Steam Flowmeters

Figure 1-21.—Fuel oil pump. such as flowmeters and draft gauges, increases safety and promotes efficiency. All of these instruments may be either indicating or recording. STEAM FLOWMETERS A Utilitiesman must be able to identify the different types of monitoring instruments and understand their operation and use. Meters used to measure quantities are divided into two general types: 1. Those indicating rate, such as flowmeters 2. Those indicating the total, such as scales Many devices are designed to measure and indicate the pressure of steam flow. One of these devices is shown in figure 1-23. This meter uses a weighted inverted bell (called a Ledoux bell) sealed with mercury. The bell moves up and down as the rate of flow changes. The movement is transmitted to a pen that records the flow. STEAM AND AIR FLOWMETERS A combustion air and steam flowmeter is shown in figure 1-24. This meter is used as a guide in controlling the relationship between air required and air actually supplied to burn the fuel. The rate of steam generation is used as a measure of air necessary to burn the required amount of fuel. The flow of gases through the boiler setting is used as a measure of air supplied. The essential parts of the meter are two airflow bells supported from knife-edges on a beam, which is supported by other knife-edges, and a mercury displacer assembly supported by a knife-edge on the beam. The bottoms of the bells are sealed with oil, and the spaces under the bells are connected to two points of the boiler setting. DRAFT GAUGES A draft gauge is a form of pressure gauge. In boiler practice, the term draft usually refers to the pressure difference producing the flow. Drafts are pressures below atmospheric pressure. They are measured in inches of water. A draft gauge is essential to boiler operation. Its use increases the safety of operation. A simple type of draft gauge is the U-tube gauge. The source of draft is connected to one leg of the U and the other end is left open. The difference between the levels of the liquid in the two legs is a measure of the draft. Water is generally used in this type of gauge. Take 1-21