A very common questions which is usually asked is how do various components installed on Remotely Operated Vehicles, diving at the depths of 3000 meters of seawater, sustain such a high pressure? How the structural integrity of these equipment is ensured?
Let’s find out..
Imagine a can of soda water submerged at the depth of 3000 meters of water, and at this depth there is approximately 3000 psi of water pressure acting on the walls of the can. What do you think will happen to the can? The obvious answer is that the can will implode!!!
So how do we ensure that the can sustains this tremendous pressure?
There could be few possible solution;
a) Make the walls of can thicker
b) Use a compensation system.
Option ‘a’ seems simple but it is not a very cost effective solution, plus it will add unnecessary weight to the component, which trust me, no one will want on a ROV (making ROV as light as possible is vital).
That brings us to the compensation System. So what really is compensation system?
The operating principle behind any compensation system is the fact that for a fluid-filled volume, any compressive pressure applied to the outside must be countered by an equal or greater force inside.
The compensator consists of a piston, one side of which is exposed to the ambient pressure, with the other side directly connected to the oil-filled housing. Doing this will ensure that at any depth, the pressure inside the housing is equal to the pressure outside.
The spring provides additional force against the piston, resulting in the pressure inside the housing being slightly higher than ambient. This simple feature ensures that in the event of a leak, oil will flow out of the housing, instead of seawater flowing into it. For this reason, the compensator contains one or more gallons of oil, which is used to back-fill the housing in the event of a small leak.
Imagine the soda can attached to the end of a compensation system and now say for example, the ROV dives at 300 meters of depth, the external pressure acting on the walls of can is approximately around 300 psi, however, this time due to compensator attached to this can, the pressure inside the can is equal to external pressure, thereby ensuring the structural integrity of the can.
This is how components of ROV sustain high pressures at great depths.