Understanding Centrifugal Pumps
Centrifugal pumps are pumps that enlarge fluid energy through the principle of centrifugal force. Centrifugal pumps can convert mechanical energy in the form of shaft work into fluid energy. It is this energy that results in the addition of the pressure head, speed head and potential head to the continuous flowing fluid. The shape of the centrifugal pump can be seen in the following figure 2.1:
The fluid flow into the rotating blade has acceleration, so the fluid flow is removed from the blades and changes to the pressure energy in the rectifier blade (in the spiral pump housing) connected to the suction valve and exhaust valve. The process of causing the fluid to come out from the blades, results in the movement of fluid in the pressure valve through the suction valve with a continuous flow direction (uninterrupted).
B. Working Principles of Centrifugal Pumps
Centrifugal pumps are one of the simplest equipment in various types of pumps. Figure 2.2 shows how this type of pump operates:
1. The liquid is forced towards an impeller by atmospheric pressure, or in the case of a jet pump by artificial pressure;
2. The impeller propeller passes kinetic energy to the liquid, causing the liquid to spin. Fluid leaves the impeller at high speed.
3. The impeller is surrounded by a volute casing or in the case of a turbine pump a stationary diffuser ring is used. Volute or stationary diffuser rings convert kinetic energy into pressure energy.
C. Working Process of Centrifugal Pumps
1. Radial fluid flow will cause a centrifugal effect from the impeller given to the fluid. The type of centrifugal pump or radial flow compressor will have a high head but low flow capacity. In this radial flow engine, the fluid enters through the center of the impeller in an essentially axial direction. The fluid exits through the gaps between the corners and disks and leaves the outside of the impeller at high pressure and the speed is rather high when entering the casing or volute.
2. Volute will change the kinetic head in the form of a high exhaust speed into a pressure head before the fluid leaves the pump output pipe. If the casing is equipped with a guide fin (guide vane), the pump is called a diffuser or turbine pump.
3. Impeller: Part of a rotating pump that converts engine power to kinetic power
4. Volute: Part of a silent pump that converts kinetic power to a pressure.
D. Centrifugal Pump Components
The main components of the centrifugal pump are shown in Figure 2.3 and are explained below:
1. Rotating component: an impeller connected to a shaft
2. Static components: casing, casing cover, and bearings.
The impeller is a round metal disc with a trajectory for installed fluid flow. Impellers are usually made of bronze, polycarbonate, cast iron or stainless steel, but other materials are also used. As pump performance depends on the type of impeller, it is important to choose a suitable design and get the impeller in good condition.
The number of impellers determines the number of stages of the pump. The one-stage pump has one impeller and is very suitable for low head (= pressure) services. The two-stage pump has two series of installed impellers for medium head service. The multi-stage pump has three impellers or more installed series for high head services.
Impellers can be classified on the basis of:
The main direction of flow from the rotation axis: radial flow, axial flow, mixed flow
1. Suction type: single suction and double suction
2. Mechanical shape or construction:
a). The closed impeller has a propeller that is covered by a mantle (= cover) on both sides (Figure 2.4). Usually used for water pumps, where the vanes are entirely enclosed in water. This prevents the transfer of water from the shipping side to the suction side, which will reduce pump efficiency. In order to separate the drainage chamber from the suction chamber, a connection is needed which moves between the impeller and the pump container. This connection is carried out by a ring mounted on the cover part of the impeller or inside the surface of the cylinder of the pump container. The disadvantage of this closed impeller is the high risk of obstacles.
b). Open and semi-open impellers (Figure 2.4) the possibility of a small blockage. However, to avoid clogging through internal recirculation, the volute or back-plate of the pump must be adjusted manually to get the correct impeller.
c). ? Vortex pump impellers are suitable for solid and “stringy” materials, but these pumps are 50% less efficient than conventional designs.
b. Piston rod
The piston rod moves the torque from the motor to the impeller during pump startup and operation.
The main function of the container is to close the impeller in suction and delivery at the end and so that it is in the form of a pressure tank. The pressure at the tip of the suction can be as small as one tenth of atmospheric pressure and at the end of the delivery it can be twenty times the atmospheric pressure at a one-stage pump. For multi-stage pumps the pressure difference is much higher. Containers are designed to hold at least twice this pressure to ensure adequate safety limits. The second container function is to provide supporting media and shaft bearings for piston rods and impellers. Therefore the pump container must be designed to:
1). Provide easy access to all parts of the pump for inspection, maintenance and repair;
2). Make leakproof containers by giving a packing box;
3). Connect the suction pipes and delivery to the flange directly;
4). Easily install easily into the driving machine (electric motor) without losing power.
