Lesson 9 - Control of Fluid Flow 1 SAQ
This lesson allows you to test yourself on the material covered in the Control of Fluid Flow 1 lesson and determine the level to which you have met the learning outcomes.
Suggested Response - Q5
*Describe the principle of operation of a positive displacement pump.
Response:
Positive displacement pumps work on the principle of volume entrapment and displacement. This principle is best described with reference to a specific positive displacement pump type. The reciprocating piston pump is described below, but you may have chosen another pump to describe.
In the figure below, we can see a cylinder with a reciprocating piston which moves upwards and downwards. The cylinder is fitted with an inlet and an outlet port, each with a valve.
As the piston moves downwards, the inlet valve is open, the outlet valve is closed, and the piston draws in liquid through the inlet port by suction. As the piston changes direction and is driven upwards, the inlet valve is closed, and the outlet valve is opened to allow the piston to pump out liquid under pressure. In this way, you can see that the cylinder and piston, together with the valves, entrap a volume of liquid, and then the piston displaces that volume through the outlet port. The suction and pressure cycles are repeated many times to pump liquid at a particular flow rate.
