Misplaced Pages

#763236

59-426: As piston (s) move along the bore of the master cylinder, this movement is transferred through the hydraulic fluid , to result in a movement of the slave cylinder(s). The hydraulic pressure created by moving a piston (inside the bore of the master cylinder) toward the slave cylinder(s) compresses the fluid evenly, but by varying the comparative surface area of the master cylinder and each slave cylinder, one can vary

118-422: A 'fully floating' design that is loose in both components. All pins must be prevented from moving sideways and the ends of the pin digging into the cylinder wall, usually by circlips . Gas sealing is achieved by the use of piston rings . These are a number of narrow iron rings, fitted loosely into grooves in the piston, just below the crown. The rings are split at a point in the rim, allowing them to press against

177-404: A common device used for delivering water to steam boilers, especially in steam locomotives. It is a typical application of the injector principle used to deliver cold water to a boiler against its own pressure, using its own live or exhaust steam, replacing any mechanical pump . When first developed, its operation was intriguing because it seemed paradoxical, almost like perpetual motion , but it

236-418: A divergent "delivery cone" which slows the jet, converting kinetic energy back into static pressure energy above the pressure of the boiler enabling its feed through a non-return valve. Most of the heat energy in the condensed steam is returned to the boiler, increasing the thermal efficiency of the process. Injectors are therefore typically over 98% energy-efficient overall; they are also simple compared to

295-407: A given amount W m {\displaystyle W_{m}} (in kg/h) of motive fluid. Other key properties of an injector include the fluid inlet pressure requirements i.e. whether it is lifting or non-lifting. In a non-lifting injector, positive inlet fluid pressure is needed e.g. the cold water input is fed by gravity. The steam-cone minimal orifice diameter is kept larger than

354-420: A large ejector for releasing the brakes when stationary and a small ejector for maintaining the vacuum against leaks. The exhaust from the ejectors is invariably directed to the smokebox, by which means it assists the blower in draughting the fire. The small ejector is sometimes replaced by a reciprocating pump driven from the crosshead because this is more economical of steam and is only required to operate when

413-452: A lighter alloy could be used. To produce pistons that could survive engine combustion temperatures, it was necessary to develop new alloys such as Y alloy and Hiduminium , specifically for use as pistons. A few early gas engines had double-acting cylinders , but otherwise effectively all internal combustion engine pistons are single-acting . During World War II , the US submarine Pompano

472-483: A modern internal-combustion engine.) Another factor is that since almost all steam engines use crossheads to translate the force to the drive rod, there are few lateral forces acting to try and "rock" the piston, so a cylinder-shaped piston skirt isn't necessary. Piston pumps can be used to move liquids or compress gases . There are two special type of pistons used in air cannons : close tolerance pistons and double pistons. In close tolerance pistons O-rings serve as

531-417: A nozzle. In general, compressible flows through a diverging duct increases velocity as a gas expands. The two sketches at the bottom of figure 15 are both diverging, but the bottom one is slightly curved, and produced the highest velocity flow parallel to the axis. The area of a duct is proportional to the square of the diameter, and the curvature allows the steam to expand more linearly as it passes through

590-503: A primary booster, a secondary high-vacuum (HV) ejector, and a tertiary low-vacuum (LV) ejector. As per the two-stage system, initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to pull vacuum to the lower intermediate pressure. Finally the booster

649-430: A sign of low pressure or failure in one of the brake circuits. Piston A piston is a component of reciprocating engines , reciprocating pumps , gas compressors , hydraulic cylinders and pneumatic cylinders , among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings . In an engine, its purpose is to transfer force from expanding gas in

SECTION 10

#1732802457764

708-422: A special cooling cavity. Injector supplies this cooling cavity «A» with oil through oil supply channel «B». For better temperature reduction construction should be carefully calculated and analysed. Oil flow in the cooling cavity should be not less than 80% of the oil flow through the injector. The pin itself is of hardened steel and is fixed in the piston, but free to move in the connecting rod. A few designs use

