Page 372 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Classification of pumps

Types of Classification Positive displacement pump Rotary type pump

Movement Liquid suck and push Liquid passes through a rotating
element

Displacement Displaced through thrust Rotating by external force
Moving member(type) Piston Impeller (turbine)
Speed Draw fluid into a cavity, or displace Have a spinning impeller that
the fluid, and then force the liquid draws the fluid into the pump and
out of the cavity trough suction. forces it out of the outlet point at an
increased velocity

Handling It can handle highly viscous fluid Unable to handle viscous fluid as
and shear sensitive fluids- or fluids well as positive displacement pump
that change when force, stress and because of the frictional losses
pressure is applied
Flow rate 1 Flow rate can increase as the 1 Need liquid in the unit to kick-
fluid gets thicker start the pressurized control
2 Maintain a constant flow rate 2 The fluid moving out of is
even as a pressure changes varying flow rate based on
pressure

Application 1 Municipal sewage system 1 Municipal water supply
2 Oil processing centers departments
3 Manufacturing centers 2 Air conditioners
3 Irrigation
4 firefighters
Power of volume Low pumping water volume High pumping water volume
Maintenance Frequent maintenance Low maintenance

Pressure Lower flow rates and higher head Volume of fluid is dependent on
than centrifugal pump static head/ pressure

Improvement of flow rate As a water viscosity increase, flow As the water viscosity increase, the
rate also increase flow rate decrease

According to types of casing Cylindrical shape Volute or constant velocity
According to stage Single /Multi cylinder Single/ multi stage
According to working head a low head- 0.4 to 55000 lpm a low head- upto 15m
b total head pressure- between b medium head- between 15m to
0.7 to 6800 bar 40m
c horsepower range- between 0.5 c high speed-beyond 40m
to 4900 HP
According to liquid handle Vertical in-closed cylindrical shape Shrouded or enclosed impeller
type

Construction and working of positive displacement pump
In positive displacement pumps, the division of reciprocating assists the liquid to flow forward from the lake. The
reciprocating parts of these pumps are a plunger, a piston otherwise a diaphragm. This type of pump includes
different types of valves such as the inlet valve and outlet valve. In the fluid suction method, the inlet valve opens
& the outlet valve stays closed.

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CITS : Automotive - Mechanic Diesel - Lesson 129 - 131