Pressure testing

[firemedic296]

technically yes, but No.. The camera when closed is equalized at sea level (1ata). at 10m below the surface the camera is "technically" at 2ata but only has 14.7psi pressure on it. So.. to test the camera to 50m or 5ata below the surface you have to multiply the number of atmospheres below the surface times 14.7. Technically you would be at 6ata but since the camera is equalized to 1ata at the surface it is basically zero.

that didn't make any since at first. not just the camera is at zero, but your pressure gauge on you compressor is callibrated to zero. 1 ata is 14.7 and 33ft kis 2ata but the gauge you buy at the store has already zeroed out the first ata.

see i told you i was confused. i just had to think for a minute and the dumb @$$ light came on. lol

 

[jetski781]

Don't feel bad I started writing and got myself confused. I rewrote that about 3 times and still could'nt come up with a good way to say the camera and guage are both zero at sea level.

 

[firemedic296]

you were saying that the camera is eqaulized, and i was thinking yes it is equalized to 14.7 and you cant take that away or you would be cheating you test to one less ata than you thought you were. but i wasn't thinking about the gauge being at zero. so i'll shut up so i wont confuse anyone else.



edit: didn't see you new post, i wish you would have just said that the first time. i might not have felt so stupid

 

[f3nikon]

Keep it simple folks! I don't use a Nikonos, but a buddy of mine does. He took an old Nikonos extension close up tube (swap meet $10) drilled and tapped a hole for a pipe fitting. Which he then attached a hose to an air compressor.

Mounted the lens to the tube then tube to the camera body, pressurize with 20 to 30 psi of air, dropped into a bucket of water then watch for the bubbles! To make sure his test fixture was working I pulled vacuum on a helium leak detector, it works just fine. The good thing about his jig is that you can run a dynamic test on the oring seals by moving the film advance, focus, aperture and shutter buttons.

To this date he has yet to flood a camera.

 

[jetski781]

Sounds ok and I hope he never does, but some of those seals are designed to work one way(pressure from the outside). Just because it does'nt leak with pressure on the inside does not meant it wont leak with pressure from the outside. The viewfinder front lense is only held in by friction and a touch of adhesive on the trim ring there is no mechanical attachment. The film counter window is pushed in from the outside and is held in place by friction as is the front lense ports. Blow a lense port and you had better hope the aperture diaphram is all the way open. The ASA/ISO knob is held in by a wire clip that seats in a half-round groove and the clip is round. The rewind shaft o-ring is also held in by a similar clip and could easily be pushed out. Try checking at 50m(75psi) and I would be willing to bet it would blow apart not only at those locations.

 

[f3nikon]

Sounds ok and I hope he never does, but some of those seals are designed to work one way(pressure from the outside). Just because it does'nt leak with pressure on the inside does not meant it wont leak with pressure from the outside. The viewfinder front lense is only held in by friction and a touch of adhesive on the trim ring there is no mechanical attachment. The film counter window is pushed in from the outside and is held in place by friction as is the front lense ports. Blow a lense port and you had better hope the aperture diaphram is all the way open. The ASA/ISO knob is held in by a wire clip that seats in a half-round groove and the clip is round. The rewind shaft o-ring is also held in by a similar clip and could easily be pushed out. Try checking at 50m(75psi) and I would be willing to bet it would blow apart not only at those locations.

I thought of this too, that is why I pumped the camera down under vacuum. This is the same as applying pressure from the outside. Negative on the inside, positive on the outside, helium leak tested fine at 6x10-6torr vacuum pressure more than enough for 300 ft depth. All the rotating seals can be tested from pressure from both directions, try this yourself, try pulling off the asa,rewind,aperture and focusing knobs. Remember its pounds per square inch of pressure, the surface area on these seals do not amount to a square inch of surface area. He did try it at 80 psi by mistake, no problems, no leaks. Maybe it was just that camera, that is why he limited the pressure to less than +30 psi. Hey, I would rather test it at low pressure than not test it at all, at the very least with this method you could find out if you forgot to install an oring altogether!

Dive Safe

 

[jetski781]

Yeh, my first thought was to make a dummy battery cap and pull a vacuum from there but my vacuum pump will only pull 1atmosphere. It WOULD be a good quick test for checking the controlls while under vacuum. Now how do I super charge my vacuum pump. I do agree any test is better than no test.

 

[f3nikon]

Yeh, my first thought was to make a dummy battery cap and pull a vacuum from there but my vacuum pump will only pull 1atmosphere. It WOULD be a good quick test for checking the controlls while under vacuum. Now how do I super charge my vacuum pump. I do agree any test is better than no test.

The battery cap maybe little tough on attach a fitting, I would use a beat up Ikelite-Nikonos sync cord. Remove the cord and just use the fitting, on the connector, to attach a plastic tubing to the vacuum pump. You can easily attach to the camera, just like connecting the sync cord, hey wait a minute I should patent that idea!

I am not sure which vacuum pump you have. Most vacuum pumps I work with, use torr, pascal, bar or inches of mercury, negative numbers for vacuum as a unit of measure. 1 atm. is positive pressure, as in underwater pressure. Vacuum is more like outer space.

Surplus stores or lab supply stores like VWR are places to get these pumps.

Dive Safe

 

[jetski781]

My vacuum pump measrures in in/hg...1atmosphere=29.9213in/hg I used atmospere because that is what the camera is rated in. The sync plug doesn't work because the connector inside the camera is sealed also. Unless the connector is damaged you would be pulling a vacuum on the sync port only. That does'nt mean you can leave the sync port plug out though. Salt water and electrical current inside the port does'nt go well together much less corrosion on the pins. however I have started machining a plug to fit the lense mount, Probably the best option for connecting a vacuum line. Although you can't check the lense that way?

 

[f3nikon]

My vacuum pump measrures in in/hg...1atmosphere=29.9213in/hg I used atmospere because that is what the camera is rated in. The sync plug doesn't work because the connector inside the camera is sealed also. Unless the connector is damaged you would be pulling a vacuum on the sync port only. That does'nt mean you can leave the sync port plug out though. Salt water and electrical current inside the port does'nt go well together much less corrosion on the pins. however I have started machining a plug to fit the lense mount, Probably the best option for connecting a vacuum line. Although you can't check the lense that way?

The seal on the connector is not a water tight seal that is why you need the sync plug to make the seal. When I mean remove the sync cord I meant cord and cord pins, camera will be pumped out just at a slightly slower rate, due to the mating pins on the camera being in the way. The air like the water, will blow right by the pins from the camera body.

Machining a plug for the lens port will do but why go through the extra work, as I said in the begining use a Nikonos, Helix or Ikelite close up extention tube and drill/tap a fitting on the tube's side, this way you can check the camera and lens at the same time.

I am not sure I follow you on the vacuum measurements, on your past post you had mention that your vacuum pump can only pull to 1 atm.? That is not even rough vacuum, 29.9 in/hg = 760 torr is the pressure of atm.(positive pressure) rough vacuum is at 5.0x10-3 torr or .001968 in/hg (negative pressure). What type of vacuum gauge are you measuring the pressures?

These are some of the reason why I don't use a Nikonos, guessing the focus and composition, I may now add flooding. Its hard to beat a 15mm wideangle Nikonos lens when its in sharp focus.

Dive Safe