Cavitation is the phenomenon of change in the vapor phase of liquid that is flowing, because the pressure is reduced to below the saturated vapor pressure. In part that is often experienced pump cavitation are suction side of the pump. This occurs when the pump suction pressure is too low to below the saturated vapor pressure, it can cause:
Noise, vibration or damage to the pump components when the fluid bubbles burst when through areas of higher pressure
Pump capacity is reduced
Pump is not able to raise the head (pressure)
The reduced efficiency of the pump.
In general, the occurrence of cavitation classified on the basis of 5 reasons:
1 Vaporisation - Evaporation.
Fluid vaporizes when the pressure becomes very low or the temperature becomes very high. Each requires a centrifugal pump head (pressure) on the suction side to prevent evaporation. The necessary pressure, prepared by the pump manufacturer and is calculated based on the assumption that the water being pumped is 'fresh water' at a temperature of 68 ºF. And this is called Net Positive Suction Head Available (NPSHA)
Because there is a reduction in pressure (head losses) on the suction side (because of the valve, elbow, reducer, etc.), then we have to calculate the total head at the suction side and Net Positive Suction commonly called Head is Required (NPSHR).
Well both affect the evaporation rate, so in order to prevent evaporation, the conditions are:
NPSHA - Vp ≥ NPSHR
Where Vp: Vapor pressure of fluid being pumped.
In other words to maintain that vaporization does not occur then we must do the following:
1 Adding Suction head, with:
Increase the level of liquid in the tank.
Elevating the tank.
Pressure tank.
Lowering the pump position (for portable pump).
Reduce head losses in the suction piping system. For example, by reducing the number of fittings, cleaning striner, check tank venting probably closed) or increasing the pump speed.
2 Reduce the fluid of temperature, with:
Cool the cooling fluid suction with
Isolate the pump suction
Prevent the temperature rise of the bypass system from the discharge pipe.
3 Reduce NPSHR, with:
Use double suction. This bias NPSHR reduces about 25% and in some cases allow the addition of pump speed by 40%.
Use pumps with lower speed.
Use the pump impeller which has openings 'hole' (eye) bigger.
Install Apoptosis, can reduce up to 50% NPSHR.
Use a smaller pump. Using 3 small pump with a capacity of half the size, the count is cheaper than using large pumps and spare her. Anyway can save energy.
Wednesday, September 3, 2014
Cavitation at the pump (2)
1 Vaporisation - Evaporation.
Next we examine briefly the second classification
2 Water ingestion - The entry of outside air into the System
Centrifugal pumps are able to handle only 0.5% of the total volume of air. More than 6% air, the consequences could be very dangerous, it can damage the pump components.
Air can enter the system through several causes, including:
Of the stuffing box packing (Section A - See Figure). It happens, if the pump from the condenser, evaporator or other equipment working in a vacuum.
Location of valve in the line above the water surface (water line).
Flange (pipe joints) are leaking.
The pull air through the vortex fluid (fluid vortexing).
If 'bypass the line' it is too close to the suction side, this will increase the air temperature on the suction side.
Reduced fluid on the suction side, this can occur if the fluid level is too low.
vortexing Fluid
Both evaporation and entry of air into the system greatly affect the performance of the pump when the air bubbles that burst when passing through the 'eye of the impeller' (Part G - See Picture) until the exit side (side with higher pressure). Sometimes, in some cases can damage the impeller or casing. The greatest effects of the air trap is the reduced capacity of the pump. 3 Internal Recirculation - Turn on the Circulation System
This condition can be seen on the outer corner (leading edge) of the impeller, close to the outer diameter, rotates back into the center of the fan. He can also occur at the beginning of the suction side of the pump.
This behind-round effects can increase the speed until it evaporates and then 'broke' when through a higher pressure. It always happens at the pump with a low NPSHA. To overcome this, we must know the value of Suction Specific Speed, which can be used to control the pump during operation, what is the safest nearby on the value of BEP (Best Efficiency Point) pump that must be taken to prevent the occurrence of problems.
Suction Specific Speed value allowed is between 3,000 to 20,000. The formula used is:
rpm = Speed Pump
Capacity = Gallons per minute, or liters per second from the largest impeller on the value of BEP (Best Efficiency Point) it.
Net Positive Suction Head = Head is Required (feet or meters) on the rpm value.
Important note:
For a double suction pump, capacity divided by 2 because there are 2 impeller eyes.
