Design of Spur Gear, Material, Beam Strength

Design of Spur Gear

Design of Spur Gear: Spur gears are used in machines, Design of gear for any machine is essential. Gear is defined as toothed wheels or multilobed cams.
Gear used to transmit power and motion from one shaft to another shaft by means of successive engagement of teeth.
Today we will discuss the Design of spur gear. Design means to develop a satisfactory solution for a given problem.
Let’s see why we need to design gear? There are lots of gears in every automatic or conventional machine; they work based on transfer motion and power from one component to another component.
See also : Zeroth Law of Thermodynamics
Automatic machines have a high degree of accuracy in the range of some micron, Gears are used in the mechanism to smooth the operation. Thus it must be designed well.

Design of Spur Gear according to Beam strength (Lewis equation)

Before I start, let's see the force acting at gearing action.

Force analysis in Spur Gear

Force analysis in Spur GearFrom the above figure, here Pt is tangential force, Pr is the radial force, and Pn is a normal force to the tooth gear.
Pt=Pncosa and Prsina
Pr=Pttana
Gear drive is generally specified by
·       Power to be transmitted
·       Speed of driving shaft
·       Velocity ratio
Power is transmitted by means of force exerted by the tooth of the driving gear on the matting teeth of the driven gear.
According to the law of gearing, this exerted force Pn is always normal to the tooth surface and acts along the pressure angle line.
Power P=Pt*V and Torque T=Pt*(D/2)

Number of teeth

In the Design of spur gear it is require to decide number of teeth on pinion and gear.
Minimum number of teeth to avoid interference is given by
Zmin=2/sin2a
Once the number of teeth is decided on pinion, the number of teeth on gear can be calculated from the velocity ratio. 
In Lewis equation Gear the tooth is treated as a cantilever beam as shown in the figure.
The tangential component causes a bending moment about the base of the tooth.

Lewis equation is based on the following assumptions


  • Bending stress due to the radial component is negligible.
  • Tangential component is uniformly distributed over the face of the width of gear.
  • Stress concentration is negligible.
  • Only one pair of teeth in contact.

Sigmab=(MY/I) , P=mbSigmabY
Y=Lewis form factor
Y=(t2/6hm)
The beam strength is the maximum value of tangential force that the tooth can transmit without bending.
Sb=mbSigmabY
In the Design of spur gear, it is require to decide weaker between pinon and gear.
Is is observed that the module and face width are same for the pinion and gear.
When same material used for the pinion and gear, the pinion is always weaker than gear.

Design of Spur Gear as per Wear Strength

Design of Spur Gear as per Wear Strength
Failure of the gear tooth due to pitting occurs when contact stress between two meshing exceeds the surface endurance limits of the material.
The analysis of wear strength was done by Buckingham.
The equation is below
SigmaC=Maximum value of compressive strength.
P=force pressing the cylinder.
b=half width of deformation.
l=axial length of the cylinder.
d1,d2= diameters of cylinders.
E1,E2= Modulus of Elasticity


FAQs

What is the Zeroth law of thermodynamics? Application, Examples


Zeroth law of thermodynamics
  1. What is the Zeroth law say?
  2. Laws of thermodynamics, zeroth first, second, third
  3. Statement of Zeroth Law
  4. Zeroth law Examples
  5. Conclusion

What is the Zeroth law say?

Zeroth law of thermodynamics: let's discuss the zeroth law of thermodynamics. It is the most fundamental law of thermodynamics. as a student, we must learn it in-depth and understand in importance 

Thermodynamics is a tricky subject that must be studied in chemistry, physics, engineering, and many other courses of academic study.

It has an incredible impact on the behavior of matter and energy.

Thermodynamic concepts may seem impossible to understand. If you go over the basics enough times, they start to make sense.

You can continue to learn more about the subject, as needed for your field of study or level of desired knowledge.

Laws of thermodynamics, zeroth first, second, third

We will begin our analysis with the infamous laws of thermodynamics. Just like Newton's laws of motion, there is a first, second, and third law.

Later in the development of the field. New, more fundamental law was added and dubbed the zeroth law.

The zeroth law of thermodynamics deals with thermal equilibrium.

Statement of Zeroth Law

It states that heat always flows in the direction of the hot object to a colder one.
, which as we recall, describes a situation in which there is no net heat flow between two systems.

Zeroth law Examples

zeroth law of thermodynamics example
The zeroth law states that if two systems are in thermal equilibrium with a third system, then those two systems are also in thermal equilibrium with each other.

In other words, if A is in thermal equilibrium with B, which is in thermal equilibrium with C, then A and C are also in equilibrium.

This may seem like a trivial statement, but it is an important one because it means that two objects at the same temperature will not exhibit heat flow when they come into contact with one another. This marks temperature as the indicator of thermal equilibrium.

If two objects are in thermal equilibrium with thermometers that read the same temperature, the objects will be in thermal equilibrium with each other, which therefore allows us to gather all kinds of thermodynamic data in our laboratories.

In studying thermodynamics, we must also learn certain definitions. We will want to be able to define a system as the collection of objects.

We are examining while the surroundings represent the environment surrounding the system, which is technically the rest of the universe. Some systems allow heat to flow in and out.

