Piston valve (steam engine)
Piston valves are one form of valve used to control the flow of steam within a steam engine or locomotive. They control the admission of steam into the cylinders and its subsequent exhausting, enabling a locomotive to move under its own power; the valve consists of two piston heads on a common spindle moving inside a steam chest, a mini-cylinder located either above or below the main cylinders of the locomotive. In the 19th century, steam locomotives used slide valves to control the flow of steam into and out of the cylinders. In the 20th century, slide valves were superseded by piston valves in engines using superheated steam. There were two reasons for this: It is difficult to lubricate slide valves adequately in the presence of superheated steam With piston valves, the steam passages can be made shorter; this following the work of André Chapelon, reduces resistance to the flow of steam and improves efficiencyThe usual locomotive valve gears such as Stephenson and Baker valve gear, can be used with either slide valves or piston valves.
Where poppet valves are used, a different gear, such as Caprotti valve gear may be used, though standard gears as mentioned above were used as well, by Chapelon and others. Most piston valves are of the "inside admission" type, where fresh steam is introduced from the boiler via the space between the two piston heads of the valve, exhaust steam leaves via the space between a piston head and the end of the steam chest; the advantage of this arrangement is that leakage, via the gland which seals the steam chest from the operating rod of the valve gear, is much less of a problem when the gland is subjected to low exhaust pressure rather than full boiler pressure. However, some locomotives, like Bulleid's SR Merchant Navy class, used "outside admission" where the reverse was true, in Bulleid's case because of the unusual chain-driven valve gear arrangement; the Swannington incline winding engine on the Leicester and Swannington Railway, manufactured by The Horsely Coal & Iron Company in 1833, shows a early use of the piston valve.
Piston valves had been used a year or two in the horizontal engines manufactured by Taylor & Martineau of London, but did not become general for stationary or locomotive engines until the end of the 19th century. When on the move, a steam locomotive requires steam to enter the cylinder at a controlled rate; this entails controlling the exhaustion of steam to and from the cylinders. Steam enters and leaves the valve through a steam port at the middle position of the piston valve. Where the valve is in contact with the steam ports, a consideration of the "lap" and "lead" is required. Lap is the amount. However, there are two different types of lap; the first kind is the steam lap, the amount by which the valve overlaps the port on the live steam side of the valve piston. Secondly, there is the exhaust lap, the amount by which the valve overlaps the port on the exhaust side of the valve piston. Exhaust lap is given to slow-running locomotives; this is because it allows the steam to remain in the cylinder for the longest possible amount of time before being expended as exhaust, therefore increasing efficiency.
Shunter locomotives tended to be equipped with this addition. Negative exhaust lap commonly known as exhaust clearance, is the amount the port is open to exhaust when the valve is in mid-position, this is used on many fast-running locomotives to give a free exhaust; the amount exceeds 1/16 in. When exhaust clearance is given. Lead is the amount by which the steam port is open when the piston is static at front or back dead centre. Pre-admission of steam fills the clearance space between the cylinder and piston and ensures maximum cylinder pressure at the commencement of the stroke; the design criteria is to both cushion or assist the mass of the piston slow down and change direction and to reach a maximum pressure of the same value as the incoming steam. At slow speeds no lead is ideal. For piston diameters and strokes of 75mm lead is not needed to cushion the pistol mass when speeds are less than 200 rpm. Engines with pistons of 24 inches plus and masses of over 5 kilos and pressures under 500 psi cushioning is beneficial.
