ABOUT PRESSURE MEASURING DEVICES

1. Topic No.3
MEASUREMENT OF LIQUID
PRESSURE IN PIPES
04 Hrs. and 12 marks
By
BAJAJ A.P.
SANDIPANI TECHNICAL CAMPUS-
FACULTY OF ENGG.-LATUR

2. 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.

3. 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.

4. 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=P2
W1h1=w2h2
But w1=ws1 and w2=ws2
Wh1s1=wh2s2
H1s1=h2s2

5. 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

6. 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

7. DEVICES FOR PRESSURE
MEASUREMENT IN PIPE
• Piezometer
• Manometer
• Pressure gauge

8. 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 pressu

9. • 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

10. 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.

11. SIMPLE U TUBE
MANOMETER
1. 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

12. SIMPLE U TUBE
Measure positive pressure Measure negative pressure
Pressure above datum x-x will be same
Pressure in left limb=pressure in right limb
Ha + h1s1= h2s2
Ha= h2s2-h1s1
Pressure above datum x-x will be same
Pressure in left limb=pressure in right limb
Ha + h1s1+ h2s2=0
Ha= -h1s1-h2s2
Ha= -(h1s1+h2s2)

13. 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

14. 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)

15. 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

16. 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.

17. 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)

18. Bourdon’s Tube Pressure Gauge

19. 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.

20. 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.