Table of Contents

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

压力计被归类为：

Simple manometers
Piezometer
U-tube manometer, and
Single column manometer
Vertical single column manometer
倾斜单柱压力计
Differential manometers
U-tube differential manometer
Inverted U-tube differential manometer

简单压力计的工作：压力计

Simple Manometers

简单的压力计是由玻璃管组成的压力计，其一端连接到要测量压力的点，另一端对大气开放。

Piezometer

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 byp = wh,where w is the specific weight of the liquid.

Limitations of Piezometer

压力计只能测量测量压力。它不适合测量负压。

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.