Source P Pellandine. Lead is necessary on locomotives designed for high speeds, under which conditions the valve events are taking place in rapid succession. Long-travel piston valves allow the use of large steam ports to ease the flow of steam into, out of, the cylinder. Given the valve's lap and travel, at what point in the piston's stroke does the valve open and close, to steam and to exhaust? Calculating an exact answer to that question before computers was too much work; the easy approximation is to pretend that both the piston have a sine-wave motion. For instance, to calculate the percent of the piston's stroke at which steam admission is cut off: Calculate the angle whose cosine is twice the lap divided by the valve travel Calculate the angle whose cosine is twice the, divided by the valve travelAdd the two angles and take the cosine of their sum; as built the Pennsylvania's I1s 2-10-0 had lap 2 inches, lead 1/4 inch and valve travel 6 inches in full gea
Slide valve
The slide valve is a rectilinear valve used to control the admission of steam into, emission of exhaust from, the cylinder of a steam engine. In the 19th century, most steam locomotives used slide valves to control the flow of steam into and out of the cylinders. In the 20th century, slide valves were superseded by piston valves in engines using superheated steam. There were two reasons for this: With piston valves, the steam passages can be made shorter; this improves efficiency. It is difficult to lubricate slide valves adequately in the presence of superheated steam; the D slide valve, or more Long D slide valve, is a form of slide valve, invented by William Murdoch and patented in 1799. It is named after the hollow central D-sectioned piston; this valve worked by "connecting the upper and lower valves so as to be worked by one rod or spindle, in making the stem or tube which connects them hollow, so as to serve for an induction pipe to the upper end of the cylinder." This allowed two valves to do the work of four.
The above description relates to an engine with a vertical cylinder, such as a beam engine. Where the cylinders are horizontal, as in a steam locomotive, the valves would be side-by-side; the balanced slide valve was invented by the Scottish engineer Alexander Allan. It was not much used in the UK but, at one time, had great popularity in the United States, it gave some of the advantages of a piston valve to a slide valve by relieving the pressure on the back of the valve, thus reducing friction and wear. The Slide Valve
Smokebox
A smokebox is one of the major basic parts of a steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler; the smoke enters the smokebox, is exhausted to the atmosphere through the chimney. Early locomotives had no smokebox and relied on a long chimney to provide natural draught for the fire but smokeboxes were soon included in the design for two main reasons. Firstly and most the blast of exhaust steam from the cylinders, when directed upwards through an airtight smokebox with an appropriate design of exhaust nozzle draws hot gases through the boiler tubes and flues and fresh combustion air into the firebox. Secondly, the smokebox provides a convenient collection point for ash and cinders drawn through the boiler tubes, which can be cleaned out at the end of a working day. Without a smokebox, all char must pass up the chimney or will collect in the tubes and flues themselves blocking them; the smokebox appears to be a forward extension of the boiler although it contains no water and is a separate component.
Smokeboxes are made from riveted or welded steel plate and the floor is lined with concrete to protect the steel from hot char and acid or rainwater attack. To assist the passage of the smoke and hot gases, a blower is used; this is a pipe ending in a ring containing pin-sized holes. The steam draws further gases through the tubes; this in turn causes air to be drawn through the firehole, making the fire burn hotter. When the locomotive is in motion, exhaust steam passes through the blastpipe, located within the smokebox; the steam is ejected through the chimney. The blastpipe is. Ashes and soot which may be present in the smoke are deposited in the smokebox; the front of the smokebox has a door, opened to remove these deposits at the end of each locomotive's working day. The handle must be tightened to prevent air leaks, which would reduce the draw on the fire and can allow any unburnt char at the bottom of the smokebox to catch fire there; some smokebox doors have a single handle in the form of a wheel.
On many steamrollers an extension to the body of the smokebox houses the bearing which supports the front roller. Due to limitations of space, these rollers have a drop-down flap instead of a circular smokebox door; the smokebox incorporates the main steam pipes from the regulator, one leading to each valve chest, a part of the cylinder casting. These may pass through the smokebox wall to join with the cylinder or may stay within the profile of the smokebox. Inside steam pipes do not require lagging as the smokebox keeps them warm, but outside steam pipes are more common for locomotives with cylinders outside the frames; some locomotive classes used both types depending on the date. Because heat losses from the smokebox are of little consequence, it is not lagged. In most cases it appears to be the same diameter as the boiler in the finished locomotive but this only because of the boiler cladding. Tank engines had their water tanks stop short of the unlagged smokebox as it could raise the temperature of the water sufficiently to cause problems with the injectors.
British Railways standard classes use this design, where a robust mesh grille is incorporated into the smokebox, forming a filter between the front tubeplate and the exhaust. Any large pieces of char passing through the boiler tubes tend to be broken up on impact with the mesh, creating finer particles which are swept up the chimney instead of accumulating in the bottom of the smokebox; this does not negate the need to clean out the smokebox but reduces the amount of work that has to be done. In the best case, smokebox cleaning could be avoided between boiler washouts at intervals of two weeks; the classic layout of a steam locomotive has the smokebox and chimney at the front of the locomotive, referred to as travelling "smokebox-first". Some designs reversed the layout to avoid problems caused by having the exhaust blowing back onto the crew. A spark arrester is installed within the smokebox; this may take the form of a cylindrical mesh running from the top of the blast pipe to the bottom of the chimney.