These systems have diathermal walls. Some systems do not allow heat to flow in and out. These systems have adiabatic walls.

No system can be truly adiabatic, but it is a useful approximation when we do calculations involving systems that permit only negligible heat transfer. With these definitions out of the way, we can move on to the first law of thermodynamics.

Conclusion

let's conclude what we learned about zeroth law, it is the fundamental law that stats about the thermal equilibrium state.

Basics of thermodynamics, zeroth, first, second, third law of thermodynamics, open system and closed systems

Basics of thermodynamics,  zeroth, first, second, third law of thermodynamics, open system and closed systems
Thermodynamics is a science dealing with energy and its transformation. The basic of thermodynamics is deals with the equilibrium and feasibility of a process.

Table of Content
  • What is Thermodynamics?
  • What is the importance of thermodynamics?
  • Laws of Thermodynamics :
  • Different Approaches to thermodynamics
  • What is System in thermodynamics?

    What is Thermodynamics?

    Thermodynamics is a science dealing with energy and its transformation.
    It deals with the equilibrium and feasibility of a process.

    It also deals with relations between heat and work and the properties of a system.

    What is the importance of thermodynamics?

    The main task of an engineer is to ensure optimum use of the resources-space, time, energy, and matter. Therefore, an engineer deals with the design and development of new processes and with the improvement of the existing processes. Before undertaking an expensive project, an engineer must know the answers to the following types of questions.
    • Is the proposed chemical reaction or physical process possible?
    • Does the reaction process go to completion, or does it proceed to a certain extent only beyond which it cannot proceed?
    • What factors govern the extent of reaction or equilibrium?
    • How much energy is required for the process to take place?
    • What is the maximum efficiency of a heat engine or the maximum coefficient of performance of a refrigerator?
    • Thermodynamics provides answers to the above types of questions.
    Also, Read

    Laws of Thermodynamics :

    Zeroth law of thermodynamics

    It deals with thermal equilibrium state and basis for measure temperature. It also gives the concept of Isotherms.

    The first law of thermodynamics

    It tells about the conversation of energy and introduces the concept of internal energy.

    The second law of thermodynamics

    It dictates the limits of converting internal energy into work and introduces the concept of entropy. It also gives ide whether a particular process is feasible or not.

    Third law of thermodynamics

    It provides a datum for the measurement of entropy.
    1. The laws of thermodynamics cannot be directly proved. They were deduced from experimental results through logical reasoning.
    2. The validity of the laws of thermodynamics rests upon the fact that, to date, no experimental evidence is available to disprove them.

    Different Approaches to thermodynamics

    There are two different approaches to the study of thermodynamics. They are macroscopic and microscopic.

    Macroscopic

    1. The structure of matter is not considered.
    2. Only a few variables are used to describe the state of matter.
    3. The values of these variables can be measured.
    4. Classical thermodynamics adopts the macroscopic approach.

    Microscopic

    1. Knowledge of the structure of mater is essential.
    2. A large number of variables are needed to describe the state of matter.
    3. The values of these variables cannot be measured.
    4. Statistical thermodynamic adopts the microscopic approach.

    In the macroscopic approach, fluids are treated as continuous rather than made up of several individual particles.

    The macroscopic approach is not valid in situations where very few molecules are involved or where the the behavior of individual particles is sought.

    As an illustration, consider the pressure of gas exerts on the walls of its container. This pressure results from the change of momentum of the molecules as they collide with the wall. However, from a macroscopic point of view, we are not concerned with the action of the individual molecules but with the time average force on a given area, which can be measured by a pressure gauge. In fact, macroscopic observations are entirely independent of assumptions regarding the nature of the matters.

    What is System in thermodynamics?

    In the scientific analysis, it is essential to clearly identify the subject matter of analysis on which we focus our attention. In mechanics, a part of the body is isolated from the rest of the universe, and we draw a free body diagram and analyze the motion by applying Newton's laws of motion. Similarly, in thermodynamics, also we identify the subject of analysis by term thermodynamics system or System for Simplicity to specify the matter on which we focus our attention.
    What is System in thermodynamics?
    A system is a definite quantity of matter bounded by some surface, which separates it from the rest of the world.

    The boundary surface may be real or imaginary. It may change in shape and size. A System may be very simple like a gas contained in a cylinder, or it may be complex like a thermal power plant. The choice of a system may differ from the person performing the analysis. Sometimes the System is also referred to as control mass.

    Surroundings

    The combination of matter and space external to the System constitutes the surroundings.

    For all practical purposes, that part of the Surroundings where the effects due to interaction between a system and its surroundings are not detectable and need not be considered.

    A system can exchange energy in the form of work and heat with its surroundings. A system that is enclosed by an adiabatic boundary cannot exchange energy as heat with its surroundings.

    Isolated System in thermodynamics

    A system that is enclosed by a rigid and adiabatic boundary cannot exchange energy either as heat or work with its surroundings. Such a system is called an isolated system.
    Isolated system in thermodynamics
    In this System, neither the mass to the energy crosses the boundaries of the System.

