5. Pumping Theory difference between PDP and
Dynamic (non PDP)
• A common application of pump that one can use in household where water
is sucked with high suction capacity from the quite a depth and deliver to the
top of the building. Here we use centrifugal pump, jet pump, submersible
pumps & turbine pumps. These have high suction capabilities.
• In positive displacement pumps PDP, the liquid transferred from pumps
suction side to its delivery in one revolution or cycle of operation of pump.
The PDP we deliver liquids or oils from suction to delivery. And when liquid
transferred to delivery one cant not get back then at suction side.
• The dynamic non PDP are in which turbine pumps, CF pumps, axial flow
pumps, are at priority. In these pumps if delivery side is shut off by a valve
the sucked fluid it will churn in side suction to delivery and vice versa. If PDP
same thing is repeated by closing the delivery side shut off valve, the fixed
volume rate of flow at the given speed of rotation the pump pressure will be
continued to build up and would be a danger of pipe line burst off due to fluid
pressure.
6. Positive Displacement Pump
• A positive displacement pump is one in which a
definite volume of liquid is delivered for each cycle of
pump operation. This volume is constant regardless of
the resistance to flow offered by the system the pump
is in,------------ provided the capacity of the power unit
driving the pump or pump component strength limits
are not exceeded
• The positive displacement pump differs from
centrifugal pumps, which deliver a continuous flow for
any given pump speed and discharge resistance.
• Positive displacement pumps can be grouped into
three basic categories based on their design and
operation. The three groups are reciprocating pumps,
rotary pumps, and diaphragm pumps.
7. Reciprocating Pumps
• With a single suction port and a
single discharge port as shown
• During the suction stroke, the
piston moves to the left, causing
the check valve in the suction
line between the reservoir and
the pump cylinder to open and
admit water from the reservoir.
• During the discharge stroke, the
piston moves to the right,
seating the check valve in the
suction line and opening the
check valve in the discharge
line.
9. Direct-Acting and Indirect-Acting
Pumps
• Direct Acting pumps powered by a reciprocating
steam piston. The piston rod of the steam piston
may be directly connected to the rod of the piston of
the pump or it may be indirectly connected with a
beam or linkage
• Indirect-acting pumps are driven by means of a
beam or linkage connected to and actuated by the
power piston rod of a separate reciprocating engine.
10. Simplex and Duplex
Pumps
• A simplex pump, sometimes referred to as a single
pump, is a pump having a single liquid (pump)
cylinder.
• A duplex pump is the equivalent of two simplex
pumps placed side by side on the same foundation.
• Duplex is one piston type is on its upstroke the other
piston is on its down stroke, and vice versa. This
arrangement doubles the capacity of the duplex pump
compared to a simplex pump of comparable design
11. Single-Acting and Double-Acting
Pumps
• A single-acting pump is one that takes a
suction, filling the pump cylinder on the
stroke in only one direction, called the
suction stroke, and then forces the liquid out
of the cylinder on the return stroke, called the
discharge stroke.
• A double-acting pump is one that, as it fills
one end of the liquid cylinder, is discharging
liquid from the other end of the cylinder
14. non PDP or Propeller Design Pump
• Most hydraulic pumps are positive-
displacement (PDP) devices
• PDP have higher efficiencies than their
non- PDP counterparts, such as
impeller or centrifugal designs
• non-PDP designs that could be used to
run hydraulic circuits. Because these
pumps only run at 50 to 75% efficiency,
they are not used in high-pressure
circuits.
• They are frequently found in systems
with high-water-content fluids (HWCF),
such as 95% water and 5% soluble oil,
• These pumps require little or no
lubrication.
• These systems usually operate at or
below 400 psi.
• Some PDP are paired with centrifugal
pumps to pressurize their inlets to
keep them from cavitations.
• Or when a PDP is run at higher rpm
than specified, the inlet may not be
large enough to let in enough fluid at
• , atmospheric pressure. In this case
a non-PDP can force fluid into the
undersized inlet and eliminate
cavitations.