Ideal to 'buy' pump with Suction Specific Speed value is less than 8500 (5200 metric) except for extreme conditions.
Mixed Hydrocarbon and hot water ideally at 9000 ÷ 12000 (5500 ÷ 7300 metric) or higher, the better.
Suction Specific Speed value that indicates high impeller eye is larger than usual and efficiency values are usually adjusted with a low NPSHR value.
Higher value of Suction Specific Speed requires special design, operation allows for cavitation.
Typically, the pump is operating below 50% of its BEP value is not reliable.
If we use an open impeller, we can correct by adjusting the adjustment of internal recirculation (clearance) impeller according to manufacturers' specifications.
type of impeller
For Closed Impeller type of problem and many more in practice be returned to the manufacturer for evaluation or maybe redesigned impellernya or change in size adjustment (clearance) on wearing the ring.
Cavitation at the pump (3)
In the last two posts: here and here, we have to know what it is cavitation, its effect and the classification of cavitation, namely:
1 Vaporisation - Evaporation.
2 Water ingestion - The entry of outside air into the System
3 Internal Recirculation - Turn on the Circulation System
Next we briefly examine the four classifications:
4 Turbulence - Turbulence Flow
We always want the fluid flow at a constant speed. Corrosion and barriers that exist in the system piping can change the speed of the fluid and any changes speed, the pressure is changed. To inhibit this, needs to be a good piping system design. Among other things meet the following conditions:
The minimum distance between the suction pump with the first elbow at least 10 X the diameter of the pipe. In many settings the pump, attach the suction bells in separate bays, so that the suction side of the pump will not interfere with the other. If this is not possible, some pumps can be mounted on the tub suction (sump) is large, provided that:
Position the pump perpendicular to the flow direction.
The distance between the two 'center line' minimum pump suction diameter twice.
All pumps in a state of 'runing'.
Upstream piping sections at least have a straight pipe with a length of at least 10 x the diameter of the pipe.
Each pump shall have a capacity of less than 15,000 gpm.
Basic adjustment should pump about 30% the diameter of the suction pipe.
Pump mounting depth relationship with a capacity adjusted to the following table:
5. Vane Passing Syndrome
Damage caused by this type of cavitation occurs when the outer diameter of the impeller passing too close to the 'cutwater' pump. The fluid flow velocity increases when the flow through the small path, the pressure decreases and causes local evaporation. Air bubbles are formed and then broke out in a place that has a higher pressure, a little outside the groove cutwater. This is what causes damage to the volute (snail home) pump.
To prevent excessive movement of the shaft, some manufacturers install a bulkhead rings on the suction eye. On the exit side (discharge), the ring can be made to extend out of the side wall of the discharge to the impeller casing.
1 Vaporisation - Evaporation.
2 Water ingestion - The entry of outside air into the System
3 Internal Recirculation - Turn on the Circulation System
Next we briefly examine the four classifications:
4 Turbulence - Turbulence Flow
We always want the fluid flow at a constant speed. Corrosion and barriers that exist in the system piping can change the speed of the fluid and any changes speed, the pressure is changed. To inhibit this, needs to be a good piping system design. Among other things meet the following conditions:
The minimum distance between the suction pump with the first elbow at least 10 X the diameter of the pipe. In many settings the pump, attach the suction bells in separate bays, so that the suction side of the pump will not interfere with the other. If this is not possible, some pumps can be mounted on the tub suction (sump) is large, provided that:
Position the pump perpendicular to the flow direction.
The distance between the two 'center line' minimum pump suction diameter twice.
All pumps in a state of 'runing'.
Upstream piping sections at least have a straight pipe with a length of at least 10 x the diameter of the pipe.
Each pump shall have a capacity of less than 15,000 gpm.
Basic adjustment should pump about 30% the diameter of the suction pipe.
Pump mounting depth relationship with a capacity adjusted to the following table:
capacity
|
Minimum depth
|
20,000 GPM
|
4 FEET
|
100,000 GPM
|
8 FEET
|
180,000 GPM
|
10 FEET
|
200,000 GPM
|
11 FEET
|
250,000 GPM
|
12 FEET
|
For metrics:
capacity
|
Minimum depth
|
4,500 M3/HR
|
1.2 METERS
|
22,500 M3/HR
|
2.5 METERS
|
40,000 M3/HR
|
3.0 METERS
|
45,000 M3/HR
|
3.4 METERS
|
55,000 M3/HR
|
3.7 METERS
|
Damage caused by this type of cavitation occurs when the outer diameter of the impeller passing too close to the 'cutwater' pump. The fluid flow velocity increases when the flow through the small path, the pressure decreases and causes local evaporation. Air bubbles are formed and then broke out in a place that has a higher pressure, a little outside the groove cutwater. This is what causes damage to the volute (snail home) pump.