    Closed System in thermodynamics

    The closed system is one in which the boundaries are closed so that no substance be may enter or leave the System.
    Closed system in thermodynamics
    In such a system, the mass of the substance within the system remains constant.
    A transfer of energy may, however, take place at the boundaries.

    Open System in thermodynamics

    The open System is one, the boundaries of which are not closed but have one or more openings through which mass transfer may also take place in addition to energy transfer.
    Open system in thermodynamics
    If the rate of mass and energy transfer concerning time is constant, the System is known as a steady flow system.

    Also, Read
    Thermodynamics Books | Thermal Engineering Books

What is the difference between Centrifugal Pump and Reciprocating Pump? | difference of cf pump and rc pump

What is the difference between Centrifugal Pump and Reciprocating Pump | difference of cf pump and rc pump
What is the difference between Centrifugal Pump and Reciprocating Pump? the difference of cf pump and RC pump: CF Pump and RC Pump, They are widely used in Industry. Pumps are used to transmitting liquid from one place to another place or from one height to another height.

Types of Pump used in Industry are based on the requirement of lifting a particular liquid. Centrifugal Pump and Reciprocating Pump are used according to its functions like types of liquid to be lifted, the viscosity of liquids, manometric head, require pressure head at the outlet, etc....

Here is the comparison between Centrifugal Pump and Reciprocating Pump

Centrifugal Pump Vs Reciprocating Pump

Centrifugal Pump

  1. The discharge is continuous and smooth
  2. It can handle a large quantity of liquid.
  3. It can be used for lifting highly viscous liquids.
  4. It is used for large discharge through smaller heads.
  5. The cost of a centrifugal pump is less as compared to the reciprocating pump.
  6. Centrifugal pump runs at high speed. They can be coupled to an electric motor.
  7. The operation of a centrifugal pump is smooth and without much noise. The maintenance cost is low.
  8. Centrifugal pump needs smaller floor area and installation cost is low.
  9. Efficiency is high.
  10. It uses an impeller for transferring energy to fluid and increases fluid pressure.
  11. In a centrifugal pump, priming is required. Without the priming water or liquid can not be transmitted.
  12. Centrifugal pump is non-postive displacement type pump.
  13. It used where higher discharge available at a low head.

Reciprocating Pump

  1. The discharge is fluctuating and pulsating.
  2. It handles a small quantity of liquid only.
  3. It is used only for lifting pure water or less viscous liquids.
  4. It is meant for small discharge and high heads.
  5. The cost of a reciprocating pump is approximately four times the cost of a centrifugal pump.
  6. Reciprocating pump runs at low speed. Speed is limited due to the consideration of separation and cavitation.
  7. The operation of a reciprocating pump is complicated and with much noise. The maintenance cost is high.
  8. The reciprocating pump requires a large floor area and installation cost is high.
  9. Efficiency is low.
  10. It uses a piston and cylinder which causes partial pressure on the fluid, and owing to fluid is sucked from the sump.
  11. Priming is not required in a reciprocating pump.
  12. The reciprocating pump is a positive displacement type pump.
  13. It used where lower discharge available at the high head.

Comparison or difference of cf pump and RC pump

What is the difference between Centrifugal Pump and Reciprocating Pump ? difference of cf pump and rc pump

All Boiler Mountings with its Functions , Construction, Working Principle, Advantages and Disadvantages , Uses

All Boiler Mountings with its Functions , Construction, Working Principle, Advantages and Disadvantages , Uses

Boiler Mountings

These are different fittings and devices which are necessary for the operation and safety of a boiler. These devices, usually are mounted over the boiler shell. According to I.B.R, the following mountings should be fitted to the boilers
  • Two safety valves
  • Two water level indicators
  • A pressure gauge
  • A steam stop valve
  • A feed check valve
  • A blow-off cock
  • A manhole
  • Mud holes or sight holes.
  • Fusible plug
Lancashire and Cornish type Boilers should be fitted with high pressure and low water safety valve.
All land boilers should have a fusible plug in each furnace.
The various mountings are discussed as follows:

1. Water level indicator

Water level indicator
Function:- The function of a water level indicator is to indicate the level of water in the boiler constantly.

Construction: Fig shows the details of a water level indicator. It is fitted on all types of boiler. It is fitted at the front end of the boiler so that it is visible to the operator.

AB is the front end plate of the boiler. W is the boiler water level. Fig shows Hopkinson's water gauge. F is a strong glass tube covered with a tough or guard glass (L) for protection, It indicates the water level. It is connected to the boilerplate, through stuffing boxes in hollow gunmetal castings (B and C). X and Y The flanges used for bolting the plate. 

Plate AB is provided with holes with inside threading for screwing these castings. The upper casting communicates with the steam space of the boiler. The lower casting communicates with the water space. These two passages are controlled by two cocks D and E These passages are open when the handles of these cocks are vertical (See Fig) A hollow gun metal column or tube G is provided in the center of the hollow gun-metal castings. This column is fitted with third cock K. It is known as drain cock or blows through cock. When the handle of this cock is vertical it is closed. H and J are two hollow gun-metal balls. Balls H and J are in the positions shown by a full circle when the gauge is in the normal working condition M, N, P and R are screwed plugs. They are provided to clean out, when necessary, of the tube and castings.