The purpose of a spark arrester is to prevent excessively large fragments of hot ash from being exhausted into the environment where they may pose a fire risk. For this reason, spark arresters are installed on locomotives running through dry environments, they should not be confused with the external spark arrestors fitted to some locomotives. The presence of a spark arrester may have a thermodynamic effect, distorting the draw of air over the fire and thereby reducing total power output, thus their use can be contentious. Locomotives fitted with a superheater will have a superheater header in the smokebox. Steam enters the header as "wet" steam, passes through a superheater element; this takes the form of a pipe. The steam enters a separate chamber in this time as superheated or dry steam; the advantage of superheating is that the steam has greater expansive properties when entering the cylinders, so more power can be gained from a smaller amoun
Condensation
Condensation is the change of the physical state of matter from the gas phase into the liquid phase, is the reverse of vaporisation. The word most refers to the water cycle, it can be defined as the change in the state of water vapour to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition. Condensation is initiated by the formation of atomic/molecular clusters of that species within its gaseous volume—like rain drop or snow flake formation within clouds—or at the contact between such gaseous phase and a liquid or solid surface. In clouds, this can be catalyzed by water-nucleating proteins, produced by atmospheric microbes, which are capable of binding gaseous or liquid water molecules. A few distinct reversibility scenarios emerge here with respect to the nature of the surface. Absorption into the surface of a liquid —is reversible as evaporation.
Adsorption onto solid surface at pressures and temperatures higher than the species' triple point—also reversible as evaporation. Adsorption onto solid surface at pressures and temperatures lower than the species' triple point—is reversible as sublimation. Condensation occurs when a vapor is cooled and/or compressed to its saturation limit when the molecular density in the gas phase reaches its maximal threshold. Vapor cooling and compressing equipment that collects condensed liquids is called a "condenser". Psychrometry measures the rates of condensation through evaporation into the air moisture at various atmospheric pressures and temperatures. Water is the product of its vapor condensation—condensation is the process of such phase conversion. Condensation is a crucial component of distillation, an important laboratory and industrial chemistry application; because condensation is a occurring phenomenon, it can be used to generate water in large quantities for human use. Many structures are made for the purpose of collecting water from condensation, such as air wells and fog fences.
Such systems can be used to retain soil moisture in areas where active desertification is occurring—so much so that some organizations educate people living in affected areas about water condensers to help them deal with the situation. It is a crucial process in forming particle tracks in a cloud chamber. In this case, ions produced by an incident particle act as nucleation centers for the condensation of the vapor producing the visible "cloud" trails. Commercial applications of condensation, by consumers as well as industry, include power generation, water desalination, thermal management and air conditioning. Numerous living beings use. A few examples of these are the Australian thorny devil, the darkling beetles of the Namibian coast, the coast redwoods of the West Coast of the United States. Condensation in building construction is an unwanted phenomenon as it may cause dampness, mold health issues, wood rot, weakening of mortar and masonry walls, energy penalties due to increased heat transfer.
To alleviate these issues, the indoor air humidity needs to be lowered, or air ventilation in the building needs to be improved. This can be done in a number of ways, for example opening windows, turning on extractor fans, using dehumidifiers, drying clothes outside and covering pots and pans whilst cooking. Air conditioning or ventilation systems can be installed that help remove moisture from the air, move air throughout a building; the amount of water vapour that can be stored in the air can be increased by increasing the temperature. However, this can be a double edged sword as most condensation in the home occurs when warm, moisture heavy air comes into contact with a cool surface; as the air is cooled, it can no longer hold as much water vapour. This leads to deposition of water on the cool surface; this is apparent when central heating is used in combination with single glazed windows in winter. Interstructure condensation may be caused by thermal bridges, insufficient or lacking insulation, damp proofing or insulated glazing.
