6th Chapter

Question 1

Power has to be supplied from an external source → four types of drives are used

Answer 1

 Electric
 Steam turbine
 Gas turbine
 Internal combustion engine

Question 2

Pumps are generally subdivided into

Answer 2

Streaming pumps and Displacement pumps

Question 3

Types of streaming pumps

Answer 3

 Centrifugal pumps
 Propeller pumps
 Jet pumps

Question 4

Types of Displacement pumps

Answer 4

 Piston pumps
 Piston diaphragm pumps
 Screw pumps
 Eccentric screw pumps
 Gear pumps
 Rotary piston pumps
 Peristaltic pumps

Question 5

Centrifugal pumps

Answer 5

 Most common pump type in the (chemical) industry.
 Universally usable pump for low viscous fluids. Large operating range for discharge head and conveying capacity.
 Design is inexpensive, simple, robust, has a high
efficiency and low power consumption, and can
be connected to an asynchronous motor.
 Suitable for handling pure and impure liquids.
 Example wastewater: impeller is constructed especially
to avoid that objects get locked inside the pump
 Open design: liquid can pass even if pump is not
running
50 – 90 %

Question 6

Closed impeller

Answer 6

Series of curved vanes attached to a central hub that extends outward between
two enclosing plates.

Question 7

Open impeller

Answer 7

Similar design, except that there are no enclosing plates → this type allows visual
inspection of the vanes.

Question 8

Centrifugal pumps are categorized into

Answer 8

radial flow, mixed flow and axial flow pumps
 Radial flow and mixed flow pumps are the most commonly used types
 Radial impellers produce relatively large pump heads with comparatively low flow.
 Axial impellers lead to a large flow but offer only low pump head.
 Mixed flow impellers lie between the two aforementioned.

Question 9

Standardized chemical pumps

Answer 9

 Pumps with standardized (DIN EN ISO 2858) dimensions and hydraulic output.

Question 10

In-line pumps

Answer 10

 Designed with the suction and discharge nozzle on the same axis, with the same nominal diameter.
 Advantages: High output, small footprint and flexible installation options → many models of in-line
pumps can be installed in either a vertical or a horizontal position

Question 11

In-line pumps have become well-established, especially in building services applications, such as

Answer 11

 Heating systems
 Air-conditioning systems
 Cooling circuits
 Service water supply systems
 Swimming pool systems
 Water supply
 Industrial recirculation systems

Question 12

Typical building types of centrifugal pumps

Answer 12

Magnetic-coupling centrifugal pumps (Magnetic-driven pumps)
 Have become popular for the transport of aggressive and toxic liquids.
Important: Venting (for the bearings)
 Separation by a non-magnetizable can (made from Cr-Ni steel, Ni-alloys or ceramics) which acts
as a hermetically sealed barrier between the atmosphere and the liquid.

Question 13

Positive displacement pumps

Answer 13

 Centrifugal pumps: Head is developed by the speed of the rotor.
 Positive displacement pumps: Maximum head achieved by the available power from the driver
that is working on the fluid.
 The overall efficiencies of displacement pumps are higher (compared to centrifugal pumps) as
internal losses are minimized.
 Oscillating: rapid opening and closing of suction and discharge valves causes pressure pulsation
 Flexibility of positive displacement pumps in handling a wide range of capacities is limited.

Question 14

Piston pumps

Answer 14

 Conveyance of the liquid as a result of an oscillating displacing piston connected to a crankshaft.
 Working chamber is alternately increased and decreased and is connected to two self-acting valves.
 Typically used for smaller applications, requiring minimal space and involving low flow rates.
For low to medium conveying capacities and up to very high pressures. Suitable as dosing pump.
60 – 95 %

Question 15

Piston diaphragm pump

Answer 15

 Perform similar as piston pumps but the displacement element is an elastic membrane made
from rubber, enforced PTFE or steel.
 Used for aggressive and solid-containing fluids and
suspensions like acids, brines or toxicants.
 Units available that are able to withstand up to
700 bar and deliver capacities > 25 m³/h.
 Hermetically sealed → elimination of all packing and seals exposed to the liquid being pumped.
Conveying of aggressive,toxic and flammable liquids
and suspensions. Suitable as dosing pump.
80 %

Question 16

Screw pump

Answer 16

Screws are rotating contactless (no metal-metal contact) in opposite direction, which allows a
good pumping performance even with non-lubricating, corrosive or contaminated fluids
Advantages
 Usually for pressures up to 70 bar (400 bar possible
for special applications)
 Wide range of applications
 No priming required (self-priming)
 Pumped capacity proportional to speed
 Pumping elements are simple to replace
 For almost all media and fluids
 High viscosities possible
 Low pressure pulsation and noise level
 Dry running possible
80 %

Question 17

Gear pump

Answer 17

 Use of two intermeshing gears rotating against each other.
Characteristics
 Quiet-running (gears supported on both sides)
 Self priming
 Used for high pressure applications up to 200 bar
 For low fluid rates
 Constant rate of delivery
 Medium to high viscosity of the fluid
 Sensitive to hard solid particles
For low flow rates and high pressures. Suitable for high
viscous liquids and as dosing pump.
50 – 95 %

Question 18

Eccentric screw pump

Answer 18

Consists of a rotating displacement element (eccentric screw, rotor) and a stator.
 The rotor is in the shape of a rounded single threaded spiral shaft with a large pitch.
 Dry running has to be avoided in order not to
damage the stator (e.g. hard rubber, PTFE).
 Eccentric screw pumps are self-priming and can
deal with fibrous media and fluids with high
viscosities.
Conveying of muddy and paste-like fluids. Direction of flow invertible.
50 – 70 %

Question 19

Rotary piston pump

Answer 19

 Rotors made of steel touch neither each other nor the casing (mechanical clearance) and offer
comparably low pressures.
 Fluids with high turbidity (particles) and a
wide viscosity range can be conveyed.
 Two rotors on parallel axes run by a synchronized gear and rotate in the opposite direction.