Working:- When the cocks D and E are opened, steam rushes from the upper passage in B and water rushes from the lower passage in C to the glass tube F. Both of them adjust their levels. This will indicate the level of water in the boiler. In hollow gun-metal column G, the water also stands at the same level.

In case, glass tube F gets broken, the steam will rush from the upper passage and the water from the lower passage because of the pressure difference between boiler pressure and atmospheric pressure. This water carries the hollow gun-metal ball J from its normal position to the position shown by a dotted circle (see Fig.) This will close the passage of water to the glass tube. Now the water rises in the hollow gun-metal column G. This water aided by the steam rushing through the upper passage will carry the ball H from its seat and placed it to the new position shown by a dotted circle. Hence the supplies both water and steam to the glass tube Fare closed. The glass tube F can be replaced by closing two cocks D and E.

The water level indicator used for high-pressure boiler should be provided with guards made of thick toughened glass which covers the front and sides of the glass tube. The boiler attendant is then protected from the flying fragments of glass when a glass tube bursts.

2. Pressure Gauge

Bouler Mountings Pressure Gauge
Function: The function of pressure gauge is to measure the pressure exerted inside the vessel OR boiler shell.

Construction - Fig shows the details of the construction of the interior of Bourdon's Pressure gauge. This gauge is generally fitted on the front side of the boiler shell. It is fitted to the steam space of the boiler shell with the help of an inverted siphon. It is usually constructed to indicate up to double the maximum working pressure. Its dial is graduated to read pressure in bar gauge (i.e. above atmospheric). The syphon of the gauge is always full of water or condensed steam.

It consists of a Bourdon's spring tube ABC. It is made of copper and bent into a circular shape. This tube has an elliptical section. The end A of the tube is plugged. The other end C is connected to a hollow block E. The lower portion of this block is threaded. The block E has a small opening for the entrance of steam or water from the boiler. The end A is connected to the link R. This is pivoted hinge at H. This carries a toothed sector. This can swing about H. The small pinion meshes with this sector, Pinion carries a pointer P fitted on its spindle. To Indicate the pressure of steam inside the boiler, this pointer moves on a graduated dial or scale. The pressure gauge components are enclosed in a circular dial casing.

Working: The movement of the free end of the elliptical tube is proportional to the difference between external and internal pressure on the tube. Since the outside pressure on the tube is atmospheric, the movement of the free end is a measure of the boiler pressure above atmospheric i.e gauge pressure.

The pressure gauge is connected with the boiler's steam space through U-tube syphon. The U-shaped syphon pipe contains water which fills the Bourdon tube. The pressure of the steam acting through the water on the inside of the tube tries to make the tube circular. One end is fixed, the free end moves. The movement at the free end is proportional to the difference in pressure as shown above. Because of pinion and gear arrangement, the slight movement of the Bourdon tube is magnified considerably and the point gives a maximum deflection that can be read on the scale.

The water in the U-tube syphon prevents the steam from coming in contact with the spring tube. This will reduce overheating and thermal stresses in the spring tube. A three-way cock is provided for connecting the boiler pressure gauge to the steam space.

3. Steam Stop Valve

Boiler Mountings Steam Stop valve
Function: The function of the steam stop valve is to regulate the flow of steam from the steam pipe to the other or from the boiler to the steam pipe.

What is a Junction Valve?

The steam stop valve when directly mounted on the steam space of the boiler shell and connected to the steam pipeline which supplies steam to the prime-mover is called a Junction valve.

Construction - As shown in the figure the flange A of the body is bolted to the boiler at the highest part of the steam space. The seat B is screwed into the body with the help of lugs C cast on its interior. Disc D has a renewable disc seat E. This seat E is screwed on to the disc D. The construction of seat is shown at (a). The valve disc D is connected to the spindle F by the nut H. The lower edge of the nut H is in contact with a collar on a lower end of the spindle. The spindle carries the disc D with it (as it is raised or lowered). But it is free to rotate within the disc.

The spindle passes through a gland and stuffing box (N) in the cover of the body. The upper portion of the spindle is screwed and passes through a nut in the crosshead or yoke P as shown in the figure. To the top of the spindle, a hand wheel M is fitted. The spindle F is square threaded. The nut is mounted over two pillars Q. The valve is operated by a hand wheel (M).

Working: When the hand-wheel is turned in an anticlockwise direction, the spindle is raised up. This will be raised up. This will raise the valve from its seat. Thus a passage for the steam from the clearance between the valve and valve seat is formed. To lower the valve, the handwheel is rotated in a clockwise direction. This rotation will close the passage for steam. This can be regulated by adjusting the position of the valve based on the requirements. Under the normal working condition, the valve is open and steam flows from the boiler to the steam pipe.

4. Feed Check Valve

Function:- It is used to control the supply of water to the boiler and to prevent the escaping of water from the boiler when the pump pressure is less or the pump is stopped.

Construction:- This is a non-return valve placed as near to the boiler as possible.

