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Pit Bottom Buffer Requirements in Man-winding Shafts – DGMS Notes, CMR Rules & 25 MCQs

Pit Bottom Buffer Requirements in Man-winding Shafts – DGMS Notes, CMR Rules & 25 MCQs

🧾 DETAILED NOTES

1️⃣ Introduction

Man-winding shafts are the most critical vertical transport systems in underground mines. To prevent cage overwind, free fall, and collision with the bottom structure, DGMS mandates several safety devices, including Pit Bottom Buffers. These act as the last protective safety barrier in case of an emergency.

2️⃣ What is a Pit Bottom Buffer?

A buffer is an energy-absorbing device installed at the bottom of a mine shaft, designed to absorb impact, stop the cage in case of an overwind, prevent structural damage, and protect workers traveling in the cage. They are also referred to as keps, catch gear, or shock absorbers.

3️⃣ Why are Buffers Needed?

They prevent accidents caused by: Overwinding, Rope breakage, Slack rope, Brake failure, Excessive lowering speed, or Operator error. They serve as fail-safe protection in case primary systems fail.

4️⃣ Legal Framework

Regulation / Act Description
CMR 2017 – Reg. 99, 100, 101 Safety Devices, Man-winding Safety, Automatic Contrivances.
MMR 1961 – Reg. 65, 66, 67 Winding Engines, Safety Catches, Shaft fittings.
DGMS Circulars Tech (Winding) 01/2008, 03/2015, 02/2019.

5️⃣ Types of Pit Bottom Buffers

  • Hydraulic Buffers: Oil-filled cylinders absorb impact. Provide smooth braking and are used in deep shafts.
  • Rubber or Spring Buffers: Cheaper, mechanical absorption. Used in shallow shafts.
  • Friction Buffers: Absorb energy through friction resistance.
  • Mechanical Catch Gear: Stops cage by gripping the guides (different from buffers but related).

6️⃣ Design Requirements (DGMS Guidelines)

  • Must withstand full-load cage impact.
  • Energy-absorbing capacity based on depth and speed.
  • Must not cause cage overturning.
  • Located at a safe distance below landing plate.
  • Interlocked with the winding system.
  • Tested periodically and free from obstruction.

7️⃣ Responsibilities

Role Responsibility
Manager Ensure provision & maintenance, approve inspection schedule, keep test reports.
Engineer Monthly inspection, ensure lubrication and repairs, check energy-absorbing capability.
Winder Operator Test buffers/safety devices before man-winding, report abnormalities immediately.

8️⃣ Testing & Examination

  • Daily visual inspection.
  • Weekly functional check of safety devices.
  • Monthly performance test.
  • Annual third-party certification.
  • Load test during major repairs.

⚙️ QUICK ONE-LINERS (Revision)

  • Pit bottom buffer = final safety barrier in shaft.
  • Required under CMR 99 & 100 and MMR 66.
  • Prevents cage impact at shaft bottom.
  • Hydraulic buffers used in deep shafts.
  • Must absorb full-load impact energy.
  • Weekly testing of winder safety devices mandatory.
  • Keps = devices to hold the cage at landings (different from buffers).
  • Winder operator tests safety devices daily before man-winding.
  • DGMS issues winding circulars for safety.
  • Prevents injuries in overwind or free fall.

🧠 DESCRIPTIVE MODEL QUESTION & ANSWER

Q. Explain the purpose, design, and DGMS requirements for Pit Bottom Buffers in man-winding shafts.

Answer:
Pit bottom buffers are energy-absorbing devices installed at the shaft bottom to prevent cage impact in case of overwind, slack rope, or brake failure. Under CMR 2017 (Reg. 99 & 100) and MMR 1961 (Reg. 66), every man-winding shaft must have properly designed, maintained, and tested buffers. Hydraulic or spring/rubber buffers are commonly used. The buffers must be able to withstand the full-load impact of the cage and ensure controlled deceleration. DGMS requires daily visual inspection, weekly functional tests, and annual certification to ensure reliability.