To prevent excessive movement of the shaft, some manufacturers install a bulkhead rings on the suction eye. On the exit side (discharge), the ring can be made to extend out of the side wall of the discharge to the impeller casing.
Influence on the performance of Pump Cavitation
In the four previous posts we have to know the influence of cavitation and cavitation classification based on the main cause.
This time we re-deepen this cavitation effect in more detail. Previously we have to know the effect of cavitation in general are as follows:
Reduced capacity of the pump
Reduced head (pressure)
The formation of air bubbles in the area of low pressure in the pump casing (volute)
Noise when the pump is running.
Damage to the impeller or pump casing (volute).
In this paper we will discuss why it all happened.
Cavitation is expressed with cavities or holes in the fluid we are pumping. These holes can also be described as bubbles, it is actually the formation of cavitation bubbles and the bubbles outbreak. Bubbles are formed when the liquid boils. Be careful to declare the same boiling water that is hot to the touch, as well as liquid oxygen will boil and nobody claimed it was hot.
Boiling of the liquid occurs when it is too hot or the pressure is too low. At sea level pressure of 1 bar (14.7 psia) water will boil at a temperature of 212oF (100oC). If the pressure drop of water will boil at a lower temperature. There is a table that states the boiling point of water at each different temperature. As an example can be seen in the following table:
Pressure unit used here is not the absolute pressure gauge, this plural is used when we talk about the suction side of the pump to avoid the minus sign. So when calling the atmospheric pressure is zero, we say 1 atm is equal to 14.7 psia at sea level and on the metric system we used to wear 1 bar or 100 kPa.
We're back to the first paragraph to explain the result of cavitation, so we better know what actually happened.
Pump Reduced Capacity
It happens because a lot of air bubbles takes place (space), and we could not pump fluid and air at the same place and time. Automatic liquid we need to be reduced.
If it's a big bubble in the eye of the impeller, the pump will lose revenue and ultimately needed freming (extra fluid on the suction side to remove air).
Pressure (Head) sometimes reduced
The bubbles are not as liquid, it can be compressed (compressible). Well, the results of this compression is to replace the head, so that the actual pump head is reduced.
The formation of bubbles at low pressure because they can not form at high pressure.
We must always remember that if the velocity of a fluid increases, the fluid pressure is reduced. This means that high fluid velocity in the low pressure area definitely.
It will be a problem at any time if there is a limited fluid flow through pipes, volute or change direction suddenly. This situation is similar to the fluid flow on a small cross-section between the tip of the impeller with volute water cut.
Damaged parts Pump
The bubble burst in its own right, this is called the opposite of exploding imploding. The bubble burst on all sides, but if he gets hit as part of a metal impeller or voluteia can not be broken from the side, the fluid entering from the opposite side at high speed followed by a shock wave that could damage the pump part. There is a unique shape that forms a circle as a result of this blow, which was hit with a metal such as a "ball peen hammer".
The most damage occurs to form right angles to the metal, but experience shows that high-speed fluid seems to come from all angles.
The higher the capacity of the pump, it seems more likely cavitation occurs. Specific values have a high speed pump impeller shape that allows it to operate at high capacity with low power and a small possibility of cavitation. It is usually found in the tubular casing, of the volute casing shaped as we often see.
This time we re-deepen this cavitation effect in more detail. Previously we have to know the effect of cavitation in general are as follows:
Reduced capacity of the pump
Reduced head (pressure)
The formation of air bubbles in the area of low pressure in the pump casing (volute)
Noise when the pump is running.
Damage to the impeller or pump casing (volute).
In this paper we will discuss why it all happened.
Cavitation is expressed with cavities or holes in the fluid we are pumping. These holes can also be described as bubbles, it is actually the formation of cavitation bubbles and the bubbles outbreak. Bubbles are formed when the liquid boils. Be careful to declare the same boiling water that is hot to the touch, as well as liquid oxygen will boil and nobody claimed it was hot.
