Untitled Flashcards Set

What is a pump?

What is a pump?

A machine that transfers energy to fluids.

What is the result of a poor pump choice?

Increase in cost of running it and increased chance of pump failure.

How are pump performance characteristics typically expressed?

Graphically.

What are important characteristics to consider for pumps?

Discharge, generated head, power requirements, efficiency.

What does discharge mean in relation to pumps?

Pump capacity.

What is generated head in relation to pumps?

Height that a pump can raise a fluid.

What are power requirements in relation to pumps?

Brake power.

What is efficiency in relation to pumps?

Energy imparted to liquid / brake power.

Why do characteristics change as a pump ages?

Parts wear down.

What is a reciprocating pump?

A pump that uses a piston to move fluid.

How does water move throughout a reciprocating pump?

The piston pulls back to create a low pressure area, opens a valve allowing water to flow in, and then pushes water out as it moves forward.

What is a positive displacement pump?

A pump that moves fluid by trapping a fixed volume and then forcing it out.

How can the water discharge pulses be controlled in a reciprocating pump?

By using multiple pistons.

What are the three kinds of positive displacement pumps?

Reciprocating pump, rotary pump, diaphragm pump.

How do rotary pumps operate?

They move fluid from the low-pressure side to the high-pressure side.

What is a flexible vane pump?

A pump with an electronically placed rotor and flexible vanes that bend against the inside of the housing.

What are vanes in relation to pumps?

Blades that guide and move fluid through pumps.

What variation exists for flexible vane pumps?

Non-flexible vanes that maintain contact with walls as the pump rotates.

What is a peristaltic pump?

A pump that has a flexible hose inside a housing and squeezes the tube to force fluid forward.

What is a rotor inside a pump?

The rotating part that drives the movement of fluid through the pump.

What happens as fluid moves forward in a peristaltic pump?

There is a drop in pressure behind the moving fluid, which draws in more fluid.

What is a diaphragm pump?

A pump where the diaphragm moves up, decreasing pressure to draw fluid in, and moves down to increase pressure and force fluid out.

What is another word for a diaphragm pump?

Membrane pump.

What is the most common pump used in aquaculture?

Centrifugal pumps.

How do centrifugal pumps work?

Water enters a low pressure area and is flung outward by an impeller.

What is an impeller?

Not the same as a propeller; it pulls water in, while a propeller pushes.

What happens to the speed and potential energy in a centrifugal pump?

As water spins around housing, it loses speed and gains potential energy.

What type of head does a centrifugal pump generate?

Static head and dynamic head.

What does static and dynamic head address in a centrifugal pump?

Static head - gravitational potential energy; Dynamic head - continuous energy input required to maintain flow.

What is a volute centrifugal pump?

A pump where the impeller spirals out.

Why is the conversion from dynamic head to static head crucial in centrifugal pumps?

It enables the pump to actually move fluid against resistance.

How does the conversion from dynamic to static head occur in a volute centrifugal pump?

By a change in housing which slows the water.

What are diffuser centrifugal pumps?

Pumps that have components attached to the housing that reduce turbulence and energy loss.

What are the three impeller designs?

Open impeller, semi-open impeller, closed impeller.

What is an open impeller?

Vaned on an incomplete disk; not very efficient but good for suspended materials.

What is a semi-open impeller?

Vaned on a complete disk.

What is the most common impeller type used in aquaculture?

Semi-open impeller.

What is a closed impeller?

Vaned between two plates; very efficient but does not handle suspended materials well.

What is a propeller?

It is designed to convert rotational motion into forward thrust.

What is cavitation?

Formation of bubbles or steam by the propeller occurring at the blades.

What limits propeller pump speeds at the blade tips?

Cavitation.

What causes water to boil at low temperatures?

Very low pressure.

What is the relationship between blade tip speed and propeller diameter?

Speed at the blade tips increases with propeller diameter.

What are mixed flow pumps?

Pumps that use both centrifugal force and lifting action of a propeller.

What are mixed flow pumps primarily used for?

Deep well turbines.

What are fish pumps used for?

To pump large numbers of fish from a raceway or pond.

What are fish pumps made of?

Soft and flexible hoses.

What is an Archimedes screw?

A device that moves water up an incline.

How much head is generated in airlift pumps?

Little head.

What is aeration?

The process of introducing air into a liquid to increase its oxygen content.

What will happen if the top of the tube of the airlift pump is too far above the water surface?

The mixture won’t leave.

What factors affect the efficiency of airlift pumps?

Volume of air injected, depth of the tube, height of the tube above the surface, depth of the air injection.

What size bubbles are more efficient in lifting water from airlift tubes?

Small bubbles.

What circumstances should airlift pumps be in ponds?

They should be on floats so the top of the pipe stays above surface water and the depth of injection is kept constant.

What do aquariums use for air supply?

Small air compressors (diaphragm pumps).

What kind of pressure and volume do small air compressors deliver?

Small volumes at high pressure.

What do larger facilities use for air supply?

Blowers.

What kind of volume and pressure do blowers deliver?

High volumes at lower pressures.

What is a regenerative pump?

A pump that behaves like a centrifugal pump but performs like a positive displacement pump.

What is the primary difference between centrifugal and regenerative pumps?

In centrifugal pumps, air only travels through the impeller once; in regenerative pumps, it takes many passes.

What method is used most often to measure water flow?

The bucket and stopwatch method.

What are head flowmeters based on and measured by?

Based on a difference in pressure; usually measured by a manometer.

What is another name for a head flowmeter?

Differential pressure (DP) flowmeter.

What are two kinds of head flowmeters?

Orifice and venturi flowmeters.

How does an orifice flowmeter work?

A plate constricts flow, forcing fluid to narrow and constrict.

How does a venturi flowmeter work?

It uses a gradually changing throat for restriction rather than a plate.

Which flowmeter has less pressure loss, orifice or venturi?

Venturi flowmeter has less pressure loss.

What are venturi and orifice flowmeters connected to?

A differential manometer.

What else could a manometer be?

A device that measures pressure.

What is the most common use for a manometer?

Most often refers to a U-shaped tube filled with fluid.

What is another name for a rotameter?

Variable area flow meter.

What are two kinds of mechanical flowmeters?

Rotameter and turbine flowmeter.

What are the two main types of Ultrasonic flowmeters?

Doppler and transit time.

What do ultrasonic transit time flow meters measure?

Time difference of ultrasonic pulses flowing in and against the direction of flow.

What are Reynold’s numbers?

Quantities used to predict similar flow patterns in different fluid flow situations.

What is kinematic viscosity?

Ratio of absolute viscosity to density.

What is viscosity in general?

Thickness of the fluid, hence resistance to flow.