Power Plant Guruji

WATER HAMMER The very large CCW flow rate results in huge kinetic energy of the flowing water, and hence it promotes severe water hammer during CCW pump start up, shutdowns and trips. How to Minimize Water Hammer To minimize water hammer the following general operating practices are used during CCW pump start up and shutdown. 1. A sufficient time delay before the next pump Is started up or shut down. This allows the energy of pressure waves in the system to destroy before the system is subjected to another flow surge. Time delay : About 5 minute 2.Proper position and slow opening / closing of the CCW pump discharge valve during pump start up and shutdown a)       Each CCW pump is started against its discharge valve fully closed or slightly pre-opened (depending on the plant) and then the valve opens gradually. b)       During normal pump shutdown first the discharge valve closes gradually and when it is fully closed (or nearly fully cl...

 1.What is the method of priming? a) With a flooded suction b) A bypass around the discharge check valve    c)The foot  valve with auxiliary liquid supply d) All of the above 2. In Priming, the removal of air by filling the pump passages i.e. flow passages e.g. The impeller and the volute casing with liquid. a) True b) False 3. For Smooth operation in centrifugal pump NPSHA should be -------- than NPSHR a) Greater b) Less 4. Adverse effects of cavitation include a) Metallic erosion b) Deterioration pump performance c) Failure of pump components and Instability in flow pattern of pumping liquid d) All of the above 5. Operating point gets at the intersection of System curve and Efficiency curve. a) True b) False 6. Flat curve a) Shows little variation of head at all flows between design point & shut-off. b) Head developed at shut-off is less than head developed at some flow between B.E.P & shut-off. c) None of the above Pump Curves - 6 Types of head vs flow rat...

  1. Flat curve Shows little variation of head at all flows between design point & shut-off. When a system consists of mostly Static Head or Static Pressure difference, it is termed a flat system curve.  Head vs Flow Flat curve What is priming in pump ? 2. Unstable curve The same head is developed at more than one flow rates . Head vs Flow Unstable curve 3. Stable curve Only one flow rate at any one head.It is called stable if it exhibits a continuously negative slope (negative differential quotient from head and flow with regard to the Q axis. Head Vs Flow Stable curve Why pumps are used in series and parallel ? 4. Steep curve Large increase in head developed at shut-off from B.E.P. When a system consists of mostly frictional resistance  it is termed a steep system curve. With a steep curve, we can notice a steeper arch, resulting in a larger head (pressure) increase as the flow decreases, compared to the Steadily rising Curve. Head Vs F...

  Pump Losses Losses in a centrifugal pump  are classified into five types namely, mechanical losses, impeller losses, leakage losses , disk friction losses and casing hydraulic losses. Recommended : Types of Mechanical Seals in Pump   How to start and stop a centrifugal pump   Cavitation formation in the pump Type of losses exists inside the centrifugal pump Casing Hydraulic Losses Leakage losses Impeller losses Disk friction losses Mechanical losses Pump casing hydraulic losses Casing hydraulic loss is caused when fluid flows through the impeller, the pump housing casing, there is a change of flow rate and inverse pressure gradient magnitude and direction of the circulation and cause vortex, resulting in energy loss. Pump leakage losses There can be slipping back of part of liquid through the clearance between the impeller and casing due to pressure difference between inlet and outlet. This loss of energy of liquid is known as leakage losses. You May Also Like...

What are Mechanical Seals for Pumps  The Sealing of a rotating shaft passing through a pump casing is also achieved by means of a rotating, optically flat seat, rubbing against a stationary, optically flat seat. Stationary seat is inserted into a gland plate or seal chamber and the spring loaded rotating face is mounted on the shaft. The spring holds the rotating face against the stationary face and sealing occurs in between rotating and stationary parallel faces. Also Read : Why use Mechanical seal in pump Gland seal vs. Mechanical seal Why priming centrifugal pumps How many types of mechanical seals are there  Shaft mounted or cartridge type Balanced and unbalanced type Pusher and non-pusher type Single and multiple seals  Externally and internally mounted seal Single and multiple spring seal  Mechanical Seal Types You May Also Like : What are the types of pump ? Coolant and lubricant Types of valve used in power plant Calculate suction head in centrifugal pump A v...

