First, the installation height of the centrifugal pump Hg
Allowable suction vacuum height Hs refers to the maximum vacuum that the pressure p1 at the pump inlet can be allowed to reach
The actual allowable suction height Hs value is not a value calculated according to the formula, but an experimentally determined value by the pump manufacturer. This value is attached to the pump sample for the user to use. It should be noted that the Hs value given in the pump sample is the value of using clear water as the working medium, operating conditions at 20°C and pressure of 1.013 × 105 Pa. When the operating conditions and working media are different, conversion is required.
(1) Clean water, but different operating conditions and experimental conditions, can be converted by the following formula
Hs1=Hs+(Ha-10.33)-(HÏ…-0.24)
(2) Delivery of other liquids When the conditions of the liquid to be transported and the villains are different from the experimental conditions, two steps are required for conversion: the first step is to detect Hs1 in the pump sample according to the above formula; the second step is to use Hs1 according to the following formula. Convert to H's
NPSH Δh
For the oil pump, the NPSH Δh is used to calculate the installation height. That is, the NPSH Δh is taken from the oil pump sample, and the value is also measured with 20°C clear water. If other fluids are transported, corrections must also be made. Check the relevant books.
From a safety point of view, the actual installation height of the pump should be less than the calculated value. Also, when the calculated Hg is negative, it means that the suction inlet of the pump should be below the liquid level of the storage tank.
Example A centrifugal pump from the sample was found to allow suction vacuum height Hs = 5.7m. It is known that the total resistance of the suction line is 1.5mH2O, and the local atmospheric pressure is 9.81 x 104Pa. The dynamic pressure of the liquid in the suction line can be ignored. Try to calculate:
(1) Pump installation when delivering water at 20°C;
(2) The installation height of the pump when it is transferred to 80°C water.
Solution: (1) Mounting height of the pump when delivering water at 20°C
Known: Hs=5.7m
Hf0-1=1.5m
U12/2g≈0
The local atmospheric pressure is 9.81×104 Pa, which is basically consistent with the experimental conditions at the time of the pump's delivery. Therefore, the installation height of the pump is Hg=5.7-0-1.5=4.2 m.
(2) Mounting height of the pump when delivering 80°C water
When transporting water at 80°C, the installation height cannot be calculated directly from the Hs value in the pump sample. The Hs must be converted according to the following formula: Hs1=Hs+(Ha-10.33)-(Hυ-0.24)
It is known that Ha=9.81×104Pa≈10mH2O, and the saturated vapor pressure of 80°C water is 47.4kPa as found in the Appendix.
Hv=47.4×103 Pa=4.83mH2O
Hs1=5.7+10-10.33-4.83+0.24=0.78m
Second, the cavitation phenomenon of centrifugal pump
The cavitation phenomenon of the centrifugal pump means that the liquid to be transported is partially vaporized due to the saturated vapor pressure at the delivery temperature being equal to or lower than the pressure at the inlet of the pump (actually at the inlet of the blade), causing the pump to generate noise and vibration. The flow rate, pressure head and efficiency of the pump have dropped significantly. Obviously, cavitation is not allowed in the normal operation of the centrifugal pump.
The key to avoiding cavitation is the correct installation height of the pump, especially when transporting volatile liquids with high temperatures.
Substituting the Hs1 value into the equation to obtain the mounting height
Hg=Hs1-Hf0-1=0.78-1.5=-0.72m
Hg is negative, indicating that the pump should be installed below the pool level, at least 0.72m below the liquid level.
Production process
Welding elbow production process, if the long radius of the elbow, you must first select specifications, put forward the tube material. Spread ratio, through theoretical calculation, the general expansion rate of 35% - 33%, and push back. Short radius 219mm general expanding diameter rate of 50%. Selected raw materials, in material according to the specifications of the elbow, then consider the radius of curvature, for example, 90 degree elbow, by its curvature can figure out how many materials can be processed with 90 DEG elbow. It can be calculated by theoretical calculation, and then cut off with the length of the length. Finally, the material pushing system. You may have seen the machine, the actual is very simple. It is a horn shaped mandrel or mandrel, the mandrel is changed from thin to thick, push the process is a process of expanding with bending. Behind a support pipe section to penetrate mandrel material, one behind the arch frame will be fixed mandrel.
Photo of our Pipe Bend:
Technological process
Seamless elbow: elbow is a kind of pipe fitting used for turning of pipe. In the pipeline system used in all the pipe fittings, the largest proportion, about 80%. In general, different forming processes are selected for different materials or wall thicknesses. At present, the factory used seamless elbow forming process, hot stamping, extrusion have.
Hot forming
Hot bend forming process is the special Elbow push processing machine, a core mold and a heating device, which makes in the mold blank in pushing mechanism driven by forward motion and in the movement is heating, expanding diameter and bending forming process. The deformation characteristics of the hot pushing elbow is based on the metal plastic deformation before and after constant volume law to determine the tube diameter, the tube diameter less than the diameter of the elbow, the through mandrel control the blank deformation process, the arc by the compression of the metal flow, compensation for expanding and other parts of the thin, in order to get uniform wall thickness of elbow.
The hot pushing elbow forming process has the advantages of beautiful appearance, uniform thickness and continuous operation, suitable for mass production. Therefore, it becomes the main processing method of carbon steel, alloy steel elbow, and is also used in some specifications of stainless steel elbow forming.
The heating method of forming process has the intermediate frequency or high-frequency induction heating (the heating coil can be multi circle or single ring), the flame heating and the reflection furnace heating.
Stamping forming
Stamping elbow is the earliest application in mass production, the forming process of seamless elbow, at present, in the production of the elbow of the commonly used specifications has been hot pushingpipe method or other forming techniques of alternative, but in some specifications of elbow due to less number of production, wall thickness too thick or too thin.
Products have special requirements are still in use. The stamping of the elbow is formed by using the tube blank equal to the outside diameter of the elbow.
Before stamping, the tube blank is placed on the lower die, and the inner core and the end mould are filled in the tube blank, and the upper die downward movement begins to press down.
Compared with the hot pushing process, stamping the appearance quality is inferior to the former; stamping elbow in the forming of arc in tension and other parts of excess metal is not the compensation, so outside the arc wall thickness reduction thin about 10%. However, due to the characteristics of the single piece production and low cost, the stamping elbow process is used for the manufacture of small batch and thick wall elbow.
Stamping elbow points cold stamping and hot stamping two kinds, usually based on the properties of materials and equipment selection of cold stamping or hot stamping.
Cold extrusion bend forming process is the use of special elbow forming machine, tube into the outer mold, mold clamping, under the push of tube billet reservation along the inner mould and the outer mould gap of movement and forming process.
The elbow made by cold extrusion technology of internal and external mold is beautiful, uniform wall thickness and small size, so it is used for stainless steel elbow, especially for stainless steel elbow. The precision of internal and external die used in this process is high, and the requirement for the wall thickness deviation of tube blank is also very strict.
Pipe Bend
Welded Pipe Bend,Steel Pipe Bend,Pressed Pipe Bend,Tube Bending
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