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Effect of Over Sizing Pumps
Purchase Cost - Increased
Power Consumption - Affected
Operation at Excess Capacity, Requires Greater NPSH (A)
High Pressure Drop through Foot Valve and Suction Lift
Cavitation - Efficiency Drop and premature Failure of Rotor
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Few Reminders on Centrifugal Pumps
Pump Selection
Do not oversize pumps. This leads to uneconomical operation and generally narrows the safe operating range of capacities.
Do no try to select pumps with excessively low NPSH (Net Positive Suction Head).
Do not falsify real available NPSH, trying to keep a margin up your sleeve. This leads to selection of pumps with excessively high Suction Specific Speeds and high minimum flows.
Do evaluate economical advantages of variable speed operation. It is more efficient and results in longer pump life.
Do not overestimate value of pump efficiency if it is obtained at the cost of reliability.
Do not use mechanical seal when packing is more than adequate for the intended service.


Installation
Do provide sufficient submergence over intake piping to prevent vortex formation.
Do not use suction elbows in a plane parallel to the shaft; place them in a plane perpendicular to the shaft.
Do not use the pump casing as an anchor for the piping. If you use expansion joints, support and anchor them independently of the pump.
Do provide adequate flow, pressure, and temperature instrumentation for each pump.
Pump and driver alignment must be rechecked under normal operating conditions.

Operation
Do not operate pumps below the recommended minimum flow.
Do not operate pumps with suction valve closed.
Do not run two pumps in parallel when a single pump can carry the reduced system load.
Do not stop a pump while it is cavitating. Re-establish normal operations first and then, stop the pump if you have to.
A pump handles liquids. Keep air out.
Do not run a pump if excessive noise or vibration occurs.
Do run spare pumps occasionally to check their availability


Maintenance
Run a performance test at reasonable intervals of time, to follow effect of increased internal clearances.
Do not open pumps for inspection unless factual or circumstantial evidence warrants it.
Do not over-lubricate grease lubricated bearings.
Do not overcool outer races of ball bearings. Inner races continue to expand and balls are squeezed out of shape.
Packing stuffing boxes is an art. Do not assign this task to inexperienced personnel.
Do not tighten stuffing box glands excessively. Let enough leakage flow to cool and lubricate packing.
Do monitor the pressure drop across suction strainers. An excessive pressure drop indicates clogging and may reduce available NPSH to a dangerous degree.
Do keep an adequate stock of spare parts.
Except in an emergency, use original equipment manufacturer's replacement spares.
Consider upgrading material for parts that wear or corrode too rapidly. This lengthens inteval between overhauls.
Do examine and recondition, if necessary, all metal-to-metal fits.
Do examine parts for corrosion, erosion, or other damage.
Do check concentricity of all parts of the rotor before reassembly.
Do use new gaskets for complete overhaul.
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Pumps and Energy Conservation
  • Pump is the only mechanical means available to transport fluids
  • 50-55% of the connected load is "Pump Load"
  • It is pertinent any system which consumes maximum energy should merit attention for "Energy Conservation"
ENERGY WASTAGE FACTORS
Electric Motor Capacity: if motor capacity is far more than the actual, losses in electric transmission increases resulting in overall wastage of energy.
  Power = V x I x Cos q
V = Voltage, I = Current, Cos q = Power factor.
Efficiency Vs. Price Trade-off: Efficiency is inversely proportional to power requirement. An efficient pump will consume less power and will be costly.
Pumps not working at duty:
Often, system designers want to be extra cautious.
More safety margins make the pump operate away from the specified duty point
.
Unrealistic Head :
Power is proportional to head
By some means, we have to control head.
Change pipe dia, length, material, and reduce number of bends, valves etc.
Huge amounts of energy can be saved if wasteful use is avoided.
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SAM equipped with test facilities for Raw material, inprocess, Hyrdotest, performance test suitable for Horizontal and Vertical for high flow rate / high energy testing. We have the ability to perform the following testing standards.

TESTING STANDARDS
TYPE OF TEST TESING STANDARD
   
RAW MATERIAL
HARDNESS TEST IS 3804
MAGNETIC PARTICLE ASTM E709/E139
ULTRASONIC TEST ASTM SA388
RADIOGRAPHY TEST ASTM E446 LEVEL IV FOR CI FAMILY
ASTEM E446 LEVEL III FOR STEEL CAST
CASTINGS
IN-PROCESS
DYE PENTRANT TEST ASTM E165
STATIC & DYNAMIC BALANCING ISO 1940-1973 (E) G.6.3 (ONLY FOR THE IMPELLER)
FINAL INSPECTION
HYDROSTATIC TEST
HIS (a) Shall be tested for 1.5 times of pressure occur at rated condition.
(b) 1.25 times of pressure occur at discharge valve closed
condition greates of (a) and (b) :
Testing duration : Min. 5 Minutes.
IS-5120 177
Amt.No.3 Sep'1984

Shall be tested for 1.5 times of max.discharge pressure experienced by the pump casing or diffuser bowl.

API 610 7TH Edition Shall be tested for 1.5 times of max. allowable working pressure.
Testing duration : 30 Minutes Minimum.
PERFORMANCE TEST
IS-5120 Shall be tested at rated speed upto 75 KW and at reduced speed for more than 75 KW.
Duration of Test : Shall not be less than 1 Hour.
Quantum of Testing

10% of a batch subject to a minimum of 10 pumps shall be tested. If the production batch is less than 10 pumps, entire batch is to be tested.

HIS

Pumps are allowed test to reduced speed and readings to be converted to rated speed as per affinity law.

API 610

As per Clause No.4.3.1.1., Performance and NPSH Tests shall be carried out as per Hydraulic Institute Standard.

NPSH TEST
HIS NPSH at duty point by suction throttling method /
Vaccum chamber method.
API 610

NPSH Test shall be carried out at following points :

1. Minimum flow 2. Rated flow.
3. Between Minimum & rated flows. 4. 110% of rated flow

( We can test NPSH at duty point a by suction throttling method )
VIBRATION
HIS As per chart No.66 & 67 of HIS with respect to
operating speed.
API 610 Sound level shall be in accordance with API 615.
Acceptable limit : 50 Microns amplitude and at the velocity of 4.5 M/Sec.
NOISE LEVEL
HIS Acceptable limit : 85 db measured at a distance of 1.5 M from the major surface of the machine.

HIS = Hydraulic Institute Standard,   API = American Petroleum Industry,   IS = Indian Standard.

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