• A non-PDP does not require a relief
valve in many installations. There is
enough slippage in most designs to
allow for stopping flow while not
over pressuring the circuit.
15. Positive Displacement Pump (PDP)
• PDP have two types
• 1. Rotary
• 2. Reciprocating
• PDP have two types from construction point
• 1. Based on delivery of oil Flow------------1. Fixed Displacement
• 2. Based on Construction 2. Variable
Displacement
• i. Gear Pump---------Fixed Displacement
• ii. Vane Pump---------Fixed and Variable
• iii. Axial Piston Pumps-------- Variable Displacement
• vi. Radial Piston Pumps-------Variable Displacement
16. Rotary Pumps
• Rotary pumps operate on the principle that a rotating
vane, screw, or gear traps the liquid in the suction side
of the pump casing and forces it to the discharge side
of the casing.
• There are many types of positive displacement rotary
pumps, and they are normally grouped into three basic
categories that include
• Gear pumps,
• Screw pumps,
• Moving vane pumps.
17. • Clearances between rotating parts, and between
rotating and stationary parts, be kept to a minimum in
order to reduce slippage. Slippage is leakage of fluid
from the discharge of the pump back to its suction.
• Due to the close clearances in rotary pumps, it is
necessary to operate these pumps at relatively low
speed in order to secure reliable operation and
maintain pump capacity over an extended period of
time. Otherwise, the erosive action due to the high
velocities of the liquid passing through the narrow
clearance spaces would soon cause excessive wear
and increased clearances, resulting in slippage.
similar to duplex double-acting steam pumps,
Gear pumps Rotary
18. • Rotary are relatively expensive pumps and can rarely
be justified on the basis of efficiency over centrifugal
pumps. However, they are frequently justified over
steam reciprocating pumps where continuous duty
service is needed due to the high steam requirements
of direct-acting steam pumps
• In general, the effective flow rate of reciprocating
pumps decreases as the viscosity of the fluid being
pumped increases because the speed of the pump
must be reduced.
• In contrast to centrifugal pumps, the differential
pressure generated by reciprocating pumps is
independent of fluid density. It is dependent entirely on
the amount of force exerted on the piston
Comparison of Reciprocating, Rotary, CF pumps
19. Simple Gear Pump
•
There are several variations of gear pumps. The simple gear pump consists
of two spur gears meshing together and revolving in opposite directions
within a casing. Only a few thousandths of an inch clearance exists between
the case and the gear faces and teeth extremities. Any liquid that fills the
space bounded by two successive gear teeth and the case must follow
along with the teeth as they revolve. When the gear teeth mesh with the
teeth of the other gear, the space between the teeth is reduced, and the
entrapped liquid is forced out the pump discharge pipe.
• With the large number of teeth usually employed on the gears, the discharge
is relatively smooth and continuous, with small quantities of liquid being
delivered to the discharge line in rapid succession
• In all simple gear pumps, power is applied to the shaft of one of the gears,
which transmits power to the driven gear through their meshing teeth.
There are no valves in the gear pump to cause friction losses as in the
reciprocating pump.
• In Centrifugal pumps high impeller velocities, with resultant friction losses,
are not in simple gear pumps.
22. Other Gear Pumps
• There are two types of gears used in gear
pumps in addition to the simple spur gear. One
type is the helical gear. A helix is the curve
produced when a straight line moves up or
down the surface of a cylinder.
• The other type is the herringbone gear. A
herringbone gear is composed of two helixes
spiraling in different directions from the center
of the gear. The herringbone gear pump is also
a modification of the simple gear pump.
• Its principal difference in operation from the
simple spur gear pump is that the pointed
center section of the space between two teeth
begins discharging before the divergent outer
ends of the preceding space complete
discharging.
