Basic introduction to Points Page 1 of 12 Uncontrolled document for information only see disclaimer** on last page Points are used to enable trains to switch tracks from one to another or into a station or siding etc. They are operated by electric powered point machines, hydraulically power clamplocks, torsion operated systems, air powered machines, mechanically operated points or train operated point machines (either by hydraulic type or spring). They also come in many different types of turnouts, these are as follows: LH & RH Turnouts (LH SHOWN) Known as Plain Leads Not all configurations are shown. Rail type: The track in the UK comes in various types, this is either Flat bottomed vertical, Flat bottomed inclined, Bull-head or UIC60 (European adopted rail). Bull head and UIC are disguisable by the way they look, but vertical and inclined look exactly the same. The only way to tell is by looking on the slide chairs it is mounted on. Either a V will be stamped on the chair for Vertical Rail, or X for Inclined. Vertical & Inclined rail are actually the same, it s the chairs it is mounted on that make it vertical or inclined.
Page 2 of 12 Basic layout of point equipment (track): Stretcher bars Types of Rail: Flat bottom and rare bull-head type rail UIC 54B type switch with UIC60 stock rail Switch length: The length of switch rails is determined by at what speed the train is to cross over to another track, the lengths are A,B,C,D,E,F,G,SG (small switch G ),H. The smallest switch is A for very slow speeds and up to H for very fast speeds. The length of switch will also determine how many stretchers should be fitted (minimum is two) and how long the backdrive will be. The switch length letter is found on the gauge blocks at the rear of the switch which hold the switch and stock together. Fastenings: The switch rail rests on slide chairs, some points are fitted with Austro or Schwihag rollers, the Austro rollers are becoming more obsolete as these take a full day to fit and are nonadjustable. The switch rail is only fixed at the rear to the stock rail by bolts and clips. The clips are either pandrol or fastclip type on modern points.
Page 3 of 12 Pandrol type E clip New modern fastclip type The slide chairs (also known as slide base plates ): Normal conventional non roller slide chair Schwihag type roller baseplate (modern) Austro-roller (becoming more obsolete) AS type chair screw used to secure the slide chairs to wooden sleepers only. M screws which are wider in diameter are used if AS screws no longer grip. Or Hilti coils are used instead (these are like large wall plugs). The track at each end is either welded together or fixed together by fishplates (left hand picture) or insulated block joints ( IBJs ) (right hand picture), if the track circuit voltage needs to be separated. Sometimes six hole insulated block joints are used which are insulated by glue and not plastic.
Track bed: Page 4 of 12 The points are mounted on mostly wooden timbers and on more modern layouts on concrete reinforced sleepers. On concrete sleepers different track components are used to secure the rails and to stop lateral movement. The track bed is made up of large stones known as ballast, this is compacted by hand using kango machines or a S&C (switch and crossing) tamping machine. The track is either level or has a cant, where it is on a bend and has to lean either left of right to enable trains to go around the bend at higher speeds. Points are usually sited on level parts of the railway away from bends. The cant is measured using a track gauge with super-elevation gauge fitted (pictured below). The track gauge: The distance between both rails has to be maintained within a pre-determined distance known as the track gauge. This depends on the type of rail installed. The track gauge pictured above also measures this distance. The tolerances are; for flat bottomed VERTICAL rail it is 1430-1438mm, for INCLINED, BULL HEAD & UIC60 rail it is 1433-1441mm. S&T equipment: Conventional fixed Stretchers: Super-elevation gauge The switch rails are independent of one another but are fixed together by stretcher bars. The new type of reinforced stretcher bar is coloured yellow and have the manufacturers name and date marks on them. The points ID number, should always be on the normally closed side and readable from the facing direction. Facing direction (arrowed). Stretcher shoe Insulated swan neck (to stop the track circuit rail voltage shorting). The soleplate. By law all points must have one to hold the gauge at the front. The new yellow stretchers are secured to the rail by stretcher shoes, these are also coloured yellow and are fixed together by using the new type hardlock bolts. The nuts used are male and female and lock together using a torque wrench set to 250Nm.
