If you are making a device to work deep underwater then the main question is whether it will be crushed by water pressure. Moreover, even a small leakage of water can lead not only to damage to expensive equipment, but in some cases may even threaten our safety. How to check the tightness of the hull in advance, on land, especially if there is not a deep lake or sea nearby? Usually for this purpose we use a strong case of the appropriate size and a powerful compressor. But where do we get all this stuff and will this test be safe for us?
We have a good answer!
Step 1: Stuff
The main items:
1. Medicine syringe ~$3 (depends on volume and quantity)
2. Pressure gauge 140 PSI ~ 100 meters underwater (or bigger up to 360 PSI ~ 250 meters) - $7
3. 1/4" Mini Brass Ball Valve - $7
and one of a pressure chamber with suitable capacity:
1. Pressure cooker (upto 60 PSI ~ 40 meters) - $30
2. or Water clear filter housing (125 PSI ~85 meters) - $13
3. or Brass water filter SX 600 (220 PSI ~150 meters) - $40
Step 2: How Does It Works
For our safety a high-pressure test needs to use water (or another liquid). In the event of leakage or even complete destruction of a housing or chamber under test, the pressure will instantaneously drop to zero and this will ensure a complete guarantee of our safety. To create a pressure of 100-300 PS you only need a few milliliters of water and in case of a leak you do not even get wet. But how can we create such a pressure without using high-cost compressors? You can do it with one finger using a regular medical syringe! Just draw water into the syringe and push the plunger. The maximum pressure will depend on the strength of your hands and the diameter of the syringe. The thinner the syringe, the more pressure you can create. For example, with a 2 ml syringe I easily create a pressure of 300-360 PSI (200-250 meters underwater!!!)
Moreover, a test with water will allow us to avoid damage to the device under test. You can perform tests even without removing the batteries from the flashlight or the photo camere from the underwater box. Since the test requires only a few milliliters of water, in the case of even the smallest leak, the pressure will drop dramatically and you will immediately see a leak of even a few drops of water!
To make your own Hyperbaric Test Chamber it is enough to choose a solid case of the appropriate size. Now make two holes in the cover and screw the ball valve and the pressure gauge. The test chamber is ready :)
Step 3: Using
We made more than 10 different test chambers. We used large pressure cookers to test underwater boxes, diy ROV thrusters to a depth of 40 meters. The filter housings are used for testing Gopro cameras, underwater lights and diving computers.
The testing process is very simple. Pour the water to the very top, put the torch and close the lid, excess water should flow. This is necessary in order to keep as little air as possible in the test chamber. Now draw water into the syringe, inject it into the chamber and close the ball valve. And so we repeat until the desired pressure is reached. It is then recommended to leave the chamber for a while under pressure as the leakage may not start immediately. If the needle of the manometer did not move, then there was no leakage. Insert the empty syringe, open the ball valve and the water will return to the syringe, now there is no pressure and the lid can be opened. Your device has been tested and ready to operate underwater.
Such a hyperbaric test chamber does not need an expensive compressor, you do not need to monitor the compressor and turn it off in time. Just push the plunger then close the valve. It's easy, absolutely safe and always ready to work.