Drawworks Disc Brakes 20 IMPROVED BRAKING RELIABILITY FOR DRILLING RIGS. As drilling depths increase and hookloads get heavier, conventional band brakes are often taxed to their limits. The National Oilwell Universal Disc Brake offers these advantages over conventional band brakes. GREATER HOLDING POWER.   The disc brake has significantly greater resistance to fade than a band brake, and requires less mechanical input force by the driller to control the heaviest loads. LESS DOWNTIME.    Change out of brake pads is easy and fast. Unlike most band brakes, there is no need to worry about kinking or other damage during removal and installation. Also, access for main- tenance is on the front side of the drum shaft. RELIABLE OPERATION.    Conservative power ratings, redun- dancy, and auxiliary back-up systems all assure reliable operation. ACCURATE CONTROL.    The brake control system, coupled with the hydraulics, provide a high degree of control. NO BRAKE HANDLE "KICK-BACK".    Dragging brake bands of conventional brakes can cause severe and dangerous brake handle kickback.  This cannot happen with disc brakes. EASE OF REMOTE CONTROL.    The brake can be controlled from positions remote from the traditional driller's position without complicated mechanical systems. LESS NOISE.    Significant noise reduction for drilling in noise sensitive environments. PROVEN.    This braking system is being used successfully on a number or rigs. ADAPTABLE.    The disc brake system replaces band brakes, upgrading your present drawworks. EASY TO RETROFIT.    The system is simple to install on existing National Oilwell drawworks. The Universal Disc Brake System consists of three major components: the discs, the hydraulic system, and the caliper assemblies. THE DISCS. The system uses two hardfaced discs machined from alloy steel with an internal water jacket. Disc thickness is three inches.  Disc diameter is normally four to five inches greater than the band brake rim. Both braking surfaces on each disc are hardfaced with a weld over- lay. The hardfacing increases disc life and minimizes surface grooving. THE HYDRAULICS. The hydraulic power unit consists of: • A stainless steel hydraulic reservoir. • An electrically-driven, variable-displacement, internally pressure- compensated hydraulic pump. • A pressure relief valve. • Two pressure reducing/relieving valves. • Four piston type accumulators. • An emergency air-driven pump and two air-piloted hydraulic valves. • Nickel plated steel block manifold. In a typical installation, the variable displacement pump is set to maintain maximum system pressure, while the relief valve will open at approximately 200 psi above the maximum pressure.  This protects the system in the event of a pump malfunction. The two primary accumulators, isolated from each other by check valves, supply pressure to the two main valves at the driller's brake handle.