  Why pumps are used in parallel and series mode ? Let us begin with the basics of centrifugal pump mode of operation. Mode of operation can be either Parallel mode and Series mode. Pumps can be arranged in parallel or serial mode to provide an additional head or flow rate capacity. Recommended for you : Why priming centrifugal pumps Calculate suction head in centrifugal pump What is parallel operation of pump ? To get constant head and additional flow pumps are arranged in parallel. Head (H) H1= H2=H3=H Constant Discharge (Q) = Sum of each Pump discharge = Q1+Q2+Q3  Parallel operation of pump Also Read : Why use Mechanical seal in pump Gland seal vs. Mechanical seal What is series operation of pump ? To get constant flow and additional head pumps are arranged in series. Discharge(Q) =Q1=Q2=Q3=Constant Head (H) = Sum of each pump head = H1+H2+H3  Series operation of pump You May Also Like : What are the types of pump ? Coolant and lubricant Boiler feed pump operation...

 What is Priming? The removal of air by filling the pump passages i.e, flow passages. eg. The impeller and the volute casing with liquid. Priming is the adding of water to the pump cavity so that enough suction can be created by the impeller to pull water. Priming in centrifugal pump  Why is Priming essential in a Centrifugal Pump? Centrifugal pump does not displace liquid positively. They cannot displace gases and Vapours. Removalof these gases, air bubbles and vapours is very essential and a must before starting any centrifugal Pump in order to extend the pump life. What are different methods of priming ? PRIMING METHODS With a flooded suction A bypass around the discharge check valve The foot valve with auxiliary liquid supply An ejector for priming A priming tank holding the supply of liquid Vacuum pumps (manually/automatically) controlled to prime the main pump Must read related posts Cavitation formation in pump Function of volute casing in pump Why use Mechanical seal ?...

  Starting procedure of Centrifugal Pump Check the cooling system and turn it on. Check the coolant flow Properly. Open the suction valve and close all the drains in the casing and piping. Prime the pump and ensure that there is sufficient liquid to feed the pump. Start the motor and let it come to the proper speed. When rated speed is reached then open the discharge valve slowly. Check the leakage in piping and stuffing box. Check all the parameters like pressure, temperature,flow, vibration Current etc. Bearing temperature should not exceed 65°C during   operation. In case of any Sound or pump shows Overheating of bearing, then the pump should be stopped. Stopping procedure of Centrifugal Pump Discharge valve should be closed first. Stop the pump motor. Close the suction valve. Close the bearing and gland cooling lines. Also read related posts Cavitation formation in pump Function of volute casing in pump Why use Mechanical seal ? Gland seal vs. Mechanical seal What are the ...

  Concept of NPSH in pump Net Positive Suction Head or NPSH represents the suction head at the pump impeller eye. It represents the head required to make the fluid flow from the suction pipe to pump impeller. For a smooth and cavitation free performance of the pump, NPSH Net Positive Suction Head must be positive and should have a value that the flowing fluid does not change under reduced pressure. Higher suction lift, higher temperature of the fluid, higher losses in pipelines, all these tend to reduce available NPSH Net Positive Suction Head. Pump designer give us the NPSHR (equired) usually depending upon the test results of the actual pump. It is necessary that the available NPSH must be higher or equal to NPSHR. NPSH calculation for suction lift Calculation of NPSHA (available NPSH) NPSHA = Pressure Acting on surface (Pa) +                                            ...

