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(e.g., passivation, hard anodize) requirements still apply. Marine

PRV designs generally utilize the stem as the adjusting screw.

Two projects I worked on at Scripps incorporated pressure com- pensation systems for operation to a max depth of 1,500m (2,220 psi). We experienced some relevant mechanical behaviors.

The ? rst was a buoyancy canister for a free-vehicle Mid-Ocean

Float in the mid-1970’s. We jokingly called ourselves “the MO-

Fia.” The free-vehicle tracked internal waves by measuring the

Illustration courtesy of The Lee Company, Westbrook, CT

Figure 2 vertical oscillations of an identi? ed thermocline. A piston in a

A PRV is represented graphically on the left. An adjustable PRV would show cylinder of a side-mounted pressure-compensated buoyancy a diagonal arrow through the spring. A check valve is represented graphically canister provided variable displacement, which changed the on the right. Minimal spring force reduces the back pressure on the system. density of the vehicle, which made the vehicle sink and rise, pulling a sting of fast-response thermistors behind it. After an- chor drop, the vehicle was on it’s way back to the surface. The buoyancy canister vented internal pressure through a single

PRV positioned at the bottom of the canister. The excess air always vented, and the unit always returned with a dry interior.

Some years later, the ATOC program used a moored low-fre- quency (150-Hz) source (Figure 1) made by HydroAcoustics (Rochester, New York) adapting an emerging environmen- tal diagnostic technique known as Acoustic Thermometry to

Illustration courtesy of Perry Oceanographics,

Riviera Beach, FL measure the volumetric average temperature of the ocean. The

Figure 3

HLF-5 source utilized an open sump hydraulic system. The in-

Perry Oceanographics’ submersible Deep Diver, ? rst introduced in 1973 as a diver lock-out sub, primarily operated in the North Sea oil ? elds. terior was pressure compensated to ambient pressure at operat- www.marinetechnologynews.com 13

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