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CAPSTAN GEAR

Posted by: Engineers Zone Posted date: Friday, December 10, 2010 / comment : 10 ,


Capstan gear is normally fitted forward and aft in ships. The forward gear may comprise a separate cable/warping head which can be used for warping or working the anchors and cables and two cable holders which are designed to work the cables only, or two cable/warping heads which can be used for warping or working the cables. Anchor gear is not now carried aft but an after capstan head is fitted for warping, replenishment-at-sea and storing duties. Capstan gears can be powered nowadays by two methods, electric or electric-hydraulic.

·         ELECTRIC OPERATED CAPSTAN GEAR
This type is in common use in ships, where it consists, generally, of Duplex capstan gear in which the functions of a cable holder and capstan are combined in each of a pair of heads as mentioned previously. It is powered by a three-speed electric motor through a slipping clutch, a primary worm reduction gear, and a secondary worm reduction gear driving the capstan heads through vertical shafts. The driving gear is mounted under the forecastle deck, underslung on a main baseplate bolted to the deckhead. Each capstan head comprises a warping barrel mounted on the same spindle as a cable holder. The warping barrel always revolves with the spindle and so is always ready to use for warping. Vertical movement is provided so that the warping barrel can engage the cable holder which can then be used to haul or veer the anchor. When veering cable the cable holder is disengaged and controlled by handbrake. Neither head can be worked by hand. In larger ships, where space is less of a problem, the motors and gearing are seated on the deck below the forecastle, the vertical shafts being carried up through the latter.
The capstan gear, in this instance, consists of port and starboard wing cable holders and a middle line warping and anchor capstan, driven by two reversible electric motors through a slipping clutch, a geared driving unit and dog clutches. The wing cable holders, a handed pair, can be driven through an arrangement of dog clutches in either direction together, or independently, or be disconnected from the vertical shafts to run freely under the control of hand operated handbrakes. The body of each holder, like the lower barrel of the duplex head, is made of cast steel Grade I and formed with snugs into which the links of the cable fit neatly. The cable holders are not keyed to their spindles and each can revolve freely on a gunmetal bush and can be connected or disconnected from its spindle by a dog clutch. The skirt, or bottom flange, of the barrel forms braking surface for a band type of control brake which controls the speed at which the cable can be run out when the cable holder is disconnected.
The middle line capstan, normally operated independently of the wing cable holders, will revolve only in one direction relative to the motor direction and may be connected to, or isolated from, the motor drive through a dog clutch or by insertion or removal of two driving pins which couple the vertical shaft to a worm wheel. In the isolated condition the capstan can be worked by hand with bars fitted into sockets in the barrel head. These bars are made of ash wood bound with steel shoes which fit into the barrel slots snugly. They are secured by pins passing through the crown plate and shoes. Pawls dropped into a ratchet track located at the base of the barrel prevent the head from running back. Portable whelps can be fitted to facilitate working the ML head as a warping barrel but the wing cable holders are designed only for working the anchor cable. The electric motors are controlled by a portable T-handle fitted in a deck socket.

·         Electric-Hydraulic Capstan Gear
There are two forms of this type of gear. In the first the hydraulic motor and gearing which drive the capstan are incorporated in the actual capstan head as shown in the sketch. By virtue of its compactness this type is usually fitted aft in more modern ships designed with a comprehensive hydraulic system serving several equipments including the after capstan. In the second type the hydraulic motor drive replaces the electric motor drive described for the electric type of capstan gear and is otherwise similar to the latter as regards the design of capstan/warping heads, gearing, etc. Generally speaking this type is replacing the electric drive type in more modern ships forward. In both cases the electric motor and pump which supplies pressure oil to the hydraulic motor, whether the latter is incorporated in the capstan head or not, are situated on the deck below the capstan gear together with the control gear. In each a hydraulic control box is sited adjacent to the capstan and it is possible to work the capstan by means of a hand pump if electric power fails or is not available.

Brake Gear
In most types of capstan gear the brake is unidirectional and its Ferodo lined brake strap (of forged steel) is controlled by a hand wheel which operates through bevel gears to rotate a screwed spindle working in a trunnion nut. The brake strap is in two parts, connected by a joint pin with its head fitted in a recess in the underside of the forked part of the strap. The strap assembly is pivot anchored by a brake bolt in the deck plate. The other end of the band carries the trunnion nut in which the screwed end of the brake spindle works to contract or expand the band.

