Positive Displacement Pumps are used to transfer fluids that have high viscosity such as food ingredients, fuels or chemical. They are also commonly employed in applications that require precise metering.
The diaphragm, piston, or helical-rotor, is pushed forward and back in a cycle. This permits them to move a fixed volume for each shaft turn.
Positive displacement pumps with a rotary, nozzle
Positive displacement pumps draw a certain amount of fluid into the pump before forcing it out via the outlet valve. These pumps are utilized for transporting liquids ranging in viscosity, from thicker than water to sludges and Emulsions. These pumps can operate at high pressures and are ideal for use in applications requiring precise dosing. They also work well for applications involving fluids that contain solid particles or abrasives. Common types of positive displacement rotary pumps are piston, diaphragm, gear rotary, and screw pumps.
Because these pumps do not have impellers, they’re not as vulnerable to issues that affect centrifugal pumps like cavitation and wear. Abrasive feeds can cause excess wear to the components of certain positive displacement pumps. This is especially the case when rotary pumps use pistons or plungers to capture and then displace fluid. It is recommended to avoid abrasive feeds when possible.
Another issue with the rotary positive displacement pumps is that they may create an intermittent discharge. This can lead to noise and vibration in the system as well as cavitation that can damage piping. This can be minimized by using multiple pumps, as well as pulsation-dampers.
Another benefit of a rotary positive displacement pump is that it can frequently self-prime. It has very little clearances. However, care should be taken to ensure the pump isn’t running dry for extended durations of time since this could reduce the effectiveness and longevity of the seal.
Positive displacement pumps that have an asynchronous pump
These pumps draw and pressurize liquid using pistons in a cylinder. The piston holds liquid between the inlet/outlet valves as it travels in a forward and back. This results in a change in pressure which overcomes the valve in the inlet, allowing liquid to exit. In contrast to centrifugal pumps which are prone to changes in viscosity and positive displacement pumps keep their flow rate in line with the pressure in the system.
These pumps are ideal for applications that require accurate metering or transfer of materials such as abrasive and dangerous substances. The pumps can also self-prime eliminating the need to manually re-prime.
The downside of these pumps, however they have a drawback that is that pressure could build up within the pipework, unless the pressure is relieved. It could be due to the pump or the liner. This causes excessive noise and vibration while operating. To reduce this issue, these pumps usually require accessories like an acoustic damper in the discharge line and pipework to ensure safety and reliability. Moreover, the internal structure of these pumps tends to make them more expensive and difficult to maintain than centrifugal options. However, their ability to handle dangerous or corrosive fluids, along with their ability to consistently perform at low-pressure settings, offset these challenges. They are a great option for applications with high-viscosity, such as the pharmaceutical industry chemical processing, chemical processing, and oil drilling industry.
Gear Pumps
Gears, unlike diaphragm pumps don’t shatter the fluid. They are ideal for shear-sensitive liquids such as emulsions and Microbial cultivation. Gear pumps are perfect for liquids with an ability to change viscosity.
They are very small and cost-effective. They are made out of stainless steel or other materials. They have high efficiency levels of up to 85% or more. Reversible, they can be operated in both directions to completely empty the contents of a hose. They also self priming which means they don’t require an external supply of air. They are generally Atex rated (explosion proof) and are able to handle solvents.
The shafts are contained within sleeves that are bonded using a recirculating polymer to provide the lubrication. The recirculating lubricant is created through the difference in pressure between the gears. They should not be allowed to dry out and require lubrication in order to prevent grinding of the gears. This can occur when the melt of polymer is too tough, or if the it is heated too much.
The gears rotate in opposing directions, picking the polymer before transferring it to exit around the edges of the meshed cogs. The gears are kept lubricated by using lubrication grooves tu dieu khien bom. They can be double or single jacketed, and equipped with various seal types – including sealing, mechanical, gland packing/stuffing, or magnetic coupling where no seal is present.
Diaphragm Pumps
Diaphragm Pumps are the most flexible pumps around the globe. They are able to be moved to any location. Just connect the liquid and air lines, and you’re good to go. If your project requires low viscosity spraying, large solid handling or chemical and physical force, these pumps can take care of it.
Diaphragm Pumps are equipped with two chambers of compressed air which contract and expand in alternating volumes. This results in the pumping effect. The pump can transfer, compress and then evacuate fluids without need for lubricant.
In the suction process the air pressure is utilized to transform the left diaphragm to convex, which allows the inlet valve to open and pumps fluid into the pump. Then the shaft of the pump shifts to the left and the diaphragm to the right shifts from a concave shape to convex, closing the outlet check valve as the fluid flows through the discharge valve.
The pressure of the air is controlled by an input regulator. If the air pressure is higher than the discharge pressure, the pumps will come to a stop. This stops the pump from causing damage to itself or system piping. This high-pressure air driven pumps can achieve the pressure of 30 psi. However the actual maximum is lower as the diaphragm breaks over this.