CHAPTER IIICLATION OF THE CENTRIFUGAL PUMP
1. Based on the type of impeller.
a. Turbine Pump
Also known as vortex, peripheral and regenerative pumps. The liquid in this type of pump is rotated by an impeller propeller at high speed for almost one rotation in a ring-shaped channel, where the impeller rotates. Energy is added to the liquid in impulses. Diffuser type well pumps are often called turbine pumps.
Figure 3.1 Turbine type pump impeller
b. Radial Flow Pump
The fluid flow into the impeller is parallel to the pump shaft and exits the blade in the radial direction. The head produced is 50 m water column and the specific rotation is lower. (this pump is used if the specific rotation of the pump is 500 ÷ 300 rpm and the head is reached above 150 ft).
In this type the impeller throws liquid into a spiral house which gradually develops. This is made in such a way as to reduce the speed of the liquid can be converted into static pressure. The house of double or twin pump snails produces almost radial symmetry at high pressure pumps and pumps designed for little flow operation. Conch houses will balance radial loads on the pump shaft so that the load will cancel each other, thereby reducing the axle load and resultant bending.
c. French type impeller:
The fluid flow into the impeller is parallel to the pump shaft and exits the blade in the radial direction. The head and specific speed (1500 ÷ 4500) are lower.
d. Mixed Flow Pump
The fluid flow into the impeller is parallel to the direction of the shaft and exits the impeller in a radial and axial direction. Compared to French type impeller pumps, the resulting head is lower with a specific rotation (4500 ÷ 8000 rpm).
e. Axial Flow Pump
The fluid flow in and out of the impeller is parallel to the pump shaft. When compared to the previous three types, the head produced by this pump is the lowest with a low specific speed.
2. Based on Number of Levels:
Can be divided into two parts as follows:
a. One level pump:
This type of pump has one impeller in moving fluid so that the total head is low.
b. Multi-storey pumps:
It is said to be multilevel because it uses several impellers mounted in series, so the head it produces is the sum of the heads produced by each impeller so it is suitable for high head pumping.
3. Based on the shape of the house:
Can be divided into three parts as follows:
a. Volut house pump:
The fluid flow from the impeller is directly taken to the volut house.
b. Diffuser house pump:
This type of pump is equipped with a rectangular blade around the outside of the impeller whose purpose is to improve pump efficiency, also to characterize the pump house, so this construction is used in large pumps with high head and multi-level pumps.
Figure 3.7 Diffuser house pump
c. Volut house type mixed flow pump:
This pump has a mixed flow impeller and a volut house without diffuser blades, but a wide channel is used to drain fluid.
Figure 3.8 Aliaran campur pump type volut house
4. Based on shaft location:
a. Upright shaft:
This pump has a shaft with an upright position.
b. Horizontal axis:
This pump has a shaft with a horizontal position.
Figure 3.10 Horizontal shaft pump
5. Based on the entry side of the impeller:
a. Single suction pump
In the type pump, the fluid enters from one side of the impeller so that an axial force will arise to the suction side. This style can be resisted by axial bearings for large sized pumps, this axial force is quite large. And to reduce axial bearing loads can be used balancing loads.
b. Double suction pump
At this pump the fluid enters from both sides of the impeller so that the axial force that occurs due to the fluid pressure entering the impeller will balance each other. This double suction pump is widely used for large capacity pumping. This pump impeller is the same as the two rear mounted single suction impellers which is almost the same as the double suction pump with almost the same construction size.
Figure 3.11 Double Suction Pump
1). Open impeller:
This impeller is used when pumped fluid conditions contain a lot of impurities such as mud, gravel and so on. This impeller is used so that there is no blockage between the bow.
2). Semi open impeller:
This impeller is used when pumped fluid conditions contain only a small amount of impurities such as waste water, and so on.
Figure 3.12 Impeller half open
c. Closed impeller (closed impeller):
This impeller is used if the fluid is pumped clean / clear like drinking water, processed petroleum (gasoline, premium, diesel), etc. The use of this impeller to obtain a higher efficiency of type a and type b above.