🧮 25 MCQs (5 Options Each – Randomized Answers)

Q1. Purpose of pit bottom buffer:

Solution: The primary function is to absorb the kinetic energy of the cage in an overwind (descending) situation.

Q2. Regulation for winder safety devices in coal mines:

Solution: Regulation 99 of CMR 2017 lists the safety devices, including automatic contrivances and buffers, required for winders.

Q3. Buffers are installed:

Solution: Pit bottom buffers are located at the bottom of the shaft, below the lowest landing level.

Q4. Hydraulic buffers are suited for:

Solution: Hydraulic buffers provide smoother deceleration and are better at absorbing the high kinetic energy of cages in deep shafts.

Q5. Energy absorption is required for:

Solution: The buffer must be designed to safely stop the cage at its maximum load (full-load) in an emergency.

Q6. Keps refer to:

Solution: Keps (or catches) are retractable supports at landings to hold the cage, distinct from buffers which are energy absorbers. (Note: The prompt incorrectly equated them; this is the correct distinction).

Q7. Testing frequency for winder safety devices:

Solution: All safety contrivances (like automatic overwind preventers) must be tested functionally at least once a week.

Q8. Overwind may cause cage to:

Solution: A downward overwind (overshoot) will cause the cage to strike the pit bottom buffers.

Q9. MMR regulation for winding engines:

Solution: Regulation 65 of MMR 1961 deals with the construction and specifications of winding engines.

Q10. Buffers must be:

Solution: The area around the buffers must be kept clear of any obstruction (water, spillage, debris) to ensure they function correctly.

Q11. Pit bottom buffer prevents:

Solution: The buffer is positioned above the shaft sump to stop the cage before it crashes into the bottom.

Q12. Winder operator checks safety devices:

Solution: The winder operator must perform a check of safety devices (like brakes, overwind preventer) at the start of their shift, before winding persons.

Q13. Mechanical catch gear is used as:

Solution: Catch gear (keps) are mechanical devices used to support or arrest the cage at landings or at the bottom.

Q14. Buffer testing requires:

Solution: The system must undergo regular functional tests (e.g., checking oil levels, spring condition) to ensure it works.

Q15. Rope break may cause:

Solution: If the rope breaks, the cage will free fall. The buffer is the last line of defense (though safety catches should engage first).

Q16. Buffers must be designed to:

Solution: Their sole purpose is to absorb the kinetic energy of the moving cage to bring it to a safe stop.

Q17. DGMS requires:

Solution: A thorough annual test and certification of critical winder safety components, including buffers, is standard practice.

Q18. Shock absorbers used in:

Solution: Pit bottom buffers (especially hydraulic or spring types) are essentially large shock absorbers.

Q19. Cage must not:

Solution: The entire safety system (brakes, overwind preventer, buffers) is designed to prevent the cage from hitting the shaft bottom (sump).

Q20. Buffer failure may lead to:

Solution: If the buffer fails during an overwind, the cage will crash into the sump, likely resulting in a fatal accident.

Q21. Shaft sump is:

Solution: The sump is the lowest point of the shaft, used for water collection, located beneath the buffer system.

Q22. Buffers must work during:

Solution: The buffer is a safety device specifically designed to activate during an overwinding (downward) event.

Q23. Energy-absorbing buffers:

Solution: By absorbing kinetic energy, they reduce the final impact force, bringing the cage to a controlled stop.

Q24. Buffer inspection should be recorded in:

Solution: All inspections, tests, and maintenance of winding components must be recorded in the winder logbook (e.g., Form 10).

Q25. Main aim of pit bottom buffer:

Solution: While it protects equipment too, the primary and most critical goal is to protect the lives of persons in the cage during man-winding.

🔗 INTERNAL LINKS

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