Manometer – types , Working , Advantages , Disadvantages
What are Manometers?
Manometers are devices used for measuring the pressure at a point in a fluid, by balancing the column of fluid by the same or another column of fluid.
This is the most simple and precise device used for the measurement od pressure. It consists of a transparent tube constructed in the form of an elongated ‘U’, and partially filled with the manometeric fliud such as mercury. The purpose of using mercury as the manometeric fluid is that their specific gravity at various temperatures are known exactly and they dont stick to the tube. The two common types of manometers are the equal limb type and unequal limb type.
Types of Manometers
Manometers are classified as:
- Simple manometers
- U-tube manometer, and
- Single column manometer
- Vertical single column manometer
- Inclined single column manometer
- Differential manometers
- U-tube differential manometer
- Inverted U-tube differential manometer
Working of Simple Manometer : Piezometer
A simple manometer is one which consists of a glass tube, whose one end is connected to a point where pressure is to be measured and the other end is open to atmosphere.
Piezometer is one of the simplest forms of manometers. It can be used for measuring moderate pressures of liquids. The setup of piezometer consists of a glass tube, inserted in the wall of a vessel or of a pipe. The tube extends vertically upward to such a height that liquid can freely rise in it without overflowing. The pressure at any point in the liquid is indicated by the height of the liquid in the tube above that point.
Pressure at point A can be computed by measuring the height to which the liquid rises in the glass tube. The pressure at point A is given by p = wh, where w is the specific weight of the liquid.
Limitations of Piezometer
1. Piezometers can measure gauge pressures only. It is not suitable for measuring negative pressures.
2. Piezometers cannot be employed when large pressures in the lighter liquids are to be measured since this would require very long tubes, which cannot be handled conveniently.
3. Gas pressures cannot be measured with piezometers, because a gas forms no free surface.
Advantages of Manometers
- Easy to fabricate and relatively inexpensive
- Good accuracy
- High Sensitivity
- Requires little maintenance
- Suitable for low pressure and low differential pressure
Applications of Manometer :
- they are used to sense differential pressure in venturimeter and other flow meters.
- They are used as level devices to sense liquid heads.
- There are used as primary standard for pressure measurements.
Disadvantages of Manometer :
- They might break during transport.
- Certain manometeric fluids cause hazards when exposed to atmosphere.
- Error is introduced if the diameter of the tube is less.
- Leveling is required.
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