Topic No.3MEASUREMENT OF LIQUID

PRESSURE IN PIPES

04 Hrs. and 12 marksBy

BAJAJ A.P. SANDIPANI TECHNICAL CAMPUS-

FACULTY OF ENGG.-LATUR

INTRODUCTION

• When fluid is in motion it have some RESISTANCE.

• It is due to FRICTION.

• When liquid flow through pipes ,it is need to study various fluid properties for hydraulic calculations.

Conversion of pressure head of one liquid into another

• Concept is based on theory of heavier liq. and lighter liq.

• Liquid having lower specific gravity exerts a less pressure as compared to liquid of higher specific gravity

• At the same height above that surface.

Conversion of pressure head of one liquid into another

Figure shows the 2 tank of different liquid of different specific gravity but exert same pressure.

P1=P2W1h1=w2h2

But w1=ws1 and w2=ws2Wh1s1=wh2s2

H1s1=h2s2

ATMOSPHERIC PRESSURE

• Height Of ATM Above The Earth Surface Is Varies From 100 To 1000

Kms.

• Air & Other Gases Posses Wt. And Exert Pressure On Earth Surface.

• It Is Very Difficult To Calculate Weight Of Air In Atm.

• Atmosphere Pressure Is Measured By Barometer.

• It Is The Force Exerted By Air On 1 Square Cm Area Of Earth

Surface Is = Air Column Of 1 Square Cm In C/S Area And Height

Equal To Atmosphere.

• 1 Atm = 10.333 Meter Of Water Or

76 Cm Of Mercury Or

101.325 KN/M2

These Are The Values Of ATM Pressure At5 Sea Level At Temperature

Fifteen Degree Celsius

Gauge and Absolute pressure

• If pressure is measured above absolute zero (vaccume),it is called ABSOLUTE PRESSURE

• If pressure is measured above atmospheric pressure it is called POSITIVE GAUGE PRESSURE

• If pressure is measured below atmospheric pressure it is called NEGATIVE GAUGE PRESSURE

• Pabsolte = Patmospheric + Pgauge

• Pabsolte = Patmospheric - Pgauge

DEVICES FOR PRESSURE MEASUREMENT IN PIPE

• Piezometer

• Manometer

• Pressure gauge

1. It is a glass tube circular in c/s

2. Bent in right angle

3. Connected to point whose pressure is to be measured

4. Second end is open to atmosphere

5. Diameter of tube should be greater than 10mm to avoid error

1. Not suitable for measuring high pressure.2. Not suitable for measuring vacuum pressure.

• It is a device used for measuring pressure at a point or pressure difference between two points.

Manometer

SIMPLE U TUBE DIFFERENTIAL U TUBE

MANOMETER

MANOMETRIC LIQUID

• It is a liquid used in manometer to measure the pressure.

• It should be heavier

• Should not stick to the surface

• Should not mix with flowing liquid.

SIMPLE U TUBE MANOMETER1. Consist of glass tube of

U shape

2. One end is connected

to pressure point

3. Another end is open to

atmosphere

4. Generally contain

mercury

SIMPLE U TUBE

Measure positive pressure Measure negative pressure

Pressure above datum x-x will be samePressure in left limb=pressure in right limb

Ha + h1s1= h2s2

Ha= h2s2-h1s1

Pressure above datum x-x will be samePressure in left limb=pressure in right limb

Ha + h1s1+ h2s2=0

Ha= -h1s1-h2s2

Ha= -(h1s1+h2s2)

DIFFERENTIAL MANOMETER

• It is used for measure the difference of pressure between two points in a pipeline.

DIFFERENTIAL MANOMETER

U-TUBE DIFFERNTIAL INVERTED U-TUBE DIFFERNTIAL

CASE1-

• Assume pressure A is greater than pressure at B

Ha+h1s1=Hb+h2s2+h3s3

Ha-Hb= h2s2+h3s3-h1s1

PA-PB=w(hA-hB)

PA-PB=9.81*(h2s2+h3s3-h1s1)

CASE-2

Assume in both pipes A and B at same level

Here S1=S3=S and H1=H2+H3

Ha+H1S1=Hb+H2S2+H3S3

Ha-Hb=H2S2+H3S3-H1S1

FROM Eqe no 1

Put S1=S3=S and H1=H2+H3

Ha-Hb = H2S2+H3S-(H2+H3)S

Ha-Hb =H2S2+H3S-H2S-H3S

Ha-Hb = H2(S2-S) m of water

U TUBE DIFFERNTIAL MANOMETER

INVERTED U TUBE DIFFERNTIAL MANOMETER

INVERTED U TUBE DIFFERNTIAL MANOMETER

• Measuring liquid is higher than liquid flowing through pipes.

• Used to measure low pressure difference.

• Liquid in manometer is lighter.

• Due to this for low pressure difference ,large deflection in measuring liq. Occur.

• Measurement can be made accurately.

U TUBE DIFFERNTIAL MANOMETER

INVERTED U TUBE DIFFERNTIAL MANOMETER

INVERTED U TUBE DIFFERNTIAL MANOMETER

• Ha-h1S1 = Hb-h2S2 -h3S3

• Ha- Hb = h1S1 -h2S2- h3S3

(M of water )

• Pa-Pb = w(Ha- Hb)

Bourdon’s Tube Pressure Gauge

Bourdon’s Tube Pressure Gauge

• Used for the measurement of relative pressures at a point in a fluid by balancing the fluid column by using spring or dead wt. Or sector and pinion arrangement.

• Classified as mechanical pressure measuring instruments

• Operate without any electrical power.

• Consist of hallow flexible metalic tube

• One end is sealed & connected to the sector and pinion arrangement

• Other end is connected to the point where pressure is measured.

Bourdon’s Tube Pressure Gauge

• When this gauge is connected to pipe.

• Fluid flow through the tube under pressure.

• Due to this pressure free end of tube will move.

• This movement will amplified by lever which is connected to sector and pinion arrangement.

• Pointer rotate on on graduate scale.

• Best suit for vertical pressure & vaccume pressure.