Gauge Pressure

Objectives

• Describe gauge pressure.

• Correctly calculate the gauge pressure for a given depth of either fresh or salt water.

• Apply the concept of gauge pressure to scuba.

Main Points

• Gauge pressure

• Calculating gauge pressure

• Application to scuba

Description

• Uses atmospheric pressure as zero.

Example 1

Calculate gauge pressure at 57' of fresh

water.

Answer: (.432psi/ft) x 57' = 24.6 psig

Convert the answer above to absolute

pressure.

Answer: 24.6psi + 14.7psi = 39.3psia

Example 2

Calculate gauge pressure at 57' of salt

water.

Answer: (.445psi/ft) x 57' = 25.365 psig

Convert the answer above to absolute

pressure.

Answer: 25.365psi + 14.7psi = 40.065psia

Application to Scuba

• The concept of gauge pressure explains why an analog depth gauge will not give an accurate reading of depth when diving at altitude.

• Care to explain?– An analog depth gauge uses 14.7 psi as 0 ft– at altitude you must dive to some depth

before you reach a pressure of 14.7 psi

Main Points

• Gauge pressure

• Calculating gauge pressure

• Application to scuba

Objectives

• Describe gauge pressure.

• Correctly calculate the gauge pressure for a given depth of either fresh or salt water.

• Apply the concept of gauge pressure to scuba.