Boiling of the liquid occurs when it is too hot or the pressure is too low. At sea level pressure of 1 bar (14.7 psia) water will boil at a temperature of 212oF (100oC). If the pressure drop of water will boil at a lower temperature. There is a table that states the boiling point of water at each different temperature. As an example can be seen in the following table:
Fahrenheit
|
Centigrade
|
Vapor pressure lb/in2 A
|
Vapor pressure (Bar) A
|
40
|
4.4
|
0.1217
|
0.00839
|
100
|
37.8
|
0.9492
|
0.06546
|
180
|
82.2
|
7.510
|
0.5179
|
212
|
100
|
14.696
|
1.0135
|
300
|
148.9
|
67.01
|
4.62
|
We're back to the first paragraph to explain the result of cavitation, so we better know what actually happened.
Pump Reduced Capacity
It happens because a lot of air bubbles takes place (space), and we could not pump fluid and air at the same place and time. Automatic liquid we need to be reduced.
If it's a big bubble in the eye of the impeller, the pump will lose revenue and ultimately needed freming (extra fluid on the suction side to remove air).
Pressure (Head) sometimes reduced
The bubbles are not as liquid, it can be compressed (compressible). Well, the results of this compression is to replace the head, so that the actual pump head is reduced.
The formation of bubbles at low pressure because they can not form at high pressure.
We must always remember that if the velocity of a fluid increases, the fluid pressure is reduced. This means that high fluid velocity in the low pressure area definitely.
It will be a problem at any time if there is a limited fluid flow through pipes, volute or change direction suddenly. This situation is similar to the fluid flow on a small cross-section between the tip of the impeller with volute water cut.
Damaged parts Pump
The bubble burst in its own right, this is called the opposite of exploding imploding. The bubble burst on all sides, but if he gets hit as part of a metal impeller or voluteia can not be broken from the side, the fluid entering from the opposite side at high speed followed by a shock wave that could damage the pump part. There is a unique shape that forms a circle as a result of this blow, which was hit with a metal such as a "ball peen hammer".
The most damage occurs to form right angles to the metal, but experience shows that high-speed fluid seems to come from all angles.
The higher the capacity of the pump, it seems more likely cavitation occurs. Specific values have a high speed pump impeller shape that allows it to operate at high capacity with low power and a small possibility of cavitation. It is usually found in the tubular casing, of the volute casing shaped as we often see.
How to Overcome Water Damage Pump
When we die the water pump / no water flow on the flame machine / spinning, first step: check the water pipe in which there is not, if there is no water or there but not full, his visor fut Means broken / leaking or there might be at the pipe or pipe joints there are leaked.
But if the water in the pipe is full, Look at the end of the pipe to exit the water there are no air bubbles; If and air bubbles in the water in the pipe full of possibilities sill leak or it could be leaking impeller room / seeped or can be suction pipe is leaking or there is a connection .But if water leaked in full pipes and no air waves, likely broken impeller, close impeller, the impeller space, damage to the impeller, the impeller closed impeller space is usually worn with age or wear due to friction, which is caused by the incoming sand or dust. If the water pump is not rotating, the first step is check the electrical installation, the cable could be broken or the switch could be damaged, if the installation was no problem, try to check the bike from the back and turn the motor rotate. If we do not want to turn the rotary spinning or weight to rotate the impeller room filled with the possibility of dirt or if the water pump dies before the sound of the water pump his hard laker likelihood worn / jammed. If the bike rotated around a light but do not want to flame / spinning please check capacitors, good capacitors means that if the problem is with its bobbin,
There are three kinds of damage spool
1 ELECTRIC SHOCK
2 BROKE
3 BURNS
If the spool there is a short circuit, the motor rotation will be slow or still water flowing but soon will die and soon will be up again by itself, In this condition the motor hot. If its spool is switched off: when the water pump broke up the main bobbin still will not spin, but on the bike there was a buzzing sound tone. If the break up is not the main spool, if the water pump is turned on and assisted dipur water pump motor will turn on and drain the water but if turned off and then turned back the water pump will not turn on again, this kind of thing can also happen if the capacitor is dead / weak. if spool short circuiting the electricity will be directly dropped simultaneously when the water pump is turned on.
