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first of all the term NPSH should be clear.It is pressure which should be available at the eye of the pump impeller,so as to avoid vaporisation of liquid.
Second which arises ,how this liquid will vaporise?Ans-if a vapour pressure of a liquid falls at constt temperature or temperature of liquid is raised at constt pressure it vaporises.In case of pump it's mostly the first case.
Now,how to manitain NPSH.
NPSHa> NPSHr (always)
where NPSHa= available NPSH
NPSHr = Required NPSH
NPSH = Hps+Hsl-Hvp-Hfl
Hps= pressure acting on the eye due to pressure in the suction drum.
Hsl = pressure acting due to height of liquid in the suction line.
Hvp= vapour pressure of the liquid
Hfl= head loss due to friction losses
Thus, to maintain the NPSH, variables in hand are,Hps and Hsl.increase the height of the suction line or increase the pressure of the suction drum.
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∙ 11y ago
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What NPSH stands for and its meaning?
Net Positive Suction Head. It is the difference between hydraulic pressure and vapor pressure, usually of concern at the inlet of a pump. Without sufficienty high NPSH at a pump inlet, there will be cavitation in the pump. Within a centrifugal pump there can be pressures lower than at the inlet as the fluid is moved by the impeller. If any of those pressures is lower than the vapor pressure, vapor pockets- bubbles- form and you get cavitation. A more complete explanation: http://en.wikipedia.org/wiki/NPSH
Can pump discharge head be negative?
When a pump is pumping water from a level that is below the pump it is called suction head. If the water to be pumped is at a level above the pump, it is positive head. The pump maybe pumping from the base of a tank to a higher level such as an elevated tank or it may be pulling water from a tank that is below the pump. The distance from the center of the pump to the top of the water level would be the foot of head. It takes 2.31 feet to make 1 P.S.I. So if it is 10 feet from the center line of the pump to the water level, you would have about 4.33 P.S.I. of head.
What is the negative suction head of the pump?
it occurs when surface of water is below the level of pumping unit
What is the difference between end suction pump and horizontal multi stage pump?
what is th different between end suction pump and singl stage pump and multistage pump
What is the meaning of end suction of pump?
A single suction pump having its suction nozzle on the opposite side of the casing from the stuffing box and having the face of the suction nozzle perpendicular to the longitudinal axis of the shaft
What is negative suction in pump?
Negative Suction Head means the pump is drawing liquid up from below its centerline. The distance between the centerline of the pump and the surface of the fluid is measured in head feet, this can be negative (below the pump) or positive (above the pump).
What is the difference between suction lift and suction head?
Suction lift is only negative. Suction head is positive or negative.Suction head is the distance between the surface of the liquid being pumped and the centerline of the pump. It can be positive or negative, and it can be affected by pressure or vacuum on the surface of the fluid. A negative suction head is also called suction lift.Example 1: A D/A under 15 psig is set 20 feet above the feed pump the effective suction head is 54 feet. (15 psig is equivalent to 34 feet of water).Example 2: A Condenser hotwell under 28 inches of vacuum (Hg) is set 16 feet above the suction of a propeller pump. The effective suction head (lift) is -15 feet.* (28"Hg = - 31 feet of water)Example 3: A sump pump is set 4 feet below the surface of the well. The effective suction head is 4 feet.*Note: Suction lift is only effective to a maximum of 21 feet, and 15 feet for hot water depending on temperature and pump slip.
What are three factors which influence the choice of pump for a particular operation?
Capacity, Net Positive Suction Head (NPSH), and Efficiency
What does it mean when your suction head is too high and your pump is not pumping water?
suction head is calculated wiht the formula head = 2.31 x psi so if your suction is 30psi then your head is around 60ft. of head. If your suction head is to high then there is not enough water to pump the needed psi for the task
Why is the suction line of a pump larger than the discharge line?
It is common practice to specify the pump suction line one size larger than the pump discharge line in order to increase the Net Positive Suction Head available (NPSHA) to the pump. A smaller suction line the same pipe size as the discharge line would result in more pressure drop in the suction line and reduce the amount of head available to the suction side of the pump. This in turn would result in an operating point closer to cavitation of the pump.
What happens when you try to stick a suction cup on a rough surface Why?
as we know that suction pump stick on a smooth non-porous surface but rough surface contains pores due to which suction pump is not able to maintain grip with the rough surface.
What NPSH stands for and its meaning?
Net Positive Suction Head. It is the difference between hydraulic pressure and vapor pressure, usually of concern at the inlet of a pump. Without sufficienty high NPSH at a pump inlet, there will be cavitation in the pump. Within a centrifugal pump there can be pressures lower than at the inlet as the fluid is moved by the impeller. If any of those pressures is lower than the vapor pressure, vapor pockets- bubbles- form and you get cavitation. A more complete explanation: http://en.wikipedia.org/wiki/NPSH
What do you mean by head of pump?
Total pump head is the sum of suction and discharge pressure in mtr. ie. 1 bar =10.33 metres of water column
Can pump discharge head be negative?
When a pump is pumping water from a level that is below the pump it is called suction head. If the water to be pumped is at a level above the pump, it is positive head. The pump maybe pumping from the base of a tank to a higher level such as an elevated tank or it may be pulling water from a tank that is below the pump. The distance from the center of the pump to the top of the water level would be the foot of head. It takes 2.31 feet to make 1 P.S.I. So if it is 10 feet from the center line of the pump to the water level, you would have about 4.33 P.S.I. of head.
What is the negative suction head of the pump?
it occurs when surface of water is below the level of pumping unit
What is vapour binding?
when pressure on the suction side of the pump drop below the vapour pressure of the liquid, vapour forms. It's caused because of insufficient suction head, high suction lift, excessive friction head, or high liquid temperature.
Why there is Sever cavitation sound at the pump suction for the A pump while there is no problem at the B pump which is operating in parallel with this pump.?
this is overhang centrifugal pump . the suction drum level , suction strainer and suction pipings were all checked and found OK