Air well Bose–Einstein condensate Cloud physics Condenser DNA condensation Kelvin equation Phase diagram Phase transition Retrograde condensation Surface condenser Groasis Waterboxx Liquefaction of gases Sources
Boiler
A boiler is a closed vessel in which fluid is heated. The fluid does not boil; the heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation and sanitation. In a fossil fuel power plant using a steam cycle for power generation, the primary heat source will be combustion of coal, oil, or natural gas. In some cases byproduct fuel such as the carbon-monoxide rich offgasses of a coke battery can be burned to heat a boiler. In a nuclear power plant, boilers called steam generators are heated by the heat produced by nuclear fission. Where a large volume of hot gas is available from some process, a heat recovery steam generator or recovery boiler can use the heat to produce steam, with little or no extra fuel consumed. In all cases the combustion product waste gases are separate from the working fluid of the steam cycle, making these systems examples of External combustion engines; the pressure vessel of a boiler is made of steel, or of wrought iron.
Stainless steel of the austenitic types, is not used in wetted parts of boilers due to corrosion and stress corrosion cracking. However, ferritic stainless steel is used in superheater sections that will not be exposed to boiling water, electrically-heated stainless steel shell boilers are allowed under the European "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors. In live steam models, copper or brass is used because it is more fabricated in smaller size boilers. Copper was used for fireboxes, because of its better formability and higher thermal conductivity. For much of the Victorian "age of steam", the only material used for boilermaking was the highest grade of wrought iron, with assembly by riveting; this iron was obtained from specialist ironworks, such as those in the Cleator Moor area, noted for the high quality of their rolled plate, suitable for use in critical applications such as high-pressure boilers. In the 20th century, design practice moved towards the use of steel, with welded construction, stronger and cheaper, can be fabricated more and with less labour.
Wrought iron boilers corrode far more than their modern-day steel counterparts, are less susceptible to localized pitting and stress-corrosion. That makes the longevity of older wrought-iron boilers far superior to that of welded steel boilers. Cast iron may be used for the heating vessel of domestic water heaters. Although such heaters are termed "boilers" in some countries, their purpose is to produce hot water, not steam, so they run at low pressure and try to avoid boiling; the brittleness of cast iron makes it impractical for high-pressure steam boilers. The source of heat for a boiler is combustion of any of several fuels, such as wood, oil, or natural gas. Electric steam boilers use resistance- or immersion-type heating elements. Nuclear fission is used as a heat source for generating steam, either directly or, in most cases, in specialised heat exchangers called "steam generators". Heat recovery steam generators use. There are two methods to measure the boiler efficiency: Direct method Indirect methodDirect method: Direct method of boiler efficiency test is more usable or more common.
Boiler efficiency = power out / power in = / * 100%Q = rate of steam flow in kg/h Hg = enthalpy of saturated steam in kcal/kg Hf = enthalpy of feed water in kcal/kg q = rate of fuel use in kg/h GCV = gross calorific value in kcal/kg Indirect method: To measure the boiler efficiency in indirect method, we need a following parameter like: Ultimate analysis of fuel Percentage of O2 or CO2 at flue gas Flue gas temperature at outlet Ambient temperature in deg c and humidity of air in kg/kg GCV of fuel in kcal/kg Ash percentage in combustible fuel GCV of ash in kcal/kg Boilers can be classified into the following configurations: Pot boiler or Haycock boiler/Haystack boiler: A primitive "kettle" where a fire heats a filled water container from below. 18th century Haycock boilers produced and stored large volumes of low-pressure steam hardly above that of the atmosphere. These could burn wood or most coal. Efficiency was low. Flued boiler with one or two large flues—an early type or forerunner of fire-tube boiler.
Fire-tube boiler: Here, water fills a boiler barrel with a small volume left above to accommodate the steam. This is the type of boiler used in nearly all steam locomotives; the heat source is inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating surface below the boiling point. The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating surface which can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple tubes. In case of a locomotive-type boiler, a boiler
Great Western Railway
The Great Western Railway was a British railway company that linked London with the south-west and west of England, the Midlands, most of Wales. It was founded in 1833, received its enabling Act of Parliament on 31 August 1835 and ran its first trains in 1838, it was engineered by Isambard Kingdom Brunel, who chose a broad gauge of 7 ft —later widened to 7 ft 1⁄4 in —but, from 1854, a series of amalgamations saw it operate 4 ft 8 1⁄2 in standard-gauge trains. The GWR was the only company to keep its identity through the Railways Act 1921, which amalgamated it with the remaining independent railways within its territory, it was merged at the end of 1947 when it was nationalised and became the Western Region of British Railways; the GWR was called by some "God's Wonderful Railway" and by others the "Great Way Round" but it was famed as the "Holiday Line", taking many people to English and Bristol Channel resorts in the West Country as well as the far south-west of England such as Torquay in Devon, Minehead in Somerset, Newquay and St Ives in Cornwall.