Question 20

Peristaltic pump

Answer 20

 The conveyed fluid is contained within a flexible tube (e.g. silicone hose).
 A rotor with a number of rollers compresses the flexible tube.
 As the rotor turns, the part of the tube under compression is pinched closed thus forcing the
fluid to move through the tube.
 The fluid is not in direct contact with moveable pump parts.

Question 21

Newtonian Fluids

Answer 21

The viscosity of Newtonian fluids ① is not affected by the magnitude and the motion that it is
exposed to. In other words, the viscosity is load-independent. Examples are water or mineral oil

Question 22

Non-Newtonian liquids

Answer 22

The viscosity of Non-Newtonian fluids is dependent on the shear rate or the shear rate history. In
other words, the viscosity does change when the liquid is agitated.

Question 23

Shear thinning fluids

Answer 23

Behavior is generally not seen in pure
liquids with low molecular masses or ideal
solutions but is often seen in polymer
solutions, molten polymers and complex
fluids and suspensions such ketchup, paint
or blood.

Question 24

Cavitation

Answer 24

If the NPSHA is lower than the NPSHR gas bubbles will form in the fluid and cavitation will occur

Question 25

Changes that affect the NPSH

Answer 25

 Source liquid level
 Height of source
 Pressure on fluid surface
 Vapor pressure
 Piping design
 Fluid velocity
 Dirty or restricted pipes
 Fluid properties

Question 26

Resistances connected in parallel

Answer 26

 Components installed in parallel reduce the total resistance in the system and consequently the
head loss.
 This results in a more flat system curve
Qtotal = Q1 + Q2

Question 27

Resistances connected in series

Answer 27

 The total head loss in a system consisting of several components connected in series is the sum of
head losses each individual element represents.

Question 28

Open systems

Answer 28

 Open systems are used to transport liquid from one point to another like in water supply systems,
irrigation systems or many industrial processes.
 The pump has to overcome both the geodetic
head of the liquid and the friction losses in the
pipes and the installed equipment.

Question 29

Open systems with positive geodetic head

Answer 29

 The pump has to provide a head that is higher
than the geodetic head (h)
 The pump has to provide the required head to
overcome also the total friction losses (Hf
) due
to the pipeline, fittings, valves, etc.
 This pressure loss is dependent on the flow Q.
 The flow Q1 and the pump size have to match
the need of the specific system.

Question 30

Open systems with negative geodetic head

Answer 30

 An example of an open system with negative geodetic head is a pressure booster system.
 The geodetic head brings water to the consumer although the pump is not running.
 The height difference h results in the flow Q0 but it is too low to ensure the required flow Q1 to the
consumer.
 The pump has to booster the head to the level H1

Question 31

Closed systems

Answer 31

 Closed systems are commonly used to transport heat energy in heating systems, air-conditioning
systems, process cooling systems etc.
 The circulated liquid is often the carrier of heat energy.
 The pump only has to overcome the sum of friction losses which are caused by all installed
equipment and pipelines.

Question 32

Speed-controlled pumps connected in parallel (1)

Answer 32

 Useful method to realize an efficient pump performance when the flow demand is varying.
 Commonly used in water supply and pressure boosting systems.
 Pumping systems consisting of two speed-controlled pumps with similar size can cover a wide
performance range.

Question 33

Pumps connected in series

Answer 33

 Generally used in systems with a high pressure demand.
 Multi-stage pumps are also based on the series principle with one stage equals one pump.
Htotal = H1 + H2

Question 34

Adjusting pump performance

Answer 34

 It is important to select a pump where the duty point is in the high-efficiency area of the pump.
Failing this, the power consumption of the pump is unnecessarily high.
 It is not always possible to select a pump that hits the optimum duty point due to the requirement
of system changes or the system curve changes from time to time.

Question 35

Most common methods Adjusting pump performance

Answer 35

(1) Throttle control
(2) Bypass control
(3) Modifying impeller diameter
(4) Speed control
Observar Diapositivas

Question 36

Throttle control

Answer 36

 The power consumption is reduced to
about 94 %*
 Head is increased from 70 to 76 m
 The overall efficiency of the pump
system is considerably reduced
 Continuous adjustment is possible

Question 37

Bypass control

Answer 37

 To reduce the flow in the system to 50 m3 h-1 the
head of the pump has to be reduced to 55 m
 This is achieved by an increase of Q to 81 m3 h-1
 Power consumption is increased up to 10 %*
whereby the degree of increase depends on the
pump type and the duty point
 Continuous adjustment is possible

Question 38

Modification of impeller diameter

Answer 38

Drop of flow and pump head if the pump
impeller diameter is reduced
 Power consumption is reduced to
around 67 %*
 The overall efficiency of the pump
system is reduced only slightly
 No continuous adjustment possible

Question 39

Speed control

Answer 39

 Flow and head are decreasing when the speed of
the pump is reduced
 Power consumption is reduced to about 65 %*
 The overall efficiency of the pump system is
reduced only slightly
 Continuous adjustment is possible