Page 555 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

552 CHAPTER 20 Tooling and Sensor Deployment
FIGURE 20.21
Subsea diamond wire saw.
20.2.4 Hydraulics
20.2.4.1 Hydraulic requirements
(Courtesy Wachs Subsea.)
Most manipulators are designed to operate at 3000 psi (200 bar). While this nominal operating pressure is preferred, systems can be operated on lower pressures with reduced performance. Operation at pres- sures below 60% of the design pressure is not recommended due to excessive performance loss.
Flow requirements are also stated in the manufacturer’s literature. The faster the arm must move, the greater the flow required. Most arms will operate satisfactorily at 30
40% of the maxi- mum stated flow. Use on ROVs with flows below this level will cause the supply pressure to drop dramatically during arm motions and is not recommended.
20.2.4.2 Hydraulic power units
HPUs, in a variety of sizes, are available to provide hydraulic power for manipulators and tool systems. An example is the 1.3 kW HPU manufactured by Sub-Atlantic (Figure 20.22). The small HPU delivers 4 lpm (1 US gpm) at adjustable pressures up to 3000 psi (200 bar). The HPU uses a gear pump driven by a 3-phase, 440 V AC electric motor. An integral, externally adjustable pressure relief valve is used to set the system pressure and a quick-change suction filter cartridge is fitted into the body.
20.2.4.3 Hydraulic valve packages
Once the hydraulic system is energized/powered by the HPU, a valve package (valve pack) sequences and directs hydraulic fluid to/from the proper actuator for functioning of selected hydrau- lic equipment. Various hydraulic valve packages are available that are composed of whichever type of valve necessary. Sub-Atlantic (Figure 20.23) provides a compact, lightweight general function valve pack made up of solenoid, proportional, or mixed valve configurations controlled by a