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Hydraulic & Pneumatic Systems

Hydraulic & Pneumatic Systems. Measuring Pressure. Atmospheric Pressure. Recall: Caused by the weight of the air molecules above us. Typically 101.3 kPa or 101 300 Pa Measured using a barometer

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Hydraulic & Pneumatic Systems

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  1. Hydraulic & Pneumatic Systems Measuring Pressure

  2. Atmospheric Pressure • Recall: Caused by the weight of the air molecules above us. • Typically 101.3 kPa or 101 300 Pa • Measured using a barometer • An altimeter is a device in an aircraft that measures the altitude of a plane using a barometer and relating that to 101.3 kPa.

  3. Gauge Pressure • Most pressure readings of gases and liquids are called gauge pressure. • They do not measure the absolute (total) pressurewhich includes atmospheric pressure. • Relationship: Gauge pressure = Absolute Pressure – Atmospheric Pressure Using symbols:

  4. Manometer psystem patm • Manometer: A device that measures gauge pressure. • Uses the weight of a fluid and the height difference. As pressure increases • Height difference increases • Water weight increases h U-tube manometer

  5. Pressure in a Manometer • Using our pressure equation we can derive the gauge pressure in a manometer: *Weight of the water is mass x gravity *Mass = density x volume * Since V = Ah; h = V/A Where: D= density (kg /m3) h = height of fluid (m) Gauge pressure formula

  6. Example #1 • A pump is connected to one tube of manometer containing water (D = 1000 kg / m3). Pressure is increased until the static pressure head (h) is 15 cm. What is the gauge pressure?

  7. Example #2 • Calculate the absolute pressure in the water behind a dam with a static pressure head of 18.0 m. The atmospheric pressure at the dam is 1.00 x 105 Pa

  8. Blood Pressure • Measured using a sphygomanometer. • Two numbers • Systolic: Maximum blood pressure • Normal value = 16 kPa • Diastolic: Minimum blood pressure • Normal value = 11 kPa • Given to you by your doctor as “16 over 11”.

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