I remember reading something here about pre pressurizing the hull before diving, but I can't find it again.
The idea was that if you have a hull that can take 10bar of outside pressure, it can reach 100m, but if you add pressure to the hull, for instance 5bar it should, theoretically be able to reach 150m? as the pressure acting on the hull is 0 at 50m right?
Is there any downsides to doing this? Two I can think of is that the electronics might not like it and that a pressurized container has a lot of energy stored in it.
Other thoughts?
Pressurized hull
Re: Pressurized hull
Commercial ROV's have compensators to pressurise some of the termination boxes as well as thruster seals etc with oil.
Compensators keep the inside pressure a few psi above water pressure so they don't have high internal pressures on the surface and the differance between inside and outside pressures is always low.
The big secret with pressures is the pressure differance between in and out, not the absolute pressure.
Pressurising your hull to 10 bar on the surface would mean you need a hull that will stand -10 bar pressure diferential at 0m and 0 bar differential at 100m.
if you dont pressurise it, then you need a hull that will withstand 0 bar differential on the surface and + 10 bar at 100m.
It's easier to design the second than the first.
Filling with oil helps as oil compresses less than air so it helps support the hull.
You could have a high pressure air supply and pressure sensors to balance internal air pressure with external water pressure at different depths. I'm tempted to try it.
Compensators keep the inside pressure a few psi above water pressure so they don't have high internal pressures on the surface and the differance between inside and outside pressures is always low.
The big secret with pressures is the pressure differance between in and out, not the absolute pressure.
Pressurising your hull to 10 bar on the surface would mean you need a hull that will stand -10 bar pressure diferential at 0m and 0 bar differential at 100m.
if you dont pressurise it, then you need a hull that will withstand 0 bar differential on the surface and + 10 bar at 100m.
It's easier to design the second than the first.
Filling with oil helps as oil compresses less than air so it helps support the hull.
You could have a high pressure air supply and pressure sensors to balance internal air pressure with external water pressure at different depths. I'm tempted to try it.
Re: Pressurized hull
A self balancing system is overkill for my part. at least for now
What you said that about the difference between inside and outside pressure being the important factor is what I was talking about. I have a hull that can easily contain a positive pressure of 10bar. meaning that at 100m, the pressure acting on the hull is 0. If I continue down to 150m. The pressure differential would only be 5bar of outside pressure (same as at 50m if the hull is not pre pressurized).
So if I ad the ability to pump pressure in to the housing before I dive, I can go deeper before the housing fails.
I was going to go oil filled and pressure compensated, but I want to try without for my first build. Just to avoid the mess if something needs to be changed/modified.
What you said that about the difference between inside and outside pressure being the important factor is what I was talking about. I have a hull that can easily contain a positive pressure of 10bar. meaning that at 100m, the pressure acting on the hull is 0. If I continue down to 150m. The pressure differential would only be 5bar of outside pressure (same as at 50m if the hull is not pre pressurized).
So if I ad the ability to pump pressure in to the housing before I dive, I can go deeper before the housing fails.
I was going to go oil filled and pressure compensated, but I want to try without for my first build. Just to avoid the mess if something needs to be changed/modified.
Re: Pressurized hull
yeah, I see your point.
I don't think the electronics etc will mind 5 bar but hull's are usually designed to take pressure on the outside not the inside.
As long as your hull will take the internal pressure I don't see any other issue.
The main things that don't like pressure are electrolytic capacitors as they are sealed cans, so avoid using them in your electronics if you can.
I've seen metal can transistors crush after going really deep too but most transistors are plastic these days.
I'm planning on a self balancing system but only using 1 bar of internal pressure differance to save blowing my seals out.
(there's a joke there about Eskimo's but not on this forum, haha
)
I don't think the electronics etc will mind 5 bar but hull's are usually designed to take pressure on the outside not the inside.
As long as your hull will take the internal pressure I don't see any other issue.
The main things that don't like pressure are electrolytic capacitors as they are sealed cans, so avoid using them in your electronics if you can.
I've seen metal can transistors crush after going really deep too but most transistors are plastic these days.
I'm planning on a self balancing system but only using 1 bar of internal pressure differance to save blowing my seals out.
(there's a joke there about Eskimo's but not on this forum, haha
)Re: Pressurized hull
olegodo wrote:I remember reading something here about pre pressurizing the hull before diving, but I can't find it again.
The idea was that if you have a hull that can take 10bar of outside pressure, it can reach 100m, but if you add pressure to the hull, for instance 5bar it should, theoretically be able to reach 150m? as the pressure acting on the hull is 0 at 50m right?
Is there any downsides to doing this? Two I can think of is that the electronics might not like it and that a pressurized container has a lot of energy stored in it.
Other thoughts?
Back in the late 90's a friend of mine designed a system to take pictures of deep ocean fish, that is about 5000 meters deep. It had a motion sensor of some sort and whenever something came in front of the camera, it flashed and took a photo.
It consisted of a flexible "bag", filled with an insulator liquid which I forget, and most (or all ?) of the hardware was thrown in there and plunged into the ocean. No solid hull whatsoever. It worked and the electronics did not mind at all.
Re: Pressurized hull
Sure, this is basically what all the commercial deep diving ROV's use. This was also what I had in mind when I started out.
The reason I have chosen not to do it this way is that I see myself wanting to change stuff a lot in the beginning. maybe some of the electronics needs to be upgraded before I find something I am satisfied with. having to drain the oil each time is a big downside to this approach.
Maybe at a later stage when I am bored of only being able to go 100m
The reason I have chosen not to do it this way is that I see myself wanting to change stuff a lot in the beginning. maybe some of the electronics needs to be upgraded before I find something I am satisfied with. having to drain the oil each time is a big downside to this approach.
Maybe at a later stage when I am bored of only being able to go 100m