• This overlapping tends to provide a steadier
discharge pressure. The power transmission
from the driving to the driven gear is also
smoother and quieter
pointed center section
23. Lobe type pump
• The lobe type pump is another variation of the
simple gear pump. It is considered as a simple
gear pump having only two or three teeth per rotor;
otherwise, its operation or the explanation of the
function of its parts is no different.
• Some designs of lobe pumps are fitted with
replaceable gibs, that is, thin plates carried in
grooves at the extremity of each lobe where they
make contact with the casing. The gib promotes
tightness and absorbs radial wear.
29. • These pumps are also known as
positive-displacement pumps. It is
also probably the world's oldest
type of pump. Recently, it has
become accepted in the United
States for general use in pumping
wastewater.
• It was based on the Archimedes
screw principle that has a revolving
shaft fitted with one, two, or three
helical blades to rotate in an
inclined trough and push the
wastewater up the trough.
• This type of pump has two very
evident advantages over the afore-
mentioned centrifugal pumps,
• (1) it can pump large solids without
clumping, (2) it operates at a
constant speed over a wide range
of flows with good efficiencies.
Blacksburg
Wastewater Treatment
Plant (SCREW PUMP)
33. Rotary Moving Vane
Pump
• The rotary moving vane pump is another type of positive displacement
pump used. The inner rotating element causes liquid to be pumped out.
• In C.F pump it the rotation of the impeller.
• In Vane pump we have cylindrical rotor that has grooves or slots along
the circumference that has housed a number of vanes . The vanes have
loose fit in side the slots.
• The ring of the cam is elliptical shape.
• Rotor with the vane are known as cartridge unit. The cartridge units are
splined on to the driving shaft. A cam ring is fitted inside the pumping
chamber of splined shaft. As the driving shaft rotates the vanes come out
of the slots due to centrifugal action.
• The design of the cam ring and the rotor does not allow them to come
out completely.
• The rotor moves with 600 rpm.
• The continuous contact of the vane tip and the ring of cam wear out their
surface. The manufactures of vane pump offers cartridge for the
replacement .
• The increase and decrease in flow rate is also possible by changing a
different cartridge kit of cam ring and vanes.
35. Vane pump curve characteristics
• Another way to increase the flow rate is to increase the
speed of the vane pump motor
• The decline in rate of speed will increase the working
pressure
• In the graph when Pump pressure is 70 bars at 1500rpm
the discharge is 17 l/ mint and the Kilo watt energy is
required about 7 kw
• The pump KW can be calculated by PQ/600 approximately
Kilo watts
• If flow rate is cc/ rev we can multiply cc with rpm and divide
by 1000 to get liters/ mint, so we have Q= Lit/mit
• We have rpm in 1000, 1500 and 3000 which are always
shown as 960 1440 and 2880 etc.
• P is in bars or psi. If bars to convert in psi just multiply with
14.5psi with bars and get P=psi
36. Example to convert 200bars in to
psi.
• If 1bar= 105
Pa;
• 1 bar= 14.5 psi; ---------1 Pascal =0.000145 psi then
200bars = 105
x 200 Pascal
• 200bars = 105
x 200 (1 Pascal)
200 bars =105
x200 (0.000145 = 2900psi)
• SIMPLE If 14.5x 200 we get = 2900 psi
• To get KW we use P*Q/600 = Lbs / in2
x liters /sec /550 ft Lbs /sec
• =( Lbs/in2
) xLs/sec x(103
/ 2.543
)x(1/12)x (sec / 550 x ft Lbs) x746
• = wattsx1000 kw
37.
38. Diaphragm pumps
• Diaphragm pumps are also classified as positive
displacement pumps because the diaphragm acts as
a limited displacement piston. The pump will function
when a diaphragm is forced into reciprocating motion
by mechanical linkage, compressed air, or fluid from a
pulsating, external source. The pump construction
eliminates any contact between the liquid being
pumped and the source of energy. This eliminates the
possibility of leakage, which is important when
handling toxic or very expensive liquids.
• Disadvantages include limited head and capacity
range, and the necessity of check valves in the suction
and discharge nozzles.