As shown in the figure, C is the check valve. The lift of the valve is controlled by an extension of the spindle of the screw-down valve V above it. V is the feed valve. A is the flange. It is bolted to the front end of the boiler shell. It is bolted at the point from which an internal pipe leads the feed water. This water is distributed to the boiler. H is the handwheel. This is used to control the positions of the valves. The construction above valve V is similar to that of the steam stop valve.

Working:- Under the normal working condition, the pressure on the feed pump side (connected to elbow E) is more than the boiler side pressure. This pressure difference lifts the check valve C. To allow the feed water to enter the boiler, the feed valve V is lifted manually by the wheel (H) and screw (S). Hence, the feed water may enter the boiler. To control the supply of feed water to the boiler, the position of the feed valve V is controlled. In the event of failure of the feed pump, the pressure on the water sump side reduces. The check valve C will be closed because of higher steam pressure. This will prevent the backflow of water from the boiler to the water sump. The check valve is to be replaced if it does not give satisfactory results. The stuffing box is provided in the valve to stop the leakage at the spindle.

5. Blow off Cock Valve

Functions:
(1) To discharge a portion of water when the boiler is in operation to blow out mud, scale or sediments periodically.

(2) To empty the boiler, when necessary for cleaning, inspection, and repair.

Construction:
It is fitted on the boiler shell directly or to a short branch pipe at the lowest part of the water space. This pipe is known as a blowdown pipe.

The figure shows a blow-off cock. It is very commonly used with all types of boilers. It consists of plug P. This plug P is made of Gunmetal. A rectangular slot is cut in this plug. This plug fits into hollow conical body B. Asbestos packing is provided at the top and bottom in the clearance groove. This plug can be rotated. A Shank S on the yop of the plug passes through the gland and a stuffing box G. Y. is a yoke. It is fitted on the top of the shank S. This yoke keeps the plugin its position with the help of studs T. The top of the shank has a square guide. The wheel is fitted in this square guide.

Working:- To operate the valve, the rectangular slot is brought in line with the passage of the body. This is possible by rotating the plug with the help of a wheel. When the slot is placed in this position, the cock is opened and all the impurities, mud, sediments, etc. start flowing out of the boiler and they are removed. When the slot is brought at right angles to the passage (as shown in Fig.) of the body, the clock is closed.

6. Fusible Plug

Function:- Its function is to protect the boiler against damage due to overheating for low water level.

Where it is fitted?

It is fitted in the crown plate of the furnace or firebox at the appropriate place.

Construction:

A common form of the fusible plug is shown in Fig It consists of a hollow gun-metal plug (A). This body is screwed into the furnace crown (B). The body has a hexagonal flange (E). This is used to tighten the body into the shell. The spanner can be used for fixing or removing it. A gunmetal plug (H) having a hexagonal flange (H) is screwed into the gun-metal body. The second hollow gun-metal plug (C), screwed into body (E) D is a third hollow gunmetal plug as shown in Fig. These two plugs are separated by an annulus of fusible metal (F). The inner surface of (C) and the outer surface of (D) are grooved such that, when fusible mental (F) is poured in (C) and (D) are locked together.

Working - In the normal working conditions of the boiler, the fusible plug is fully submerged underwater. This is so because, under normal conditions, the proper water level is maintained and can be checked by the water level indicator. Under the circumstances, the heat from the fusible plug is being conducted to water. This keeps the fusible metal at an almost constant temperature, much below its melting point. When the water level falls below the fusible plug, the plug gets uncovered from water. The upper portion of the plug gets exposed to the steam space. The steam cannot keep the plug cool. This will overheat the fusible metal The plug falls down along with the fusible metal making a hole. The steam and water, being under pressure immediately reach the firebox and extinguish the fire. The attendant is cautioned against overheating and burning of the fire tubes etc. Before starting the boiler again the operator fixes a new fuse. The fusible plug should be renewed generally after about two years as they are liable to become defective over a long period of use One plug is provided for each furnace.

7. Safety Valves

Function:- It is a device attached to the steam space of the boiler shell, which opens automatically to discharge some steam and to prevent the steam pressure inside the boiler to exceed.

There are four types of safety valves generally fitted on a boiler :
(a) Dead-Weight Safety Valve
(b) Lever-Weight Safety Valve
(c) Spring Loaded Safety Valve
(d) High Steam and low-water safety Valve

The spring-loaded safety valve is used with locomotive and marine boilers. The other types of valves are used with stationary boilers.

7.1 Dead-weight Safety Valve

This valve is used only with the stationary type of boilers. It is the most elementary type of safety valve.
Construction :
The figure illustrates a Dead Weight Safety valve. G is a bottom flange. The flange is directly fitted on the steam space of the boiler shell.

This flange carries a vertical steel pipe C. The steam exerts pressure through this pipe. A is the valve. This valve rests on the valve seat B. This valve seat is fixed to the top of the vertical pipe C. This valve has an enclosed discharge which leads the escaping steam to a pipe, connected to the discharge casing H. This casing carries the steam to a convenient point outside the boiler house.

