1) U-Tube Manometer:

This manometer is very simple to construct. It consists of a U – shaped bent tube whose one end is attached to the gauge point ‘A’ and other end is open to the atmosphere. It is then filled with a fluid.  The density of the fluid dictates the range of pressures that can be measured.

If one port is left open to the atmosphere and the other port is connected to the pressure to be measured, the device acts as a gauge pressure meter.  If both ports are connected to two different unknown pressures, the instrument acts as a differential pressure gauge.

 It can measure both positive and negative  pressures. It contains liquid of specific gravity greater than that of a liquid of which the pressure is to be measured.

where ‘γ’ is Specific weight of the fluid, ‘P’ is Pressure at A (which u r going to calculate).
Hence; Pressure at A is P = γ₂h₂ – γ₁h₁

2) Differential U-Tube Manometer:

Differential U-tube manometer  is very  similar to the U-tube manometer as we discussed above. Here one open end (which was considered as atmospheric end in U-Tube manometer )  is connected to another  pressure point i.e  

This manometer is basically used to measure the differences between to different points or you can say we ae going to calculate  the difference .

Pressure difference between A and B is given by equation

After rearranging

3) Inverted U-Tube Manometer:

Inverted U-Tube manometer is used for the measurement of small pressure differences in liquids. It consists of an inverted U – Tube containing a light liquid. This is used to measure the differences of low pressures between two points where  better accuracy is required. It generally consists of an air cock at top of manometric fluid type.

 Note : Inverted U-tube differential manometer will be used for measuring the vacuum pressure. Inverted U-tube differential manometer will have one inverted U-tube contained with light liquid.

Let us consider that inverted U tube differential manometer is connected with two points in two pipes as displayed here in following figure. These two pipes are filled with different specific gravity liquid. As displayed here in figure, point A and point B are at different level.

Pressure difference can be calculated from the below mentioned equation

P_A – ρ₁gH₁ – ρ_mg(H₂– H₁) = P_B – ρ₂gH₂

P_A – ρ₁g H₁ = P_B – ρ₂g H₂ – ρ_L g H

After rearranging

P_A – P_B = ρ₁g H_{1 –} ρ₂g H₂ +  ρ_mg(H₂– H₁)

Where ρ_{m = density of manometric fluid}

ρ_{2 ,} ρ_{1  = desity of two different fluids}

4) Micro Manometer:

The micromanometer is a special type of  of liquid column manometers that which is based on the principle of inclined tube manometer. It used for the measurement of extremely small differences of pressure or very low pressure differences. One can say micro-manometer is the modified form of a simple manometer whose one limb is made of larger cross sectional area. It measures very small pressure differences with high precision.

Let ‘a’ = area of the tube,
A = area of the reservoir,
h₃ = Falling liquid level reservoir,
h₂ = Rise of the liquid in the tube,
By conversation of mass we get A*h₃ = a*h_{2
Equating pressure heads at datum we get}
P₁ = (ρ_m – ρ₁)*gh₃ + ρ_m*gh₂ – ρ₁*gh₁

5) Inclined Manometer:

Inclined manometer is used for the measurement of small pressures and is to measure more accurately than the vertical tube type manometer. Due to inclination the distance moved by the fluid in manometer is more. An inclined manometer is a slightly curved tube with a liquid inside, typically a form of oil mixture. Along the tube’s middle portion are graduations. The graduations are commonly hundredths of an inch, depending on the manometer’s manufacturer.

Benifits :

The manometer’s inclined angle provides many advantages. A small or low amount of pressure against the inclined manometer will produce a large liquid movement relative to the tube’s graduations. As a result, the graduation scale can be very precise–down to a hundredth of an inch accuracy.

Pressure difference between A and B is give by equation.

Read Also :  Venturi Flow Meter 

Pitot Tube Working Principle

Coriolis Mass Flow Meter

References : NPTEL    SCIENCING