Memoirs of a GDC intern

Of course you can see where am heading to….brakes. Starting with the eddy current brakes that are normally referred to as the auxiliary brake system that is applied while the travelling block is being lowered to just reduce the speed of descent so that the main mechanical brakes can be applied at minimum effort. This helps to ensure that the main brakes do not wear off that fast as this would shorten their working life and increase the expenses of replacing the brake pads now and then. I remember on Rig 2, we only replaced the brake pads once and as I went round the rigs, there was no where we did that again. On the side of the eddy current brake was a coupling handle that we always ensured was locked in place and that the eddy current brake water cooling system was always running to dissipate the heat generated.

Then you could be wondering how the eddy current brake (ECB) works…it just supplies a series of coils with a strong current that creates a magnetic flux. The shaft attached to the drawworks has a large steel drum that rotates around the coils cutting through the magnetic field such that it acts like the opposing pole of a magnet creating a drag resistance to rotation….slowing down the drum thus allowing the best moment to apply the main brakes. Normally, the heat generated is so much hence the need for water cooling.

One can actually hear a lot of noise as the clutch release valve vents out air while doing the fast disconnection of pads from the clutch drum. This noise could really shock me to y nerves on the first few days before I got used to it.

The main brake system is a hydraulically operated disk brake type with double brake pads and an open-close brake tong. Seeing the hydraulic lines running all the way to the HPU made me remember my hydraulics system class work as I appreciated its application here. The drum also had an anti-clash system that I was taught about too…just a safety system to ensure the crown block did not hit the top of the mast and the drilling line did not excessively fill the drum to an extend of blocking it. This crown saver system works such that when actuated, the crown toggle valve on the drawworks sends an air signal to an air operated pilot valve on the front of the hydraulic manifold on the HPU (Hydraulic Power Unit) so that the valve caused 2-position,4-way valves in the manifold to exhaust their pilots, shift and dump pressure from the emergency calipers and holding onto the drum thus preventing the travelling block from striking the crown.

Some of the defects we checked on the chain with Ndereba at GDC Rig 2 were tension of the chain, missing end-plates and wear or damage on the chains. He told me about the small lubrication pump that constantly sprays oil onto the chains to keep the lubricated and cooled.