Controls
In all cases the capstan heads are controlled from the weather deck by means of a portable handle which fits into a socket let into the deck. The handle incorporates a pointer to indicate the handle position relative to the control markings marked on the flange of the socket. In addition the electrically driven capstan includes an emergency stop button set in the deck near to the control handle to stop the capstan in emergency.

TYPES OF FANS

Posted by: Engineers Zone Posted date: Friday, December 10, 2010 / comment : 2 ,


Two types of fan are in general use in ships are, centrifugal fans and axial flow fans.

Centrifugal fans consist essentially of a 'wheel' or 'runner' made up of radial blades rotating in a casing of the scroll form. The wheel is rotated at high speed by an electric motor on the same shaft.' Air is drawn in at the 'eye' of the fan, i.e. into the centre of the wheel and thence between the blades which give it rotation. The centrifugal force due to its rotation expels the air outwards towards the circumference and into the delivery trunk. A fan is said to be 'right handed' or 'left handed' according to whether the rotation is clockwise or anti-clockwise when viewed from the motor to the wheel.

Axial flow fans work on the same principle as the propellers of aircraft. They consist primarily of an impeller (or propeller) with blades mounted on a 'nacelle' enclosing an electric motor inside a circular trunk having a small clearance from the blades. Provided a straight length of trunk can be arranged at the inlet and outlet ends they can be designed to be as efficient as the centrifugal type For a given volume output and pressure, and can be used to distinct advantage where economy of space is important. The modern practice is to use this type for 1 group systems and machinery spaces.

Fans are not placed in bathrooms, wash places, drying rooms or other compartments containing humid air, nor in compartments where sparking could cause an explosion. They are usually suspended from the deck head or seated on the deck in a position affording an efficient arrangement of trunking. Non-air conditioned spaces of ships serving in tropical climates are fitted with fans of the open propeller type to provide additional means of rapidly circulating the air. Three types of open propeller fan are used. Slow-running overhead fans with wooden blades about 3 ft 6 inch diameter are fitted in wardrooms, officers' messes, dining halls, recreation and similar spaces. Small table fans with rubber blades 10 inch diameter are fitted in cabins and with rubber or steel blades 12 inch diameter in offices and mess spaces. Larger 16-in diameter fans with aluminium alloy blades (Hurricane type) are fitted in dining halls and large mess spaces. 

TYPES OF DAVITS

Posted by: Engineers Zone Posted date: Thursday, December 09, 2010 / comment : 4



TYPES OF DAVITS

·         HINGED SCREW TYPE
The majority of the older frigates and destroyers retain the hinged screw type of davits for general use. These davits can be turned in or out to the desired out reach by rotating a handle connected to a worm and wormwheel, the latter operating a screw thread on the extending arm. The davit arms are of I-bar section and so shaped that the boat, in the inboard stowed position, is upright when bearing against the griping pads. The weight of the boat is taken on keel chocks fitted to each davit.
The disadvantage of this type of davit lies in their hand operation and the fact that independent control of each of a pair can result in undue strains on the davits and operating gear due to unsynchronized movements.

·         GRAVITY TYPE
This consists of two portions, the davit arm and the deck frame which forms the runway for the arm. When the boat is being lowered the davit arm travels down the runway until it reaches a fixed stop by which time the boat is clear of the ship's side and disengaged from the davit head hook or 'tusk' which takes the weight of the boat when turned in. Continued veering on the winch allows the boat to travel vertically downwards. During the hoisting operation the ball-weight on the hoist wire engages a stop at the davit head, whereupon the boat and davit arm move as one until the fully housed position is reached. During this latter stage the weight of the boat is automatically transferred to the hook or tusk, thus relieving the tension in the hoist wire.

·         PIVOT TORQUE TYPE
This has a deck frame and davit arm which together with the boat hinges about the deck pivot. To overcome the initial resistance to hinging outboard, should the ship have an adverse heel, a coiled spring is fitted between deck frame and davit arm. This spring is designed with sufficient effort to bring the C.G. of the davit outboard of the pivot pin under all normal angles of ship heel. As in the gravity type davit the weight of the boat is taken by a hook or tusk at the davit head, engagement or disengagement with which occurs during the hinging process.

