The main steering gear is arranged so that after a single failure in its piping system or one of the power units, the defect can be isolated so that steering capability can be maintained or speedily regained.

It refers to the operation of the steering gear even in the event of failure of one power actuating system with either 100% power or 50% power. i.e., a single failure concept can be either a 100% redundant system or a 50% redundant system.

It refers to the operation of two steering gears with at least two separate and independent power actuating systems, and each of them shall be capable of meeting the requirement. In case one system fails, it can be detected and isolated, and the other system comes into action.

Case 1: Consider an oil leak from any pipe for cylinders 1 and 2 with the No. 1 pump running:

1. No. 1 tank level will come down to L1, and it will sound an alarm on the bridge and in ECR
2. When the tank level further drops to L2, i.e. low-low level, the no. 1 pump stops.
3. Stopping the No. 1 pump also stops the attached auxiliary pump. So the line pressure drops, due to which the normally closed by-pass valves ‘X’ and ‘Y’ open.
4. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. A, B and C are normally open valves. The electric signal will close them. So, systems 1 and 2 will be completely separated. Thus, the defective system, I.e. system 1, is isolated.
5. Along with the operation of the auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close it. This enables cylinders 3 and 4 to be in normal operation.
6. It should also be noted that since system 1 is completely isolated, there is no oil pressure to operate the bypass valve. So the by-pass valves remain open, thereby removing the hydraulic lock for the ram movement in cylinders 1 and 2

Case 2: Consider an oil leakage from any pipe of cylinders 3 and 4 with the No. 1 pump running:

Points 1, 2 and 3 are the same as case 1

1. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. This will shut the normally open valves A, B and C. Thus, systems 1 and 2 will be completely separated
2. Along with the operation of auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close. So, cylinders 3 and 4 will come into normal operation.
3. Now, since the leak is between the pipe of cylinders 3 and 4, the level of the no. 2 tank will drop to L1 and give an alarm.
4. The level will further drop to L2, but the pump will not stop and changeover to ensure that the leak is from the pipe of cylinders 3 and 4
5. When the no. 2 tank level drops to L3, the no. 2 pump stops and the no. 1 pump starts to operate the steering using cylinders 1 and 2
6. Starting the no. 1 pump will ensure that the by-pass valve ‘X’ is shut, and stopping the no. 2 pump will ensure that the by-pass valve ‘Y’ is open