* Nomenclature

Left-hand turnout
 

Right-hand turnout

* Common components
Stretcher Bars
   

* Legal requirement on turnouts
* Insulator required for correct track circuit operation

 Point locking
* LUL provides facing point locks on all points where there are signalledmoves in a facing direction on or potential foul of passenger lines. This requirement includes shunting trains as well as passenger trains. Facing point locks may also be provided in depots or yards but are only mandatory when associated with a signalled passenger train moves.

Switch blade closed. If switch was open, the dab would be in the other port

* In four foot / six foot Point locking is generally achieved using lock dogs on lock notches on the lock bars (Clamplocks use a different system, covered later)

* Lock dogs are moved out of the notches before the drive moves the switch rails and hence lock bars

 Glass Enclosed valve for Point ground Lock

GLASS ENCLOSED(GE) VALVE TERMINALS

GLASS ENCLOSED(GE) FOR POINT GROUNDLOCK(2)

* This valve is a self contained unit with an integral transformer and rectifier, a soft iron core and, in some cases, a capacitor.

* The operation of the valve is controlled from a 100V or 110V AC supply. This is rectified to DC inside the valve enclosure to energise the coil so that the pin valve forced opened. Air is then supplied to the ground lock (WL) unit to lift the locking dab and free the points.

* Loss of air supply or power to the valve will cause the points to remain locked (fail safe arrangement).

Point Auxiliary valve for Pneumatic Point Machines

POINT AUXILIARY NW/RW VALVE FOR PNEUMATIC POINT MACHINES

* The point auxiliary unit has two glass enclosed valve sattached to it: one used to control the supply of compressed air to drive the points normal and a second to drive the points reverse.

* The electrical feed to the corresponding point control is normally maintained at all times, even when all movement is completed. The exception to this is with clamp lock points where the valves are normally de-energised.

TYPES OF POINT MACHINES

* 4 Foot Point
* 6 Foot Point
* Chairlock Point

* Clamplock Point
* M63 or Style 63 Point (Same machine, different name)
* Surelock Point

FOUR FOOT POINTS

* The Four Foot point mechanisms are mechanical devices mounted within the four foot, normally mounted on the
continuous rail side.

* The versions of the 4ft point mechanism are categorized as left-hand and right-hand, depending on whether they are installed to the left or right side of the track center line, with points viewed in the facing direction.

* The following two assemblies differ between the left-hand and right-hand version of the 4ft point mechanism:
1. Point and lock mechanism
2. PL&D Box

FOUR FOOT ESCAPMENT

Escapement is part of mechanism of four foot points driven by motor and having locking dabs for facing point locks and locking ports for ground lock. The points are operated via a crank driven from the escapement.

FOUR FOOT POINTS

* Electro-pneumatic or Electro-hydraulic operation.

a. Electro-hydraulic operation on Central Line.
b. Electro-pneumatic operation on Jubilee, Northern and Piccadilly lines.

* Mounted between the running rails.
* Can be used on Bullhead and Flat Bottom rail.
* Right-handed or left-handed machines in operation.

FOUR FOOT PL&D BOX

FOUR FOOT POINT MECHANISM

FOUR FOOT PL&D CONTACT ARRANGEMENT

FOUR FOOT GROUND LOCK

* In addition to the facing point locks a ground lock must also be fitted to air operated points used for facing passenger train moves. The reason for this is certain types of machine maintain stored energy, which is capable of moving the points under fault conditions, and also without the ground lock the mechanism has very little resistance to movement under vibration.

* A ground lock (WL) is a device which locks the points in position by inserting a dab into one of a pair of ports in the drive mechanism when the lifting magnet is de-energised and the points are fully in the correct position.

* The ground lock must be independently energised. A contact is made when the dab is fully in a locking port. It must also be detected; this can be done separately if not integral to the points detection as is the case with chair locks.

* It is not mandatory to provide either a facing point lock or ground lock when the points are only ever used for trailing moves, unless sectional route releasing is required in which case the points would be held by a ground lock.

FOUR FOOT GROUND LOCK

‘V’ Style Frame Chairlock Point Circuits

The Point Control, Lever Lock and Indication circuits for Chairlocks are identical to the Four  Foot point circuits already discussed.

Detection

Unlike Four Foot points, a Chairlock layout uses two separate and independent detection units, one for each rail switch. Each unit proves that its corresponding switch is either fully home and locked or open sufficiently.

The four contacts in each unit are labelled four, three, two and one with the number four contact always drawn at the top as shown in the contact arrangements for both layouts Figs 5.2 and 5.4.