The valve seat is fixed down by a ring casing M and screws as shown in Fig. (only one screw is shown for conveniences.) The securing ring has feathers S cast on to it which act as guides for the valve A. D is a weight carrier. It is suspended from the top of the valve. The weights E are C.I rings. These rings are enclosed in the Cl. case or cover. The load on the valve consists of (a) weight of the carrier (5) Weight of the rings (c) Weight of the cover. (d) Weight of the valve. This load balances the total steam pressure on the valve when it is blowing off. Two-step screws 'K' on the casing is provided to stop the blowing off of the valve in case the steam pressure is more than the predetermined pressure and the valve lifts from its seat. This is necessary for the event of the rush of wet steam due to priming At P, Pipe is connected for draining the casing

Working: The valve will stick to its sent B, as long as the pressure exerted on the vale A is less than the predetermined value. When the pressure exerted by the steam on the valve becomes more than the predetermined value, the valve is lifted from its seat. This predetermined value of pressure is adjusted by the force acting from above the weights etc. Because of the lifting of the valve, the steam will go to the atmosphere through the discharge pipe H. The valve comes back to its seat when the upward steam pressure is less than the downward force exerted by the weights, etc. This will help to maintain constant pressure inside the boiler shell.

Merits of dead weight safety valve:

1. Simple in design.
2 Give a quite and satisfactory operation.
3. From the pressure adjustment viewpoint, it can not be easily tempered.

Demerits:

1. Unsuitable for any boiler subjected to vibration and movement (ie. Locomotive boiler)

2. Because of the requirement of a large amount of weight to balance steam pressure, this valve is not suitable for use on the high-pressure boiler.

7.2 Lever Loaded Safety Valve:

Boiler Mountings lever safety valve
Construction:- A good design of this type of valve is shown in the figure. The valve consists of a C.I. OR cast steel body B. The flange is required to fit this C.I. body on the boiler with the help of bolts (not shown in figure 6.14). A gun-metal seat S is fixed to the top of the valve body. It is possible to replace the seat as and when required. V is a gun-metal valve. It rests on the seat S. C is a lever made from wrought iron or mild steel. The lever has its fulcrum at F. This lever is loaded by the weight W. The thrust is transmitted to the valve through the short hinged strut R. To prevent corrosion, the pins of the pin joints are made of gunmetal. Alternatively, the holes in the lever are bushed with gun-metal and in that case, the pins are made from mild steel. The pins
must be an easy fit in the lever.

The load W is fixed to the lever by a pin and padlock as shown in the figure. G is a fork It acts as a lateral guide to the lever. This fork G is generally bridged over the lever at the top. This is necessary to prevent the blowing of the valve in the case of in case of breaking of the lever or removal of the weight.

Working:

The valve will close the opening by sticking to its seat S, as long as the upward pressure exerted by the steam on the valve V remains less than the predetermined value adjusted by weights, weight carrier, and lever. When the steam pressure becomes more than this predetermined value, the valve V is lifted from seat S. The leakage will reduce the steam pressure in the boiler. When the upward pressure is of the steam on the valve becomes less than the valve V comes back to its seat.

Use: This type of valve is used only with the stationary types of boilers.

Disadvantages: The disadvantages of this valve are
(i) It is possible of tempering with this valve by placing a piece of wood or metal on the lever under the bridge.
(ii) The effect of a small addition to the weight is magnified considerably in its action on the valve.

7.3 Spring Loaded Safety Valve

Boiler Mountings Spring Loaded Safety Valve
Construction: The valve shown in Fig. was introduced by Mr. John Ramsbottom on British Railways. Hence it is also known as the Ramsbottom safety valve.

As shown in the figure, there are two Valves V of the same size. These valves are placed on their seat in the upper ends of two hollow standards C. These standards are united by bridge B and a flange or base A. This valve is fitted to the steam space of the boiler shell with the help of base A. It is fitted on the top of the boiler, over fire-box. The valves V are held down by the helical spring S. This spring is made of round or square spring steel wire. This spring is in tension. The valve is also held down by lever L. The lever has two pivots P and Q. P is joined to the lever by pin while Q is forged on the lever. These conical pivots rest on two respective valves and force them to remain on their seats.

The upper end of the spring is hooked to an arm R of the lever, midway between the valves. The lower end of the spring is hooked to the shackle D This shackle is fixed to the Bridge as shown in the figure. Two links E are provided in the valve to prevent the valves from being blown away in the event of the spring breaking. These links are provided on either side of the lever. These links are connected with the help of pins as shown in the figure. The lower pin passes through the shackle D while the upper pin passes through a slot in the arm R of the lever. The lever L has an extension to the right. Hence it may be lifted or pull down to test whether the valves are free to act properly or not.

Working:- The valves are lifted from their seats and allow the steam to escape to the atmosphere when the pressure of steam inside the boiler shell exceeds the normal working pressure. The valve will remain in an open position until the pressure falls below the specified limit. The valves are brought back to rest on their seats by the spring force.

Advantages :
(1) It is not affected by jerks and vibrations
(2) Heavyweights are eliminated.
(3) Maintenance and examination are easy.

Disadvantage: As the valve opens the force exerted by the spring increases. This defect is eliminated by using a long spring.

