testing UW equipment

Hi:

I have some prototipes of a push button I sent to a machinist.

He came with this idea about testing them: use the buttons in a sealed acrilic box (I made the buttons as a "stand alone" unit, so I can screw them in any acrilic box. I´ll post photos...). Presurise the inside of the box (with a regular tire valve screwed in the box. Then submerge the box in the water to check out for bubbles...

As I understand, every 10 meters deep I have a 1Kg/cm2 plus (15 Lbs?). So to check the buttons for 30m I should give pressure to the box up to 4Kg/cm2...ok?

I know in a housing is the opposite. The water pressure is high while the air pressure is low...could this way of testing work anyway?

Thank you

Alejandro

Hi:

I have some prototipes of a push button I sent to a machinist.

He came with this idea about testing them: use the buttons in a sealed acrilic box (I made the buttons as a "stand alone" unit, so I can screw them in any acrilic box. I´ll post photos...). Presurise the inside of the box (with a regular tire valve screwed in the box. Then submerge the box in the water to check out for bubbles...

As I understand, every 10 meters deep I have a 1Kg/cm2 plus (15 Lbs?). So to check the buttons for 30m I should give pressure to the box up to 4Kg/cm2...ok?

I know in a housing is the opposite. The water pressure is high while the air pressure is low...could this way of testing work anyway?

Thank you

Alejandro

Hola Alejandro,

Actually, you need to pull a vacuum on the inside of the box. Buttons are made to keep water out, so are designed for pressure from the outside. Pressurizing the inside of the box will be putting the pressure on the wrong end of your buttons. If you can find a automotive brake tester (hand held versions are available and cheap), which pulls a vacuum on the brake lines, you can use the brake tester to pull a vacuum on your box. The brake tester comes with a gauge, so you can easily see if you have a leak.

Air is less dense than water, so when you pull a vacuum on our box, you will even have a more accurate method of testing for leaks.

Added bonus to using a brake tester is that if you do have a leak nothing gets ruined by water.

Good luck,

Barry

Good advice,

But pulling a vacuum will only give you one bar of pressure differential at the most. That equates to 10 meters water depth.

Barry has a good design for a pressure chamber which you should ask him about. Pressure testing using an acrylic box sounds very dangerous. Look at safety first and always and good luck!

James

Good advice,

 

But pulling a vacuum will only give you one bar of pressure differential at the most. That equates to 10 meters water depth.

 

Barry has a good design for a pressure chamber which you should ask him about. Pressure testing using an acrylic box sounds very dangerous. Look at safety first and always and good luck!

 

James

James is 100% correct about the vacuum only testing for around 30'. I left off a vital step in my procedure -- After vacuum testing, then I test in a pressurized paint tank that is full of water.

Barry

James is 100% correct about the vacuum only testing for around 30'. I left off a vital step in my procedure -- After vacuum testing, then I test in a pressurized paint tank that is full of water.

Barry

Thanks a lot!!

I will keep it in mind...

Best regards

Alejandro

I couldn´t find a pressure chamber I could build, so I started with my original idea and made a change:

I´m still adding pressure to a box with the push buttons screwed in, but in an INVERSE POSITION: The button inside and the shaft outside. I will check them with the box inside the water looking for bubbles. I can check them dinamically pulling the shafts...

http://picasaweb.google.com/XTREME.ALEK/UN...081754270579314

http://picasaweb.google.com/XTREME.ALEK/UN...081776346612178

http://picasaweb.google.com/XTREME.ALEK/UN...081776346612178

http://picasaweb.google.com/XTREME.ALEK/UN...081786549834642

http://picasaweb.google.com/XTREME.ALEK/UN...081657322584802

Could this still work?

I´m applying the pressure in the right direction, but AIR pressure (less density than water...)

This are the push buttons:

http://picasaweb.google.com/XTREME.ALEK/UN...081732830962194

http://picasaweb.google.com/XTREME.ALEK/UN...081664650730274

http://picasaweb.google.com/XTREME.ALEK/UN...081685536780306

By the way...

How should I do to make the photos show in the post instead of the links?...

Thank you

Best regards

Could this still work?

I´m applying the pressure in the right direction, but AIR pressure (less density than water...)

If you're designing something to work with o-rings, I've found this handbook to be invaluable:

http://www.parker.com/literature/ORD%20570...ng_Handbook.pdf

If you follow the recommendations in that handbook, your seals will work, they will work well, and they will work for a long time. The handbook is conservative, in that you can break many of their rules and still get a good reliable seal, but it will require more testing to prove that. For example, they recommend against using silicone rubber with saltwater, but there are many reliable underwater camera housings that do exactly that.

Getting back to your question, if you're testing in anything other than real-world, worst-case conditions, you need to decide what type of failure you're testing for. In my mind, these are the main causes of seal failure, in no particular order:

1. contamination

2. bad surface finish or hairline scratches

3. seal extrusion

4. the seal not seating properly in the groove

5. worn out seals

6. the housing bending so that the seal doesn't fit into the groove

7. chemical attack on the housing, shaft, or seal

Your test with air will actually be better than testing with water for something like #2, the hairline cracks. Because water beads up on rubber seals, water doesn't leak through some of the smallest cracks, but air does (this is the principle used in waterproof/breathable fabrics like Gore-Tex). So testing with air and the buttons backwards will be a conservative test as far as detecting surface scratches or cracked seals.

On the other hand, you also want to test the actual surfaces that will be used, and you want to make sure that the housing bends in the way you expect it to bend, and you want to make sure that small amounts of contamination or silt or crystallized salt won't compromise your seal.

