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Usually, the air-bottle assembly will consist of six air-
pressure bottles and associated valves, each bottle containing
approximately 25 cu ft of air. The bottles are interconnected.
Using an air-operated isolation valve, remotely controlled from the
driller's control panel, allows up to 60% of the operating bottle
volume to be isolated temporarily. This eliminates the need to
reduce the entire system pressure to perform operations requiring
significantly reduced pressure.
At full capacity, the fluid supply unit storage reservoir
contains 395 gal of hydraulic fluid. Also included are two air/oil
pumps, a filtering system, and a fluid sensing system. The fluid
sensing system automatically maintains the hydraulic fluid level of
the accumulator at a safe level by pumping the hydraulic fluid
back into the system when required.
It is important to use a hydraulic fluid with excellent
physical properties with respect to viscosity and sensitivity to
changes in temperatures.
The air supply system should consist of two or more air
compressors and associated dryers to provide dry, high-pressure
air to the system (3,500 psi). One or more air storage bottles
ensure a ready supply of high-pressure air to both the motion
compensator and tensioner systems. Operating controls and
indicators are installed on the driller's control panel located on the
drilling floor. This enables the driller to operate and monitor the
entire motion compensator system. The manually operated
controls open and close the valves, adjust the operating system
pressure to the operating load, and raise or lower the isolated
system pressure. Large, easy-to-read gauges display the various
system pressure readings, and indicators show the lock pin
position and piston rod(s) extension.
A motion compensator system functions as a hydraulically
loaded tension spring with an adjustable tension effort. The
compensator's hydraulic operating system is passive. Rather than
being driven by hydraulic pumps, the system is energized by a
compressed air supply system that acts on a given amount of
hydraulic fluid by means of an accumulator. Ideally, the volume of
fluid never changes but is displaced back and forth between the
compensator and accumulator by the compensator piston. The
piston, then, carries the hook load by virtue of hydraulic pressure,

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