Mud Pumps Information
Mud pumps are large, reciprocating pumps that are used to circulate the “mud” on a drilling rig. Reciprocating pump means they are similar to a conventional auto engine, but they use their pistons in reverse to pump, instead of delivering the power of combustion to the crankshaft. They can deliver pressures up to 7,500 psi consistently. Mud pumps ensure that drilling mud is circulated to the bottom of the hole at the right pressure and volume to carry drilling debris out of the well hole.
Mud pumps are classified by their number of pistons. Two pistons make it a duplex, three pistons make it a triplex, and six pistons make it a hex pump. The most common arrangement is three pistons inline, or a triplex pump. The fluid end of the pump, the equivalent of its cylinder head, and the cases can be removed and accessed easily so the valves, bearings and pistons inside can be serviced easily. The high pressures and the viscous gritty drilling mud wear out its internal parts rapidly.
Mud pumps can be further classified as to whether they are single or double-acting pumps. This means that each piston either has one or two working ends. Single action means they pump in just one direction while double action means that the piston pumps mud in both directions.
Most mud pumps have a crosshead crank gear. That means the piston connecting rod is fixed perpendicularly into the back of the piston head and there is an intermediate rod that connects the crankshaft journal to the end of the piston rod. The piston rod is fixed in place with a sleeve so no sideways forces will act on the piston, or the pistons won’t rock back and forth in their cylinder bore unlike a simple car engine. They are usually spray cooled, where cooling water is sprayed directly onto the pump’s pistons, liners and other moving parts.
Mud pumps are incorporated into well drilling rigs, so they are generally not stand-alone devices. Mud pumps have a drive motor and are hooked up to the mix tanks to supply mud as needed. The input and output fluid ends of the pump are piped directly to the drilling string and the annulus of the borehole. The pumps usually have pulsation dampeners on both the fluid inlet and outlet ends to smooth out pressure variations in the mudflow.
Mud pumps are usually driven by electric or diesel motors. Diesel motors are best suited for remote locations. The motors are geared down since most pumps run at around 100 to 200 rpm as the motors usually rotate much faster. Most electric driven pumps use AC motors and there are DC motor rigs available, as well. The largest mud pumps are rated at over 2,500 hp.
The drilling fluid, or mud, is circulated through the fluid end of the pump. It is pumped down through the center bore of the drill shaft and its bit, the drill string. The mud returns to the surface through the borehole annulus, or the space between the shaft and the borehole’s inner diameter. A deep well, like an offshore oil drilling rig, requires pressures of 7,500 psi, to force the mud down and back. These wells can be 10 miles below the surface of the water and ocean bed. Drilling mud is usually a water-based viscous slurry of suspended clay-like colloids, but it can vary depending on where it is used or what the well is being drilled for. It can also be an oil or synthetic fluid based fluid mixture. The mud mixture is usually stored in a large mix tank.
As with most pumps, the specifications are mostly based on the pressure needed at a specified flow rate. For mud pumps pressures are very high, from 5,000 to 7,500 psi, and mud flow rates vary from 100 to 1,300 gallons/minute.