Use: This type of valve is most suitable for portable

Machine Design By VB Bhandari Pdf free Download

Machine Design By VB Bhandari Pdf free Download

[PDF] Machine Design By VB Bhandari Free Pdf Download

What is Machine Design?
Machine design occupies a prominent position in the curriculum of Mechanical Engineering.
Design of Machine Element It consists of applications of scientific principles, technical information and innovative ideas for the development of a new or improved machine.
I know the task of a machine designer is not easy, as a designer, we have to make the proper dimensional element. I remember working as a designer is a lot harder. As a designer one has to think from many sides.

About VB Bhandari Book

In the context of today's technical and social climate, the designer's task has become increasingly difficult.
Today's designer is required to account for many factors and considerations that are almost impossible for one individual to be thoroughly conversant with.
He must have an exclusive competence of his own and a reasonable knowledge of other "instruments."
New to this Machine Design By VB Bhandari Edition
After the publication of the second edition in 2007, it was observed that there was a need to incorporate a broader coverage of topics in the textbook to suit the content of 'Machine Design' syllabi of various universities in our country.
One complete chapter on 'Design of Engine Components' (Chapter 25) and half a chapter on 'Design of Riveted Joints' (Chapter 8) are added to fulfil this requirement.
Design of Engine Components includes cylinders, pistons, connecting rods, crankshafts and valve-gear mechanism. Design of Riveted Joints includes strength equations, eccentrically loaded joints and riveted joints in boiler shells.
I giving you the importance of this edition is changes the style of solving numerical examples. A 'step-by-step' approach is incorporated in all solved cases of the book. It will simplify and clarify the understanding of the examples.
 Download Thermal Engineering/Thermodynamics Books
Key Features of Design Element By VB Bhandari book This book contains two new chapters, namely Design of Riveted Joints and Design of Engine Components. Numerical examples are solved with a step-by-step approach.

Design of Machine Elements Book By V B Bhandari – PDF Free Download

Machine Design By VB Bhandari Pdf free Download
We Can not provide Link for this Book because of Copyright issue. But You Can buy it From Online Store.I have provided you a link of it at below

Chapter Contents By Design Element By VB Bhandari Pdf

1. Introduction 2. Engineering Materials 3. Manufacturing Consideration in Design 4. Design Against Static Load 5. Plan Against Fluctuating Load 6. Power Screws 7. Threaded Joints 8. Riveted and Welded Joints 9. Shafts, Keys and Couplings 10. Springs 11. Friction Clutches 12. Brakes 13. Belt Drives 14. Chain Drives 15. Rolling Contact Bearings 16. Sliding Contact Bearings 17. Spur Gears 18. Helical Gears 19. Bevel Gears 20. Worm Gears 21. Flywheel 22. Cylinders and Pressure Vessels 23. Miscellaneous Machine Elements 24. Statistical Considerations in Design 25. Design of Engine Components.
 Also Download : Mechanics Of solids By SS Bhavikakatti
About the Author of Book
V B Bhandari retired as Professor and Head, Department of Mechanical Engineering at Vishwakarma Institute of Technology, Pune. He holds First-Class BE and ME degrees in Mechanical Engineering from Pune University, and his teaching experience spans over 38 years in Government Colleges of Engineering at Pune, Karad and Aurangabad. He had a postgraduate teacher of Pune University, Shivaji University and Marathwada University. And as a national Scholar, he received five prizes from Pune University, After his academic career.
Professor Bhandari was a member of 'Board of Studies in Mechanical Engineering' and a member of 'Faculty of Engineering' of Pune University.
Silent Features Of VB Bhandari pdf Book
The main features of the book are as follow:
(i) SI system of units used throughout the book
(ii) Indian standards used throughout the book for materials, tolerances, screw threads, springs, gears, wire ropes and pressure vessels
DISCLAIMER: I am not the original publisher of this Book/Material on net.Thank You !!!

Study Of Cup type Current Meter - Hydraulic Machine

Study Of Cup type Current Meter

STUDY OF CUP TYPE CURRENT METER

AIM:

To study of the principle, construction and working of cup-type current-meter.

APPARATUS:

Cup type current meter with dead weight and other accessories, recorder, string, etc.

PRINCIPLE:

Current meters are a miniature reaction turbine when placed in a stream of moving water. It rotates with a speed proportional to the velocity of flow at that point. It can be calibrated by observing its rpm. When mobbing with a carriages mounted on rails across still waters at low velocities. Then it can be used to measure velocities of flow at different points in a stream. Once the velocities at several points in a cross section are known calculation of discharge is a simple mathematical or graphical problem.

THEORY:

A current meter consists of a rotating element which when placed in flowing water rotates at a definite speed which is proportional to the velocity of the water. By measuring the number of revolutions the velocity of the water can be measured. The main two classes of various types of current meters are:-
1. Cup Meter, in which the rotating element rotates in a vertical axis.
2. Propeller current meter or screw type, in which the rotating element is mounted over a horizontal axis.