Figure 3.13 The impeller is closed
B. Calculating Pump Performance
The work displayed by a pump is a function of the total head and the weight of the liquid pumped within the given time period. The pump piston rod power (Ps) is the power that is sent to the pump piston rod, and can be calculated as follows:
Pump piston power Power Ps = HP hydraulic power / Pump efficiency? Pump
Or Pump efficiency? Pump = Hydraulic power / Pump piston power
Pump output, HP water power or hydraulic cell power (hp) is the HP power of the liquid sent by the pump, and can be calculated as follows:
The hydraulic power of the cell = Q (m3 / sec) x (hdhs in m) x? (kg / m3) x g (m / sec2) / 1000
Q = flowrate
hd = head dump
hs = head sucking
? = fluid density
g = gravitational acceleration
C. Difficulties in the Assessment of Pumps
In practice, it is more difficult to assess pump performance. Some important reasons are:
1. The absence of specific pump data:
Pump specification data is needed to assess pump performance. Most companies do not hold original equipment documents (OEMs) that provide these data. In such cases, the percentage of the pump load for the pump flow or head cannot be estimated satisfactorily.
2. Difficulties in flow measurement:
It is difficult to measure the actual flow. Several methods are used to measure flow. In most cases, the flow rate is calculated based on the type of fluid, head and pipe size, etc., but the calculated image may not be appropriate. Another method is to divide the volume of the tank with the time used by the pump to fill the tank. However, this method can only be applied if one pump is in operation and if the tank discharge faucet is closed. The most sophisticated, precise and time consuming method for measuring pump flow is by measuring using an ultrasonic flow meter.
3. Improper Calibration of Pressure Gauges and Measurement Instruments:
Correct calibration of all pressure gauges on suction and discharge lines and other power measuring instruments is important to get the right measurements. However, calibration does not always have to be done. Sometimes a correction factor is used if the measuring device and instrument are not properly calibrated.
Both will result in improper assessment of pump performance.
This section covers the main areas for repairing pumps and pumping systems. The main areas for energy savings include:
a) Choose the right pump;
b) Control flow flow with speed variations;
c) Pumps in parallel arrangement to meet various demands;
d) Dispose of flow control valves;
e) Dispose of by-pass controls;
f) Control start / stop the pump;
g) Improve the balance of the impeller.
D. Characteristics of Centrifugal Pumps
a) Impeller type depends
b) Type of Impeller between Bearings / joints
c) Regenerative Turbine Types
d) Special Variations
Before conducting the experiment, prepare the equipment in advance to facilitate the dismantling and installation, while the equipment needed includes:
1. Plastic hammer;
2. Iron hammer;
3. Key “L” (1 set);
4. Ring Key (to taste);
5. Punch (1 set);
7. Extraktor (1 set);
B. Type of Centrifugal Pump
The type of pump used as practice material is:
Lower Pumpen Fabrik LUNERURG GMBH
Nr.409237 Dot 3013
TUP CM 40-160
The demolition procedure is:
1. Draw / sketch the Centrifugal pump in full;
2. Empty the lubricating oil;
3. Hold the position of the pump (vertical shaft), after the inner cover bearing is released first;
4. Open the binding bolts between the pump house and the pump frame;
5. Open the pump circuit at the same time with the lubricating house;
6. Remove the oil house from its axis;
7. Separate the pump frame from the pump house;
8. Separate the pump housing from its axis;
9. Open the impeller from the shaft;
10. Clean all dismantled parts.
D. Experiment analysis
After carrying out the demolition, then analyze the materials we use. In this case we have to analyze the components of the Centrifugal Pump itself, whether it can still function properly or not.
1. Give signs on the pump unit;
2. Be careful not to let the lubricant scatter;
3. Use the extractor set;
4. Carefully disassembly, the extractor position must be perpendicular to the base, do not tilt, because it can damage the bearing;
5. Check each component for possible: thirst, cracking, loose, and so on. If the damage is still within the limits of tolerance, then make repairs. If not, do a change with the new one.
E. Work Safety
In every activity, work safety is one of the main parts that need to be considered. So that work safety can be achieved while practicing, do the following:
1. Before practicing clean the work environment;
2. Get rid of unnecessary equipment that can cause accidents;
3. Use equipment in accordance with its functions;
4. Follow work and safety procedures;
CONCLUSIONS AND SUGGESTIONS
Based on the results of the Centrifugal Pump practice it can be concluded:
1. Changing mechanical energy into hydraulic energy through centrifugal activity, which is fluid pressure pumped;
2. The working principle is simple, easy to understand;
3. So that the pump can always operate properly, do maintenance continuously;
1. Perform checks regularly, make repairs if needed;
2. To support the practice, the authors hope that the Medan State Polytechnic provides more adequate facilities;
3. When practice takes place do it earnestly;
4. After completing the practice, clean the equipment used, to extend the life of these tools.