WPpump Water Pump



Gear pump in the special conditions

Gear pump in the special conditions
Many applications, the pump does not simply conveying low pressure water medium at room temperature.
As the viscosity increased, the centrifugal pump will become inefficient, users need to consider using positive displacement pumps (PD pumps or positive displacement pump). When the pressure increases, the positive displacement pump unsustainable. When the temperature rises. The other pump will fail.
So when you need the pressure of more than 35 kilograms, or 300 degrees Celsius, or viscosity of up to hundreds of thousands or millions of centipoise how to do? Maybe some pumps specially designed or modify existing designs to meet one or two requirements, but how to do when working conditions require pumps to meet all of these harsh conditions?
This requires high-performance external gear pump designed for such harsh working conditions. This pump is optimized for materials, gaps and design, you can deal with any one or all of these conditions.
External gear pump, two of the same size of the meshing gear shaft. Drive shaft connecting the motor or reducer (flexible coupling) and led the other axes. Heavy duty industrial gear pump, gear normally associated with the axis for a part of the overall tolerance of the journal is very small.
The gear shaft as a whole in order to withstand high torque loads under high pressure, high viscosity. Four journal at the sliding bearing dynamic support to pump lubricated bearings.
There are three common forms of gear: straight teeth, helical and herringbone gear. These three forms have their own pros and cons of different applications.
Straight teeth is the most simple form, in the high-pressure conditions for the optimal application, because there is no axial thrust, and high transmission efficiency.
Minimum pulse of the helical gear in the transportation process, and quieter at higher speeds, because the tooth meshing is gradual. However, due to the role of the axial driving force, the choice of bearing material may cause the pressure drop is limited, dealing with low viscosity. Because the axial force of the gear into the bearing section friction, high hardness bearing material so that only selected special design or in its section in order to deal with this axial thrust.
Herringbone gear, helical gear form, back to back, slightly lower than the straight-tooth pulse, and the axial force can be balanced. However, high manufacturing costs, assembly / disassembly difficult, because it must be installed in pairs. In the application of high viscosity, liquid curing, easy or very large pump, it is indeed the drawbacks.
The operating principle of the external gear pump is very simple, the liquid enters the pump suction side, the interdental hole meshing inhalation, and then be driven in the interdental holes to reach the exit end of the outer edge along the gear shaft. Re-meshing teeth liquid launched hole into the back pressure at.
In theory, positive displacement pump rated flow and pressure-independent. However, the volume of failure or internal leakage is a form of positive displacement pumps are inherent. In order to achieve the required pressure differential and rated flow, gear pumps must overcome this leakage.
Internal leakage between four kinds: 1: gear journal bearing between 2: the gear end bearing face: top gear and the pump casing 4: meshing teeth.
Maximize the bearing capacity of the pump, the gap in the co-ordination between the components must be as small as possible to limit leakage. However, only narrow the gap is not as simple to say, but also must consider other factors such as temperature, viscosity, and material selection.
Leak from the inside is not all bad. Gear pump, some within the leakage must be used to lubricate the internal channels, and form a liquid membrane supported in a dynamic gear shaft in the sliding bearing. The correct design, the internal leakage flow rate of 1-3%.
The material selection is very important in the selection of high-temperature industrial pump. Gear pump is often used to transport the high corrosion resistance, abrasion resistance, or the volatility of fluids. Pump shell, shaft and bearing material first to match with the pumped liquid. Additional considerations at high temperatures, the pump design becomes more complex, and even need to consider the thermal expansion of various materials.
As mentioned earlier, the internal gap be as small as possible in order to achieve the highest pressure. At high temperatures, the pump due to thermal expansion of components in the existing gap “expansion.” This is beyond the usual scope of consideration of the most common gear pump manufacturers. Overestimate the material thermal expansion can cause the pump gap is too loose, but can not produce the desired pressure; underestimate the thermal expansion will cause the locking of the pump when the process temperature is reached. Based on the original? Pump for high or low temperatures are often in the non-design temperature can not be run.
For example, if the pump is 316 stainless steel, gear shaft 440B stainless steel, bearing graphite. 316 stainless steel thermal expansion rate 17×10-6mm/mm/deg C, 440B is 11×10-6mm/mm/deg C, and carbon is 3.6×10-6mm/mm/deg C,. The pump manufacturer must be calculated at high temperatures, the capacity of the pump within the gap.
Pump warm-up is necessary, it can avoid the high temperature shock so that part is damaged. Recommended when pumping fluid temperature is higher than 150 ° C preheat. When the use of mechanical seals, the pumps need to be preheated to 30 ℃ operating temperature within the sealing surface to prevent damage. Jacketed pump by steam, heat medium, and electric heating to preheat.
Viscosity is the resistance of the fluid flow, high viscosity conditions, the first question is how to make the fluid into the pump. The pump must turn very slowly so that the fluid into the engagement between the teeth hole, the hole formed suction fluid sucked into the pump. The gap is more tightly within the sealing of the pump, the better, the stronger the suction.
Once the fluid enters the pump, the internal gap according to the viscosity of properly defined. The gap is too small will restrict the flow of fluid in the channel, the bearing and lack of lubrication and overheating; the gap is too large, liquid film strength decreased and can not support and lubrication of the gear shaft, resulting in direct contact with the journal and bearing, leading to failure in advance.
Dealing with high-viscosity fluid is another important factor is the high torque of the drive gear, gear shaft must be sufficiently solid to pass high torque of the drive machine. The tooth design is very important, too big is not enough transportation efficiency is too small you can not afford high torque.
Loaded in the teeth of the gear shaft torque and shear force with increasing viscosity and pressure increase, these factors combined with high temperature, gear shaft and tooth design became very important, because the coefficient of elasticity of the metal parts with increasing temperature drops.
High pressure, high viscosity, high temperature conditions so that users no longer selection of centrifugal pumps in favor of the positive displacement pumps (PD pumps). When these conditions become particularly harsh, and many other forms of PD pump to use limit, the only remaining option is the external gear pump.
External gear pump manufacturer, but few can meet these conditions. The informed user choice should be demanding applications?? Experience, successfully deal with these conditions can be traced back to supplier records.