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Using Pressure to Find Undersea Treasures

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Using Pressure to Find Undersea Treasures

For treasure hunters and salvagers trying to find historical and valuable items from ships that sank centuries ago, there are two options: sucking up or blowing away the sand — both involve pressure. Vacuuming sand from the bottom of port channels is common for dredging operations that relocate the sand to provide accessibility to ships. One recent project used a vacuum (negative pressure) approach with a two-mile-long, 30-inch-wide pipeline to transport the sand.

In contrast, treasure hunters just need to move the sand out of the way so they can see objects that have settled below layers of silt. They are not concerned with where the sand goes, so positive pressure has proven to be the technique of choice. Using a method invented in the 1960s by legendary salvager Mel Fisher, steel tubes called mailbox blowers, redirect engine wash from a boat’s propellors downward to clear the ocean bottom some 30 feet underwater. For a given size opening, the size of the props and their speed determine the depth and intensity of the jet from the prop wash.

Two 33-inch diameter mailbox blowers clear away sand 30 feet underwater. Source: History Channel.

The amount of pressure developed is not measured, but it must be sufficient to reveal the desired objects.

Salvaged Spanish gold coin from the wreck of the 1715 Treasure Fleet was located by pressure.
Source: History Channel Beyond Oak Island.

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A Pressure Treat

A Pressure Treat

Pressure treating wood stabilizes its dimensions, protects it from insects, increases its resistance to water and chemicals and reduces cracking. The pressure treating process involves both vacuum and pressure. Initially, a vacuum removes the air from the cavities in the wood to create space for the preservation solution. The vacuum levels in a given process vary but could range from -700 mmHg to -730 mmHg.

Then, a protective solution, commonly alkaline copper quat or ACQ, is forced deep into the wood under high pressure in an autoclave. A hydraulic overpressure of 12 atmospheres or somewhere between 100 and 200 psig is common.

In general, the basic procedure consisting of initial vacuum, filling, application of pressure, discharging the solution, recovery vacuum and return to atmospheric pressure at the end of a cycle.

In the United States, the chemical protection from applying high pressure (in psi) is measured in the pounds of chemical per cubic foot (PCF) increase in the density of the wood. The density ranges from 0.40 PCF for ground contact to 0.60 PCF for foundations.

A basic pressure treating process uses pressure and vacuum.
Source: Nash by Gardener Denver.

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Body Pressures

Body Pressures

Common body pressure measurements include blood pressure (80/120-mm (300 mm Hg, max)), respiratory pressure (4 kPa) and intraocular pressure for glaucoma testing (15 mm Hg). However, there are several other pressure measurements made at different body locations, most are made for diagnostic purposes. These include:

intra-bladder pressure (IBP) 12.3 ± 4.5 mmHg depending on body position to about 22 mmHg.
intragastric pressure, (IGP) 15.5 ± 3.5 mmHg vs 18.0 ± 8.7 mmHg
intra-abdominal pressure (IAP) typically less than 12 mmHg
anorectal manometry (ARM) 49 ± 3 mmHg resting to 238 ± 38 mmHg maximum squeeze range
vacuum (negative pressure) for an electric breast pump 0-270 mmHg

Similar to blood pressure and intraocular pressure, higher than normal readings identify potentially dangerous health situations. For example, an IAP equal to or above 12 mmHg is called Intra-abdominal Hypertension (IAH). Also, an IAP above 20 mmHg with evidence of organ dysfunction/failure defines abdominal compartment syndrome (ACS). Both of these higher than normal readings are known to cause significant morbidity and mortality among critically ill patients.

For healthy subjects, anal pressure is highly reproducible on separate days. ARM measurements in resting mode vary from 49 ± 3 to 58 ± 3 mmHg in women and from 49 ± 3 to 66 ± 6 mmHg in men. In contrast, maximum pressures range from 90 ± 9 to 159 ± 45 mm Hg in women and from 218 ± 18 to 238 ± 38 in men.

Oral to anal pressures vary depending on the location of the muscle cross sectional area (MCSA).
Source: Physiology of the Gastrointestinal Tract .

Depending on the location, a significantly lower pressure can be a problem, too. For most people, blood pressure in the foot is similar to the blood pressure in the arm. A pressure drop of as little as 10% can indicate peripheral artery disease (PAD).

Not all pressures are positive measurements or made for diagnostic purposes. For example, an electric breast pump uses a vacuum (negative pressure) as high as 270 mmHg to collect milk for newborns.

For all of these body pressure measurements, highly accurate microelectromechanical systems (MEMS) pressure sensors can provide an essential tool for optimum healthcare.

Comments/Questions?
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