P R E S S U R E.

PRESSURE CONVERSIONS :

1Psi               = 27.74 H2O
1Kg/cm Sq    = 14.223psi
1 Bar             = 14.504 psi
1 Kpa            = 0.145 psi
1 Kg/cm Sq   = 10,000mm of H2O
1 Bar             = 1.0197 Kg/cm Sq
1 Torr            = 1 mm of Hg

Que. :  What is absolute pressure ?

Ans. :  Absolute pressure is the total pressure present in the system

Abs. pressure = Gauge pressure + Atm. pressure.

PRESSURE GAUGE

Que. :  What is absolute zero pressure ?

Ans. :  Absolute zero = 760 mm Hg Vacuum.

PRESSURE SWITCH

Que. :  What is the maximum Vacuum ?

Ans. :  The maximum Vacuum = 760 mm Hg.

PRESSURE SWITCH FOR WATER SERVICE

Que. :  What is Vacuum ?

Ans. :  Any pressure below atmospheric pressure is vacuum.

           

Atm = 760 mm                0 Vacuum                Zero Gauge

  _______________________________

'

'

' _______  Max. Vacuum 760 mm HG

Zero  Absolute.

Que. :  What are the primary elements for measuring pressure ?

Ans. :  The primary elements used for measuring pressure are :

1. Bourdon tube.

2. Diaphragm.

3. Capsule.

4. Bellows.

5. Pressure Springs.

The above are known as elastic deformation pressure elements.

Type of Bourdon tubes.

1. ' C ' type.

2. Spiral.

3. Helix.

Diaphragm : The diaphragm is best suited for low pressure measurement.

Capsules : Two circular diaphragms are welded together to form a pressure capsule.

Material Used : phosphor bronze, Ni-spanc stainless steel.

Bellows : Bellows is a one - piece, collapsible, seamless metallic unit with deep folds formed from very tin walled tubing.

Material used : Brass, phosphor bronze, stainless steel. Used for high pressure.

PRESSURE SPRINGS : Pressure springs of helical or spiral shape used for measuring high pressures.

Que. :  What is the principle of a pressure gauge ?

Ans. :  Pressure works on Hooks law.

Principle : "Measuring the stores in an elastic medium"

Que. :  Draw and explain a pressure gauge ? What is the used of a Hair spring ?

Ans. :  The parts of a pressure gauge are :

1. 'C' type Bourdon tube.

2. Connecting link.

3. Sector gear.

4. Pinion gear.

5. Hair Spring.

6. Pointer.

7. Dial.

Uses of Hair Spring : Hair spring serves two purposes name

1. To eliminate any play into linkages.

2. It serves as a controlling torque.

Que. : How will you calibrate an absolute pressure transmitter  vacuum manometer  Range 0-400mm abs. ?

Ans. :  The procedure for calibration is as follows :

1. Connect air supply to the transmitter.

2. Connect a test gauge of  0-1.4 Kg/cm2 to the output.

3. Connect Vacuum pump with tee off to the manometer.

4. Apply 760 mm Vacuum ( or nearest ) and adjust zero.

5. Apply 360 mm Vacuum adjust span. ( 760 - 360 = 400 mm abs. )

Que. :  You are given a mercury manometer range 0 -760 mm ? A vacuum gauge reads 60 mm vacuum. The test manometer reads 50 vacuum ? Which of the two in correct.

Ans. :  The transmitter is correct because 760 - 50 = 710 mm abs.