·         TRAVERSING GANTRIES
Traversing gantries are employed in aircraft carriers where the boats are stowed in boat bays at gallery deck level. These enable the boats to be lifted clear of the crutches (usually hinged), traversed outboard and lowered well clear of the ship's side. To allow for the rise and fall of the boat whilst still attached to the falls, a compensating mechanism is fitted in the lead of wire from the winch. This gear is designed to automatically 'shorten' or 'lengthen' the falls in phase with the boat's vertical movement. A man at the forward and after ends of the boat is able to retain the disengaging hook and the fall block together without difficulty.

The latest ships are equipped with either gravity or pivot torque types. Both are fully power operated and employ a single wire for boat hoisting and turning the boat to the stowed position, thus economizing considerably in manpower. Both davits of a pair are operated by a common drive and the problem of synchronized operation does not arise.

Power is not required for lowering a boat, control being exercised simply by a brake on the winch. The winches are fitted with cranked handles for operation should power fail when raising a boat. Neither of these types of davit have arrangements for combating wave motion so that the use of the nylon grommet or strop (foul weather pendant) becomes an essential safety measure.

All davits are tested with a static load of twice the working load and a running load of one and a half times the working load. In the latter case the boat is raised and lowered (or traversed if applicable) so as to test all parts of the system throughout its designed range.
               

ASSESSMENT OF REQUIREMENTS FOR NON-AIR CONDITIONED SPACES

Posted by: Engineers Zone Posted date: Thursday, December 09, 2010 / comment : 0 ,


For some compartments air conditioning is not practicable or desirable. These include compartments from which large quantities of wild heat and/or moisture must be removed; compartments in which unpleasant, toxic or explosive gases are liable to collect; and compartments like storerooms the contents of which are not sensitive to temperature or humidity. Such compartments must be supplied with sufficient air to maintain habitable conditions and for each type of compartment a maximum acceptable operating temperature is stated in °C or °F above the entering air dry bulb temperature.

ASSESSMENT OF REQUIREMENTS FOR AIR CONDITIONED SPACES

Posted by: Engineers Zone Posted date: Thursday, December 09, 2010 / comment : 0 ,


The basis of design of the normal air conditioning system for any compartment or group of compartments is the removal of sufficient heat and moisture to maintain a reasonable standard of bodily comfort for the personnel to carry out their duties. The heat generated or 'heat load' as it is called, arises from four sources:

a.        The men in the compartment.
b.       Machinery, electrical apparatus, lighting, etc. in the compartment.
c.        Conduction through the boundaries of the compartments from adjacent compartments,from the sun and from the sea.
d.       Fresh air which has to be cooled from outside air temperature to the compartment temperature.

The outside air temperature is assumed to be 31°C DB/27°C WB for tropical conditions and 34°C DB/30°C WB for extreme tropical. The maximum acceptable temperature within the compartment is taken as 30°C DB/22°C WB unless otherwise stated in the design requirements. The total heat load is calculated using standard formulae to obtain the quantity of air required. The capacity of the plant is then chosen to suit this heat load and after grouping of compartments the task of deciding the sizes of fans, coolers and layout of trunking can proceed.

RULE FOR WATERTIGHT AND GASTIGHT CONTROL MARKINGS

Posted by: Engineers Zone Posted date: Wednesday, December 08, 2010 / comment : 1


Observance of the rules for the control of watertight and gastight openings is the responsibility of ALL PERSONNEL and they must be continually aware of which watertight and gastight condition is in force and also of the requirements of each condition. Watch on the maintenance of the condition set is kept by NBCD patrols or by frequent rounds by the Watch on deck or Duty Watch according to the state of readiness, and the type and size of ship. The rules for control markings are:-

·         ‘X’ SHUT IN ALL WATERTIGHT CONDITIONS. To be opened only by permission. If required to be kept open, then a sentry must be posted or other arrangements made for the opening to be shut instantly on order, or a ‘MBLO’ disc must be used.
·         ‘Y ’SHUT IN CONDITION Y AND Z. Open in condition X-ray. When shut, may normally be opened for passage or use but must be immediately shut again. If required to be kept open in conditions Yankee or Zulu, the rules as for X-ray opening apply.
·         ‘Z’ SHUT IN CONDITION  Z. Open in conditions X-ray and Yankee. When shut, the rules as for Yankee openings apply.
·         ‘A’ SHUT IN CONDITION A. When condition Alfa is in force, openings so marked are not to be opened without specific permission from HQ1.
·         ‘M’ in condition Alfa only, openings so marked are under the control of the user department. User departments must ensure that the orders regarding their ’M’ openings are clear and fully understood by their personnel.
·         ‘R’ Fittings and equipment so marked must continue to run or remain open for recirculation.

