- #1
balotpinoy
- 12
- 0
a pump capacity of 10 m^3/hr at 30 meters head. what does the 30 meters head mean?
thank you..
thank you..
Understanding Pump Capacity at 30m Head
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Discussion Overview
The discussion revolves around understanding the concept of pump capacity, specifically a pump rated at 10 m3/hr at a 30-meter head. Participants explore the implications of the head measurement, its application in Bernoulli's equation, and the calculation of flow rates in different piping scenarios.
Discussion Character
- Exploratory
- Technical explanation
- Mathematical reasoning
- Debate/contested
- Homework-related
Main Points Raised
- One participant seeks clarification on the meaning of "30 meters head" in the context of pump capacity.
- Another participant explains that the 30 meters head represents the pressure difference across the pump and can be related to the height of a fluid column.
- A question is raised about using the head in Bernoulli's equation as work done on the fluid, with a formula proposed for verification.
- Further discussion confirms that terms in Bernoulli's equation can be expressed in units of length, and multiplying by density and gravitational constant yields pressure units.
- A participant inquires about the need for pump efficiency deductions in calculations.
- Another participant presents a scenario involving two discharge lines at different elevations and seeks guidance on using the pump data in Bernoulli's equation to compute flow rates.
- A response emphasizes the necessity of a pump curve for accurate calculations, explaining how head varies with flow rate for centrifugal pumps and questioning the applicability to positive displacement pumps.
- A participant asserts that they are working with a positive displacement pump and describes their approach to solving for pressure and velocity using Bernoulli's equation, asking for confirmation and further steps.
- Another participant suggests that if it is indeed a positive displacement pump, the 30 meters head may not be relevant for determining flow rates in the two lines, prompting a discussion about pressure drops in the system.
Areas of Agreement / Disagreement
Participants express differing views on the relevance of the 30 meters head in calculations, particularly in the context of positive displacement versus centrifugal pumps. There is no consensus on the best approach to calculate flow rates in the given scenario, and multiple perspectives on the application of Bernoulli's equation are presented.
Contextual Notes
Participants note the importance of additional data points for accurate pump performance analysis, such as a pump curve, and highlight the potential complexities introduced by system resistance and pressure drops in the piping layout.
- #2
gmax137
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The pump increases the pressure downstream, relative to the pressure upstream. The 30 meters head is the difference in pressure 'across' the pump (discharge pressure minus suction pressure). Pressure (force per area) can be expressed in height (meters) by considering the pressure at the base of a column of the pumped fluid 30 meters tall. To change the units of 'head' to units of 'pressure' you need to know the weight density of the fluid.
- #3
balotpinoy
- 12
- 0
so can i use it in Bernoulli's equation as work given to the fluid?
- head x density x gravitational constant
is that right?
- head x density x gravitational constant
is that right?
- #4
gmax137
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Right. V^2/2g z P/\rho g all have units of length.
And if you multiply each by g \rho you get units of pressure
And if you multiply each by g \rho you get units of pressure
Last edited:
- #5
balotpinoy
- 12
- 0
no more deductions for pump efficiency?
- #6
balotpinoy
- 12
- 0
kindly help me with this one..
i want to compute the actual volumetric flowrate in line 1 & 2. discharge for both lines are in different elevations. given data for me is these;
mono pump capacity= 10 m3/hr at 30 meters
line 1 from tee to discharge is a 2-inch pipe
line 1 discharge elevation= 12 meters
line 2 from tank bottom to discharge is 3-inch pipe
line 2 discahrge elevation=11.5 meters
fittings/valves are present along the line, pls bear with my drawing..
i've been trying to figure out how I am going to use the available pump data in my bernoulli's equation.
and another thing is the flowrate. can i directily solve for velocity of fluid at the pump discharge from the given flowrate..
thank you in advance..
i want to compute the actual volumetric flowrate in line 1 & 2. discharge for both lines are in different elevations. given data for me is these;
mono pump capacity= 10 m3/hr at 30 meters
line 1 from tee to discharge is a 2-inch pipe
line 1 discharge elevation= 12 meters
line 2 from tank bottom to discharge is 3-inch pipe
line 2 discahrge elevation=11.5 meters
fittings/valves are present along the line, pls bear with my drawing..
i've been trying to figure out how I am going to use the available pump data in my bernoulli's equation.
and another thing is the flowrate. can i directily solve for velocity of fluid at the pump discharge from the given flowrate..
thank you in advance..
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- #7
gmax137
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Education Advisor
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You need more than one data point for the pump. Typically you have a 'pump curve' which shows the head at various flowrates. As the flowrate is decreased towards zero, the head will rise to the 'shutoff head', and as flow is increased the head will drop off. Then you can plot the pump curve along with the system resistance curve (basically bernoulli solved for head loss). Where the two curves cross, that's the operating point.
Above describes the situation for a centrifugal pump. If you have a positive displacement pump, the flowrate is constant; all you need is bernoulli. But I don't think you have a PD pump, because then the 'at 30 meters head' doesn't make sense.
Above describes the situation for a centrifugal pump. If you have a positive displacement pump, the flowrate is constant; all you need is bernoulli. But I don't think you have a PD pump, because then the 'at 30 meters head' doesn't make sense.
- #8
balotpinoy
- 12
- 0
its a PD pump and that's the only data available for that pump since its old already.
so far here is what i did with my problem;
to solve for Q in lines 1 & 2, i first computed for Pressure at point B (pls refer to attached drawing) using bernoulli's equation in pipe A-B using 30 meters head as pump work and obtained my velocity at point B using the flowrate/area of pipe.
is it correct? and if so, how can i proceed to solve for flowrates in both lines?
thank you again..
so far here is what i did with my problem;
to solve for Q in lines 1 & 2, i first computed for Pressure at point B (pls refer to attached drawing) using bernoulli's equation in pipe A-B using 30 meters head as pump work and obtained my velocity at point B using the flowrate/area of pipe.
is it correct? and if so, how can i proceed to solve for flowrates in both lines?
thank you again..
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- #9
gmax137
Science Advisor
Education Advisor
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If it is a PD pump then you know the flowrate, right? The 30 meters head is misdirection - a red herring. All you need to figure out is the split between Line 1 and Line 2. What can you say about the pressure drops BD and BC? How do those pressure drops vary with flowrate?