767-411: A steam jet to convert the pressure energy of the steam to velocity energy, reducing its pressure to below that of the atmosphere, which enables it to entrain a fluid (e.g., water). After passing through the convergent "combining cone", the mixed fluid is fully condensed, releasing the latent heat of evaporation of the steam which imparts extra velocity to the water . The condensate mixture then enters

826-465: A steep face on the inlet side and a gentle curve on the exhaust. Despite this, cross scavenging was never as effective as hoped. Most engines today use Schnuerle porting instead. This places a pair of transfer ports in the sides of the cylinder and encourages gas flow to rotate around a vertical axis, rather than a horizontal axis. [REDACTED] Media related to Deflector pistons at Wikimedia Commons In racing engines, piston strength and stiffness

885-487: A supply of live steam if no exhaust steam was available. Injectors can be troublesome under certain running conditions, such as when vibration causes the combined steam and water jet to "knock off". Originally the injector had to be restarted by careful manipulation of the steam and water controls, and the distraction caused by a malfunctioning injector was largely responsible for the 1913 Ais Gill rail accident . Later injectors were designed to automatically restart on sensing

944-414: A two-stage system consists of a primary high-vacuum (HV) ejector and a secondary low-vacuum (LV) ejector. Initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to finally pull vacuum to the required pressure. In operation a three-stage system consists of

1003-439: A valve to prevent air being sucked in at the overflow. Efficiency was further improved by the development of a multi-stage injector which is powered not by live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the residual energy in the exhaust steam which would otherwise go to waste. However, an exhaust injector also cannot work when the locomotive is stationary; later exhaust injectors could use

1062-404: A valve, but O-rings are not used in double piston types. Injector An injector is a system of ducting and nozzles used to direct the flow of a high-pressure fluid in such a way that a lower pressure fluid is entrained in the jet and carried through a duct to a region of higher pressure. It is a fluid-dynamic pump with no moving parts except a valve to control inlet flow. Depending on

1121-399: Is a piston for a petrol engine that has been reduced in size and weight as much as possible. In the extreme case, they are reduced to the piston crown, support for the piston rings, and just enough of the piston skirt remaining to leave two lands so as to stop the piston rocking in the bore. The sides of the piston skirt around the gudgeon pin are reduced away from the cylinder wall. The purpose

1180-516: Is defined as ratio of the injector's outlet pressure P 2 {\displaystyle P_{2}} to the inlet pressure of the suction fluid P 1 {\displaystyle P_{1}} . The entrainment ratio of the injector, W s / W m {\displaystyle W_{s}/W_{m}} , is defined as the amount W s {\displaystyle W_{s}} (in kg/h) of suction fluid that can be entrained and compressed by

1239-446: Is mostly to reduce the reciprocating mass, thus making it easier to balance the engine and so permit high speeds. In racing applications, slipper piston skirts can be configured to yield extremely light weight while maintaining the rigidity and strength of a full skirt. Reduced inertia also improves mechanical efficiency of the engine: the forces required to accelerate and decelerate the reciprocating parts cause more piston friction with

SECTION 20

#1732802457764

1298-406: Is needed for at least a short length adjacent to each wheel, whenever the wheel can move relative to the car's chassis (this is the case on any car with steering and other suspension movements; some drag racers and go-karts have no rear suspension, as the rear axle is welded to the chassis, and some antique cars also have no rear suspension movement). A reservoir above each master cylinder supplies

1357-443: Is on the picture. This type of piston is widely used in car diesel engines . According to purpose, supercharging level and working conditions of engines the shape and proportions can be changed. High-power diesel engines work in difficult conditions. Maximum pressure in the combustion chamber can reach 20 MPa and the maximum temperature of some piston surfaces can exceed 450 °C. It is possible to improve piston cooling by creating

1416-411: Is required for excess steam or water to discharge, especially during starting. If the injector cannot initially overcome boiler pressure, the overflow allows the injector to continue to draw water and steam. There is at least one check valve (called a "clack valve" in locomotives because of the distinctive noise it makes ) between the exit of the injector and the boiler to prevent back flow, and usually

