Positive Displacement Pumps Flashcards Preview

Fourth Year Millwright > Positive Displacement Pumps > Flashcards

Flashcards in Positive Displacement Pumps Deck (30)
Loading flashcards...

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

Relief valves


As pressure rises what happens to volumetric efficiency?

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


Describe volumetric efficiency

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


What is a disadvantage of piston and plunger pumps?

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


Why can a plunger pump only be single acting?

Because they have no piston just a rod


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

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


Why are diaphragm pumps useful?

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


What are some common materials used for the diaphragm?

PTFE, Teflon, flexible stainless steel


What is a rotary pump?

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


Is a rotary pump considered continuous flow?

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


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

They handle abrasives better than any other type of rotary pump


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

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


Where axial and the radial piston pumps used?

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


What are the reciprocating pump type designs?

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


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

With the connecting rod and a crosshead


What opens and closes valves on the plunger pump?

Pressure differential on the suction and discharge strokes


How is metering usually achieved on a plunger pump?

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


Which ways can a diaphragm pump be driven?

They can be mechanically, hydraulically or pneumatically


How was the pneumatically activated diaphragm pump adjusted?

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


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

The circumferential piston pump


Which pump has a football shaped rotor?

The external vane pump


Describe a flexible tube pump.

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


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

Flexible liner pump


What type of pump is often used to pump milk?

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


Describe a single rotor screw pump

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


How are vanes normally replaced?

They need to be replaced as a set.


What is the poppet valve usually used for?

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


Which check valves can handle solids

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


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

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


What are pulsating dampeners used for?

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