The company's locomotives, many of which were built in the company's workshops at Swindon, were painted a Brunswick green colour while, for most of its existence, it used a two-tone "chocolate and cream" livery for its passenger coaches. Goods wagons were painted red but this was changed to mid-grey. Great Western trains included long-distance express services such as the Flying Dutchman, the Cornish Riviera Express and the Cheltenham Spa Express, it operated many suburban and rural services, some operated by steam railmotors or autotrains. The company pioneered the use of more economic goods wagons than were usual in Britain, it operated a network of road motor routes, was a part of the Railway Air Services, owned ships and hotels. The Great Western Railway originated from the desire of Bristol merchants to maintain their city as the second port of the country and the chief one for American trade; the increase in the size of ships and the gradual silting of the River Avon had made Liverpool an attractive port, with a Liverpool to London rail line under construction in the 1830s Bristol's status was threatened.
The answer for Bristol was, with the co-operation of London interests. The company was founded at a public meeting in Bristol in 1833 and was incorporated by Act of Parliament in 1835. Isambard Kingdom Brunel aged twenty-nine, was appointed engineer; this was by far Brunel's largest contract to date. He made two controversial decisions. Firstly, he chose to use a broad gauge of 7 ft to allow for the possibility of large wheels outside the bodies of the rolling stock which could give smoother running at high speeds. Secondly, he selected a route, north of the Marlborough Downs, which had no significant towns but which offered potential connections to Oxford and Gloucester; this meant. From Reading heading west, the line would curve in a northerly sweep back to Bath. Brunel surveyed the entire length of the route between London and Bristol himself, with the help of many, including his solicitor Jeremiah Osborne of Bristol law firm Osborne Clarke who on one occasion rowed Brunel down the River Avon himself to survey the bank of the river for the route.
George Thomas Clark played an important role as an engineer on the project, reputedly taking the management of two divisions of the route including bridges over the River Thames at Lower Basildon and Moulsford and of Paddington Station. Involvement in major earth-moving works seems to have fed Clark's interest in geology and archaeology and he, authored two guidebooks on the railway: one illustrated with lithographs by John Cooke Bourne; the first 22 1⁄2 miles of line, from Paddington station in London to Maidenhead Bridge station, opened on 4 June 1838. When Maidenhead Railway Bridge was ready the line was extended to Twyford on 1 July 1839 and through the deep Sonning Cutting to Reading on 30 March 1840; the cutting was the scene of a railway disaster two years when a goods train ran into a landslip. This accident prompted Parliament to pass the 1844 Railway Regulation Act requiring railway companies to provide better carriages for passengers; the next section, from Reading to Steventon crossed the Thames twice and opened for traffic on 1 June 1840.
A 7 1⁄4-mile extension took the line to Faringdon Road on 20 July 1840. Meanwhile, work had started at the Bristol end of the line, where the 11 1⁄2-mile section to Bath opened on 31 August 1840. On 17 December 1840, the line from London reached a temporary terminus at Wootton Bassett Road west of Swindon and 80.25 miles from Paddington. The section from Wootton Bassett Road to Chippenham was opened on 31 May 1841, as was Swindon Junction station where the Cheltenham and Great Western Union Railway to Cirencester connected; that was an independent line worked by the GWR, as was the Bristol and Exeter Railway, the first section of which from Bristol to Bridgwater was opened on 14 June 1841. The GWR main line remained incomplete during the construction of the 1-mile-1,452-yard Box Tunnel, ready for trains on 30 June 1841, after which trains ran the 152 miles from Paddington through to Bridgwater. In 1851, the GWR purchased the Kennet and Avon Canal, a competing carrier between London, Reading and Bristol.
