Positive displacement pump has more variation than dynamic pump. Generally it is divided into two large groups, rotary pump and reciprocating pump. Both are still divided into various types of pumps again. And here are the pumps:
- Positive Displacement Rotary Pump
This rotary type moves the working fluid through a rotary mechanism by make a vacuum effect so it can suck the working fluid from the inlet side, and move it to the outlet side. If there is air trapped inside the rotary pump, it will naturally discharge the air, thereby reducing the need to vent the air trapped inside the pump manually.
Here are all kinds of rotary pumps:
- Internal Gear Pump
This pump uses two gears as a working fluid driver inside the pump casing. One gear drives and the other becomes driven. The driving gear is inside the driven gear. For more details please see the following picture.
And here is the process whereby the working fluid is pumped by this internal gear pump.
The working fluid enters through the pump inlet toward the outer gear rotated by the inner gear. The fluid moves toward the outlet side as a result of the drive from the outer gear. Furthermore the inner gear goes into the sidelines of the outer gear to push the working fluid to exit through the outlet side of the pump.
- External Gear Pump
Same with the internal gear pump, this external gear pump –or typically called gear pump– also uses two gears as its main component. What distinguishes is that both gears are in parallel positions, and the driving gear is not inside the driven gear.
- Screw Pump
Screw pump was first developed by Archimedes. This why a screw pump also called Archimedes Screw Pump. Single screw rotor was used to move water from the river at lower point to the rice fields for irrigation purposes.
The screw pump design has evolved into several types such as twin-rotor, triple-rotor, and 5-rotor. The differences is in the number of the screw. Here is a screw pump video with twin-rotor.
The working principle of screw pump with multi-rotor is when working fluid entering through the inlet side of the pump, moved by the rotor screw through the sidelines of the outer side. Upon reaching the outlet side, the fluid will be pushed out of the pump.
- Progressive Cavity Pump
This type of pump is the development of a screw type pump. The working principle was first introduced by Rene Moineau in the 1930s. The pump consists of both helical rotor and stator, but the stator designed to have a spiral pitch distance which is 2 times larger than the pitch of the rotor. The progressive cavity pump rotor is connected to the shaft driven by an electric motor. Among the shafts with the rotor is connected by flexible coupling which when the shaft rotates, this clutch moves to follow the movement of the rotor and shaft. For more details please note the following animation.
Spiral design of the rotor and stator form a cavity (cavities) in it, which is when the rotor cavity as if it moved toward the pump outlet. This space is the space to move the working fluid.
Progressive cavity pumps can be used in various types of working fluids, from dilute fluids to high-viscosity fluids. However, this pump does not match the solid particles. For operational purposes, this pump needs to be carried out a priming process as well as discharge of air trapped (venting) in it before operating. It aims to extend the life of the pump.
- Rotary Lobe Pump and Rotary Piston Pump
The rotary lobe pump is similar to a gear pump, it’s just using a kind of lobe-shaped rotor. There are two lobe rotor inside the pump casing, which are both driven by a driving source and arranged by gear that is outside the body of the pump so that the rotor rotates in rhythm. The rotation of the rotor gives rise to empty space so that the fluid can enter into it and move to the outlet side. On the outlet side the two rotor lobes meet so close the existing cavity and push the working fluid out through the pump outlet.
Rotary piston pump is the development of a rotary lobe pump. The rotary piston pump rotors are designed in such a way that the pump cavity volume becomes wider. In addition to the pump outlet side, the pump rotor no longer “squeezes” the working fluid out as in the rotary lobe pump, but the rotary piston pump rotation shape will push the fluid out to the outlet side of the pump.
- Vane Pump
This rotary pump uses a cylinder in the rotor section, a spring-mounted cylinder base connected to the pump rotor. The rotor axis is not aligned with the pump casing axis, so that when the rotor rotates, the rotor cylinder will follow the shape of the casing and push the working fluid to the outlet.
- Peristaltic Pump
The last rotary type is a peristaltic pump. This type of pump uses a working principle similar to the peristaltic movement of the esophagus. This pump uses a kind of elastic hose as a working fluid conduit. The hose is pressed by the rotor with the tip of the roller to form a push motion.
Peristaltic pumps were initially widely used in laboratories only, but along with the development of rubber technology, current peristaltic pumps can be used for “heavy” materials including solid materials.
- Positive Displacement Reciprocating Pump
The reciprocating pump uses a piston that moves back and forth as its working component, and directs the working fluid flow to only one direction with the help of a check valve. This positive displacement pump has a widespread work cavity during fluid sucking, and will push it by narrowing down the working cavity. With the help of check valve to regulate fluid flow direction, there will be harmonic pumping process.
The reciprocating pump consists of several types:
- Piston Pump
This pump uses a piston to suck and push the working fluid. The number of pistons depends on the manufacturer’s design that adapts to the system requirements. The less number of pistons in the pump, the flow of water out will be more unstable. To obtain a stable fluid flow can be used pressure relief valve or pump with more pistons.
- Plunger Pump
This type of pump is similar to a piston pump. What distinguishes is not using a piston, the pump that drives the fluid does not fully fill the cylinder room. For more details see the picture of the difference between the piston pump with the following plunger pump.
- Diaphragm Pumps
The pump is also similar to the piston pump but the pump component that performs the back and forth motion is the diaphragm connected to the crank of the drive. The diaphragm will move forward and backward to create changes in the space cavity inside the pump. With the help of check valve then the fluid flow of work can occur.
Diaphragm pumps generally operate at lower pressures than piston or plunger pumps. However, because of its unique design, the diaphragm pump can continue to operate even when there is no fluid flowing in it. And automatically when the working fluid is available again, this pump can naturally primed and vented.
- Swashplate Pump
The last type of pump we will discuss is a swashplate pump. This pump is the development of the piston pump. Some pistons are arranged parallel to the one end connected with the upright plate, while the other end is connected to the sloping plate. As the pump shaft rotates the parallel piston-piston rotates to produce a movement back and forth. To better understand this type of pump, let’s consider the following animated video.
What is interesting about this pump is that the fluid flow discharge can be greatly changed. This can be done by altering the angle of the slope of the plate connected to the pump pistons.