1475-445: Is split, with the greater part of the flow leaving the system, while a portion of the flow is returned to the jet pump installed below ground in the well. This recirculated part of the pumped fluid is used to power the jet. At the jet pump, the high-energy, low-mass returned flow drives more fluid from the well, becoming a low-energy, high-mass flow which is then piped to the inlet of the main pump. Shallow well pumps are those in which

1534-435: Is typically much higher than that of a passenger car engine, while the weight is much less, to achieve the high engine RPM necessary in racing. Hydraulic cylinders can be both single-acting or double-acting . A hydraulic actuator controls the movement of the piston back and/or forth. Guide rings guides the piston and rod and absorb the radial forces that act perpendicularly to the cylinder and prevent contact between sliding

1593-399: The amount of force and displacement applied to each slave cylinder, relative to the amount of force and displacement applied to the master cylinder. The most common vehicle uses of master cylinders are in brake and clutch systems. For hydraulic brakes or clutches alike, flexible high-pressure hoses or inflexible hard-walled metal tubing may be used; but the flexible variety of tubing

1652-399: The application, an injector can also take the form of an eductor-jet pump , a water eductor or an aspirator . An ejector operates on similar principles to create a vacuum feed connection for braking systems etc. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream. The steam injector is

1711-401: The benefit is reduced. [REDACTED] Media related to Slipper pistons at Wikimedia Commons Deflector pistons are used in two-stroke engines with crankcase compression, where the gas flow within the cylinder must be carefully directed in order to provide efficient scavenging . With cross scavenging , the transfer (inlet to the cylinder) and exhaust ports are on directly facing sides of

1770-406: The collapse in vacuum from the steam jet, for example with a spring-loaded delivery cone. Another common problem occurs when the incoming water is too warm and is less effective at condensing the steam in the combining cone. That can also occur if the metal body of the injector is too hot, e.g. from prolonged use. The internal parts of an injector are subject to erosive wear, particularly damage at

1829-479: The combining cone minimal diameter. The non-lifting Nathan 4000 injector used on the Southern Pacific 4294 could push 12,000 US gallons (45,000 L) per hour at 250 psi (17 bar). The lifting injector can operate with negative inlet fluid pressure i.e. fluid lying below the level of the injector. It differs from the non-lifting type mainly in the relative dimensions of the nozzles. An overflow

Master cylinder - Misplaced Pages Continue

1888-406: The connecting rod is angled for much of its rotation, there is also a side force that reacts along the side of the piston against the cylinder wall. A longer piston helps to support this. Trunk pistons have been a common design of piston since the early days of the reciprocating internal combustion engine. They were used for both petrol and diesel engines, although high speed engines have now adopted

1947-413: The cylinder to the crankshaft via a piston rod and/or connecting rod . In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder. An internal combustion engine is acted upon by the pressure of

2006-399: The cylinder wall than the fluid pressure on the piston head. A secondary benefit may be some reduction in friction with the cylinder wall, since the area of the skirt, which slides up and down in the cylinder is reduced by half. However, most friction is due to the piston rings , which are the parts which actually fit the tightest in the bore and the bearing surfaces of the wrist pin, and thus

2065-418: The cylinder wall. To prevent the incoming mixture passing straight across from one port to the other, the piston has a raised rib on its crown. This is intended to deflect the incoming mixture upwards, around the combustion chamber . Much effort, and many different designs of piston crown, went into developing improved scavenging. The crowns developed from a simple rib to a large asymmetric bulge, usually with

2124-515: The cylinder with a light spring pressure. Two types of ring are used: the upper rings have solid faces and provide gas sealing; lower rings have narrow edges and a U-shaped profile, to act as oil scrapers. There are many proprietary and detail design features associated with piston rings. Pistons are usually cast or forged from aluminium alloys . For better strength and fatigue life, some racing pistons may be forged instead. Billet pistons are also used in racing engines because they do not rely on

2183-488: The duct. An ideal gas cools during adiabatic expansion (without adding heat), releasing less energy than the same gas would during isothermal expansion (constant temperature). Expansion of steam follows an intermediate thermodynamic process called the Rankine cycle . Steam does more work than an ideal gas, because steam remains hot during expansion. The extra heat comes from enthalpy of vaporization , as some of

