The invention relates to a downhole tractor having at least one hydraulic drive section, comprising a first hydraulic supply line for actuating at least one hydraulic cylinder for actuating at least one tractor arm and a second hydraulic supply line for driving at least one hydraulic motor for rotating at least one tractor wheel. The downhole tractor further comprises a hydraulic power pack configured for supplying hydraulic fluid to the hydraulic supply lines. The hydraulic power pack comprises a pressure-setting valve provided in between the first hydraulic supply line and the second hydraulic supply line, wherein the pressure-setting valve is configured for feeding excess hydraulic fluid in the first hydraulic supply line to the second hydraulic supply line to increase the speed of the downhole tractor.

A hydraulic control circuit operable to selectively hydraulically link first and second hydraulic actuators and to bypass that hydraulic link.

A locking mechanism for a base plate of a vibratory compactor includes a locking actuator configured to alternately lock and unlock the base plate relative to the vibratory compactor, and a hydraulic control circuit in fluid communication with a source of pressurized hydraulic fluid and the locking actuator. The hydraulic control circuit includes a hydraulic pilot-pressure-actuated, 2-position spool valve, wherein the spool valve is configured to move to a first position when pressurized hydraulic fluid from the source is supplied to the spool valve in a first direction, and move to a second position when the pressurized hydraulic fluid from the source is supplied to the spool valve in a second direction. In the first position of the spool valve the pressurized hydraulic fluid moves the locking actuator to a locked position, and after the locking actuator is in the locked position, the pressurized hydraulic fluid operates a hydraulic motor configured to power the vibratory compactor. In the second position of the spool valve the pressurized hydraulic fluid moves the locking actuator to an unlocked position.

A locking mechanism for a base plate of a vibratory compactor includes a locking actuator configured to alternately lock and unlock the base plate relative to the vibratory compactor, and a hydraulic control circuit in fluid communication with a source of pressurized hydraulic fluid and the locking actuator. The hydraulic control circuit includes a hydraulic pilot-pressure-actuated, 2-position spool valve, wherein the spool valve is configured to move to a first position when pressurized hydraulic fluid from the source is supplied to the spool valve in a first direction, and move to a second position when the pressurized hydraulic fluid from the source is supplied to the spool valve in a second direction. In the first position of the spool valve the pressurized hydraulic fluid moves the locking actuator to a locked position, and after the locking actuator is in the locked position, the pressurized hydraulic fluid operates a hydraulic motor configured to power the vibratory compactor. In the second position of the spool valve the pressurized hydraulic fluid moves the locking actuator to an unlocked position.

A pressure-balance valve for balancing the pressures of fluids admitted into the pressure-balance valve via respective second ducts. The pressure-balance valve has both a chamber for guiding movement in translation of a piston, and also fluid flow paths, each comprising a said second duct and a first duct for admitting a fluid coming from the same fluid source as the fluid flowing in its second duct. Each of the first ducts is provided with a shutter co-operating with a ramp arranged on the piston. Movement of the piston in translation as a result of a pressure difference between the fluids respectively admitted into the second ducts causes one of the shutters to slide along the corresponding ramp and consequently allows additional fluid to be delivered from a first duct to the second duct of the same fluid flow path.