Pressure Test #4

This morning I completed the final pressure test and reached 8 meters down (11.76 psi).  Toward the end of this update I have outlined the reasons for stopping here.  The window gave no resistance to the pressure at that depth.  It was experiencing about 2,778 lbs/sq.in (1,263 kg/sq.in), even after hitting it all over with a rubber mallet, just to be sure.

Fig. #1.  5 meters down.

Fig. #1.
10/01/2017

Fig. #2.  6 meters down. 

Fig. #2.
10/01/2017

Fig. #3.  7 meters down. 

Fig. #3.
10/01/2017

Fig. #4.  8 meters down.

Fig. #4.
10/01/2017

Fig. #5.  Upon closer inspection I noticed that the ball valve had began to crack at 8 meters.  In case it suddenly failed whilst pulling a vacuum, and possibly damaging the pump if derbies went up the pipe, I decided to stop and replace it.

But after another look around the sub I saw that most of the plates making up the dome had began to go flat under the pressure.  These plates were actually made from a thinner steel than the rest of the hull.  I could go inside and weld more support for them but I'd have to stop at some point.

So I've decide that 8 meters is more than enough for a un-pressurized dive and will make it the maximum.  For safety I'll add a buffer below that of about 2 meters, so 6 meters un-pressurized.

I have also added these numbers to the Specifications page.

Fig. #5.
10/01/2017

Next will be Stage Two of testing.  As shown here.

Pressure Test #3

Yesterday evening I bolted and sealed the new front window in place and this morning I resumed pressure testing.  I managed to get it down to seven meters (10.29 lbs/sq.in [4.6kg]) today before a few leaks stopped it from going any further.  Besides the leaks, that are now fixed, an area on both sides of the hull directly beneath the conning tower began to give in (Fig. #2).

Over all though everything else was fine - including the window which would have had about 2,430 lbs (1,105 kg) across it.

Fig. #1.  Currently at two meters.

Fig. #1.
08/01/2017

Fig. #2.  It's hard to see, but the hull has given in a little at the places marked with an X.

Fig. #2.
08/01/2017

Fig. #3.  I'll be welding in some reinforcement over the next few days that will strengthen up the area shown in Fig. #2.  I originally had some here but it got removed when the tower went on and I forgot to put it back.   Hopefully I'll have both sides done tomorrow, but it'll depend on if I can replace my gas cylinder tomorrow or not.

Fig. #3.
08/01/2017

I plan to resume testing by mid week.

Pressure Test #2

Just a quick update today.  Yesterday I replaced both 3mm thick windows with 6mm thick ones and let the sealant dry over night.  This evening after work I resumed pressure testing.  At about five meters down (approx seven psi) the front window cracked and the hull lost its vacuum.

I made a crucial mistake with this window, and that was to use the old 3mm window's holes as a template to drill into this one.  I didn't think about the fact it would curve slightly different to the 3mm one, being a lot thicker, and of course some of the holes didn't match up toward the end of the window.  I then decided just to clamp it down, seal it up and test it anyway.

I concluded that it cracked due to a few reasons;

1. it didn't have any bolts in the last few holes so the forces may not have been equal across the window, also this section may have flexed more against the seal under pressure.
2. the forces involved in the straps holding the window to a curve would have not been there in the final build, and...
3. the main reason of using poly-carbonate is that it can be flexed quite dramatically and not break, so even under normal atmosphere pressures the whole window is under a lot of stress just simply being held in a curve.  That, coupled with the pressure difference would have added to why it cracked.

For next time, I plan to get the piece remade, and if possible have it heated and curved to the right shape.  I will make sure to drill the holes by holding the window in place, and I will put every single bolt in!

At least this will give it a good chance for next time.

Fig. #1.  The crack occurred when the window had approx 780kg across it at roughly five meters down.

Fig. #1
04/01/2017