TRUNKING IN SHIP

Posted by: Engineers Zone Posted date: Wednesday, December 08, 2010 / comment : 0 ,


The method of ventilation and output are decided as discussed above, but to decide the size of fan to handle the total amount of air required it is necessary to investigate by calculation the resistance which will have to be overcome by the air in passing through the trunks and out through the louvres or terminals. Considering any one system, losses of head occur through friction of the air passing through the trunk, changes of section, bends in trunking, fittings such as coolers, heaters, valves, gas flaps, and discharges. Each of these losses is proportional to the square of the velocity of flow. The loss of head due to friction in straight trunking is proportional to the length of trunking and inversely proportional to the linear dimension of the trunk section. Apart from the obvious desirability of minimizing the length of all trunks, the principal points requiring consideration from the practical point of view are as follows:

·         ADOPTION OF EFFICIENT SHAPE OF SECTION
The rate of air supply to, or exhaust from, a compartment having been decided from consideration of its nature and size, comfort of the personnel there, or technical reasons, the sectional area of trunking will depend on the available fan pressure after deduction of 'fixed' resistance items such as coolers, heaters, etc. To simplify calculations the 'Equal Friction per Foot' method is used, the basis of which is to convert all bends and changes of section to an equivalent length of straight trunking to which is added the actual straight length of trunking in feet to give the total equivalent length of straight trunking. Knowing the total equivalent length of straight trunking, the volume of air passing through the trunking and the pressure available, the diameter of circular trunking for each section of the system can be obtained from standard trunk friction charts. Having determined the diameter of circular trunking it remains to decide the best practicable shape of section. Circular trunking is more efficient than rectangular but saving in time, space and cost of manufacture results in the adoption of the latter in the general case. Small trunks are more easily constructed circular. A rectangular trunk can be made in a variety of ratios of sides for the same equivalent diameter of section. Undue 'flattening' of the section for such reasons as increased head room or clearance of unimportant obstructions must be avoided. In warships the ratio of the sides of any trunk must not exceed 4 to 1.

·         Minimization of the number of bends and changes of section. Complete avoidance of change of direction is impossible, but by adopting easy bends with large radius, a material improvement is effected. Sudden changes of section must be avoided and in cases where a local enlargement is necessary, the change in sectional area must be carried out gradually to minimize loss of head. In cases where these preventive measures cannot be taken a splitter must be fitted inside bends or changes of section to reduce the resistance as much as possible by preventing the formation of eddies.

·         Layout of trunking 
 The trunking must be led in such direction and be of such length as to ensure a good distribution of air within the compartment. The layout should be such that the air leaving supply louvres does not pass directly to the exhaust trunk or other opening acting as exhaust in the compartment ('short circuiting'). Similarly in compartments exhausted by fan, the exhaust inlet in the compartment must be situated remote from doorways or hatches so that the fresh air travels some distance before being drawn into the exhaust inlet. The vertical position of the exhaust inlet will depend upon the nature of the noxious gases in the compartment. If these are lighter than cold air, the inlet is placed near the crown of the compartment, and if heavier than cold air, near the bottom.

PIPING IN SHIPS

Posted by: Engineers Zone Posted date: Wednesday, December 08, 2010 / comment : 3 ,


Copper-Nickel-Iron Alloy Piping (90/10) is used for the piping of the saltwater main and its branches, sanitary system, hangar and magazine spraying systems, hull and fire, fire and bilge, and hangar spray pump sea suctions, risers, overboard discharges and pump leak-offs, overboard discharges from water/fuel displacement systems, salt water supply to and overboard discharges from bathroom ejectors, bathroom drains within the bathroom (except as stated below) and urinal drains.

Galvanized Mild Steel Piping is used for all suctions to compartments, overboard discharges of salvage pump systems, suction stand pipes, ejector suctions to bathroom sumps, portable diesel pump sea suction, scuppers and drains, soil pipes, suction pipes within fresh water storage tanks, oil fuel residue suctions, air escape pipes, and all pipes within FFO tanks where the tank structure is galvanized. Steel pipes below 11/2-inch bore are connected by screwed sleeves and large pipes by flanges welded to the pipes, the flanges being welded prior to galvanizing.

