Forsthoffer's Rotating Equipment Handbooks Vol 2: Pumps

Pumps come in a variety of sizes for a wide range of applications. They can be classified according to their basic operating principle as dynamic or displacement pumps. Dynamic pumps can be sub-classified as centrifugal and special effect pumps. Displacement pumps can be sub-classified as rotary or reciprocating pumps.

Pump is a device that moves or compresses liquids and gases. Pumps are used in a variety of machines and other devices, including home heating systems, refrigerators, oil wells and water wells, and turbojet and car engines. The fluids (gases or liquids) moved by pumps range from air for inflating bicycle tires to liquid sodium and liquid potassium for cooling nuclear reactors. Most pumps are made of steel, but some are made of glass or plastic. Gas pumps are also called compressors, fans, or blowers. Types of Pumps  Dynamic Pump: Dynamic pumps maintain a steady flow of fluid.  Positive Displacement Pump: Positive displacement pumps, on the other hand, trap individual portions of fluid that are in an enclosed area before moving them along. Dynamic pumps  Centrifugal pumps consist of a motor-driven propeller like device, called an impeller, which is contained within a circular housing. The impeller is a wheel of curved blades that rotates on an axis. Before most centrifugal pumps can start pumping liquid, they must be primed (filled with liquid). As the impeller rotates, it creates suction that draws a continuous flow of fluid through an inlet pipe. Fluid enters the pump at the center of the impeller and travels out along the blades due to centrifugal (outward) force. The curved ends of the blades sweep the fluid to an outlet port. Centrifugal pumps are inexpensive and can handle large amounts of fluid. They are widely used in chemical processing plants and oil refineries.  Axial-flow pumps have a motor-driven rotor that directs fluid along a path parallel to its axis. The fluid thus travels in a relatively straight path from the inlet pipe through the pump to the outlet pipe. Axial-flow pumps are most often used as compressors in turbojet engines. Centrifugal pumps are also used for this purpose, but axial-flow pumps are more efficient. Axial-flow compressors consist of alternating rows of rotors and stationary blades. The blades and rotors produce a pressure rise in the air as it moves through the axial-flow compressor. Air then leaves the compressor under high pressure.  Jet pumps get their name from the way they move fluid. They operate on the principle that a high-velocity fluid will carry along any other fluid it passes through. Most jet pumps send a jet of steam or water through the fluid that needs to be moved. The jet carries the fluid with it directly into the outlet pipe and, at the same time, creates a vacuum that draws more fluid into the pump. The amount of fluid carried out of most jet pumps is several times the amount in the jet itself. Jet pumps can be used to raise water from wells deeper than 60 meters. In such cases, a centrifugal pump at ground level supplies water for a jet at the bottom of the well. The jet carries well water with it back up to ground level. Jet pumps are also used in high vacuum diffusion pumps to create a vacuum in an enclosed area. In high vacuum diffusion pumps, a high-velocity jet of mercury or oil vapor is sent into the enclosed area. The vapor molecules collide with the molecules of air and force them out the outlet port.  Electromagnetic pumps are used chiefly to move liquid sodium and liquid potassium, which serve as coolants in nuclear reactors. These pumps consist of electrical conductors and magnetized pipes. The conductors send current through the fluid, which thereby becomes an electromagnet. The fluid is then moved by the magnetic attraction and repulsion (pushing away) between the fluid's magnetic field and that of the pipes. The fluid is therefore moved in an electromagnetic pump in much the same way as an armature is moved in an electric motor. Positive displacement pumps  Rotary pumps are the most widely used positive displacement pumps. They are often used to pump such viscous (sticky) liquids as motor oil, syrup, and paint. There are three main types of rotary pumps. These types are: (1) gear pumps, (2) lobe pumps, and (3) sliding vane pumps.  Gear pumps consist of two gears that rotate against the walls of a circular housing. The inlet and outlet ports are at opposite sides of the housing, on line with the point where the teeth of the gears are fitted together. Fluid that enters the pump is trapped by the rotating gear teeth, which sweep the fluid along the pump wall to the outlet port.  Lobe pumps operate in a manner similar to gear pumps. However, instead of gears, lobe pumps are equipped with impellers that have lobes (rounded projections) fitted together. Lobe pumps can discharge large amounts of fluid at low pressure. Sliding vane pumps consist of a slotted impeller mounted off-center in a circular housing. Sliding vanes (blades) move in and out of the slots. As the vanes rotate by the inlet port, they sweep up fluid and trap it against the pump wall. The distance between the impeller and the pump wall narrows near the outlet port. As the fluid is carried around to this port, the vanes are pushed in and the fluid is compressed. The pressurized fluid then rushes out the outlet port.  Reciprocating pumps consist of a piston that moves back and forth within a cylinder. One end of the cylinder has an opening through which the connecting rod of the piston passes. The other end of the cylinder, called the closed end, has an inlet valve or an outlet valve, or both, depending on the type of pump. In some reciprocating pumps, the inlet valve or the outlet valve is on the piston. Common reciprocating pumps include lift pumps, force pumps, and bicycle tire pumps.  Lift pumps draw water from wells. In a lift pump, the inlet valve is at the closed end of the cylinder and the outlet valve is on the piston. As the piston is raised, water is drawn up through the inlet valve. As the piston moves down, the inlet valve closes, forcing water through the outlet valve and up above the piston. As the piston is raised again, the outlet valve closes and the water is lifted to an opening, where it leaves the pump. At the same time, more water is drawn through the inlet valve. It is theoretically possible for a lift pump to raise water in a well almost 10 meters. However, because of leakage and resistance, a lift pump cannot raise water that is deeper than about 7.5 meters.

This work on basis of literary studies and analysis of the author are examined the principle of action and some characteristics of the medical gear pump. Below are shown the ways to determine the basic parameters of these dispensers. There have been some experimental studies on these characteristics.

The aim of this project is to design a positive displacement rotary pump for small scale applications. The design is in such a way that it combines the advantages of both rotodynamic and positive displacement pumps. Currently available centrifugal pumps cannot attain high heads, and reciprocating pumps are less efficient and requires much space. When centrifugal pump is used as a jet pump, it delivers fluids at a high head, but in the expense of efficiency. To overcome these negatives of currently available pumps, a new design of a rotary type positive displacement pump is developed. This design imitates the working of a normal reciprocating pump, but in a rotary action. This consumes less space compared to a reciprocating pump of same capacity. The main part of the pump is a cam which is mounted on a rotating shaft that rotates in a cylindrical casing. The cam is designed in such a way that it always maintains contact with the walls of the casing as it rotates. A spring loaded blade acts as the cam follower and moves in an accurately machined slot in the casing. The blade and the slot are of rectangular cross section. This blade separates suction and delivery sides of the pump. Inlet and outlet ports are placed on either sides of this blade. This pump does not require inlet and outlet valves. The discharge from the pump is continuous. It also eliminates the crank and connecting-rod mechanisms and delivers a smooth operation.