There is again a very simple way to solve our water pump so durable. durable
1 Place the installation of the water pump should be clean of dust and avoid damp areas
2. When there are animals immediately clean though just what else ants rats, once I find there is no water pump because of the way because there are worms in its fans, and is very much due to the water pump on fire ant nest
3. not get wet
4.Do not exposed to the direct rays of the eye
But if the water in the pipe is full, Look at the end of the pipe to exit the water there are no air bubbles; If and air bubbles in the water in the pipe full of possibilities sill leak or it could be leaking impeller room / seeped or can be suction pipe is leaking or there is a connection .But if water leaked in full pipes and no air waves, likely broken impeller, close impeller, the impeller space, damage to the impeller, the impeller closed impeller space is usually worn with age or wear due to friction, which is caused by the incoming sand or dust. If the water pump is not rotating, the first step is check the electrical installation, the cable could be broken or the switch could be damaged, if the installation was no problem, try to check the bike from the back and turn the motor rotate. If we do not want to turn the rotary spinning or weight to rotate the impeller room filled with the possibility of dirt or if the water pump dies before the sound of the water pump his hard laker likelihood worn / jammed. If the bike rotated around a light but do not want to flame / spinning please check capacitors, good capacitors means that if the problem is with its bobbin,
There are three kinds of damage spool
1 ELECTRIC SHOCK
2 BROKE
3 BURNS
If the spool there is a short circuit, the motor rotation will be slow or still water flowing but soon will die and soon will be up again by itself, In this condition the motor hot. If its spool is switched off: when the water pump broke up the main bobbin still will not spin, but on the bike there was a buzzing sound tone. If the break up is not the main spool, if the water pump is turned on and assisted dipur water pump motor will turn on and drain the water but if turned off and then turned back the water pump will not turn on again, this kind of thing can also happen if the capacitor is dead / weak. if spool short circuiting the electricity will be directly dropped simultaneously when the water pump is turned on.
There is again a very simple way to solve our water pump so durable. durable
1 Place the installation of the water pump should be clean of dust and avoid damp areas
2. When there are animals immediately clean though just what else ants rats, once I find there is no water pump because of the way because there are worms in its fans, and is very much due to the water pump on fire ant nest
3. not get wet
4.Do not exposed to the direct rays of the eye
Water pumps dead
This shows that there is no power that goes into the water pump. The first steps are to check the source of the Stop The electricity can contact or switch. If the input voltage, check Switch Water level in the water storage (if using Water Level Sensor). The next check in Automatic Pressure Switch for water pump that does not use water Tandon alias faucet is opened the pump is on, tap on the pump cover off.
If the terminal voltage up to the water pump but the pump motor does not live and no sound at all can be ascertained from the water pump broke spull or Thermal Switches that are in spull water pump broke. Or it could be spull been burned by the conditions in which the wire has been broken. Because usually when burning but do not drop effect will make our home electrical MCB Trip due to a short-circuit.
For the record checks should not be used because it was detected only Testpen Phasenya alone while its neutral .And not tespen were sometimes lit because the induced voltage.
If the terminal voltage up to the water pump but the pump motor does not live and no sound at all can be ascertained from the water pump broke spull or Thermal Switches that are in spull water pump broke. Or it could be spull been burned by the conditions in which the wire has been broken. Because usually when burning but do not drop effect will make our home electrical MCB Trip due to a short-circuit.
For the record checks should not be used because it was detected only Testpen Phasenya alone while its neutral .And not tespen were sometimes lit because the induced voltage.
Living with the sound of the water pump should not then die.
The meaning of life is the water pump but the sound is not normal. Suppose spotted and buzzing and as the rotor is not spinning or rotation as the rotor life but weak then die. If left long the pump will live longer with conditions as above and then die again. It happened because the water pump problem on its components could be due to the capacitor is weak or dead, Bearing (laker) jammed, or it could be conceded blog Pump sand or dirt. For certain pump can also stalled because of As rusty and glue on the stator as it may be some days not in turn. This case was caused spull of hot water pumps and safety of spull the Thermal Switch will be disconnected and reconnected when the heat down. More severe if spull was not using Thermal Switch effect spull will surely burn.
With defective parts replacement parts as mentioned above is usually the pump will return to normal. Spull short pump between the main rolls and rolls Auxiliary also will result in something like this. Damage to the capacitor is not always physically visible, sometimes capacitor exploded or cracked, sometimes the shape is still intact but is dead also.
With defective parts replacement parts as mentioned above is usually the pump will return to normal. Spull short pump between the main rolls and rolls Auxiliary also will result in something like this. Damage to the capacitor is not always physically visible, sometimes capacitor exploded or cracked, sometimes the shape is still intact but is dead also.
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