Brake valve device for industrial vehicles

Abstract

A spool-out type booster brake valve device for industrial vehicles is configured to allow hydraulic working fluid to be supplied not only to a booster chamber but also to a master chamber thereby eliminating the need to use a separate brake fluid reservoir tank for supplementing brake fluid in the master chamber. The brake valve device is used in an industrial vehicle equipped with a fluid pump, a reservoir tank and a brake actuator. The brake valve device includes a valve body having an inlet port, a drain port, a brake port, a booster chamber communicatable with the pump via the inlet port and a master chamber communicatable with the brake actuator via the brake port. The master chamber is connected to the inlet port to receive working fluid from the pump. A valve spool is slidably fitted in the valve body through the booster chamber and the master chamber, the valve spool being shifted between an idle position and an operating position. The brake valve device also includes a booster sleeve and a master piston which are moved along with the valve spool in response to the shifting movement of the valve spool into the operating position, thereby reducing the volume of the master chamber so that the fluid in the master chamber can be introduced into the brake actuator via the brake port.