Page 5 of 12 Before yellow stretchers were introduced, they were black and were secured using either square headed black bolts or hexagon black bolts with spring washers. The stretchers and bolts are still widely used on many points, but if a fault (ie crack is detected) they should then be changed to yellow. These type of stretchers are known as fixed, this is because they are drilled and cannot be altered once bolted. The stretchers come in two formats (on plain leads only); these are either long or short. The long ones are only used at the front position (at the toe), and all the rest are the short type. The long stretcher is basically longer because it has what is known as a kicking strap which protrudes through both sides of the points to stop the switch rail from possible lifting although very rare. On switch diamonds (machine operated) the stretchers are the same but use coloured angled shoes (these are used to make sure the stretchers are straight and do not bend because of the extreme angles of the switch rails). On switch diamonds that are operated by clamplocks, the stretchers are installed with the insulation in the middle and also use coloured shoes. On double slip layouts, there are four different coloured shoes used; black, grey, green & red. Switch diamonds with yellow stretchers, coloured shoes (grey & white) and insulations set in the middle. Old style fixed black stretchers using hexagon black bolts (plain lead set shown). Adjustable stretchers: Modern point layouts rebuilt on concrete sleepers will more than likely have adjustable stretchers, these are not fixed and can be adjusted at anytime to alter the FWC or switch openings. The brackets which they are fixed to are totally different to the shoes mentioned above. The stretchers have no swan neck insulations but have rubber insulations at both ends where they are fixed to the brackets. They are held in place by either half-lock nut type nuts or hardlock nuts. Both configurations require different maintenance techniques. Adjustable stretchers can only, at the moment, be fitted to UIC type rail. There are also less fitted; a C type switch UIC54B rail for instance will only have two stretchers fitted as opposed to three on vertical and inclined points. Also modern points are fitted with an additional detector at mid position to double check the points are fitting up along the entire length.
Backdrives: Page 6 of 12 FWC on open side RSO on closed side Pictured above is a LH backdrive fitted to a C switch. All Vertical track points over a C switch MUST have a backdrive fitted and all Inclined track points over D switch MUST also have one fitted. The backdrive is used to push up the rear of the points and hold them there by using cranks and rodding. They help maintain the RSO and FWC and prevent FBC. RSO (residual switch opening): the small closed gap that should be between 1.5-2mm. FWC (free-wheel clearance): the other open gap in which the train wheel flange runs through mentioned later. FBC (flange back contact): if the FWC & RSO are incorrect and track gauge is wide, the train wheel may hit the back of the switch rail and cause the stretchers to break. The backdrives come in many many different configurations, they can be fitted to the left, right or in the centre (known as a four foot backdrive), these are used in limited clearance areas where normal (six foot) backdrives cannot be installed, such as stations or cuttings. Backdrives now come as a kit and are installed on plates instead of bolted through the sleeper. The price of a typical kit can start at around 2000. The operating equipment: Four foot backdrive Lock fender Pictured above is a HW point machine on points fitted with adjustable stretchers.
Page 7 of 12 998 type detector used to detect points N or R Clamp used to secure points out of use. Above is a mechanically operated set of points by lever in signalbox. HW point machine basic layout: Drive rod, this drives the points normal or reverse. HW1000/2000 machine Lock fender, this connects both switch rails as a connection point for the lock rod. This with the lock rod, locks the points either normal or reverse. The lock rod, connects to the lock blades. Short detection rod. This detects the nearest to machine switch rail. The long detection rod. This detects furthest switch rail from machine. Switch rail bracket, lock arm s are fixed to this. Lock body. Clamplock operated basic plain lead layout: Centre thrust bracket, the hydraulic actuators are fixed here. Brass locking piece. Inside the body, two microswitches copy the fixed and adjustable cams to detect the points closed and locked. Lock arm, this locks the switch blade to the stock rail via brass locking piece. Hydraulic actuators, these drive the points normal or reverse. Adjustable tie-bar, holds drive lock slides together. Drive lock slide, this pushes lock arm in and up to lock switch blade.