Ontario Operator-in-Training (OIT) Practice Exam

What distinguishes a centrifugal pump from a positive displacement pump?

1. Centrifugal pumps use air pressure

2. Centrifugal pumps push fluid mechanically

3. Centrifugal pumps throw fluid at high speeds

4. Positive displacement pumps cannot handle high speeds

The correct answer is: Centrifugal pumps throw fluid at high speeds

Centrifugal pumps are distinguished by their operation, which involves throwing fluid at high speeds. This is achieved through the rotation of a wheel known as an impeller, which imparts kinetic energy to the fluid as it moves through the pump casing. The design allows the fluid to be accelerated outward from the center of the impeller, utilizing centrifugal force to move the fluid through the discharge pipe. This characteristic of high-speed fluid movement is key to the centrifugal pump's efficiency in applications requiring the transfer of liquids over relatively low viscosities. The ability to handle large volumes of fluid quickly makes centrifugal pumps particularly effective for many industrial and municipal applications, such as water supply and sewage treatment. Additionally, while positive displacement pumps do not operate by creating high speed but rather by effectively displacing a fixed amount of fluid with each cycle of operation, it’s essential to recognize that their mechanics differ fundamentally. Positive displacement pumps can handle higher viscosities better than centrifugal pumps but at lower flow rates and pressures. Thus, the distinguishing feature of centrifugal pumps lies primarily in their method of moving fluid rapidly, which sets them apart from positive displacement types.