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Net positive suction head:2687833 | NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller. | 1 |
Net positive suction head:2687833 | A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | 0 |
In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | Net positive suction head:2687833 | 1 |
In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | 0 |
NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller. | In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | 1 |
NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller. | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 1 |
In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | 1 |
In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | The violent collapse of the cavitation bubble creates a shock wave that can carve material from internal pump components (usually the leading edge of the impeller) and creates noise often described as "pumping gravel". Additionally, the inevitable increase in vibration can cause other mechanical faults in the pump and associated equipment. | 0 |
where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | 1 |
where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | 1 |
where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 0 |
Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | 1 |
Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | 1 |
Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | The NPSH appears in a number of other cavitation-relevant parameters. The suction head coefficient is a dimensionless measure of NPSH: | 0 |
Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | 1 |
Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | 0 |
Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 1 |
Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | The NPSH appears in a number of other cavitation-relevant parameters. The suction head coefficient is a dimensionless measure of NPSH: | 0 |
This is the standard expression for the available NPSH at a point. Cavitation will occur at the point "i" when the available NPSH is less than the NPSH required to prevent cavitation (NPSH"R"). For simple impeller systems, NPSH"R" can be derived theoretically, but very often it is determined empirically. Note NPSH"A"and NPSH"R" are in absolute units and usually expressed in "m" or "ft," not "psia". | Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 1 |
This is the standard expression for the available NPSH at a point. Cavitation will occur at the point "i" when the available NPSH is less than the NPSH required to prevent cavitation (NPSH"R"). For simple impeller systems, NPSH"R" can be derived theoretically, but very often it is determined empirically. Note NPSH"A"and NPSH"R" are in absolute units and usually expressed in "m" or "ft," not "psia". | i.e.: 8 bar (pump curve) plus 10 bar NPSH"A" = 18 bar. | 0 |
This is the standard expression for the available NPSH at a point. Cavitation will occur at the point "i" when the available NPSH is less than the NPSH required to prevent cavitation (NPSH"R"). For simple impeller systems, NPSH"R" can be derived theoretically, but very often it is determined empirically. Note NPSH"A"and NPSH"R" are in absolute units and usually expressed in "m" or "ft," not "psia". | Experimentally, NPSH"R" is often defined as the NPSH3, the point at which the head output of the pump decreases by 3 % at a given flow due to reduced hydraulic performance. On multi-stage pumps this is limited to a 3 % drop in the first stage head. | 1 |
This is the standard expression for the available NPSH at a point. Cavitation will occur at the point "i" when the available NPSH is less than the NPSH required to prevent cavitation (NPSH"R"). For simple impeller systems, NPSH"R" can be derived theoretically, but very often it is determined empirically. Note NPSH"A"and NPSH"R" are in absolute units and usually expressed in "m" or "ft," not "psia". | Net positive suction head:2687833 | 0 |
Experimentally, NPSH"R" is often defined as the NPSH3, the point at which the head output of the pump decreases by 3 % at a given flow due to reduced hydraulic performance. On multi-stage pumps this is limited to a 3 % drop in the first stage head. | Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | 1 |
Experimentally, NPSH"R" is often defined as the NPSH3, the point at which the head output of the pump decreases by 3 % at a given flow due to reduced hydraulic performance. On multi-stage pumps this is limited to a 3 % drop in the first stage head. | The NPSH appears in a number of other cavitation-relevant parameters. The suction head coefficient is a dimensionless measure of NPSH: | 0 |
Experimentally, NPSH"R" is often defined as the NPSH3, the point at which the head output of the pump decreases by 3 % at a given flow due to reduced hydraulic performance. On multi-stage pumps this is limited to a 3 % drop in the first stage head. | In a pump, cavitation will first occur at the inlet of the impeller. Denoting the inlet by "i", the NPSH"A" at this point is defined as: | 1 |
Experimentally, NPSH"R" is often defined as the NPSH3, the point at which the head output of the pump decreases by 3 % at a given flow due to reduced hydraulic performance. On multi-stage pumps this is limited to a 3 % drop in the first stage head. | Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 0 |
The calculation of NPSH in a reaction turbine is different to the calculation of NPSH in a pump, because the point at which cavitation will first occur is in a different place. In a reaction turbine, cavitation will first occur at the outlet of the impeller, at the entrance of the draft tube. Denoting the entrance of the draft tube by "e", the NPSH"A" is defined in the same way as for pumps: | Note that, in turbines minor friction losses (formula_12) alleviate the effect of cavitation - opposite to what happens in pumps. | 1 |
