DESIGN AND FABRICATION OF WATT AND PORTER GOVERNOR
The aim of our project is to develop prototype of a product “watt and porter governor”. The function of the governor is to maintain the speed of an engine within specified limits whenever there is a variation of load. It is a dynamic device done in the field of manufacturing technology. It's rather
inexpensive and can be used in almost all vehicles. The governor generally consists of a sleeve which is attached to a throttle valve. When the sleeve reaches its lowest position, the engine should develop
maximum power. On the sudden removal of load its sleeve should reach the top most position at once. Its sleeve should float at some intermediate position under normal operating conditions.
When the load on an engine increases or decreases, obviously its speed will respectively decrease or increase to the extent of variation of load. This variation of speed has to be controlled by the governor, within small limits of the mean speed. This necessities that when the load increases and consequently the speed decreases, the supply of fuel to one engine has to be increased accordingly, to compensate for the loss of the speed, so as to bring back the speed close to the mean speed. Conversely when the load decreases, and the speed increase, the supply of fuel has to be reduced. This implies that the governor should have its mechanism working in such a way, that the supply of
fuel is automatically regulated according to the load requirement for maintaining approximately a constant speed.
|DESIGN AND FABRICATION OF WATT AND PORTER GOVERNOR|
A governor, or speed limiter, is a device used to measure and regulate the speed of a machine, such as an engine. A classic example is the centrifugal governor, also known as the watt or fly-ball governor, which uses weights mounted on spring-loaded arms to determine how fast a shaft is spinning, and
then uses proportional control to regulate the shaft speed. Centrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. Early steam engines
employed a purely reciprocating motion, and were used for pumping water – an application that could tolerate variations in the working speed. It was not until the Scottish engineer James Watt introduced the rotative steam engine, for driving factory machinery, that a constant operating speed became necessary.
Between the years 1775 and 1800, Watt, in partnership with industrialist Matthew Bolton, produced some 500 rotati-ve beam engines. At the heart of these engines was Watt‟s self-designed "conical pendulum" governor: a set of revolving steel balls attached to a vertical spindle by link arms, where the controlling force consists of the weight of the balls.
Building on Watt‟s design was American engineer Willard Gibbs who in 1872 theoretically analyzed Watt‟s conical pendulum governor from a mathematical energy balance perspective. During his graduate school years at Yale University, Gibbs observed that the operation of the device in practice was beset with the disadvantages of sluggishness and a tendency to over correct for the changes in speed it was supposed to control.
(i) A governor, or speed limiter, is a device used to measure and regulate the speed of a machine, such as an engine. A classic example is the centrifugal governor, also known as the Watt governor, which uses weights mounted on loaded arms to determine how fast a shaft is spinning, and then
uses proportional control to regulate the shaft speed. The watt governor is named after James Watt who used it for steam engines. James Watt designed his first governor in 1788 following a suggestion from his business partner Matthew Boulton. It was a conical pendulum governor and one of the final
series of innovations Watt had employed for steam engines. James Watt never claimed the centrifugal governor to be an invention of his own.
Centrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. It is therefore a misunderstanding that James Watt is the inventor of this device.
(ii) A giant statue of Watt's governor stands at Smethwick in the English West Midlands. It is known as the fly ball governor.
(iii) Another kind of centrifugal governor consists of a pair of masses on a spindle inside a cylinder, the masses or the cylinder being coated with pads, somewhat like a drum brake. This is used in a spring-loaded record player and a spring-loaded telephone dial to limit the speed.
(iv) The major advantage of the governors is rather inexpensive and highly efficient.
CLASSIFICATION OF GOVERNORS:
The governors may, broadly, be classified as
1. Centrifugal governor
2. Inertia governor
Governors may further be classified as follows:
1. Pendulum type (Watt governor)
2. Loaded type
A frame is a structural system that supports other components of a physical construction.
A spindle is a rotating axis of the machine, which often has a shaft at its heart. The shaft itself is called a spindle, but also, in shop-floor practice, the word often is used metonymically to refer to the entire rotary unit, including not only the shaft itself, but its bearings and anything attached to it.
An electric motor converts electrical energy into mechanical energy. Most electric motors operate through interacting magnetic fields and current carrying conductors to generate force, although electrostatic motors use electrostatic forces.