Copper-Nickel-Iron Alloy Piping is connected as follows by flanges if the bore is 2 inches or more and smaller pipes by brazed core unions, capillary type fittings or compression fittings of the non-manipulative type. Ferrous fittings are not fitted in copper-nickel-iron systems. Copper and coppernickel- iron pipes are kept clear of aluminium alloy structure. At least 1/2 inch is provided between the pipes or the pipe insulation and the structure. Corrosion pieces, consisting of renewable 12-inch lengths of galvanized mild steel, are fitted between dissimilar metals in such piping normally dealing with salt water such as suctions to gland and plummer block compartments but are not normally required in dry suction systems.

No non-ferrous piping is introduced into any part of the ship so low as to come into contact with bilge water. Unless unavoidable, pipes containing liquid are kept out of compartments accommodating important electrical apparatus. The seating of pipe joints directly above electrical equipment is prohibited. No electrical installation is earthed to any water system and electric cables or associated fittings are not attached to such piping. Pipes connected to the outer bottom or to protective bulkheads are worked with generous bends, or alternatively with weakened shearing joints, so that they cannot act as struts in the vent of deflection of the structure.

VARIOUS UNDERWATER VALVES IN SHIPS

Posted by: Engineers Zone Posted date: Wednesday, December 08, 2010 / comment : 1 ,


Generally speaking the body, bottle, bridge and cover of all valves are made of gunmetal whereas the valve, disc, spindle, thrust collar, studs and nuts are of aluminium or bronze. Soft faces are made of vulcanized synthetic rubber, except in ball plug valves where they are of an approved low friction type material.


VARIOUS UNDERWATER VALVES FITTED INCLUDES:

SEA OR COCK VALVE
Sea valves, normally of the screw down type, metal seated, are fitted for admitting salt water into the ship for flooding compartments and to supply the various salt water pumps in the system. In way of the double bottom they are secured to the inner bottom by a flange connected to the inlet tube between inner and outer bottom. Outside the double bottom the seacock is fitted to a distance piece on the outer bottom. Gratings of galvanized mild steel are fitted to the sea inlets as near as possible to the outer bottom plating. 
Where the sea tube serves more than one valve the clear area of the opening in the grating is suitable for the total number of valves using that tube. Zinc protectors are fitted inside the tube to take the effect of galvanic action set up by the non-ferrous material of the seacock as described in the chapter on cathodic protection. To enable compartments containing explosives or inflammable material to be flooded in dry dock, flooding bonnets are provided which can be secured to the mouth of the inlet tube after removing the grating. A flooding bonnet consists of a number of hose connections welded to a base plate. As the water falls below the inlet, when docking, the grating is removed and the bonnet secured in place, hoses being led from the hose connections to the shore hydrant. The bonnet is removed and the grating replaced when the vessel is being undocked. Pump suctions connected to a seacock used for flooding magazines or other danger spaces must be taken from the sea side of the master valve of the seacock.

SCREW-DOWN VALVE  
Screw-down valves fitted with soft face and renewable seats are fitted for isolation and control purposes, e.g. on branches from the salt and fresh water mains, and on filling pipes discharging into fresh water filling funnels. Alternatively diaphragm valves are used. Where it is desired to run pipes at right angles and space is limited, screw-down right-angle valves are fitted.

SCREW-DOWN NON-RETURN VALVE
Screw-down non-return valves fitted with soft face and renewable seats are fitted to all suction leads to ensure that the pumps are kept flooded. Their design is similar to the SDV except that the' bottle' has a longer neck with an expansion chamber on the valve. When the spindle is in the open position, the valve slides up the neck of the bottle when the pump is drawing, and falls back on the seating when suction is lost.

SCREW-DOWN NON-RETURN AND FLOOD VALVE
Screw-down non-return flood valves fitted with soft face and renewable seats are fitted to all suction leads where it is required to flood the compartment via the suction pipe. This valve is similar in action to SDNRV for pumping, but has a still longer neck to allow the valve to be lifted clear of the seating for flooding purposes. The inlet to the pump is inclined in order to facilitate the flow of water when pumping. Such valves are fitted at the feet of  branches to bottom compartments.

