BY AVINASH TIWARI
Working Principle Of Pump & Its Types. Types Of Impeller & Vanes. Velocity Triangles. Performance Curves. Pump Operation in Series & Parallel. Other Topics
Some Basic Terms Cavitation & its remedies. NPSHA & NPSHR. Specific Speed & Suction Specific Speed.
THE HYDRAULIC MACHINE WHICH CONVERTS MECHANICAL ENERGY TO HYDRAULIC ENERGY (NORMALLY PRESSURE ENERGY)
Pumps DYNAMIC
POSITIVE DISPLACEMENT
CENTRIFUGAL RADIAL MIXED AXIAL SPECIAL EFFECT JET GAS LIFT HYDRULIC RAM ELECTROMAGNETIC
RECIPROCATING STEAM POWER METERING ROTARY SINGLE MULTIPLE
Conversion Of Mechanical Energy To Hydraulic Energy
DISCHARGE NOZZLE INSIDE MOUNTED, TANDEM SEALS STUFFING BOX COVER COOLING MEDIUM IN
WEARING RINGS
COOLING MEDIUM
SUCTION NOZZLE
LUBRICANT IN
BEARING ISOLATOR
BAFFLE
SHAFT
MOTOR END
CLOSED, RADIAL FLOW, SINGLE STAGE, IMPELLER STUFFING BOX
BEARING HOUSING BEARINGS
GLAND
OIL-RINGS RADIAL BEARING
SHAFT SLEEVE
VOLUTE CASING WEARING RINGS
BASED ON FLOW
Single Stage Pump
Multi Stage Pump
Single Suction
Double Suction
Single Volute
Double Volute
Radially Split
Axially Split
BASED ON SHAFT ORIENTATION •HORIZONTAL •VERTICAL
BASED ON BEARING SUPPORT •OVERHUNG •BETWEEN BEARING
OPEN TYPE SEMI OPEN TYPE CLOSED TYPE
Open Type
Semi Open Type
Closed Type
RADIAL VANES ( β=90)
The vanes of this type of impeller are radially oriented. BACKWARD CUVED VANES(β<90) The vanes of this type of impeller are oriented backward with direction of rotation. FORWARD CURVED VANES(β>90) The vanes of this type of impeller lean forward with direction of rotation.
RADIAL VANES
u = VwR
αR
βR VrR = Vf VB
Velocity triangle for radial vanes
BACKWARD CUVED VANES
VwB βB
αB
Vf
VB
VrB
u
Velocity triangle for backward curved vanes
FORWARD CUVED VANES
VwF u αF
βF Vf
VrF VF
Velocity triangle for forward curved vanes
PROVIDES GRAPHICAL REPRESENTATION OF THE
• • • •
RELATIONSHIP BETWEEN HEAD, BHP,EFFICIENCY AND NPSHR AGAINST CAPACITY. Q-H Curve (Capacity-Head Curve) Q-BHP Curve (Capacity-Power Curve) Q-η Curve (Capacity-Efficiency Curve) Q-NPSHR Curve (Capacity- NPSHR Curve)
BHP
H
η NPSHR
Q
H
Q
H
Q
H
Q
Discharge vessel pump
Suction vessel
SYSTEM CHARACTERISTIC CURVE SYSTEM HEAD CURVE
HEAD DEVELOPED BY PUMP
HEAD DEVELOPED BY PUMP
DUTY POINT VARIABLE HEAD FIXED HEAD
HEAD (H)
SYSTEM HEAD
FLOW RATE (Q)
Pump A
Pump B
Pump B
Pump A
DIFFERENTIAL HEAD
DEVELOPED BY PUMP AT ZERO FLOW. ACHIEVED AT COMPLETE CLOSURE OF DELIVERY VALVE. HELPS IN SELECTING PUMP AND DESIGNING H DOWNSTREAM PIPING AND EQUIPMENTS.
Shut Off Head
Q
The maximum flow that
a pump can deliver Value is required to determine the motor rating for parallel H operation or when pump is required to be started with open discharge valve.
