Design and calculation of water pumps and pumping stations
This method of superimposing flow rates under constant head! In fact, it will
When the water head loss of the pipeline is regarded as zero, the working conditions after parallel connection are calculated
Click "But in actual projects, the pipeline layout may be different! Water
The pump model may not be the same model! The head loss is also different!
Therefore! The heads of water pumps working in parallel are different. In this case,
In this case, the method of flow superposition under equal head conditions cannot be directly used.
There is no method to draw the characteristic curve of the parallel water pump! The characteristic curve of the parallel water pump after the parallel connection can only be obtained by the folding method"
2! Graphical method of parallel working conditions of water pumps
!Illustration of parallel working conditions of two water pumps of the same model, same water level, and same pipeline
!" First draw the parallel characteristic curves of two water pumps %!0#&!O#
As shown in Figure!3##! Draw!## the characteristic curves of the two water pumps on the coordinate diagram! Since the two water pumps have the same model!
Therefore, the characteristic curves are the same. Because the two water pumps pump water in the same suction well! From the two points of suction port 5#6 to the pressure water pipe intersection
The pipe diameters at sink 4 are the same! The lengths are also equal! Therefore $&@; 1$&A;! The static lifts are equal! Therefore! The lifts of the two water pumps are
"The lifts are equal" so that the flow superposition method under equal lifts can be used to draw the parallel characteristic curve of the water pump. Specifically
The step is to first pick any point on the curve! Then! Double the corresponding flow rate at the same ordinate value! That's it!
The curves drawn must be connected with smooth curves, which are two sets of water.
Pump parallel characteristic curve
Figure!3## Two water pumps of the same model, same water level, and arranged symmetrically in parallel
#" Draw the pipeline system characteristic curve! Find the parallel operating point
According to the above analysis, it can be seen that the static head of the two water pumps is the same! The head loss in the pipeline is also the same! That is, after the two pumps are connected in parallel,
The head of each water pump is equal! And equal to the total head! Then we have
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Chapter 1 Basic knowledge of water pumps
Formula %!3?& is the pipeline system characteristic curve equation! Based on this, the pipeline system characteristic curve can be drawn! See Figure!3##
The !3$&@;Q curve "This curve intersects the %!0#&!!# curve at point 3." The abscissa of point 3 is the parallel operation of two water pumps.
The total flow rate of O#! The ordinate is equal to the head of the two pumps. Point #4 is called the parallel operating point.
$" Find the operating point of each pump
Draw a horizontal line parallel to the horizontal axis through 3 points! The characteristic curve of the single pump is at $ point! This $ point is when working in parallel! Each single pump
The flow rate of the working condition point is !#!Head #!1##1#4". From $ point, a vertical line is drawn to intersect! 3! curve at 9 o'clock! Intersect! 0$
The curves at point 9 and point 9 respectively represent the efficiency point and shaft power point of each single pump in parallel connection"
If the second pump is stopped and only one pump is turned on, then point 1 in Figure 3## can be approximately regarded as a single pump
Working condition point "The water pump flow rate at this time is!T! The head is #T! The shaft power is $T"
From Figure!3## we can see the following points"
%!&The total flow rate when two water pumps work in parallel is not equal to twice the flow rate when a single pump works alone! That is !!O#’
#!T!!!1!!O#V!T&!T"The steeper the pipeline characteristic curve!!! the less"
%#&The total head when the water pumps are connected in parallel #!O#1#! Taiwan %#T! That is, the parallel work of the water pumps can not only increase the flow! The head
There is also a small increase"
%$&The power of a water pump when working alone is much greater than the power of a single pump when working in parallel! Therefore, when selecting a motor
The selection should be based on the power of a water pump when working alone"
!Two" multiple water pumps of the same model working in parallel
The characteristic curves of multiple water pumps of the same model working in parallel can also be obtained using the transverse addition method! As shown in Figure 3#$, five units of the same model are
%!&When water pumps work in parallel, it cannot be simply understood as doubling the number of parallel water pumps! The flow rate will increase by one.
For example, when tapping the potential of an old pump house and expanding it, the water passing capacity of the pipeline must be considered at the same time! After calculation under parallel working conditions,
After calculation and analysis, determine whether the number of parallel water pumps should be increased $
%#&When multiple water pumps work in parallel! The working point of each pump when working in parallel is different from the working point of each pump working alone.