SCREW-DOWN DIAPHRAGM VALVE
Screw-down diaphragm valves are fitted in main suction systems where a high vacuum is essential in preference to screw-down valves. In this type of valve a flexible diaphragm isolates the fluid controlled by the valve from the valve operating mechanism.

PLUG VALVE
This is a form of shut-off valve, used where a full on or full off control is required, having a 'plug' which may be tapered, parallel or spherical in shape. It incorporates design features which reduce friction between the plug face and the body seat during operation and seals them against leakage. This type of valve has the advantage that it offers low resistance to flow.

BUTTERFLY VALVE
The flow regulator in this type of valve is a metal disc rotating in axial trunnion bearings. The valve has a resilient lining in the body incorporating the seat and may be used to control the flow from full open to full off according to the service required. These valves are now fitted in preference to double faced sluice valves in fluid systems in sizes above 4-in nominal bore. For smaller sizes valves of the full bore plug type are preferable.


SLUICE VALVE
Sluice valves are used for local connection between two or more compartments, e.g. one double bottom compartment draining into another. In shape they may be square or circular and consist of a casting with machined faces over which slides the valve casting operated by gearing.

SCREW-DOWN AND NON-RETURN DRAIN VALVE
These are fitted in flats and auxiliary machinery spaces for draining into compartments below. The non-return is fitted in the pipe below the deck leading to the compartment below, and is necessary to prevent water entering the compartment above should the one below be flooded.

STORM VALVE
Storm valves are simple non-return valves and are fitted to all drain and soil pipes discharging overboard, to prevent flooding when the sea rises above the outlet. Positive closing type storm valves are fitted when required. All storm valves are faced with leather to minimize noise when the vessel is rolling.

NON-RETURN VALVE
Non-return valves are fitted to prevent reversal in direction of flow, e.g. on the return piping in hot water circulating systems. They are also fitted on the discharge side of pumps to prevent back pressure.

REDUCING VALVE
Reducing valves are fitted where a low pressure service is supplied from another of higher working pressure. They are provided with renewable seats and discs of erosion resistant material. Where suitable, pressure reduction is achieved by the comparatively simple process of fitting an orifice plate of nylon or aluminium bronze. A diagrammatic sketch is given to illustrate the action of a reducing valve. When no pressure is on the spring and the inlet is open to water pressure, the valve A and piston B are in equilibrium, so that no water passes through the valve. When pressure is put on the spring to the required indicator setting, the valve A opens to let water through, until the pressure above A just exceeds that to which the spring is set: the valve A then closes against the spring. This action is repeated as the water is used.

GOVERNORS

Posted by: Engineers Zone Posted date: Monday, November 29, 2010 / comment : 4 , ,


  • The function of governor is to regulate the mean speed of an engine, when there are variations in the load.
  • Ex. When the load on an engine increases, it becomes necessary to increase the supply of working fluid.
  • When the load decreases, less working fluid is required.
  • It automatically controls the supply of working fluid to the engine with the varying load condition and keeps the mean speed within certain limits.
Note:
The function of a flywheel in an engine is entirely different from that of a governor. It controls the speed variation caused by the fluctuations of the engine turning moment during each cycle of operation. It does not control the speed variations caused by a varying load. The varying demand for power is met by the governor regulating the supply of working fluid.
Types of Governors:
  1. Centrifugal governors
  2. Inertia governors
Centrifugal Governor:
The centrifugal governors are based on the balancing of centrifugal force on the rotating balls by an equal and opposite radial force, known as the controlling force.
Watt Governor:
The simplest form of a centrifugal governor is a watt governor. It is basically a conical pendulum with links attached to a sleeve of negligible weight.
Porter Governor:
The porter governor is a modification of a watt governor, with a central load attached to the sleeve.
Proell Governor:
The Proell governor has the balls fixed at the end point to the extension of the links.
Hartnell Governor:
A Hartnell governor is a spring-loaded governor. It consists of two bell crank levers pivoted at the point to the frame. The frame is attached to the governor spindle and therefore rotates with it.
Hartung Governor:
In this type of governor, the vertical arms of the bell crank levers are fitted with spring balls which compress against the frame of the governor when the rollers at the horizontal press against the sleeve.
Wilson-Hartnell Governor:
A Wilson-Hartnell governor is a governor in which the balls are connected by a spring in tension. An auxiliary spring is attached to the sleeve mechanism through a lever by means of which the equilibrium speed for a given radius may be adjusted. The main spring may be considered of two equal parts each belonging to both the balls.
Pickering Governor:
A pickering governor is mostly used for driving a gramophone. It consists of three straight leaf springs arranged at equal angular intervals round the spindle. Each spring carries a weight at the center. The weights move outwards and the springs bend as they rotate about the spindle axis with increasing speed.
Sensitiveness of Governor:
The sensitiveness is defined as the ratio of the difference between the maximum and minimum equilibrium speeds to the mean equilibrium speed.
Stability of Governor:
- For a stable governor, if the equilibrium speed increases, the radius of governor balls must also increase.
- A governor is said to be unstable, if the radius of rotation decreases as the speed increases.
Isochronous Governors:
A governor is said to be isochronous, when the equilibrium speed is constant (i.e., range of speed is zero) for all radii of rotation of the balls within the working range, neglecting friction. The isochronism is the stage of infinite sensitivity.
Hunting:
A governor is said to be hunt if the speed of the engine fluctuates continuously above and below the mean speed.
Effect and Power of a Governor:
- The effect of a governor is the mean force exerted at the sleeve for a given percentage change of speed (or lift of the sleeve).
- The power of a governor is the workdone at the sleeve for a given percentage change of speed. It is the product of the mean value of the effort and the distance through which the sleeve moves.
Controlling force:
When a body rotates in a circular path, there is an inward radial force or centripetal force acting on it. In case of a governor running at a steady, the inward force acting on the rotating balls is known as controlling force.

