Positive Displacement Pumps are used to transfer fluids that have high viscosity, such as food ingredients, fuels or chemicals. They are also used for applications that require precise metering.
They function by switching back and forth strokes from diaphragm, piston, or helical rotor. They can convey an amount of fluid every time a shaft turns.
Rotary Positive Displacement Pumps
Positive displacement pumps draw a certain quantity of liquid into the pump, and force it out via the outlet valve. These pumps are utilized for the transportation of liquids with a viscosity from thinner than water, to sludges and Emulsions. They are able to operate at high pressures, and are perfect for use in applications requiring precise dosage. These pumps are recommended when working with fluids that contain hard particles or abrasives. The most common kinds of Rotary positive displacement pumps comprise diaphragms, pistons, rotary, and screw pumps.
These pumps are less prone to issues like wear and cavitation that can happen with centrifugal pumps. Abrasive feeds can cause excess wear to the components of some positive displacement pumps. This is particularly the case for rotary pumps that utilize pistons or plungers for the purpose of capturing and displacing fluid. Avoiding feeds with abrasive particles when feasible.
Another problem with Rotary positive displacement pumps is that they may generate pulsating discharge. This could cause vibration and noise within the system, as well as cavitation that can damage piping. But, this could be minimized by using multiple pump cylinders and pulsation dampers.
A rotary positive displacement pump can also self-prime. This is due to the small clearances within the pump. It is essential to not allow the pump to be running dry for long durations as this will decrease its effectiveness and reduce life expectancy.
Reciprocating Positive Displacement Pumps
These pumps pressurize and draw fluid by using pistons within a cylindrical. When the piston is moved around, it traps a liquid volume between the outlet and inlet valves, creating a differential pressure that overcomes the valve that allows fluid to leave. Positive displacement pumps don’t alter their flow rate according to changes in viscosity, unlike centrifugal pumping systems.
These pumps are ideal for use in applications that require accurate measurement or transfer of material which include abrasive as well as hazardous substances. They also self-prime, which eliminates the need to manually re-prime tu dieu khien may bom.
The downside of these pumps, however they have a drawback that is that pressure could build up within the pipework, unless the pressure is released. This could be by the liner or the pump. This causes excessive noise and vibration while working. To combat this the pumps need accessories such as pulsation dampeners for the discharge lines and pipework. These pumps are also difficult to maintain and cost more because of their internal design. But their ability to handle corrosive or dangerous fluids, along with their capacity to perform consistently in low pressure settings, overcome these issues. These pumps are ideal for applications involving high viscosity in the drilling industry, chemical processing and pharmaceutical industries.
Gear Pumps
As opposed to diaphragm pumps don’t cause shear to the fluid. They are perfect for shear-sensitive liquids, such as emulsions and Microbial cultures. Gear pumps are ideal for liquids with an ability to change viscosity.
They are lightweight and affordable. They are made from stainless steel or other materials. They are efficient with levels of 85percent or more. Reversible, they are able to be operated in any direction to completely empty the contents of a pipe. They also self priming ensuring they do not require an external supply of air. They are usually Atex-rated (explosionproof) and are able to handle solvents.
The shafts are enclosed in sleeves that rest on one the other. Lubrication is provided by a recirculating lubricant. The recirculating lubricant is created by the pressure difference between the gears. They are only able to run dry for a limited period of time, and must be clean and lubricated to prevent gears galling. This can happen if the polymer melt is hard enough or the the shear temperatures are too high.
Gears are rotated in opposite directions, taking in polymer. The polymer is transferred to the cogs on the outside. Gears are kept lubricated by using grooves for lubrication. Single or double-jacketed, they can be fitted with a range of seals that include sealing, mechanical, gland packing/stuffing and magnetic coupling if no seal is in place.
Diaphragm Pumps
Diaphragm Pumps are the most flexible pumps available in the world. They are able to be transportable to any place. Just attach the air and liquid lines and you’re ready to go. These pumps are capable of handling all kinds of applications, whether low viscosity spraying or large solid handling.
Diaphragm Pumps have two chambers of compressed air which expand and contract in alternating volumes. This creates the effect of pumping. The hermetic seal that is created between the diaphragm, the drive mechanism, and the chamber of compression permits the pump to move the pressure, compress and then evacuate a medium without requiring a lubricant.
During the suction stroke the air pressure is applied on the left diaphragm, causing it to transform it from a flat to a convex shape and opens the inlet check valve and draws fluid into the pump. The shaft of the pump moves to the left, and the diaphragm on the right shifts from a concave shape to convex. This is closing the outlet check valve while the fluid flows through the discharge valve.
The air pressure is controlled by an input regulator. If the air pressure exceeds the discharge pressure, the pumps will just come to a stop. This prevents the pump from harming its own system or piping. This kind of high-pressure air driven pump can reach the ultimate pressure of 30 psi, however the actual pressure is lower as the diaphragm can break over the pressure.