Horizontal directional drilling system

A dual rod drill drive assembly comprising:

• an outer drive shaft driven by a first hydraulic motor, the outer drive shaft configured to rotate an outer drill rod of a drill string;
• an inner drive shaft positioned within a sleeve that is rotated by a second hydraulic motor, wherein the drive shaft is configured to slide axially relative to the sleeve and to rotate with the sleeve;
• a hydraulic pump configured to drive hydraulic fluid into the sleeve to extend the inner drive shaft relative to the sleeve;
• a drilling mud delivery interface unit mounted to the outer drive shaft configured to direct drill mud into the drill string;
• a seal assembly configured to prevent drilling mud delivered via the drilling mud interface from contaminating hydraulic fluid in the hydraulic drive system, the seal assembly including:
• a first radial seal that includes a mud interface and a hydraulic fluid interface;
• a hydraulic fluid port extending from the mud delivery interface that directs the hydraulic fluid from the pump through a portion of the outer drive shaft to the hydraulic fluid interface;
• and
• auxiliary radial seals positioned between the drill mud delivery interface and the outer drive shaft that are configured to prevent mud from exiting the mud delivery interface into the environment outside of the hydraulic drive system, wherein hydraulic fluid from the pump is provided to the auxiliary radial seals to provide back pressure opposite the mud interface of the radial seals, and wherein the pressure in the hydraulic fluid provided to the auxiliary radial seals is equal to, or greater than, the pressure in the hydraulic fluid provided to the hydraulic fluid interface of the first radial seal.

A drilling machine comprising:

• a. a tubular drilling mud delivery interface unit;
• b. a drill string driver comprising:
• a gearbox;
• an outer drive tube;
• an inner drive member wherein a portion of the inner drive member is within the outer drive tube;
• a main seal assembly between the outer drive tube and the inner drive member;
• c. wherein a portion of the drill string driver is within the drilling mud delivery interface unit;
• the tubular drilling mud delivery interface unit comprising:
• a non-rotating outer sleeve with an inlet port for the drilling mud, and an inlet port for pressurized oil;
• a first seal assembly that prevents drilling mud from leaking past the non-rotating outer sleeve and the drill string driver wherein the first seal assembly comprises a first seal that separates the drilling mud and the pressurized oil and a second seal that separates the pressurized oil and the ambient environment;
• a second seal assembly that prevents drilling mud from leaking past the non-rotating outer sleeve and the drill string driver wherein the second seal assembly comprises a third seal that separates the drilling mud and the pressurized oil and a fourth seal that separates the pressurized oil and the ambient environment;
• d. wherein the main seal comprises:
• a fifth seal that separates the drilling mud from the pressurized oil;
• a sixth seal that separates the pressurized oil and the gearbox;
• e. wherein the drill string driver further includes an aperture with an opening between the first and second seals, an opening between the third and fourth seals, and an opening between the fifth and sixth seals.