Difference between Hardness and Toughness

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 7

Hardness

i. It is the property of the material to resist scratching, abrasion, indentation or penetration.

ii. Hardness of a material is stated relative to the hardness of other material.

 

iii. Important in shafts, bearing whichever is having relative motion.

Toughness

i. Ability of a material to withstand both elastic and plastic deformation, shock and vibration.

ii. Toughness is measured in terms of the energy a material can absorb before a actual failure takes place.

iii. Important in structural members, machine parts which are subjected to shock and vibration. E.g. shafts, spring.

Moment of Momentum Equation

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 0 , ,

Moment of momentum equation is derived from moment of momentum principle, which states that the resulting torque acting on a rotating fluid is equal to the rate of change of moment of momentum.

Moment of momentum per second = rQ x V x r

Where r = density of fluid

Q = rate of flow of fluid

V = velocity of fluid

r = radius of curvature

Continuity Equation

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 0 , ,

The equation based on the principle of conservation of mass is called continuity equation.

r1A1V1 = r2A2V2

Where V = Average velocity

r = Density

A = Area of pipe

If the fluid is incompressible, then r1=r2 and continuity equation reduces to A1V1 = A2V2

Types of fluid

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 0 , ,


The fluids may be classified into the following five types:
a. Ideal fluid – A fluid, which is incompressible and is having no viscosity, is known as an ideal fluid. Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity.
b. Real fluid – A fluid, which possesses viscosity, is known as real fluid. All the fluids, in actual practice, are real fluids.
c. Newtonian fluid – A real fluid, in which the shear stress is directly proportional to the rate of shear strain (or velocity gradient), is known as Newtonian fluid.
d. Non-Newtonian fluid – A real fluid, in which the shear stress is not proportional to the rate of shear strain, is known as non-newtonian fluid.
e. Ideal Plastic fluid – A fluid, in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain, is known as ideal plastic fluid.

Radiation Heat Transfer:

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 0 ,

  • When heat transfer takes place through electro magnetic waves between two bodies isolated together in a vacuum, the phenomenon is called radiation
  • The rate at which the energy is radiated by a black body at temperature T is given by Stefan-Boltzman law

Q = σ A T4

Where

Q = rate of energy radiation, watt

A = surface area radiating heat, m2

σ = Stefan-Boltzmann constant, 5.67x10-8 W/m2k4

Fourier’s Law:

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 1 ,

Fourier’s law of heat conduction states that the rate of heat flux is linearly proportional to the temperature gradient.

q α dt/dx

q = -k (dt/dx)

k = constant of proportionality which is the property of the material through which heat is being conducted and is known as thermal conductivity.