Big! When selecting a pump, you should take into account both working conditions! Make sure that the water pumps work in the high-efficiency area. If the selected water pump is often operated alone
Mainly! Then! When working in parallel, it should be considered that the flow rate of each single pump will be reduced! The head will be increased. If you choose
When pumping, we focus on the fact that each pump often runs in parallel! You should pay attention! When each pump runs alone, the corresponding flow rate will increase!
The shaft power will also increase. As the number of parallel pumps increases, the operating point of each pump will move to the side with higher lift. There are too many pumps.
It is possible that the operating point will move out of the range of the high-efficiency section"
!Three "Two water pumps of different models working in parallel at the same water level
This situation is different from the above mainly because the characteristic curves of the two water pumps are different! The hydraulic power of the water flow in the pipeline is wrong.
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Design and calculation of water pumps and pumping stations
It is said that "So! The head loss from the self-priming pipe ends 5 and 7 to the collection point 6 is not equal %, that is)$&@A’$&FA&" Two water
After the pumps are connected in parallel, the head at the operating point of each pump is not equal, that is)#!’##&"Therefore, equal head cannot be used directly
Use the method of flow superposition to draw the sum %!0#& curve after parallel connection"
It can be seen from Figure 3#0 that when pump# and pump$ work in parallel, the water heads of the pressure measuring pipes at pipeline convergence point 6 are equal.
! Whether it is the water delivered by water pump # to 6 o'clock! or the water delivered by water pump $ to 6 o'clock! After reaching 6 o'clock! It has
The specific energies must be the same"
Figure!3#0 Two water pumps of different models working in parallel at the same water level
From the above analysis, we know that the heads of pump # and pump $ are not equal. The main reason is that the head losses of sections 56 and 76 are not equal.
Same! If the head loss $&@A! of 56 pipe sections at the corresponding flow rate is deducted from the total head #! of the water pump #, it is equal to
The height difference between the water surface of the pressure measuring tube and the water surface of the suction well at gathering point 6 is #A! This #A value is equivalent to diverting the water pump # to 6 o’clock.
The head of the hour! That is to say, the factor of head loss of pipe section 56 is deducted! The water pump # can be regarded as moving to 6 o'clock." The same way
Reasonable! If the head loss $&FA of 76 pipe sections under the corresponding flow!# is deducted from the total lift ## of the water pump, its value is also
It is equal to the height difference #A between the water surface of the pressure measuring tube and the water surface of the suction well at convergence point 6, which is equivalent to moving the water pump$ to 6 o'clock.
As "Working at 6 o'clock", the heads of pump # and pump $ are equal! Therefore, the folding method can be drawn using the flow superposition method under equal head.
Parallel operating characteristic curves of pump# and pump$"
The specific solution steps of the graphical method are as follows"
%!&First draw %!3$&@A& and %!3$&AF& curves$ under the abscissa
%#&Use the characteristic curve method to derive the curve from the water pump characteristic curve %!3#&# and %!3#&$ under the corresponding flow conditions.
Deduct the head loss $&@A and $&FA! online to get the deflection characteristic curve %!0#&T#
Chapter 1 Basic knowledge of water pumps
The %!0!&# curve and the %!0!&$ curve are at #% point and $% point. Each point is the power point and efficiency when two water pumps work in parallel.
Point! The #U point corresponds to the power value of the # pump. The point corresponds to the power value of the $ pump. $$ $#% point corresponds to the efficiency of the # pump.
Rate value!#
Corresponding to the efficiency value of pump number $
"The total power of two water pumps working in parallel is the sum of the power of the two water pumps!
That is, the total efficiency can be calculated as follows)
The above method is also applicable to situations where the pipeline layout is different or the water level is different. For example, in northern my country, well groups are used to collect data.
Groundwater water supply system! Analysis from the working condition of the water pump! It is equivalent to several water pumps working in parallel when the pipeline layout is asymmetrical
When calculating the working conditions, it is only necessary to calculate the static head #>
Calculate from a common datum! Then make corresponding corrections! Other algorithms are similar."