2242-434: The expanding combustion gases in the combustion chamber space at the top of the cylinder. This force then acts downwards through the connecting rod and onto the crankshaft . The connecting rod is attached to the piston by a swivelling gudgeon pin (US: wrist pin). This pin is mounted within the piston: unlike the steam engine, there is no piston rod or crosshead (except big two stroke engines). The typical piston design

2301-427: The first engine design to place the gudgeon pin directly within the piston. Otherwise these trunk engine pistons bore little resemblance to the trunk piston; they were extremely large diameter and double-acting. Their 'trunk' was a narrow cylinder mounted in the centre of the piston. [REDACTED] Media related to Trunk pistons at Wikimedia Commons Large slow-speed Diesel engines may require additional support for

2360-479: The flue gases from the boiler which are then ejected via the chimney. The effect is to increase the draught on the fire to a degree proportional to the rate of steam consumption, so that as more steam is used, more heat is generated from the fire and steam production is also increased. The effect was first noted by Richard Trevithick and subsequently developed empirically by the early locomotive engineers; Stephenson's Rocket made use of it, and this constitutes much of

2419-497: The ground surface for easy maintenance. The advent of the electrical submersible pump has partly replaced the need for jet type well pumps, except for driven point wells or surface water intakes. In practice, for suction pressure below 100 mbar absolute, more than one ejector is used, usually with condensers between the ejector stages. Condensing of motive steam greatly improves ejector set efficiency; both barometric and shell-and-tube surface condensers are used. In operation

Master cylinder - Misplaced Pages Continue

2478-575: The gudgeon pin. Lubrication of the crosshead has advantages over the trunk piston as its lubricating oil is not subject to the heat of combustion : the oil is not contaminated by combustion soot particles, it does not break down owing to the heat and a thinner, less viscous oil may be used. The friction of both piston and crosshead may be only half of that for a trunk piston. Because of the additional weight of these pistons, they are not used for high-speed engines. [REDACTED] Media related to Crosshead pistons at Wikimedia Commons A slipper piston

2537-471: The injector became widely adopted for steam locomotives as an alternative to mechanical pumps. Strickland Landis Kneass was a civil engineer , experimenter, and author, with many accomplishments involving railroading. Kneass began publishing a mathematical model of the physics of the injector, which he had verified by experimenting with steam. A steam injector has three primary sections: Figure 15 shows four sketches Kneass drew of steam passing through

2596-486: The jet assembly is attached directly to the main pump and are limited to a depth of approximately 5-8m to prevent cavitation . Deep well pumps are those in which the jet is located at the bottom of the well. The maximum depth for deep well pumps is determined by the inside diameter of and the velocity through the jet. The major advantage of jet pumps for deep well installations is the ability to situate all mechanical parts (e.g., electric/petrol motor, rotating impellers) at

2655-462: The lighter weight slipper piston . A characteristic of most trunk pistons, particularly for diesel engines, is that they have a groove for an oil ring below the gudgeon pin , in addition to the rings between the gudgeon pin and crown. The name 'trunk piston' derives from the ' trunk engine ', an early design of marine steam engine . To make these more compact, they avoided the steam engine's usual piston rod with separate crosshead and were instead

2714-401: The locomotive smokebox. The sketch on the right shows a cross section through a smokebox, rotated 90 degrees; it can be seen that the same components are present, albeit differently named, as in the generic diagram of an injector at the top of the article. Exhaust steam from the cylinders is directed through a nozzle on the end of the blastpipe, to reduce pressure inside the smokebox by entraining

2773-407: The many moving parts in a feed pump. Fluid feed rate and operating pressure range are the key parameters of an injector, and vacuum pressure and evacuation rate are the key parameters for an ejector. Compression ratio and the entrainment ratio may also be defined: The compression ratio of the injector, P 2 / P 1 {\displaystyle P_{2}/P_{1}} ,