The calculation of NPSH in a reaction turbine is different to the calculation of NPSH in a pump, because the point at which cavitation will first occur is in a different place. In a reaction turbine, cavitation will first occur at the outlet of the impeller, at the entrance of the draft tube. Denoting the entrance of the draft tube by "e", the NPSH"A" is defined in the same way as for pumps: | Applying the first law of thermodynamics for control volumes enclosing the suction free surface "0" and the pump inlet "i", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 0 |
Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | Note that, in turbines minor friction losses (formula_12) alleviate the effect of cavitation - opposite to what happens in pumps. | 1 |
Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | 0 |
Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 1 |
Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | This phenomenon is what manufacturers use when they design multistage pumps, (Pumps with more than one impeller). Each multi stacked impeller boosts the succeeding impeller to raise the pressure head. Some pumps can have up to 150 stages or more, in order to boost heads up to hundreds of metres. | 0 |
Note that, in turbines minor friction losses (formula_12) alleviate the effect of cavitation - opposite to what happens in pumps. | The calculation of NPSH in a reaction turbine is different to the calculation of NPSH in a pump, because the point at which cavitation will first occur is in a different place. In a reaction turbine, cavitation will first occur at the outlet of the impeller, at the entrance of the draft tube. Denoting the entrance of the draft tube by "e", the NPSH"A" is defined in the same way as for pumps: | 1 |
Note that, in turbines minor friction losses (formula_12) alleviate the effect of cavitation - opposite to what happens in pumps. | i.e.: 8 bar (pump curve) plus 10 bar NPSH"A" = 18 bar. | 0 |
Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | 1 |
Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | Note that, in turbines minor friction losses (formula_12) alleviate the effect of cavitation - opposite to what happens in pumps. | 0 |
Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | If an NPSH"A" is say 10 bar then the pump you are using will deliver exactly 10 bar more over the entire operational curve of a pump than its listed operational curve. | 1 |
Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller. | 0 |
Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | 1 |
Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | 1 |
Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | 1 |
Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller. | 0 |
Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | Example: A pump with a max. pressure head of 8 bar (80 metres) will actually run at 18 bar if the NPSH"A" is 10 bar. | 1 |
Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | 1 |
Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | i.e.: 8 bar (pump curve) plus 10 bar NPSH"A" = 18 bar. | 1 |
Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | 0 |
Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | If an NPSH"A" is say 10 bar then the pump you are using will deliver exactly 10 bar more over the entire operational curve of a pump than its listed operational curve. | 1 |
Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | The violent collapse of the cavitation bubble creates a shock wave that can carve material from internal pump components (usually the leading edge of the impeller) and creates noise often described as "pumping gravel". Additionally, the inevitable increase in vibration can cause other mechanical faults in the pump and associated equipment. | 0 |
Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | If an NPSH"A" is say 10 bar then the pump you are using will deliver exactly 10 bar more over the entire operational curve of a pump than its listed operational curve. | 1 |
Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | 0 |
Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | 1 |
Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically—possibly stopping flow altogether—and prolonged exposure will damage the impeller. | 0 |
Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | 1 |
Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation: | 0 |
Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | 1 |
Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | where formula_2 is the absolute pressure at the inlet, formula_3 is the average velocity at the inlet, formula_4 is the fluid density, formula_5 is the acceleration of gravity and formula_6 is the vapor pressure of the fluid. Note that it is equivalent to the sum of both the static and dynamic heads – that is, the stagnation head – from which one deducts the head corresponding to the equilibrium vapor pressure, hence "net positive suction head". | 0 |
Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | 1 |
Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | 1 |
Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | 1 |
Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 0 |
Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | 1 |
Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | Example Number 1: A tank with a liquid level 2 metres above the pump intake, plus the atmospheric pressure of 10 metres, minus a 2 metre friction loss into the pump (say for pipe & valve loss), minus the NPSH"R" curve (say 2.5 metres) of the pre-designed pump (see the manufacturers curve) = an NPSH"A" (available) of 7.5 metres. (not forgetting the flow duty). This equates to 3 times the NPSH required. This pump will operate well so long as all other parameters are correct. | 1 |
Example Number 3: A well or bore running at 70 degrees Celsius (158F) with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump, minus a temperature loss of 3 metres/10 feet = an NPSH"A" (available) of (negative) -12.4 metres. Adding the atmospheric pressure of 10 metres and gives a negative NPSH"A" of -2.4 metres remaining. | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | 1 |
Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | Applying Bernoulli's principle from the draft tube entrance "e" to the lower free surface "0", under the assumption that the kinetic energy at "0" is negligible, that the fluid is inviscid, and that the fluid density is constant: | 0 |
Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | 1 |
Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | Net positive suction head:2687833 | 0 |
Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | 1 |
Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | The calculation of NPSH in a reaction turbine is different to the calculation of NPSH in a pump, because the point at which cavitation will first occur is in a different place. In a reaction turbine, cavitation will first occur at the outlet of the impeller, at the entrance of the draft tube. Denoting the entrance of the draft tube by "e", the NPSH"A" is defined in the same way as for pumps: | 0 |
A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | Using the situation from example 2 above, but pumping 70 degrees Celsius (158F) water from a hot spring, creating negative NPSH, yields the following: | 1 |
A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | The violent collapse of the cavitation bubble creates a shock wave that can carve material from internal pump components (usually the leading edge of the impeller) and creates noise often described as "pumping gravel". Additionally, the inevitable increase in vibration can cause other mechanical faults in the pump and associated equipment. | 0 |
A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | Example Number 2: A well or bore with an operating level of 5 metres below the intake, minus a 2 metre friction loss into pump (pipe loss), minus the NPSH"R" curve (say 2.4 metres) of the pre-designed pump = an NPSH"A" (available) of (negative) -9.4 metres. Adding the atmospheric pressure of 10 metres gives a positive NPSH"A" of 0.6 metres. The minimum requirement is 0.6 metres above NPSH"R"), so the pump should lift from the well. | 1 |
A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | The violent collapse of the cavitation bubble creates a shock wave that can carve material from internal pump components (usually the leading edge of the impeller) and creates noise often described as "pumping gravel". Additionally, the inevitable increase in vibration can cause other mechanical faults in the pump and associated equipment. | 0 |
A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | Example: A pump with a max. pressure head of 8 bar (80 metres) will actually run at 18 bar if the NPSH"A" is 10 bar. | 1 |
A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | 1 |
Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | This phenomenon is what manufacturers use when they design multistage pumps, (Pumps with more than one impeller). Each multi stacked impeller boosts the succeeding impeller to raise the pressure head. Some pumps can have up to 150 stages or more, in order to boost heads up to hundreds of metres. | 1 |
Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | Where formula_14 is the angular velocity (in rad/s) of the turbo-machine shaft, and formula_15 is the turbo-machine impeller diameter. Thoma's cavitation number is defined as: | 0 |
Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | Remember that positive or negative flow duty will change the reading on the pump manufacture NPSH"R" curve. The lower the flow, the lower the NPSH"R", and vice versa. | 1 |
Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSH"R" value and this may result in a very expensive pump or installation repair. | Note that, in turbines minor friction losses (formula_12) alleviate the effect of cavitation - opposite to what happens in pumps. | 0 |
NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | Example: A pump with a max. pressure head of 8 bar (80 metres) will actually run at 18 bar if the NPSH"A" is 10 bar. | 1 |
NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | Vapour pressure is strongly dependent on temperature, and thus so will both NPSH"R" and NPSH"A". Centrifugal pumps are particularly vulnerable especially when pumping heated solution near the vapor pressure, whereas positive displacement pumps are less affected by cavitation, as they are better able to pump two-phase flow (the mixture of gas and liquid), however, the resultant flow rate of the pump will be diminished because of the gas volumetrically displacing a disproportion of liquid. Careful design is required to pump high temperature liquids with a centrifugal pump when the liquid is near its boiling point. | 0 |
NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | A minimum of 600 mm (0.06 bar) and a recommended 1.5 metre (0.15 bar) head pressure “higher” than the NPSH"R" pressure value required by the manufacturer is required to allow the pump to operate properly. | 1 |
NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | 0 |
NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | Lifting out of a well will also create negative NPSH; however remember that atmospheric pressure at sea level is 10 metres! This helps us, as it gives us a bonus boost or “push” into the pump intake. (Remember that you only have 10 metres of atmospheric pressure as a bonus and nothing more!). | 1 |
NPSH problems may be able to be solved by changing the NPSH"R" or by re-siting the pump. | Net positive suction head:2687833 | 0 |
If an NPSH"A" is say 10 bar then the pump you are using will deliver exactly 10 bar more over the entire operational curve of a pump than its listed operational curve. | Remembering that the minimum requirement is 600 mm above the NPSH"R" therefore this pump will not be able to pump the 70 degree Celsius liquid and will cavitate and lose performance and cause damage. To work efficiently, the pump must be buried in the ground at a depth of 2.4 metres plus the required 600 mm minimum, totalling a total depth of 3 metres into the pit. (3.5 metres to be completely safe). | 1 |
If an NPSH"A" is say 10 bar then the pump you are using will deliver exactly 10 bar more over the entire operational curve of a pump than its listed operational curve. | Using the above application of Bernoulli to eliminate the velocity term and local pressure terms in the definition of NPSH"A": | 0 |
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