End Of Curve Q
For Speed Held Constant
Q2 D2 = Q1 D1
TDH 2 D 2 = TDH 1 D 1
2
BHP 2 D 2 = BHP 1 D 1
3
For Diameter Held Constant
Q 2 RPM 2 = Q 1 RPM 1
TDH 2 RPM 2 = TDH 1 RPM 1
2
BHP 2 RPM 2 = BHP1 RPM 1
3
WEAR RINGS: Provide easily and economically renewable leakage joints between impeller and the casing Mating wear surfaces of hardenable materials shall have a difference in 50 BHN unless both wear surface have hardness at least 400 BHN Can be of various types depending upon liquid handled, pressure differential across leakage joint and rubbing speed For certain sewage service and slurry service pumps, water flushed wear rings are used Most common ring constructions are,
Flat type L-type Step type Labyrinth type
FLAT TYPE WEAR RING: •
Leakage joint is straight and annular Suction head ring
Suction head
Impeller
Axial clearance between impeller and casing ring is large and hence velocity of liquid flowing through it is low Impeller ring Casing ring
Path of flow of liquid is broken due to steps and a relief chamber Casing ring
Impeller ring
Relief chamber
They have two or more annular leakage joints and relief chambers
Relief chambers act to dissipate the velocity head and offer resistance thus reducing leakage Casing ring
Impeller ring Relief chamber
Formation and subsequent collapse of vapor
bubbles in a liquid due to dynamic action.
It is the loss of metal due to collapsing of vapor
bubbles against the metal surfaces of impeller or casing.
IDENTIFICATION Reduction of both total head and output capacity Steady crackling sound in and around pump suction Random crackling sound with high intensity knocks
indicates recirculation due to inadequate NPSH
A measure of cavitation
σ= HSV / HV
HSV = Available NPSH HV = Pump head
Critical σ =1.042*10-3 (Ns) 4\3
Cavitation No Should Not be less than Critical
Value
Pressures generated by centrifugal pump exert forces on both stationary and rotating parts
Design of these parts balances some of the forces
Separate means are required to counterbalance other forces
Axial thrust on an impeller is the sum of unbalanced forces acting in the axial direction
There are separate ways of balancing axial thrust in single stage and multi stage pumps
Axial thrust in single stage pumps can be balanced by, • Providing wearing ring on the back of the impeller along with balancing
holes and balancing chamber • Providing pump out vanes or radial ribs on the impeller
Axial thrust in multi stage pumps can be balanced by, • Providing balancing drums • Providing balancing disks • Providing a combination of balancing drum and disk • Providing opposed impellers to counter each other’s axial thrust
Pump is provided with both front as well as back wearing ring, inner diameter of both rings being same
Balancing chamber is provided at the back of the impeller which is kept at pressure approximately equal to suction pressure
This is achieved by drilling balancing holes through the impeller
Leakage past back wearing ring is returned to suction area through balancing holes
Pump out vanes or radial ribs are provided on the back shroud of the impeller
Function is to reduce pressure at the back hub of the impeller
Such vanes also prevent foreign matter from lodging in back of the impeller and interfering the proper operation of pump and stuffing box
This design is hence used in pumps handling gritty liquids
Balancing chamber at the back of last stage impeller is separated from pump interior by a drum called balancing drum, keyed or screwed to the shaft
Balancing drum is separated by a small radial clearance from stationary part with a balancing drum head, fixed on the casing
Balancing chamber is maintained at suction pressure by connecting with pump suction or suction vessel
Leakage between balancing drum and balancing drum head occurs due to pressure differential
Balancing using balancing drum
Principle is similar to that of a balancing drum
The disk is fixed to and rotates with the shaft
Balancing disk is separated by a small axial clearance from stationary part with a balancing disk head, fixed on the casing
Leakage through this clearance flows into the balancing chamber and to suction from there
Balancing using balancing disk
An even no. of single suction impellers are used One half of the impellers faces one side while the other half faces the other side Thrust on the first half is compensated by the thrust in the opposite direction on the other half
Balancing using opposed impellers
Net Positive Suction Head Available (NPSHA):
Excess pressure of the liquid in meter absolute over its vapor pressure as it arrives at the pump suction Net Positive Suction Head Required (NPSHR):
Positive head in meter absolute required at the pump suction to overcome pressure drops due to shock and turbulence as the liquid strikes the impeller
Speed at which a geometrical similar impeller
would run if it were of such a size as to unit discharge against unit head.. Useful dimensional parameter for classifying the overall geometry and performance characteristic of impeller Measure to decide the type of impeller to be used. Nq = N (Q)1/2 (H)3/4 specific speed ∝ Q , as H = constant specific speed ∝ 1/H, as Q = constant
Index relating flow, NPSHR, and rotative speed for
pumps of similar geometry. Calculated for pump’s performance at BEP with maximum diameter impeller. Provides an assessment of the pump’s susceptibility to internal recirculation Nqs = N (Q)1/2 (NPSHR)3/4 Value of suction specific speed of a pump remains constant.