When we select a pump, we will learn about the pump head. Maybe you will be confused about this, don’t worry, this article will explain to you in detail the pump head, how to calculate, the influencing factors and how to select, so that you can have a clear understanding of it.
What Is Pump Head?
Simply put, pump head is the height of the liquid that the pump draws out of the pool, pressurizes it, and then lifts it to a certain position. The unit of measurement for pump head is meters or feet, and it is an important parameter to measure the delivery capacity of the pump.
If you want to understand the pump head clearly, you must first understand the components of the pump head. The pump head consists of suction head, discharge head and total head.
Suction Head
The suction head refers to the vertical height distance between the liquid level in the water pool and the pump suction inlet.
When calculating, we need to pay attention that the suction head also needs to consider cavitation and pipe friction.
Discharge Head
The discharge head refers to the vertical distance from the pump outlet to the maximum height the pump can lift the liquid.
Like the suction head, this does not refer to the simple vertical height. In practical applications, we also need to consider the horizontal distance of the pipeline and the friction loss of the pipeline.
Total Head
The total head refers to the sum of the suction head and the discharge head. But it does not mean that this is the total head. There is another important parameter, namely the pipeline loss, which will be explained in detail in the following content.
Read the following so you can understand pump head calculations more clearly.
How To Calculate Pump Head?
Pump Head Formula
H=Hd + Hs
H=Total Head
Hs=Suction Head
Hd=Discharge Head
(The formula only applies to simple cases.)
When the liquid level is above the pump inlet, the pump is in positive pressure suction, so the suction head is positive. Conversely, the pump is in negative pressure suction, and the suction head is negative. (refer to the figure below)
Notes On Pump Head Calculation: Static Pressure
When we calculate the total head of the pump, we need to pay attention to one issue, the vertical distance between the liquid level and the pump inlet.
When the liquid level is above the pump inlet, the liquid provides static pressure to the pump. Therefore, we can understand that the greater the vertical distance of the liquid level above the pump inlet, the greater the static pressure it provides, and the higher the pump can lift the liquid (note: Also consider pipeline losses).
Factors Affecting Pump Head
1. Pipeline loss: When fluid passes through a pipe or elbow, it will produce losses such as friction, impact, and vortex.
2. Fluid density and viscosity: When the fluid we transport is not just clean water, for example, when using a slurry pump to transport slurry, silt, etc., the pump needs a higher head to overcome these difficulties.
3. Flow rate: Generally speaking, the flow rate of a pump is inversely proportional to the head, that is, when the flow rate increases, the pump head will decrease, and conversely, when the flow rate decreases, the head will increase.
Of course, sometimes the relationship is not inversely proportional. Read the following content to learn more about the pump performance curve.
How to Read and Use Pump Performance Curves for Proper Selection?
How To Read A Pump Curve?
Before reading a pump performance curve, you must first understand the definitions of the values in the curve.
For example, the pump performance curve of the M150KSH shown in the figure.
Flow rate: The X-axis is the flow rate of the pump, in m3 /h, which represents how much flow the pump can deliver.
Head: The Y-axis is the pump head, measured in meters, which represents how high the pump can lift the fluid.
Efficiency: Efficiency is expressed in %. The larger the value, the higher the efficiency of the pump and the better the performance of the pump.
Learn More: How to Read a Pump Curve? Formula, Pump Selection and More
How To Select A Pump From Curve?
Make basic selection in 3 steps!
1. Determine your job requirements
For example, you need a pump head of 50m and a flow rate of 600m3 /h.
2. Find the right pump operating point
Intersection point: Find the intersection point of the X-axis (600m3/h) and the Y-axis (50m) in the graph and see which curve it is on.
Rotational speed: For example, if point A is near the 1140r/min curve, it means that this model may be selected.
3. Check efficiency and NPSH
Efficiency: Point A falls near the 52% efficiency curve, indicating that the efficiency of the pump is 52%.
NPSH: NPSHr (net positive suction head required) is about 8m at point A, so the NPSHa (net positive suction head available) of the pump must be greater than 8m to ensure the minimum pump inlet pressure, otherwise cavitation may occur.
Learn more: What is Pump Cavitation? Tips to Detect and Prevent It
Note: This step is a simple selection. In actual application, the density, viscosity and on-site working conditions of the fluid must also be considered. If necessary, please be sure to contact the pump manufacturer for selection.
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Head And Pressure
Head and pressure are two completely different concepts, but they are closely related to each other.
Pump head is how high the pump can lift the fluid, which has nothing to do with the density of the fluid. Pressure is the pressure the fluid is subjected to in the pump and pipeline, which is related to the density of the fluid.
For example, there is a pump with a pump head of 50m. If we use this pump to transport clean water and slurry, the pressure of the fluid will be greater because the density of the slurry is large, but the head of the two fluids will not be affected and will both be 50m.
FAQ
Rated Head and Maximum Head
The rated head is the head of the pump when it is at its optimal efficiency point. At this time, the pump has the best efficiency, the most stable operation and the longest service life.
The maximum head is the head at 0 flow, also known as the shut-off head. This is only a head limit value. In actual work, the pump head must not exceed 110%-120% of the rated head, otherwise the pump will be unstable during operation and shorten the service life of the pump.
What Is Head Range In Water Pump?
The head range is the range between the minimum and maximum head that the pump can provide when working.
Simply put, it is the vertical difference between the minimum and maximum heights that the pump can lift water. It can also be understood as the range of energy that the pump can provide after overcoming friction and the gravity of water.
The head range is generally expressed in m. For example, the head range is 5-35m. The head range can help you choose a suitable model when selecting a pump, and it is an important parameter for pump selection.
Which Pump is Suitable for Small Discharge and High Head?
1. Piston pump/plunger pump: Piston pump is a positive displacement pump. It relies on the movement of the piston in the pump to squeeze the water and discharge it. The pressure is very high and the discharge is very small. It is suitable for precision and high-pressure working conditions.
2. Multistage centrifugal pump: Multistage centrifugal pump has multiple impellers, each of which can provide a part of the head. The head is very high and suitable for medium and low discharge and high head high pressure working conditions.
3. Diaphragm pump: Diaphragm pump is also a positive displacement pump. It relies on the reciprocating motion of the diaphragm in the pump to move water. It has a higher pressure and is suitable for medium and low flow conditions.
What is Static Head of Pump?
Static head refers to the vertical height difference from the water source suction port to the discharge port of the water pump without considering factors such as pipe friction.
The static head is generally used to preliminarily determine the head required by the pump.
What is Pump Shut Off Head?
As the name suggests, the shut-off head is the head of the pump when the pump outlet is closed. At this time, the pump flow is 0 and the pump pressure is maximum. It can also be understood as the maximum head or dead head of the pump. However, the shut-off head is only a theoretical data used to determine the ultimate pressure that the pump can withstand.
Pump Capacity Vs Head
The pump capacity and pump head are inversely proportional on the pump curve. When the pump capacity (flow rate) is larger, the head will be smaller. Conversely, when the pump capacity (flow rate) is smaller, the head will be larger.
The unit of pump capacity is generally expressed in m³/h, and the head is expressed in m.