The GWR
Poppet valve
A poppet valve is a valve used to control the timing and quantity of gas or vapour flow into an engine. It consists of a hole round or oval, a tapered plug a disk shape on the end of a shaft called a valve stem; the portion of the hole where the plug meets with it is referred to as the'seat' or'valve seat'. The shaft guides the plug portion by sliding through a valve guide. In exhaust applications a pressure differential helps to seal the valve and in intake valves a pressure differential helps open it; the poppet valve was most invented in 1833 by E. A. G. Young of the Newcastle and Frenchtown Railroad. Young patented his idea but the Patent Office fire of 1836 destroyed all records of it; the word poppet shares etymology with "puppet": it is from the Middle English popet, from Middle French poupette, a diminutive of poupée. The use of the word poppet to describe a valve comes from the same word applied to marionettes, which – like the poppet valve – move bodily in response to remote motion transmitted linearly.
In the past, "puppet valve" was a synonym for poppet valve. The valve stem moves up and down inside the passage called guide, fitted in the engine-block; the head of the valve called valve face, is ground to a 45 degree angle, so as to fit properly on the valve seat in the block and prevent leakage The poppet valve is fundamentally different from slide and oscillating valves. The main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication. In most cases it is beneficial to have a "balanced poppet" in a direct-acting valve. Less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces; the solenoid coil has to counteract only the spring forcePoppet valves are used in many industrial processes, from controlling the flow of milk to isolating sterile air in the semiconductor industry. However, they are most well known for their use in internal combustion and steam engines, as described below. Presta and Schrader valves used on pneumatic tyres are examples of poppet valves.
The Presta valve has no spring and relies on a pressure differential for opening and closing while being inflated. Poppet valves are employed extensively in the launching of torpedoes from submarines. Many systems use compressed air to expel the torpedo from the tube, the poppet valve recovers large quantity of this air in order to reduce the tell-tale cloud of bubbles that might otherwise betray the boat's submerged position. Poppet valves are used in most piston engines to open and close the intake and exhaust ports in the cylinder head; the valve is a flat disk of metal with a long rod known as the'valve stem' attached to one side. In early internal combustion engines it was common that the inlet valve was'automatic', i.e. opened by the suction in the engine and returned by a light spring. The exhaust valve had to be mechanically driven to open it against the pressure in the cylinder. Use of automatic valves simplified the mechanism but "valve float" limited the speed at which the engine could run, by about 1905 mechanically operated inlet valves were adopted for vehicle engines.
Mechanical operation is by pressing on the end of the valve stem, with a spring being used to return the valve to the closed position. At high revolutions per minute, the inertia of the spring means it cannot respond enough to return the valve to its seat between cycles, leading to "valve float" known as "valve bounce". In this situation desmodromic valves can be used which, being closed by a positive mechanical action instead of by a spring, are able to cycle at the high speeds required in, for instance and auto racing engines; the engine operates the valves by pushing on the stems with cams and cam followers. The shape and position of the cam determines the valve lift and when and how the valve is opened; the cams are placed on a fixed camshaft, geared to the crankshaft, running at half crankshaft speed in a four-stroke engine. On high-performance engines, the camshaft is movable and the cams have a varying height so, by axially moving the camshaft in relation with the engine RPM, the valve lift varies.
See variable valve timing. For certain applications the valve stem and disk are made of different steel alloys, or the valve stem may be hollow and filled with sodium to improve heat transport and transfer. Although a better heat conductor, an aluminium cylinder head requires steel valve seat inserts, where a cast iron cylinder head would have employed integral valve seats in the past; because the valve stem extends into lubrication in the cam chamber, it must be sealed against blow-by to prevent cylinder gases from escaping into the crankcase though the stem to valve clearance is small 0.04-0.06 mm, so a rubber lip-type seal is used to ensure that excessive oil is not drawn in from the crankcase on the induction stroke, that exhaust gas does not enter the crankcase on the exhaust stroke. Worn valve guides and/or defective oil seals can be diagnosed by a puff of blue smoke from the exhaust pipe on releasing the accelerator pedal after allowing the engine to overrun, when there is high manifold vacuum.
Such a condition occurs. In multi-valve engines, the conventional two-valves-per-cylinder setup is complemented by a minimum of an extra intake valve (three-valve cylinder hea
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