Lloyd


 

[Buldawg76]

Lloyd
That's so simple yet perfectly effective for the test you are doing. it just shows that you don't need a big company or bankroll to perform valid testing of components in a very structured and professional method.

It reminds me of my days at Harley in research and development working with engineers to test to failure the required components on bikes to validate the design and manufacturing processes. Man do I ever miss that job since it was like going to play every day but getting paid to play as hard as I could everyday. 

Mike

[Rob M]

very elegant design LLoyd. I had to read the fill /bleed procedure twice ..However , you failed to disclose where you sourced a military grade bomb vest? 

[lloyd-ss]

Buldawg, having a fun place to go to work is a great situation.  You had a good deal there. 
Rob M, I hope I explained it well enough.  All of the filling is done directly from the hyd hand pump, and the hyd multiplier is only used to top up the final pressure.  Of course, I haven't actually "tested" anything yet   , but that will be soon, with a video. BTW, the "bomb vest" consisted of some old, heavy, braided rugs laid over top of the whole set-up.  Almost as good as those wire rope blasting mats that excavators use.
Lloyd

[Rob M]

very good explanation, a cheap high pressure test vessel is a 90 gram co2. Others have pushed them to 14,000 before failure( in the event you wanted to test the system before blowing a pcp tube)

[Buldawg76]

very good explanation, a cheap high pressure test vessel is a 90 gram co2. Others have pushed them to 14,000 before failure( in the event you wanted to test the system before blowing a pcp tube)

Rob
That good to know since I have my 1077 converted to HPA using a 90 gram cartridge in a ASA adapter and filling to only 1400 psi but it alleviates the FPS drop using CO2 when rapid firing the gun and gets 60 shots per fill on free air not CO2.

mike

[lloyd-ss]

Here's a video of the first real test using the hydraulic multiplier. The results were impressive.
More info to follow.
Lloyd 

[Sfttailrdr46]

Can't wait to see the results of the titanium tubes actually can't wait for you to start producing titanium air tubes for the Marauder  because the stock tube weighs a ton, Correct me if I am wrong but you could set the pressure at say 3600 psi with the titanium air tube and regulate it down and get more usable shots from a stock length air tube or even more shots from a titanium double tube set up and have a tremendous weight saving even with the additional storage over a stock setup

[lloyd-ss]

Can't wait to see the results of the titanium tubes actually can't wait for you to start producing titanium air tubes for the Marauder  because the stock tube weighs a ton, Correct me if I am wrong but you could set the pressure at say 3600 psi with the titanium air tube and regulate it down and get more usable shots from a stock length air tube or even more shots from a titanium double tube set up and have a tremendous weight saving even with the additional storage over a stock setup

Don,
You are correct about the performance of the Titanium tube.  If you used a Ti tube (alloy 3Al-2.5V cwsr) of exactly the same dimensions as the Marauder rifle tube (23" long x 1.25 O.D. x .093 wall), with a few strategic strength improvements on a few of the other components,  you'd be able to install a Huma reg near the valve, and fill the front end of the tube to 4500 psi instead of the factory 3000 psi.  Depending on where you had the reg set, you could effectively double the shot count on a single fill.  You would also save one full pound of weight from the Ti tube (2.25 lb for the steel tube, 1.28 lb for the Ti tube).  The safety factors of the 2 tubes, even with the different pressures, would be pretty much identical.  Of course, the Ti tube material is very pricey at about $4.00/inch, and that's before it even gets on a machine.  Also, would need to check with the Huma folks to make sure the reg is rated for 4500 psi input.
I won't personally be able to make any M-Rod tubes because my lathe is limited to 1" dia thru the head stock, but I do have a very good local source who makes many of my production items that has the capability.
Lloyd

[Sfttailrdr46]

Can't wait to see the results of the titanium tubes actually can't wait for you to start producing titanium air tubes for the Marauder  because the stock tube weighs a ton, Correct me if I am wrong but you could set the pressure at say 3600 psi with the titanium air tube and regulate it down and get more usable shots from a stock length air tube or even more shots from a titanium double tube set up and have a tremendous weight saving even with the additional storage over a stock setup

Don,
You are correct about the performance of the Titanium tube.  If you used a Ti tube (alloy 3Al-2.5V cwsr) of exactly the same dimensions as the Marauder rifle tube (23" long x 1.25 O.D. x .093 wall), with a few strategic strength improvements on a few of the other components,  you'd be able to install a Huma reg near the valve, and fill the front end of the tube to 4500 psi instead of the factory 3000 psi.  Depending on where you had the reg set, you could effectively double the shot count on a single fill.  You would also save one full pound of weight from the Ti tube (2.25 lb for the steel tube, 1.28 lb for the Ti tube).  The safety factors of the 2 tubes, even with the different pressures, would be pretty much identical.  Of course, the Ti tube material is very pricey at about $4.00/inch, and that's before it even gets on a machine.  Also, would need to check with the Huma folks to make sure the reg is rated for 4500 psi input.
I won't personally be able to make any M-Rod tubes because my lathe is limited to 1" dia thru the head stock, but I do have a very good local source who makes many of my production items that has the capability.
Lloyd

Lloyd that would make the overall weight without scope ~7 lbs without changing the balance So we are talking  approximately $100 plus machining. and with a rifle for the field we now have a really great hunting rifle so for someone so inclined that makes for a nice working project rifle. I could see someone gathering parts over time and turning a plain jane .25 Marauder into the talk of the town.