TOOTHED WHEELS OR GEARS : Classification

Posted by: Engineers Zone Posted date: Sunday, November 28, 2010 / comment : 0 , ,



In precision machine, in which a definite velocity is of importance, the only positive drive is by means of gears or toothed wheels. It is also provided, when the distance between the driver and the follower is very small.
Classification:

1. According to the position of axes of the shafts.
  1. Parallel
  2. Intersecting
  3. Non-intersecting and non-parallel
  • The two parallel and co-planar shafts connected by gears are called spur gear and this arrangement is known as spur gearing. These gears are parallel to the axis of the wheel.
  • Another name given to the spur gearing is helical gearing, in which the teeth are inclined to the axis45°.
  • The double helical gears are known as herringbone gears.
  • The two non-planar or intersecting, but co-planar shafts connected by gears are called bevel gears and the arrangement is known as bevel gearing.
  • Bevel gears, like spur gears may also have their teeth inclined to the face of the bevel, in which case they are known as helical bevel gears.
  • The two non-intersecting and non-parallel i.e., non-coplanar shafts connected by gears is known as skew bevel gears or spiral gears and the arrangement is known as skew bevel gearing or spiral gears.
  • This type of gearing also have a line contact, the rotation of which about the axes generates the two pitch surfaces known as hyperboloids.
2. According to the peripheral velocity of the gears.
  1. Low velocity – less than 3m/sec
  2. Medium velocity – between 3 and 15m/sec
  3. High velocity – more than 15m/sec
3. According to the type of gearing
  1. External gearing
  2. Internal gearing
  3. Rack and Pinion
  • In external gearing, the gears of the two shafts mesh externally with each other. The larger of these two wheels is called spur wheel and the smaller wheel is called pinion. In an external gearing, the motion of the two wheels is always unlike.
  • In internal gearing, the gears of the two shafts mesh internally with each other. The larger of these two wheels is called annular wheel and the smaller wheel is called pinion. In an internal gearing, the motion of the two wheels is always like.
  • Sometimes, the gear of a shaft meshes externally and internally with the gears in a straight line. Such a type of gear is called rack and pinion. The straight-line gear is called rack and the circular wheel is called pinion. With the help of a rack and pinion, we can convert linear motion into rotary motion and vice versa.
4. According to position of teeth on the gear surface. The teeth on the gear surface may be straight, inclined or curved.
  • The spur gears have straight teeth where as helical gears have their teeth inclined to the wheel trim. In case of spiral gears, the teeth are curved over the rim surface.

Water Chiller

Posted by: Engineers Zone Posted date: Friday, November 26, 2010 / comment : 0 ,

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Water chillers are used in a variety of air conditioning and process cooling applications. They are used to make cold water that can be transported throughout a facility using pumps and pipes. This cold water can be passed through the tubes of coils in order to cool the air in an air conditioning application or it can provide cooling for a manufacturing or industrial process.
Systems that employ water chillers are commonly called chilled water
systems.

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There are several types of water chillers that are differentiated by the
refrigeration cycle they use or the type of compressor.

Absorption water chillers make use of the absorption refrigeration cycle and donot have a mechanical compressor involved in the refrigeration cycle. Absorption water chillers are the subject of a separate clinic.

Water chillers using the vapor-compression refrigeration cycle vary by the type of compressor used. Reciprocating and scroll compressors are typically used in smaller chillers. Helical-rotary (or screw) compressors are typically used in medium-sized chillers. Centrifugal compressors are typically used in larger chillers.

Source : Trane Guide

Classification Of Pumps

Posted by: Engineers Zone Posted date: Tuesday, November 23, 2010 / comment : 0 , ,

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Source : Alfa Laval Pump Handbook

What is a Pump?

Posted by: Engineers Zone Posted date: Tuesday, November 23, 2010 / comment : 0 , ,

There are many different definitions of this but it can be best described as:

‘A machine used for the purpose of transferring quantities of fluids and/or gases, from one place to another’.

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A TYPICAL PUMP INSTALLATION

This is illustrated below transferring fluid from tank A to spray nozzles B.

Pump types generally fall into two main categories – Rotodynamic and Positive Displacement, of which there are many forms.

The Rotodynamic pump transfers rotating mechanical energy into kinetic energy in the form of fluid velocity and pressure. The Centrifugal and Liquid Ring pumps are types of rotodynamic pump, which utilise centrifugal force to transfer the fluid being pumped.

The Rotary Lobe pump is a type of positive displacement pump, which directly displaces the pumped fluid from pump inlet to outlet in discrete volumes.

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