Positive displacement pumps are usually used to transfer fluids that have a high viscosity for example, chemical or food additives. They are also used for applications that require precise metering.
The diaphragm, piston, or helical-rotor is pushed forward and back in the course of. This permits them to move a fixed volume per shaft revolution.
Rotary Positive Displacement Pumps
Positive displacement pumps pull a particular quantity of liquid into the pump and force it out through the outlet valve. These pumps can transport liquids of any viscosity, from thicker than a drop of water to emulsions and sludges. They are able to operate at high pressures, and are ideally suited to applications that require precise dosing. These pumps are preferred for fluids that contain solid particles or abrasives. There are a variety of positive displacement rotary pumps, such as piston as well as gear rotary, screw and pumps.
Since these pumps don’t have impellers, they’re less susceptible to issues that affect centrifugal pumps, like cavitation and wear. Abrasive feeds can cause excess wear on the parts of some positive displacement pumps. This is especially true when rotary pumps use pistons or plungers in order to trap and displace fluid. This is why abrasive feed should be avoided whenever possible.
The discharge that pulsates is another problem that is associated with positive displacement rotary pumps with tu dieu khien bom. This could cause vibration and noise within the system and cavitation that can damage piping. But, this could be reduced through the use of several pump cylinders as well as Pulsation dampers.
Another advantage of a rotary positive displacement pump is that it can typically self-prime. It has very little clearances. However, care must be taken to ensure the pump does not run dry for extended durations of time since this can reduce the efficiency and life span of the seal.
Reciprocating Positive Displacement Pumps
These pumps draw and pressurize fluid using pistons inside a piston. The piston traps liquid in the valves at the outlet and inlet as it moves back and forward. This causes a difference in pressure which overcomes the valve on the inlet, allowing fluid out. Unlike centrifugal pumps that are sensitive to changes in viscosity, positive displacement pumps maintain their flow rate independent of system pressure.
These pumps are ideal for use in applications that require accurate metering or transfer of materials such as abrasive and dangerous substances. In addition, they’re self-priming, which reduces downtime and labor costs by eliminating the need for manual priming and re-priming.
The downside of these pumps they are prone to pressure that could build up within the pipework until the pressure is relieved. This can be caused by the pump or the liner. This results in excessive noise and vibration when running. To mitigate the effects of this, they typically require accessories like an acoustic damper in the pipework and discharge line to ensure safety and reliability. They are also expensive to maintain and costly because of their design. However, their ability to handle corrosive or dangerous fluids, along with their ability to consistently perform in low pressure settings, overcome these issues. They are a great option for applications that require high viscosity in the pharmaceutical as well as chemical processing and oil drilling industry.
Gear Pumps
Unlike diaphragm pumps, gears don’t cause shear to the fluid. They are great for moving shear sensitive liquids like emulsions, microbial cultures, and food products. Gear pumps are great for liquids that have a tendency to change viscosity.
They are very compact and cost efficient. They are made out of stainless steel, or any other material. They offer high efficiency levels of 85% and more. Reversible, they can be operated in both directions to empty the entire contents of the hose. They also self priming ensuring they do not require an external air supply. They are usually Atex certified (explosion proof) and are able to handle solvents.
The shafts are enclosed in sleeves that rest on one other, and lubrication is provided by a recirculating lubricant. The recirculating polymer is created through the pressure difference between the two gears. They are only able to run dry for a limited duration and must be well lubricated to avoid gears galling. This can happen when the melt of the polymer is too hard or the shear temperature is too high.
The gears rotate in opposing directions picking up the polymer and conveying it to exit around the edges of the meshed cogs. Lubrication grooves are used to ensure that the gears are well-lubricated. They can be single or double jacketed and fitted with different seal types – including mechanical, gland packing/stuffing, or magnetic coupling when no seal is present.
Diaphragm Pumps
Diaphragm Pumps are the most flexible pumps available worldwide. They can be easily transported to any location. Just connect the air and liquid lines and you’re ready to go. If your project requires low viscosity spraying or large solid handling, chemical or physical aggression, these pumps are able to take care of it.
Diaphragm Pumps contain two chambers of compressed air which contract and expand in alternating volumes. This causes the effect of pumping. The pump is able to transfer, compress, and evacuate mediums without the use of the use of lubricants.
When suction is applied, air pressure is applied to the left diaphragm to change it from a flat to convex and opens the check valve for inlet and draws fluid into the pump. The shaft of the pump shifts to the left, and the diaphragm to the right changes from concave to convex shape, closing the outlet check valve while fluid is pumped through the discharge valve.
The pressure of the air is controlled by an input regulator. The pumps will stop if the air pressure is higher than the pressure at which they discharge. The pump won’t damage its own system pipes or. This type of high-pressure, air driven pump is able to reach the maximum pressure of 30 psi however the actual pressure is lower as the diaphragm breaks above the pressure.