Hi:

I have some prototipes of a push button I sent to a machinist.

Thank you

Alejandro

Alejandro,

Looks like you have a winner here with those pushbuttons. Are you going to try to sell some to the rest of us DIYers?

Keep us informed on your pressure tests. I know you already know this, but please add pressure slowly, which will be a hard task with your small box. Also, put something between you and the box just in case the box comes apart.

Good luck,

Barry

Thanks a lot!!!

This is a first phase test. I´m testing the button, but I´m testing how well I can do a thread in acrilyc and how well the buttons seal to that. I´m planning my housing in 12mm thick acrilyc with a 20mm back cover.

This test is primary to tell to the machinist: "it´s ok, make me some more".

I will check with some other parts and the whole system (still to be made...)

Thanks for the link to the handbook!!

Best regards from Buenos Aires

Alejandro

Hello Barry!

Thanks. The push buttons looks good. I took some ideas from Marc Furth controls, some ikelite controls and from a DIY video housing that had threaded modules for buttons. I wanted to get controls that I could put wherever I need, and in case I should change the housing, I could re-use the parts.

I´ll try to test them deeply.

As I live in Argentina I find difficult to send parts...But they´re simple. I could draw a schematic if you want. Sure any machinist could make them easily. The body is a 10mm thread, 20mm long hex head bolt, machined round with a 6.25/3 mm hole to accomodate the button. The button are two stainles steel bars united: 6mm and 3mm with grooves for the o-ring and safety clip.

I tried the pressure test with the little box. It didn´t explode, but started to leak seriously when I went over 2Kg/cm2. I gave pressure with a foot pump with gauge. I could only get 3Kg/cm2 briefly once, because of the leaking (with the box into the water).

The buttons seemed to be ok, but I think I need a better way to test. I will try a metal case if I can...

Thanks for all the responses

Best regards

Alejandro

Thanks a lot!!!

This is a first phase test. I´m testing the button, but I´m testing how well I can do a thread in acrilyc and how well the buttons seal to that. I´m planning my housing in 12mm thick acrilyc with a 20mm back cover.

Best regards from Buenos Aires

Alejandro

Hola Alejandro,

Threading into acrylic is fairly easy, just be sure to have a sharp tap and go slowly. After the initial start of the threads, turn the tap around 3/4 to 1 turn then back off, repeat, repeat. The method described takes longer but will assure a nice thread without having the already cut away chips break your threads. I also ocassionally use WD40 to squirt into my threaded hole while tapping. The WD40 seems to lubricate the tool, making it cut faster, and makes the acrylic thread look and be cleaner.

Extruded acrylic does not work as nicely as cast acrylic. Extruded acrylic will gum up when cutting or cutting your threads, while cast acrylic works like a dream. Of course, cast acrylic is more expensive but worth the price in my book.

Buena suerte,

Barry

James is 100% correct about the vacuum only testing for around 30'. I left off a vital step in my procedure -- After vacuum testing, then I test in a pressurized paint tank that is full of water.

Barry

Hi Barry,

1. Do you have a picture to show this pressurized paint tank?

2. Is it a fairly easy DIY project?

3. and up to what pressures can one test with it?

This sounds like a very handy tool to test some of the smaller DIY projects I'm thinking about doing.

In my younger years I hydro-tested scuba tanks for a dive store, so I'm somewhat familiar with the principles involved.

Thank you for any information!

Bo

Pressurizing the inside of a container with air (any gas) is far more dangerous than pressurizing the inside with water. When using air, the air compresses and generates potential energy. This energy can be released if the unit breaks under stress. That released energy can send parts flying at high speed and do some serious dammage.

Using water (or another liquid) generats next to no potential energy since the water does not compress. When water pressure tested, if the device fails, very little water needs to leak out to relieve all the pressure so there is no energy to project pieces.

This method of water based testing is used in industry for testing high pressure equipment such as tanks, columns, reactors, etc. for just the reasons described above.

Similarly, if you test with water on the inside, you do not need to immerse the test box. You would see the water leak out. This also matches the actual underwater condition of water on the high pressure side, air on the low pressure side.

I test all my housing I’ve made with pool filter tanks. With adequate city water pressure you can test all the seals with out the dangerous effects using air pressure. A simple garden hose connected to the bottom of the tank with a valve on top of the tank letting the air out as you fill the tank. When the water reaches the top of the tank, simply close the valve off. Place a maximum depth gauge inside the tank. Place something in front of the push button controls and if they have moved after the test you’ll know what depth the controls will move at. You can usually buy used tanks from pool supply stores. I suggest buying a stainless steel tank, their usually rated for higher working pressures. Place a water pressure gauge on the tank will let you vary the pressure inside the tank, Marc

I test all my housing I’ve made with pool filter tanks. With adequate city water pressure you can test all the seals with out the dangerous effects using air pressure. A simple garden hose connected to the bottom of the tank with a valve on top of the tank letting the air out as you fill the tank. When the water reaches the top of the tank, simply close the valve off. Place a maximum depth gauge inside the tank. Place something in front of the push button controls and if they have moved after the test you’ll know what depth the controls will move at. You can usually buy used tanks from pool supply stores. I suggest buying a stainless steel tank, their usually rated for higher working pressures. Place a water pressure gauge on the tank will let you vary the pressure inside the tank, Marc

Thanks Marc,

Good idea! I was wanting something that could hold a small housing with port and test at greater depth than a home pool. I will look around for an used one.

Bo