INGENIEUR
Figure 3.2.2 : Jetting system hydraulic diagram .
or tank for soft start-up . During any first-time vehicle firing up , there will normally be an unstable spike in the system ’ s hydraulic pressure due to air or moisture . A soft start system creates a stable hydraulic pressure and flow across the entire system . Any high pressure or sudden spike will be directed to the reservoir . Only after a stable hydraulic pressure is achieved will the bypass valve be closed and the system is safe to be used .
In most cases , a mechanical soft start will provide a cheaper solution as it does not require as big a space as an electrical soft start . So most ROV developers prefer a mechanical soft start .
Every subsea housing component such as the subsea motor , valve pack , junction box , bearing housing , etc . that are filled with oil , must be provided with an independent or sharing bellow compensator . The primary reason for this is to provide a safety measure during any leakage of these components . Oil from the compensator flows to the leaking component until it runs out . This provides enough time for the system to be lifted out of the sea water . If the recovery takes a very long time , the leaking component may not be able to be compensated with the available oil from the compensator and sea water will rush into the component . However , the overall system will still work if this happens . Once the vehicle is on the ship ’ s deck , it will be flushed clean by fresh water after all repairs are done and before hydraulic oil is introduced .
The electric motor is installed inside a housing , which is designed to have a good heat releasing capacity . The motor will then be filled with oil to reduce the amount of heat generated during operation . Normally the motor is a 4-pole type instead of 2-pole due to its high torque capability and where it is not required to run at high speeds . Power is supplied to the rotating device by means of electromagnetic induction . Induction motors are now the preferred choice for industrial motors due to their rugged construction , absence of brushes ( which are required in most DC motors ) and the ability to control the speed of the motor . As the motor is running , the pump runs by means of the coupling and key which are connected between the pump and motor shaft . The pump pumps the oil to the valve pack and the flow is controlled by the control valve manifold ( servo valve , aux valve , etc .) before it is pumped to the systems . Normal system pressure is around 200-210 bar .
The jetting unit ’ s hydraulic system may have same configuration as the main system except that there is an additional hydraulic motor that drives the water pump , to provide sufficient speed for the required flow and pressure . In most cases a
66 VOL 92 OCTOBER-DECEMBER 2022