The sleeve valve is a type of valve mechanism for piston engines, distinct from the more common poppet valve.
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can
A ruler, sometimes called a rule or line gauge, is an instrument used in geometry, technical drawing, printing and engineering/building to measure distances and/or to rule straight lines.
The Watt governor is a simple governor but is not terribly accurate where very fine control of speeds in needed and so was super ceded in many applications by more specialized and accurate governors, however for many agricultural end pumping engines where absolute speed was not essential it survived and can still be seen on numerous preserved engines.
(i) Power supply
(ii) 230 V AC, Single phase, Variac.
(i) Spindle: Stainless Steel
(ii) Fly balls: Cast Iron
(iii) Arms: Stainless steel
(iv) Frame: Mild steel
The function of the governor is to regulate the mean speed of an engine, when there are variations in the load .e.g. when the load on an engine increases, its speed decreases therefore it becomes necessary to increases the supply of working fluid .On the other hand, when the load on the engine decreases, its speed increases and thus less working fluid is required. The governor
automatically controls the supply of the working fluid to the engine with the varying load conditions and keeps the mean speed within certain limits.
A little consideration will show ,that when the load increases ,the configuration of the governor changes and a valve is moved to increase the supply of the working fluid ; conversely , when the load decreases , the engine speed increases and the governor decreases the supply of working fluid.
Probably the most widely used governor in the early days; it is named the watt governor because James Watt applied it to his early beam engines. He did not however invent it as it had been in use on wind and water mills many years before this. A belt or gearing from the engine crankshaft drives the input shaft 'm' causing the bevel gears 'l' to revolve and in turn rotate the vertical shaft
'a'. The bracket 'b' at the top of 'a' supports two arms 'c' which are pivoted at the top, at the end of the arms are two very heavy metal weights 'B' partway along the arms 'c' are fixed two pivoted link arms 'd'which link to a collar 'c' which rotates with them but is able to slide up and down shaft 'a'.
|WORKING OF WATT AND PORTER GOVERNOR|
The up and down motion of this collar is followed by a pair of pins 'f' which move a bell crank 'g' which is in turn linked to a throttle actuating rod 'I' linked to a throttle or butterfly valve in the supply of steam to the engines cylinder which can allow more or less steam through.
At rest the governor weights are held in the lowest position by gravity, the throttle will be in its most open position. As the engine speed increases these weights rotate faster until centrifugal force exceeds that of gravity and they fly further outwards and as a result of the linkages, upwards, this movement is transmitted to the throttle valve which begins to close. The faster the governor is
driven the further out the weights move and the more the throttle is closed, until the amount of steam it lets through balances the demand and the engine speed stabilizes.
FABRICATION OF PORTER GOVERNOR
Fabrication as an industrial term refers to building metal structures by
cutting, bending and assembling.
The fabrication of porter governor involves:
i. Turning operation in lathe. (spindle)
ii. Threading operation in lathe.( Spindle)
iii. Drilling holes in porter arms, frame and dead weight.
iv. Step turning of sleeve.
v. Cylindrical grinding for good surface finish.
vi. Welding operation. (Frame and Arms).
vii. Gas cutting of frame.
The fabrication of the components is similar to that of the watt governor. As the Dead weight is the only inclusion to watt governor setup.
(i) On aircraft propellers the governor senses shaft rpm, and adjusts or controls the angle of the blades to vary the torque load on the engine. Thus as the aircraft speeds up (as in a dive) or slows (in climb) the RPM is held constant.
(ii) Centrifugal flyweight mechanism driven by the engine is linked to the throttle and works against a spring in a fashion similar to that of the pneumatic governor, resulting in essentially identical operation.
(iii) Pneumatic governor. However, the centrifugal design is more sensitive to speed changes and hence is better suited to engines that experience large fluctuations in loading.
(iv) Electronic servo motor is linked to the throttle and controlled by an electronic module that senses engine speed by counting electrical pulses emitted by the ignition system or a magnetic pickup. The frequency of these pulses varies directly with engine speed, allowing the control module to apply a proportional voltage to the servo to regulate engine speed. Due to their sensitivity and rapid response to speed changes, electronic governors are often fitted to engine-driven generators designed to power computer hardware, as the generator's output frequency must be held within narrow limits to avoid malfunction.