2832-491: The master cylinder with enough brake fluid to avoid air from entering the master cylinder (even the typical clutch uses brake fluid, but it may also be referred to as "clutch fluid" in a clutch application). Each piston in a master cylinder operates a brake circuit , and for modern light trucks and passenger cars, usually, there are two circuits for safety reasons. This is done in a diagonally split hydraulic system i.e. one circuit operates front left and right rear brakes, while

2891-433: The metal parts. Steam engines are usually double-acting (i.e. steam pressure acts alternately on each side of the piston) and the admission and release of steam is controlled by slide valves , piston valves or poppet valves . Consequently, steam engine pistons are nearly always comparatively thin discs: their diameter is several times their thickness. (One exception is the trunk engine piston, shaped more like those in

2950-415: The reason for its notably improved performance in comparison with contemporary machines. The use of injectors (or ejectors) in various industrial applications has become quite common due to their relative simplicity and adaptability. For example: Jet pumps are commonly used to extract water from water wells . The main pump, often a centrifugal pump , is powered and installed at ground level. Its discharge

3009-613: The secondary works the other two wheels. If there is a failure in one of the brake lines or the caliper seal, one of the circuits will still be intact and still be able to stop the vehicle. Each circuit works on opposite corners in order to avoid destabilizing the vehicle that would happen if only one axle has brakes while the other axle has none. With only one circuit working there are significantly longer stopping distances and repairs should be done before driving again. When inspecting brake pads and rotors for wear, drivers and mechanics need to look out for uneven component wear since it could be

SECTION 50

#1732802457764

3068-405: The side forces on the piston. These engines typically use crosshead pistons. The main piston has a large piston rod extending downwards from the piston to what is effectively a second smaller-diameter piston. The main piston is responsible for gas sealing and carries the piston rings. The smaller piston is purely a mechanical guide. It runs within a small cylinder as a trunk guide and also carries

3127-429: The size and architecture of available forgings, allowing for last-minute design changes. Although not commonly visible to the naked eye, pistons themselves are designed with a certain level of ovality and profile taper, meaning they are not perfectly round, and their diameter is larger near the bottom of the skirt than at the crown. Early pistons were of cast iron , but there were obvious benefits for engine balancing if

3186-408: The steam condenses back into dropplets of water intermixed with steam. At the end of the nozzle, the steam has very high velocity, but at less than atmospheric pressure, drawing in cold water which becomes entrained in the stream, where the steam condenses into droplets of water in a converging duct. The delivery tube is a diverging duct where the force of deceleration increases pressure, allowing

3245-471: The stream of water to enter the boiler. The injector consists of a body filled with a secondary fluid, into which a motive fluid is injected. The motive fluid induces the secondary fluid to move. Injectors exist in many variations, and can have several stages, each repeating the same basic operating principle, to increase their overall effect. It uses the Venturi effect of a converging-diverging nozzle on

3304-652: The throat of the delivery cone which may be due to cavitation . An additional use for the injector technology is in vacuum ejectors in continuous train braking systems , which were made compulsory in the UK by the Regulation of Railways Act 1889 . A vacuum ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its rugged simplicity and lack of moving parts. A steam locomotive usually has two ejectors:

3363-420: The train is moving. Vacuum brakes have been superseded by air brakes in modern trains, which allow the use of smaller brake cylinders and/or higher braking force due to the greater difference from atmospheric pressure. An empirical application of the principle was in widespread use on steam locomotives before its formal development as the injector, in the form of the arrangement of the blastpipe and chimney in

3422-400: Was fitted with a prototype of the infamously unreliable H.O.R. double-acting two-stroke diesel engine. Although compact, for use in a cramped submarine, this design of engine was not repeated. [REDACTED] Media related to Internal combustion engine pistons at Wikimedia Commons Trunk pistons are long relative to their diameter. They act both as a piston and cylindrical crosshead . As

3481-562: Was later explained using thermodynamics . Other types of injector may use other pressurised motive fluids such as air. The injector was invented by Henri Giffard in early 1850s and patented in France in 1858, for use on steam locomotives . It was patented in the United Kingdom by Sharp, Stewart and Company of Glasgow . After some initial scepticism resulting from the unfamiliar and superficially paradoxical mode of operation,

#763236