Positive Displacement Pumps In Detail Flashcards
Describe positive displacement pumps.
They have an expanding cavity on the suction side of the pump where liquid flows into and a decreasing cavity on the discharge side where liquid is forced out of.
Describe Vane PD pump types and list an advantage and disadvantage.
Vane designs vary to draw fluid into and out of the chamber.
Developed a good vacuum.
Efficiency drops with viscosity, can be prone to leaks, and is not suitable for high pressures.
Describe the piston pump.
Give an advantage and a disadvantage.
Fluid is drawn in and out by a piston and will deliver fluid at high pressures.
They full on their own.
They are costly because accurate measurements are required, low volume rates of flow and aren’t suited for liquids containing suspended solids.
Describe the flexible member pump.
What are the two types.
Contains a flexible component that may be a vane, tube, or liner. The two types are the diaphragm pump and the peristaltic pump: both are slow, but the first can handle high solids content.
Describe the single screw pump.
Give an advantage and a disadvantage.
Looks like a rotaing screw that carries a liquid.
Capable of handling high solids content, simple construction, high reliability, and high efficiency for viscous fluids ~ saves power.
Bulky.
Describe gear pumps.
Give an advantage and a disadvantage.
Fluid is carried between the openings of the gears. At all times, during the motion, the gears are touching at one point, preventing fluid escaping that section.
Can handle a wide range of viscosities.
Not good with abrasions.
Describe the lobe pump.
Fluid is carried between rotor lobes, which cooperate to provide continuous sealing between the pump inlet and outlet.
Main 2 differences between gears and lobes?
Gears have multiple arms compared to lobes with a few. Also, lobes are touching each other and the outer walls of the enclosure. Gears only touch each other.
Advantages of Lobe pumps?
Can pass medium solids, no metal to metal contact, no pulsating discharge.
Disadvantages of lobe pumps?
Requires timing gears, reduced lift with thin liquids and larger and more expensive than others.
Describe circumferential piston pumps.
Fluid is carried in spaces between piston and surfaces, not requiring contact between rotor surfaces. The green one.
What is needed on the discharge side of PD pumps? Why is it necessary, and what hat are the two types?
A relief valve is necessary in order to protect the pump equipment from over-pressure situations. Manufacturers can either make an internal or an external pressure relief valve.
