Steam Boiler: Preesure in Boiler

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Pressure Gauge with Diaphragm

Pressure gauge with diaphragm is pressure gauge which uses diaphragm to measure pressure. The meaning of diaphragm is a material which easy to bend or so-called membrane, which is usually made of thin metal, leather, rubber, clan, etc. The working principle pressure gauge with diaphragm is shown in Figure 1 based on the resilience properties of metal / thin plate due to the curvature of iteration pressure at membrane plane, the membrane device is used to measure the difference of two different pressures.

The ability of pressure gauge with diaphragm to read the different pressure is based on:

The area of membrane.
Thick membrane.
Type of membrane material.

The advantages of pressure gauge with diaphragm as follow:

- Very sensitive due to changes in pressure

- Can be used to measure the height of liquid surface

- Can be used for different pressure

- Can be used at transmitter

- Can be used to measure flow

Figure 1: Pressure Gauge with Diaphragm

Pressure Gauge with Bellow

Pressure gauge with bellow is the pressure gauge that is equipped with bellow. Bellow is thin metal which is shaped like an accordion bellow. Same as pressure gauge bourdon tubes, bellow also expands when the inside pressure is greater than outside pressure.

Any changes in inside pressure of bellow will produce mechanical motion backward or forward. Movement of backward and forward through tuns and twister tube then to be converted into the form of circular movement of pointer on scale numbers that have been calibrated as shown in Figure 1 below.

Figure 1: Pressure Gauge with Bellow

Pressure Gauge-Bourdon Tube

Pressure gauge with bourdon tube is a pressure gauge with is equipped with metal which easy to expands and hole is created on the metal. One end is created with closed condition and other end is made open to be connected with the pressure which then to be measured how much the pressure it is. This end is called as socket.

Generally the working principle of the pressure gauge with bourdon tube is the pressure will be measured enter into bourdon tube through socket, this pressure will result bourdon tube expands, so it will cause mechanical movement on the closed end. This movement is then forwarded to a wheel arrangement - the gear lever through liaison which is called as Lever. This gear consists of two gears namely: motion gears and pinion gears.

Motion gears is directly connected with lever, while the pinion gears is welded with pointer so when the bourdon tube moves, the pointe will also move as shown in Figure 1 below.

Figure 1: Pressure Gauge with Bourdon Tube

Definitions for Pressure in Boiler

Pressure is the force that occurs for each unit area in the plane, the unit of pressure which is widely used is kg/m2, Newton/m2, lb/inc2, kip/ft2 and so on. Besides that, there are units of pressure that are known and used in steam boiler or power plant such as atmospheric, Bar, psig).

In addition to a wide - range unit used for pressure, the pressure can be also classified based in its definition either for liquid, gas, vapor or steam. There are three types of pressure:

Absolute pressure

Absolute pressure is the actual pressure of fluid

Pressure Gauge

Pressure gauge is measurement of how much the pressure of fluid compared to the outside air pressure (atm).

Vacuum Pressure

Vacuum pressure is equal to the pressure gauge but it is smaller than the atmospheric pressure (atm).

The differences of absolute pressure and pressure gauge can be seen from its unit. Absolute pressure can be expressed as Psi (Pound square inch), then the pressure gauge is expressed in psig (pound / square inch gauge).

Pressure gauge consists of main elements of material which easy to expand and still use manual systems and mechanical motion can be classified as follow:

- Pressure Gauge with Bourdon Tube

- Pressure Gauge with Below

- Pressure Gauge with Diaphragm