This drive gear reduces maintenance and decreases the pump’s overall footprint.
by Shaun White, White Star Pump Company
July 3, 2014

Adding the time-tested worm drive gear to a quadraplex mud pump can improve the mud pump power end’s life while reducing maintenance and the pump’s overall footprint. Though metal worm gears have been used for years in applications ranging from coal crushing and steering naval ships to pumps used for hydraulic fracturing, their successful implementation into constant-duty drilling mud pumps is only possible now.

A quadraplex worm drive mud pump

The Change to Worm Gear

If worm drive gear is better than a pinion and bull gear, why has it not been used in constant-duty mud pumps in the past? The limitations of the original triplex mud pump—designed more than 50 years ago and, until recently, continually copied—prevented a worm drive gear’s use. Because triplex pumps are inherently imbalanced, their crankshafts and frames are regularly flexed. A triplex mud pump’s bearings are housed in the frame of the pump. With the bearings outside the pump, the crankshaft is unsupported at the middle piston, which means the crankshaft will flex or bow when under load. This flexing crankshaft creates an unstable connection between the pinion and bull gear. Though this flex will prematurely fatigue the crankshaft and frame, fortunately the pinion and bull gear can accommodate this movement generated by the flexing crankshaft. Worm drives have many advantages when compared to pinion and bull gears, but they cannot accommodate the crankshaft movement found in traditional triplex pumps. The only way to successfully run a worm gear on constant-duty mud pumps is to properly stabilize the crankshaft. Because the pressure and flow rate required for drilling continue to increase, the quadraplex mud pump was designed to stabilize and support the crankshaft to improve gear life. To accomplish this, the quadraplex pump houses the bearing inside the pump immediately adjacent to the connecting rods, eliminating the long bending moment experienced in triplex pumps and stabilizing the quadraplex crankshaft. The quadraplex pump’s four-piston design and balanced crankshaft eliminate the potential for flexing, creating a stable connection and allowing the use of reliable and long-lasting worm drive gearing. Its modern design is a perfect match for the long-life worm gear. The quadraplex mud pump experiences 300 percent less variations in crank shaft loads and has 40 percent lower peak bearing loads. These improvements create a greatly increased life cycle throughout the pump’s entire power end.

Worm Gear Benefits

What are the benefits of using a worm gear driven pump over the traditional pinion and bull gear? Employing a worm drive instead of traditional mechanical drives eliminates the need for many moving parts that are often required in pump unitization—such as belts, chains, reduction gearing and right-angle drives.

A quadraplex mud pump with a worm gear drive and diesel engine

A quadraplex pump with worm drive gearing is a simpler mud pump with fewer parts and assemblies to fail. Some of the worm drive gearing benefits include:

  • The worm drive gearing delivers improved and longer service life.
  • With the worm hub directly in line with the pump, bulky and dangerous belts and guards are eliminated, requiring much less space to unitize and power the mud pump. The worm drives included as part of a unitized quadraplex mud pump offer gear ratios up to 12.4 to 1, eliminating the need for expensive reduction gearing on engines up to 2,100 rpm. Eliminating the reduction gearing significantly reduces parasitic loads and improves efficiency, saving money in the day-to-day operations of the drilling rig.
  • While premium worm gears initially cost more than conventional pinion and bull gears, the increased capital expense is offset by their long life, reducing the downtime and maintenance costs associated with pinion and bull gears.
  • The premium for the quadraplex worm drive is further offset by the elimination of costly unitization equipment and the maintenance of belts and chains.
  • Based on the smooth force provided by the worm drive to the crankshaft, the crankshaft or gears may never need to be replaced. However, in the event of human error, such as dropping a wrench between the gear and worm drive, the quadraplex pump’s innovative design makes worm gear replacement simple.
  • While the quadraplex is built to outlast even the highest cost triplex pumps, it significantly outperforms them. When compared to inexpensive pumps, a quadraplex pump delivers lower life-cycle costs. Though it will take many years to prove its longevity, a drilling program will gain from improved pump performance from day one.
  • Even the highest-priced competitive pump will require replacement of all unitization components before a quadraplex pump’s worm drive fails.
  • Trailer or inline unitizations are greatly simplified.

In addition to its application to mechanical pumps, the quadraplex worm drive option can be beneficial when applied to electric alternating-current or direct-current drive pumps, with which the simplicity of its direct in-line connection eliminates unitization elements.