CONSTRUCTION:

As shown in figure, the cup type current meter (mfg. by watts) is shown in figure. The current meter consists of six conical cups mounted over a vertical spindle arranged or fixed in a horizontal plane.  At every revolution or after every five revolutions a signal is transmitted to the observer or to a revolution counter through electrical contacts. The entire meter is suspended by a cable in order to maintain the vertical stability of the cable in tension or to maintain the instrument perfectly aligned, a stream lined weight also called “dead weight” is provided at the bottom of it as shown in figure. Opposite to the cups, on the tail portion, fins are provided to maintain the meter truly in direction of flow inside the water. In order to place the meter in horizontal position i.e. to maintain the horizontal stability, a sliding weight is provided in the fins which can be adjusted accordingly with the help of screw and nut arrangement. A locking device prevents the cups from rotating when not in use.
The vertical spindle arrangement connected to the cups rotates inside a bearing located inside a steel frame. Above the bearing, there is a pivot made up of hardened steel. The locking device clamps the wheel and releases the meter weight.

WORKING:

• The cable is connected to the lifting link of the meter and lowered down at the point where velocity measurement is to be carried out.
• The working device is unlocked. The batteries are inserted in the recorder box so that electric circuit can be completed.
• The instrument is placed in such a direction along the flow that tail piece points in direction of flow, so that flow coming over it gets streamlined before coming upon the cups.
• According to the magnitude of the velocity of flow, cup rotates along the vertical axis in horizontal plane, contact is established in electrical circuit for every revolution.

MEASUREMENT OF SPEED:

• Meter is submerged under water and motion of water in the stream actuates it driving the rotary elements at a proportional to the velocity of flow.
• Bearing friction should be eliminated and the bearings in which the spindle carrying cups revolves should be watertight.
• Upper end or the bearing spindle extends above the bearing into an airtight chamber containing an arrangement of electrical contacts closed by a cam or eccentric device.
• A dry cell of 4 volts and a bell or a buzzer constitutes the rest of the circuit.
• By counting the number of beats in a known time noted by a stopwatch, the rpm can be calculated. Then the velocity can be determined from the calibration curve.
• When a number of current meters are working simultaneously individual counting is not possible and an automatic recorder is necessary.
• Arrangement generally, employed consists of a type chronograph and a chronometer.
• A paper strip is continually fed to a chronograph at a constant speed by means of clockwork and chronometer.
• After a certain number of revolutions a signal are received energizing a coil wound an electromagnet which deflects a pen marking a stroke on the paper strip.
• Time is printed on the paper and by counting the number of strokes in a known time interval.

RATING OF CURRENT METER:

Rating of current meter means establishing a definite relationship between observed number of revolutions made in unit time by rotating element and the velocity of the flow. This is done in a rating channel or tank usually between 30m to 100m in length and at least 2m wide and 2m deep containing water at rest. On two sides of channel rails are laid on which trolley runs at different speeds. Current meter at the corresponding values of speeds of trolley are noted. The statistical rating or a rating table is prepared. A typical rating curve is as per below formula
The curve approximately is to be a straight line, mathematically written as:
v = an + b;
Where, v = velocity in m/sec.
a  = slope of rating curve
n  = revolutions per second
b  = intercept on y axis
Two equations are sometimes obtained, one for low velocities and other for high velocities. Such rating curves or rating tables are supplied by the manufacturer. However, after the current meter is in use for about 100 working hours, the rating curves or table should be checked.

ADVANTAGES:

• Cup- type current meter is sturdier than Amsler pitot tube and hence its life is longer.
• It is more compact than Amsler pitot tube, hence, more easily carried from one place to another.
• With the help of chain, they can be inserted in lower depth in the stream than Amsler pitot tube.
• Comparatively more accurate measurement of velocity than Amsler pitot tube.
• The cup type current meter can be used for measuring higher range of velocities than Amsler’s pitot tube.
• Quick and easy measurement is possible.
• the digital display for counting
• From the calibration chart for number of revolutions versus velocity we can directly state the velocity looking into the chart.
• With the help of velocity measured one can also calculated the discharge required.

DISADVANTAGES:

• More costly than Amsler pitot tube so, initial instrument cost is high.
• It is more in weight than Amsler pitot tube, so carrying it far larger distance along rivers can be more cumbersome.
• For very large number of revolutions, and very less number of revolutions, rating curve differs so velocity measurement has to be checked from rating curve.
• Excess impurities or mud gets clogged in the cups of current meter resulting in improper velocity calculations.
• More moving parts, bearing, etc require more maintenance than Amsler’s pitot tube.
• If there is leakage of electric current then improper reading will be observed.
• A number of gauge points are required along a stream for the average velocity.
• The stream flow should be as steady as possible for accurate measurement.
• Frequent calibration is necessary.

APPLICATIONS:

• In India, cup type current meter is widely used for stream gauging.
• Also used for all routine gauging of rivers, hence mostly in open channels only.
• In case of larger diameter pipes, where accessibility is no problem, current meters are used to measure discharge after the velocity is known.
• Propeller type of current meter is comparatively smaller in size than cup type current meter and hence due to more compactness is suitable for use near boundaries of rivers.
REMARKS:
The flow is assumed to be a steady flow with tolerable impurities. Effect of friction at the surface of meter is neglected. Loss of velocity due to body bends, etc. is neglected. Best working condition of current meter is obtained from “rating chart curves”.