Positive Displacement Pumps

Question 1

What is incorporated on the discharge side of most positive displacement pumps?

Answer 1

Relief valves

Question 2

As pressure rises what happens to volumetric efficiency?

Answer 2

A system pressure rises so does the internal leakage which results in a reduction of efficiency

Question 3

Describe volumetric efficiency

Answer 3

Volumetric efficiency = actual output
———— X 100
Theoretical output

Question 4

What is a disadvantage of piston and plunger pumps?

Answer 4

They cannot handle abrasives and must not run dry or the packing will be compromised.

Question 5

Why can a plunger pump only be single acting?

Answer 5

Because they have no piston just a rod

Question 6

Is a double-acting piston pumps stroke volume equal on both sides?

Answer 6

No. Because of the space the piston rod occupies the volume discharged on the return stroke is less

Question 7

Why are diaphragm pumps useful?

Answer 7

The diaphragm completely seals and isolate the pumped liquid from the rest of the pump therefore it is useful with toxic or hazardous liquids. They can also handle some solids, they are self priming, and they can be run dry

Question 8

What are some common materials used for the diaphragm?

Answer 8

PTFE, Teflon, flexible stainless steel

Question 9

What is a rotary pump?

Answer 9

Consists of a rotor or rotors turning inside a closed casing with the minimum clearance. The rotors maybe gears vanes lobes screws or pistons

Question 10

Is a rotary pump considered continuous flow?

Answer 10

Although it delivers much smoother flow than reciprocating pumps they are not considered continuous flow

Question 11

What is a single road or screw pump with an elastomeric stator or liner used for?

Answer 11

They handle abrasives better than any other type of rotary pump

Question 12

What is the difference in delivery of flow between positive displacement pumps and dynamic pumps?

Answer 12

Dynamic pumps deliver smooth continuous delivery, and positive displacement may have pulsating delivery

Question 13

Where axial and the radial piston pumps used?

Answer 13

They are used in the hydraulic systems requiring high speeds and high pressures

Question 14

What are the reciprocating pump type designs?

Answer 14

Plunger, piston, and diaphragm pumps. They are used for high pressure controlled flow and metering purposes

Question 15

How is the rotary motion of the prime mover converted to reciprocating in a plunger pump?

Answer 15

With the connecting rod and a crosshead

Question 16

What opens and closes valves on the plunger pump?

Answer 16

Pressure differential on the suction and discharge strokes

Question 17

How is metering usually achieved on a plunger pump?

Answer 17

With the variable speed drive, or an adjustable calibrated connecting rod

Question 18

Which ways can a diaphragm pump be driven?

Answer 18

They can be mechanically, hydraulically or pneumatically

Question 19

How was the pneumatically activated diaphragm pump adjusted?

Answer 19

By adjusting the air inlet flow and pressure. This pump has an infinite variation in flow and head, the pump pressure can never exceed the air inlet pressure

Question 20

What type of positive displacement pump delivers a constant volume and pulse free flow?

Answer 20

The circumferential piston pump

Question 21

Which pump has a football shaped rotor?

Answer 21

The external vane pump

Question 22

Describe a flexible tube pump.

Answer 22

Flexible tube of the last material is squeezed by compressing rotating ring or shoe. As the rotor turns the tube is compressed in the liquid is pushed out of the pump

Question 23

Which pump has an eccentric Cam that rotates with the flexible liner?

Answer 23

Flexible liner pump

Question 24

What type of pump is often used to pump milk?

Answer 24

The flexible vane pump. The flexible nature of the vanes means it does not need a relief valve, when pressure gets high the vanes simply bend over

Question 25

Describe a single rotor screw pump

Answer 25

It is a type of peristaltic pump. It has a corkscrew like rotor with a single external thread that operates inside a liner or stator

Question 26

How are vanes normally replaced?

Answer 26

They need to be replaced as a set.

Question 27

What is the poppet valve usually used for?

Answer 27

Only clear liquids as the flow has to pass through the poppet port

Question 28

Which check valves can handle solids

Answer 28

Ball check valves allow this passage of solids up to the size of the opening between the ball in the seat. Flap valves can pass solids and slurries but can only handle low pressures

Question 29

Which check valve can handle higher pressure stem guided or wing guided?

Answer 29

Stem guided are only suitable for low pressures, wing guided can handle high pressures but only with clear fluids

Question 30

What are pulsating dampeners used for?

Answer 30

There used to maintain constant pressure and flow with positive displacement pumps. They are similar to a hydraulic accumulator