bolted to the air expansion flask manifold. The fluid end of the accumulator is flanged and bolted to the accumulator nozzle, which contains a fluid-level indicator, a device used to indicate to the engine-room operator whether the system has the proper amount of fluid. The fluid indicator registers the following three conditions—DRAIN (excessive amount of fluid in the system), BATTERY (proper amount of fluid in the system), and FILL (insufficient amount of fluid in the system). The floating air-fluid separator piston is made of aluminum alloy and has two sets of V-ring packing (one for the air side and one for the fluid side), which prevent air from leaking past the piston into the fluid side of the accumulator, or fluid from leaking into the air side. Two slipper cages with phenolic slippers are fitted onto the piston to act as a bearing surface between the piston and the cylinder wall. The phenolic slippers are replaceable and must be replaced when the maximum allowable wear  has  been  reached.  This  is  to  prevent metal-to-metal wear between the piston and the accumulator wall. An eyebolt is provided on the air side of the piston to aid in removing the piston from the accumulator when maintenance is required. The fluid side of the piston has a striker rod that actuates a fluid-level indicator located in the accumulator nozzle. The fluid-level indicator has a drive shaft that extends through the nozzle from side to side and is secured in place by flanges and bolts. O-rings provide a seal against leakage of fluid around the drive shaft. Gears are secured onto the shaft inside the nozzle. These gears mate with teeth on the actuator rod, which extends fore and aft in the nozzle, and the fluid-indicator rod, which is vertical and extends through the top of the nozzle. An O-ring prevents leakage around the indicator rod. When the striker rod on the piston makes contact with the actuator rod, the drive shaft rotates, causing the indicator rod to move down. See figure 3-9. An indicator plate is mounted on top of the nozzle. The  plate  has  the  readings  DRAIN,  BATTERY,  and FILL.  The  indicator  rod  is  a  differential  rod;  and  any time  the  piston  striker  rod  is  not  in  contact  with  the actuator   rod,   accumulator   pressure   working   on   the differential  area  of  the  indicator  rod  will  cause  the indicator rod to rise to the DRAIN position. The engine crosshead  must  always  be  in  its  BATTERY  position when the fluid level of the arresting engine is checked. FLUID REPLENISHMENT SYSTEM LEARNING   OBJECTIVE:    Describe    the components of the fluid replenishment system. In any hydraulic system, small amounts of fluid are lost due to leakage. Fluid also contracts when cold and expands  when  hot.  To  compensate  for  leakage  and expansion  or  contraction  of  the  hydraulic  fluid  in  the hydraulic system of the Mk 7 arresting engines, a fluid replenishment system is provided. See figure 3-10. The fluid replenishment system consists of a small hand pump, mounted on the lower engine frame that is connected  by  piping  to  the  engine  accumulator  and  a 6-gallon  stowage  tank.  If,  because  of  leakage  or  fluid contraction while the engine crosshead is in BATTERY, the fluid-level indicator reads FILL, the supply valve in the  piping  is  opened  and  the  hand  pump  is  operated until  the  indicator  reads  BATTERY.  A  fluid  filter  is located   in   the   supply   line   to   filter   the   fluid   being pumped    into    the    accumulator.    If    the    fluid-level indicator reads DRAIN, the return valve located in the return  line  is  opened,  and  fluid  from  the  accumulator drains into the replenishment tank. When the fluid-level indicator reads BATTERY, the return valve is closed. 3-13 VALVE (RETURN) STRAINER FILTER TANK HAND PUMP FLUID LEVEL INDICATOR VALVE (SUPPLY) ABEf0310 Figure 3-10.—Fluid replenishment system.