From Mechanical Engineering License Review, Fifth Edition

14-1 General

With the exception of the fact that gases are compressible the theory of design for equipment to move gases and vapors is similar to that of pumps for liquids. Heads developed in terms of feet of fluid being pumped are almost identical for equivalent circumferential speeds as for centrifugal pump designs. Axial flow impellers impart similar heads to both liquids and gases and valve actions in positive displacement compressors are quite similar to those of piston water pumps.

When considering the compression of gases, the machines are usually referred to as fans (centrifugal and propeller), blowers (centrifugal and lobular), and compressors (multistage centrifugal, lobular, and piston).



Find the motor size needed to provide the forced-draft service to a boiler that burns coal at the rate of 10 tons per hr. The air requirements are 59,000 cfm, air is being provided under 6 in. water gauge (WG) by the fan which has a mechanical efficiency of 60 per cent. Assume fan to deliver at a total pressure of 6 in. WG.


A blower with the inlet open to the atmosphere delivers 3,000 cfm of air at a pressure of 2 in. WG through a duct 11 in. in diameter, the manometer being attached to the discharge duct at the blower. Air temperature is 70 F, and the barometer pressure is 30.2 in. Hg. Calculate the air horsepower.



The horsepower is determined by the basic formula given as

We must convert the 6 in.

Products & Services
HVAC Fans and Blowers
HVAC fans and blowers are used to move air through heating, ventilating, and air conditioning (HVAC) systems. They are an integral part of the air handling systems that bring or draw fresh air into buildings.
Pressure Blowers and Fans
Pressure blowers and fans are used to create and sustain a positive pressure for inflatable structures, clean rooms, laboratories, and medical facilities. Pressurization blowers are fans that create a positive pressure in a sealed or restricted environment.
Fan and Blower Repair Services
Fan repair services and blower repair services maintain, refurbish and repair fans and blowers.
Mechanical Vacuum Pumps and Systems
Mechanical vacuum pumps and systems contain devices such as pistons, claws, scrolling spirals, and diaphragms to isolate and compress air.
Regenerative Blowers
Regenerative blowers are low pressure, high volume blowers that generate centrifugal airflow.  They are used in compression, vacuum, and industrial blower applications.

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