A horizontal pipeline AB of diameter d conveys water, flowing from A to B . The U-tube manometric liquid can be used for the measurement of:
The manometers measure the difference between a known and an unknown pressure by observing the difference in heights of two fluid columns.
In a U-tube manometer, the pressure is balanced using another liquid of higher density. It consists of a glass tube bent in a U-shape; one end of which is connected to the point where pressure is to be measured and the other end open to the atmosphere. The tube contains a manometric liquid of known specific gravity which is greater than the specific gravity of the fluid for which the pressure has to be measured.
The manometric liquid used for measurement depends upon the pressure range and the nature of the fluid whose pressure is to be measured. When the pressure to be measured is large, mercury is used as a manometric liquid. Water can be used as the manometric liquid when the measurement is to be made in a gas.
U-tube differential manometer:
It consists of a U-tube containing a heavy liquid.
The two ends of the tube are connected to the points whose difference is to be measured.
It is used for measuring the difference of pressure between two points in the flow section to which it is connected.
PA + γpy + γmΔx − γp(y − Δx)= PB
⇒ PA – PB = (γm – γp)Δx
PA = fluid pressures at points A
PB = fluid pressures at points B
γm = the specific weight of manometric liquid:
γp = the specific weight of the liquid in the pipe
Δx is the difference in levels of manometric liquid.