Point

 Important facts  - 

1. There should be no change in gradient within 30 m in case of BG and 15 m in case of MG of the point.

2. For IRS point Stroke is 143 mm and  opening is 115+_ 3mm.For IRS clamp type point machine maximum stroke is 220 mm.

3. For TWS Point stroke is 220 mm and opening is 160 mm.Tolerance is not mentioned anywhere.

4. Clearance of check rail ( Wing Rail) on crossing is 44 mm to 48 mm.

5. Chipped/ Cracked Switch -  Chipped length is the portion where tongue rail has worn out for a depth of more than 10 mm over a continuous length of 10 mm.If the total  chipped length is 200 mm within 1000 mm from toe of switch rail, this switch rail will be called Chippped Switch.

6. Knife Edged tip- If thickness of tip is less than 2 mm over a length of  more than 100 mm anywhere upto a distance of 1000 mm from its toe, then it is knife edged tip.

7. Vertical wear - It is measured at a point where tongue and stock rail are at same level.Vertical wear  allowed is 8 mm for 60 kg

IRS Point Machine -  throw is 143 mm ( 160 mm for TWS)

143 mm = 115 (opening) + 25 (gap at JOH) + 3 (idle stroke)

 Normal Working Voltage-110 V DC

Minimum Working Voltage- 60 V DC

 Normal Working current-   2-3 Amps ( 3 to 5 Amp for TWS)

Slipping Current/Obstruction Current- 

       A) Upper Limit- 1.5 to 2 times of Normal Working current 

        B) Lower Limit- Difference between Normal Working current and Slipping current shall not less than 0.5 amps

 Minimum AC immunity- 160 V AC

Friction clutch movement is 270 degree. Mechanical snubbing is achieved in Friction clutch. Friction clutch slips from 10 to 15 seconds during Obstruction.

 Mode of Locking  - Rotary type locking ( only closed switch is locked) in IRS

In TWS, closed switch is locked through Rotary type locking and open switch is locked through fish tail so it is called clamp type locking.

Operation Time- 3-5 Second ( 5-6 Second)

Space between 3rd and 4th Sleeper  - 685 mm for IRS (1 in 8.5 point)   

695 mm for IRS (1 in 12 point)                                                              745 mm for TWS point.

Test Load on Throw bar - 450 kg ( 550 kg for TWS)

Slipping Load - 580 kg ( 700 kg for TWS)

Stalling Load - 1000 kg for all Point machines 

No of teeth in main gear rim is 92 teeth.

No of teeth in motor pinion is 12 teeth.

04 detection and 04 control contacts.

Test gauges   1.62 mm - Go test 

                        3.25 mmm - maintenance purpose 

                         5 mm - Obstruction test

Point machine /EPD should be provided at Min distance of 1060 mm from nearest C/L of track

Motor used is DC  series  split field motor. It means it's coils are divided into two pieces and connected in series ( two coils for Normal and two coils for Reverse) to enhance its strength. The quality of a motor,depends upon the insulation of its coil.

If this insulation is weak and after repeated operation, coppor conductor in touch each other and motor can burn. 

That's why insulation of point motor should be 10 Mega Ohms for new motor.To check it, first we will megger between C and N terminals, then C and R terminals.Practically it will work for 2 to 3 Mega ohms also. In regular maintenance or inspection, meggering of motor is not required.  It can be done if there is intermittent failure. Insulation is B grade Insulation.  Design is C10 ( it will only operate for 10 s after giving feed).

SAE 30 oil is poured in reduction gear in once in six months.Quantity is 150 ml to 180 ml.

Facing point and trailing point- Same point can be facing of a train and trailing for another train according to their direction of movement.If the Train is entering into face of point ,then it is facing otherwise it is trailing.

Trailable or Non trailable point -

Maximum points are Non trailable. In these point  we need to alter the position of point for Normal and Reverse  trailing movements. We can not do both the movement in one position.In the  trailable point, there is no  need to change the position of point for trailing movement either from Normal or Reverse.In this case point is on loose heels which is not in practice now a days.

Stalling Load  - It is minimum load at which Mechanical fuse ( Bearing Pedestral) breaks during trailed through movement due to pressure of wheel on closed switch. Breaking of mechanical fuse saves the other parts of point machine. Mechanical fuse is connected with throw rod and friction clutch. Value of Stalling Load is 1000 kg for both IRS and TWS Point machines. 

Points are of two types 1/12 and 1/8.5.In 1/12 points, distance  between Normal and Reverse rail is 1 m after movement of 12 m from toe of point.

In 1/8.5 points, this distance will be achieved after movement of 8.5 m from toe of the point. Curve on 1/8.5  points are more compare to 1/12 points.Length of crossover of 1/8.5 m point is 54 sleepers ( 33 m). Length of one sleeper is around 600 mm. Length of Crossover is from SRJ to ahead of crossing.

In 1/12 points,  the  length of crossover is 83 sleepers (55m).

In main line points only 1/12 point is permitted.

Maximum speed on 1/8.5 m point is 30 kmph for ordinary point and 60 kmph for TWS point.

Obstruction Test- Insertion of a 5 mm Obstruction between the switch rail and the stock rail of a Facing point, at approximately 150 mm from the toe of the switch rail to prevent the point from being locked is called Obstruction Test.

Minimum Clearance from bottom of rails and top of the ground connection is 25 mm.

Minimum Clearance of Check Rail

At Curve -44 mm

LC gate - 51 mm.

Minimum depth of space for wheel flange from Rail level -38 mm.

Minimum radius of curve -175 mm (10 degree)

Clearance from bottom of the rail for ground connection rods - 25 mm