A positive displacement pump moves fluid by constantly trapping a fixed amount of the fluid and then displace it into an outlet pipe. This positive displacement can be achieved in a number of different ways, leading to a variety of different positive displacement pumps that can pump many different fluids, from oil to water to coffee. They can be used as oil pumps, carbonators, air-injectors, and a variety of other applications. Most PD Pumps are rotary pumps, but some, such as diaphragm pumps, are not.
PD pumps do not have a shutoff head like many other pumps, so it is important to always have a release or safety valve. Some of them have internal safety vales, if they do not, a valve is needed for the outlet pipe. If for some reason the outlet is closed, pressure will continue to build until the pipe bursts or the pump is severely damaged.
Gear pumps – such as the range of Koshin Gear Pumps that we supply – work by using the meshing and separating of gears to pump the fluid. The gears rotate, seperating on the inlet side to draw in the fluid, and meshing on the outlet side to force the fluid out. Due to their ridgid nature, Gear Pumps can operate a high pressure with viscous fluids, and are perfect for use with various kinds of oil. You can find more info on these pumps here.
Rotary Piston Pump
The rotating piston pump is a specially designed pump mantufactured for pumping fluids that have extremly high viscosities (200 000 cps) and are pumped at high temperatures (300ºC). It is able to do this due to its unique design, which combines rotary and piston technology to allow pumping of fluids that would cause other pumps to seize. More information can be found here.
Sliding Vane Pumps
A sliding vane pump uses vanes mounted on a rotor to pump fluid. The vanes slide in and out of the rotor as it turns, trapping liquid between the rotor and the pump wall, forcing the fluid through the pump and into the outlet pipe. These pumps are useful for pumping at very low pressure. More information in these pumps can be found here.
Flexible impeller pumps work by deforming a special flexible impeller. As it deforms on the outlet side, it pushes the fluid out of the pump, whist on the inlet side, the impeller returns to it’s normal state, creating suction. The diagram shows this process in more detail. Flexible impeller pumps are gentle on fluids, but still have a high self-priming action. As they are industrial pumps, they are widely used in the chemical, food processing, wine-making, and cosmetic industries. More information can be found here.
Air Operated Double Diaphragm Pumps
These pumps, as indicated above, are non-rotary pumps. Instead they use two flexible diaphragms and a non-return valve on both the inlet and the outlet pipes. The diaphragms are moved using pressurised air. When the volume of the chamber inside the pump is increased by flexing the diaphragm, the outlet valve opens and fluid is sucked into the pipe, and when the chamber volume is decreased, the inlet valve closes and the outlet valve opens, allowing the fluid to flow out of the pump. More information can be found here.