  What is  Cavitation? Derived from the Latin word 'Cavus', which means a cavity or a hollow space. Defined as the rapid formation and collapse of cavities in a flowing liquid in regions of very low pressure. If the pressure at any point inside pump particularly at the suction line, drops below the vapour pressure corresponding to the temperature of liquid, the liquid will vaporize and appear as cavities of vapour or vapour bubbles. These cavities are carried up stream along with the liquid until a region of high pressure formed inside the impeller, where the cavities collapse with a tremendous impact on the side walls of impeller vanes. This phenomenon is called cavitation. How does cavitation occur ? Cavitation occurs when a pump is under low pressure or high vacuum conditions,  it does not receive enough flow. When this happens, bubbles or cavities will form at the eye of the impeller. This formation and ...

  Function of volute casing in centrifugal pump? Functions of a pump volute: To convert kinetic energy impaired by the impeller into  pressure energy To minimize losses during this energy conversion process The pump casing does not take any part in dynamic head generation The best volutes are of constant velocity design Kinetic energy is converted into pressure energy only in the  diffusion nozzle immediately after the volute throat Various types of volute Single volute Double volute Vertical pump with diffuser Volute with diffuser vanes Circular volute Double Volute A double volute casing has two single volutes 180° apart Total throat area of two volute is same as the throat area of a comparable  single volute Double volute significantly reduces the radial load problem of the  single volute pump Hydraulic performance of a double volute pump is nearly the same as  that of a single volute Double volute pump is around 1-1.5 point less efficient at   B.E....

 Why Use Mechanical Seals ? 1. Lower Mechanical Losses Mechanical seals cause lesser mechanical losses compared to packed glands and thus makes the pump more efficient. Mechanical losses due to frictional drag of the shaft sleeve running against packing account for the largest of the mechanical losses generally incurred in a centrifugal pump. 2. Lesser Sleeve Wear For mechanical seal fitted pumps handling clean, non-corrosive liquids, shaft protecting sleeve can be eliminated. Even where shaft sleeves are used, they are not subject to wear for mechanical seal fitted pumps. In case of packed gland pumps the sleeve under the packing is subjected to wear especially when the pump liquid contains abrasive particles or when the packing sit fixed very tightly on the sleeve. Sleeve damage is costly not only because of the cost of sleeve but also due to the time involved in replacing the worn sleeve with a new one. 3. Seals high pressure as well as low pressure Increased pressure ...

Gland Seal vs. Mechanical Seal – What’s the Difference? Gland Packing  Advantages Lower initial cost Easily installed & dismantled when lantern rings and glands are split Good reliability to medium pressure  & shaft speed Can handle a large axial  movements (Thermal expansion of stuffing box Vs shaft) Leakage tends to increase gradually, giving warning of impending breakdown Gland Packing Disadvantages Relatively high leakage Requires regular maintenance Wear of shaft & shaft sleeve can be relatively high Power loss may be high Relatively high product loss Mechanical seals Advantages Negligible or no leakage Requires no maintenance Eliminates sleeve wear/shaft wear Very high reliability Can handle higher pressure & speed Application range far wider-Easily applied to carcinogenic, toxic,flammable or radio-active fluids Low power loss Mechanical seals Disadvantages Higher initial cost May require some disassembly of pump parts. Example - Coupl...

Pump introduction What is a pump ? Rotating machine which transfer liquid from one place to another or from lower level to higher level. It convert mechanical energy into hydraulic energy. Adds engery to the liquid so as transfer liquid. Adds engery to the liquid so as to transfer liquid : From one elevation to desired elevation by increasing potential energy. Against rsistance at reciver end against resistance in piping system With a desired flow velocity Functions of pump Mechanical energy to Hydraulic energy Kinetic energy Pressure energy Potential energy A pump does not create pressure, it only provides flow. Pressure is a just an indication of the amount of resistance to flow. Types of pump 1.Positive displacement pump 2.Non positive displacement pump Non positive displacement pump 1.jet pump 2.centrifugal pump Positive displacement pump 1.Rotary pump 2.Reciprocating pump Rotary pump 1.Gear pump 2.Lobe pump 3.Screw pump 4.Vane pump Reciprocating pump 1.Piston pump 2.Diaphargam pum...