Forklift trucks and masts therefore

A hydraulic arrangement for an extensible mast, comprising:

• a hydraulic pump fluidly communicating with a hydraulic reservoir;
• a hydraulic feed-through cylinder connected to a first mast column such that extension of the feed-through cylinder moves a section of the mast;
• a first valve arrangement fluidly interposed between the pump and the reservoir on one side of the first valve arrangement and the feed-through cylinder on another side of the first valve arrangement such that the first valve arrangement controls fluid communication between the pump and the feed-through cylinder and also controls fluid communication between the feed-through cylinder and the reservoir;
• a hydraulic free-lift cylinder fluidly communicating with the feed-through cylinder such that hydraulic fluid is communicated to and from the free-lift cylinder via the feed-through cylinder;
• a hydraulic lift cylinder connected to a second mast column such that extension of the lift cylinder moves the section of the mast;
• a balance pipe fluidly connecting the feed-through cylinder with the lift cylinder;
• a second valve arrangement fluidly interposed between the pump and the lift cylinder such that the second valve arrangement controls fluid communication between the pump and the lift cylinder;
• a controller operably connected with the first valve arrangement and with the second valve arrangement wherein the controller operates the first valve arrangement and the second valve arrangement;
• a first pressure sensor communicating with the controller and arranged to sense pressure of hydraulic fluid supplied to the feed-through cylinder;
• and
• a second pressure sensor communicating with the controller and arranged to sense pressure of hydraulic fluid supplied to the lift cylinder;
• wherein the controller is configured to operate the first valve arrangement and the second valve arrangement based at least in part on pressures sensed by the first pressure sensor and the second pressure sensor.

A method of operating a lift mast comprising a first section, a second section moveable within the first section, a third section moveable within the second section, and a carriage moveable within the third section, the method comprising:

• receiving a lift command at a controller;
• in response to receiving the lift command, activating a pump via the controller and opening a first valve arrangement via the controller such that the pump fluidly communicates with a feed-through cylinder;
• providing pressurized hydraulic fluid to a free-lift cylinder via the pump through the first valve arrangement and through the feed-through cylinder;
• and
• in response to receiving the lift command, keeping a second valve arrangement closed via the controller such that pressurized fluid is communicated from the feed-through cylinder to a lift cylinder via a balance pipe, but pressurized fluid is not supplied to the lift cylinder from the pump through the second valve arrangement.