View Full Version : Pressure threads update

08-17-2001, 01:33 AM
if a hydarulic unit fails, it generally leaks, or blows an end cap off.

if it's full of something compressible like air it's a bomb.

the hydro testers use the bath of water to measure the change in volume of your flexing tank.

the hydro testers fill your unit with water to pressurize it, so if it does fail it's not such a bomb.

04-16-2004, 01:52 PM
Hello all,

Just a quick update on my hydraulic cylinder problem..

I ended up making steel end caps instead of the aluminum ones...I have tested the cylinder at 10,000 psi...No problems yet..

I have cycled the cylinder about 50 times now, and I will continue to cylce for another 50 to 100 more times...

Thanks to all who replied..a lot of good ideas out there...


Herb Helbig
04-16-2004, 03:27 PM
It might be interesting to place a dial caliper around the cylinder while pressure testing to see if the expansion is noticable.


Mike W
04-16-2004, 05:07 PM
Something told me that steel would work. Glad you got it going.

04-16-2004, 09:55 PM
If it is expanding then assuming you have the room shrink on a steel sleeve.

04-17-2004, 02:20 AM
If it is expanding and not returning to the original size exactly, it's a bomb waiting to blow.

04-17-2004, 08:52 AM
I don't know how it is done with hydraulics, but with coded pressure vessels such as boilers and pressure tanks, the normal hydro test is done at three times the operating pressure.
I would think a similar safety factor should be applied to an item such as this as well.
If you intend to sell this to the public, unless you have engineering data to support the design parameters and follow recognized or mandatory test procedures, you would be hung out to dry in the event of a failure. If injuries occurred, criminal charges could result.

04-17-2004, 11:24 AM
There is a safety rating for hydraulics as well...What I normally do is come up with a prototype and test it under my conditions, then I will send the setup out to get tested to see what pressures will blow it up...

The pressure should be 3 times the normal operating pressure for me to pass it off...This situation that I am doing will not be anything to do with the public...

This project is just for a learning curve for myself...Like I said before, I am just trying to get my feet wet when it comes to high pressure hydraulics...What better way to learn than to use an actual model instead of just numbers on paper...

I have now cycled this cylinder about 100 or so times and there is no failure yet...I have allready learned a bunch of stuff with this project...


04-17-2004, 07:17 PM
Thanks for the clarification Brent. We would hate to lose you to the legal system.

04-17-2004, 08:05 PM
topic rescue

04-17-2004, 10:02 PM
On the water bath testing: We had a man testing heat exchangers, submerged in water, water in the exchanger. Exchanger failed

He was leaning on the tank, the shock wave ruptured and pulverized most of the internal parts, instant death. A (not the THE) properway to test is fill with non compressible liquid, submerge, get way back and apply pressure, THEN lower pressure and measure (if you have maximum expansion sizes).

04-18-2004, 01:12 AM
Pretty cool. How do you crank the psi to 30,000? Put the filled cylinder in a press?

04-18-2004, 01:21 AM
Thats how I do it at work,I once built a ram,piston and cylinder out of hardened bearing steel,it was capable of 120,000 psi,but it was only a .500" bore.Something special for the Navy,never did find out what it was for.

04-18-2004, 07:41 PM
I have no way to test anything over 10,000 psi...i send it out and they put in a big tank filled with water, and then they test it with their equipment...being in the tank of water is so when the cylinder fails, it fails inside of the tank...