1) ABSTRACT
The project which we undertook was based on the study of a gear pump & its manufacturing process. The project is study material type project. In that we are having a working model of gear pump. We are studying the principle of working, manufacturing process & its application. Based on this study, we are making a report which will be benefited to students who will study the subject INDUSTRIAL FLUID POWER. Working model is useful in our laboratory & useful for better understanding the working of gear pump to the student in future.

Chapter 1 BASICS OF PUMPS
1. INTRODUCTION
1.1 What are pumps and pumping systems?

Pump is a device which is used to pumping the fluid at various heights. It is similar to the heart in the human body. A hydraulic pump is a mechanical device which converts mechanical energy into hydraulic energy. It provides the force necessary to move a liquid, thus transmitting power. Pumping systems account for nearly 20% of the world’s electrical energy demand and range from 25-50% of the energy usage in certain industrial plant operations.

Pumps have two main purposes:
 Transfer of liquid from one place to another place (e.g. water from an underground aquifer into a water storage tank)
 Circulate liquid around a system (e.g. cooling water or lubricants through machines and equipment) The main components of a pumping system are:
 Pumps (different types of pumps are explained in section 2)
 Prime movers: electric motors, diesel engines or air system
 Piping, used to carry the fluid
 Valves, used to control the flow in the system
 Other fittings, controls and instrumentation
 End-use equipment, which have different requirements (e.g. pressure, flow) and therefore determine the pumping system components and configuration.
 Examples include heat exchangers, tanks and hydraulic machines.

Fig. Pumping System

2. TYPE OF PUMPS This section describes the various types of 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 positive displacement pumps (Figure 1).

2.1. Positive displacement pumps Positive displacement pumps are distinguished by the way they operate: liquid is taken from one end and positively discharged at the other end for every revolution. Positive displacement pumps are widely used for pumping fluids other than water, mostly viscous fluids. They have fixed displacement. Widely used in the hydraulic systems. A positive displacement pump is one that displaces (delivers) the same amount of liquid for each rotating cycle of the pumping element. Constant delivery during each cycle is possible because of the close-tolerance fit between the pumping element and the pump case. That is, the amount of liquid that slips past the pumping element in a positive displacement pump is minimal and negligible compared to the theoretical maximum possible delivery. The delivery per cycle remains almost constant, regardless of changes in pressure against which the pump is working. Note that if fluid slippage is substantial, the pump is not operating properly and should be repaired or replaced. Positive displacement pumps can be of either fixed or variable displacement. The output of affixed displacement pump remains constant during each pumping cycle and at a given pump speed. The output of a variable displacement pump can be changed by altering the geometry of the displacement chamber. Other names to describe these pumps are hydrostatic for positive displacement and hydrodynamic pumps for non-positive displacement. Hydrostatic means that the pump converts mechanical energy to hydraulic energy with comparatively small quantity and velocity of liquid. In a hydrodynamic pump, liquid velocity and movement are large; output pressure actually depends on the velocity at which the liquid is made to flow.
Positive displacement pumps are further classified based upon the mode of displacement:
 Reciprocating pump In the Reciprocating pumps displacement is by reciprocation of a piston plunger. Reciprocating pumps are used only for hydraulic circuits, pumping viscous liquids and oil wells.
e.g. swash plate type pumps, bent axis pump
 Rotary pumps The displacement is by rotary action of a gear, cam or vanes in a chamber of diaphragm in a fixed casing. Rotary pumps are further classified such as internal gear, external gear, lobe and slide vane etc. These pumps are used for special services with particular conditions existing in industrial sites. E.g. gear pumps, vane pump, lobe pump etc. In all positive displacement type pumps, a fixed quantity of liquid is pumped after each revolution. So if the delivery pipe is blocked, the pressure rises to a very high value, which can damage the pump.
2.2 Dynamic pumps Dynamic pumps are also characterized by their mode of operation: a rotating impeller converts kinetic energy into pressure or velocity that is needed to pump the fluid. A non-positive displacement pump produces a continuous flow. However, because it does not provide a positive internal seal against slippage, its output varies considerably as pressure varies. Centrifugal and propeller pumps are examples of non-positive displacement pumps. If the output port of a non-positive displacement pump were blocked off, the pressure would rise, and output would decrease to zero. Although the pumping element would continue moving, flow would stop because of slippage inside the pump. In a positive-displacement pump, slippage is negligible compared to the pump’s volumetric output flow. If the output port were plugged, pressure would increase instantaneously to the point that the pump’s pumping element or its case would fail (probably explode, if the drive shaft did not break first), or the pump’s prime mover would stall.

