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.
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