If the right-hand switch is closed when the points are Normal (Fig 5.1) this will be a Normal contact. It follows that the left-hand unit is the opposite (Fig 5.2).

Right hand unit

If the right-hand switch is open when the points are Normal (Fig 5.3) it will be a Reverse contact. It follows that the left-hand unit is the opposite (Fig 5.4).

left hand unit

Although there are four contacts in each unit, contact number one is used exclusively for the control of the WL and therefore there are only three contacts available for the detection circuit. Number two contact is used for the open switch detection and contact numbers three and four are used for the closed switch detection.

The detection circuit needs to check the contacts in both units before picking up the WKR. If the left-hand turnout above is in the Normal position (Fig 5.3) the right-hand unit proves that its associated switch is open a minimum of 3 1/2″ (89 mm). The left-hand unit proves that its switch is both fully home and locked.

Fig 5.5 below shows a typical detection circuit for a left hand turnout, single ended set of Chairlocks. The BX supply to the WKR is always fed to the right-hand unit on terminal 3:3 (this is also the same for a right-hand turnout) from here it is looped to 2:2 on the same unit. The feed then goes to 3:3 on the left hand unit to the WKR. The NX returns via 4 and 4:4 on the left hand unit.

As with Four Foots the looping in the units is there to change swap the BX and NX supplies over in order to drive the three position WKR Normal or Reverse.

Left-hand turnout, single ended Chairlock detection circuit

It should be noted that there is no WL proving contact in the circuit as it is indirectly proved via the mechanical design of the Chairlock unit. The contact box is sprung to the neutral position and relies on the WL to maintain pressure on the cam follower arm which in turn follows the profiles of the lock and switch detection cams to make the contacts.

If the WL is not fully de-energised it will not apply pressure on the cam follower arm and therefore the contacts will remain broken (regardless of whether the points are actually mechanically home and locked).

Fig 5.6 below is an example of a left hand turnout, double ended layout detection circuit.

Right-hand Turnout, Single End, With WL

Right-Hand Turnout, Double Ended, Without WL

Right-hand Turnout, Double Ended, WL At ‘A’ End

Right-hand Turnout, Double Ended, WL At ‘B’ End

Left-hand Turnout, Single End, Without WL

Left-hand Turnout, Single End, With WL

Left-hand Turnout, Double Ended, Without WL

Left-hand Turnout, Double Ended, WL At ‘A’ End

Left-hand Turnout, Double Ended, WL At ‘B’ End

Left-hand Turnout, Double Ended, WL At Both Ends

Right-hand Turnout, Single End, Without WL, V’ Style Frame Four Foot Point Circuits, Right-hand Turnout, Double Ended, WL At ‘A’ End,  Right-Hand Turnout, Double Ended, Without WL, Right-hand Turnout, Double Ended, WL At ‘A’ End, ight-hand Turnout, Double Ended, WL At ‘B’ End,  Left-hand Turnout, Single End, Without WL,  Left-hand Turnout, Single End, With WL, Left-hand Turnout, Double Ended, Without WL, Left-hand Turnout, Double Ended, WL At ‘A’ End, Left-hand Turnout, Double Ended, WL At ‘B’ End,Left-hand Turnout, Double Ended, WL At Both Ends, Railway Right-hand & Left-hand Turnout Point Circuits

Railway WL Control :- Contact number one on the open switch is used to control the de-energising of the WL in the same way that the AN & BR contacts are used on a set of Four Foots points. In the Normal position (Fig 5.7) the L.H. WL is locking the points. When they are thrown Normal to Reverse, the WL is energised via 1’s contact on the R.H. unit

In the Reverse position (Fig 5.8) the Right-hand WL is locking the points. When they are thrown Reverse to Normal, the WL is energised via 1’s contact on the Left-hand unit Fig 5.9 shows a typical WL control circuit using contact number one in the respective units.

This section shows a selection of Chairlock point circuits controlled from a ‘V’ style frame

Right-hand Turnout, Single End, With WL

Left-hand Turnout, Single End, With WL

Right-hand Turnout, Double Ended, WL At Both Ends

Left-hand Turnout, Double Ended, WL At Both Ends

Left-hand Turnout, Double Ended, WL At Both Ends

Flat Bottom Four Foot Point Circuits

The widespread introduction of plug-in ‘Q’ style relays and track conversions from bullhead to flat bottom rail has brought about improvements in the design of the four foot point circuits. We shall take a look at the differences in the circuits, firstly at the Point Control and Lever Lock circuits and then at the Detection and WL control circuits.