There are two types of dynamic pumps:
 Centrifugal pumps These are the most common pumps used for pumping water in industrial applications. Typically, more than 75% of the pumps installed in an industry are centrifugal pumps. For this reason, this pump is further described below.

 Special effect pumps are particularly used for specialized conditions at an industrial site.

How a centrifugal pump works
A centrifugal pump is one of the simplest pieces of equipment in any process plant. Figure below shows how this type of pump operates:
 Liquid is forced into an impeller either by atmospheric pressure or in case of a jet pump by artificial pressure.
 The vanes of impeller pass kinetic energy to the liquid, thereby causing the liquid to rotate. The liquid leaves the impeller at high velocity.
 The impeller is surrounded by a volute casing or in case of a turbine pumps a stationary diffuser ring. The volute or stationary diffuser ring converts the kinetic energy into pressure energy.

Fig. Working & details centrifugal pump

Chapter 2 GEAR PUMPS
1. INRODUCTION Gear pumps are widely used in various hydraulic system used in the industries, by rotating the gear by external source creating the vacuumed pressure fluid is taken in by suction port & then delivered outside at constant pressure. gear pump is a positive displacement (PD) type of pump generally used for the transfer and metering of liquids. The pump is so named because it has two gears that are side-by-side or external to each other. (This nomenclature differentiates it from an internal gear pump, which has one gear positioned inside the other.) The gear pump is a precision machine with extremely tight fits and tolerances, and is capable of working against high differential pressures.

2. WORKING PRINCIPLE The working principle of the external gear pump is illustrated in Figure 1. A drive gear (that is driven by a motor) rotates an idler gear in the opposite direction. When the gears rotate, the liquid, which is trapped in the gear teeth spaces between the housing bore and the outside of the gears, is transferred from the inlet side of the pump to the outlet side. It is important to note that the pumped liquid moves around the gears and not between the gears. The rotating gears continue to deliver a fresh supply of liquid from the suction (inlet) side of the pump to the discharge (outlet) side of the pump, with virtually no pulsations. The meshing of the gears on the discharge side of the pump forces the liquid out of the pump and into the discharge piping. Pump forces the liquid out of the pump

3. TYPES OF GEAR PUMP
A. EXTERNAL GEAR PUMP
B. INTERNAL GEAR PUMP

A. EXTERNAL GEAR PUMP This pump is as shown in above fig. Gear pumps can be divided into external and internal gear types. A typical external gear pump is shown in Figure These pumps come with a straight spur, helical, or herringbone gears. Straight spur gears are easiest to cut and are the most widely used. Helical and herringbone gears run more quietly, but cost more. A gear pump produces flow by carrying fluid in between the teeth of two meshing gears. One gear is driven by the drive shaft and turns the idler gear. The chambers formed between adjacent gear teeth are enclosed by the pump housing and side plates (also called wear or pressure plates). A partial vacuum is created at the pump inlet as the gear teeth un mesh. Fluid flows in to fill the space and is carried around the outside of the gears. As the teeth mesh again at the outlet end, the fluid is forced out. Volumetric efficiencies of gear pumps run as high as 93% under optimum conditions. Running clearances between gear faces, gear tooth crests and the housing create an almost constant loss in any pumped volume at a fixed pressure. This means that volumetric efficiency at low speeds and flows is poor, so that gear pumps should be run close to their maximum rated speeds. Although the loss through the running clearances, or “slip,” increases with pressure, this loss is nearly constant as speed and output change. For one pump the loss increases by about 1.5 gpm from zero to 2000 psi regardless of speed. Change in slip with pressure change has little effect on performance when operated at higher speeds and outputs. External gear pumps are comparatively immune to contaminants in the oil, which will increase wear rates and lower efficiency, but sudden seizure and failure are not likely to occur.

B. INTERNAL GEAR PUMP Internal gear pumps, Figure below, have an internal gear and an external gear. Because these pumps have one or two less teeth in the inner gear than the outer, relative speeds of the inner and outer gears in these designs are low. For example, if the number of teeth in the in neared outer gears were 10 and 11 respectively, the inner gear would turn revolutions, while the outer would turn10. This low relative speed means a low wear rate. These pumps are small, compact units Fig. external gear pump & internal gear pump