The present invention relates to storage tanks and, in particular, to a hatch cover system for bulk carriers.
Dry bulk carriers are typically used to transport dry particulates, such as dry granular bulk cement, and will be described with reference to mobile units commonly known as dry bulk transports. Therein, a mobile storage unit transported by a tractor includes a main pressure reservoir for loading, holding, and unloading material. The material is loaded through a hatch on the top of the reservoir. After loading, the hatch is mechanically closed and sealed. For unloading, a pneumatic system is used to pressurize the reservoir and discharge the material through discharge openings in the bottom of the reservoir. According, the hatch system for such units must provide a plurality of distinct functions. First the hatch must open for the delivery of contents. Second, the hatch must close securely for transport. Third, the hatch must be securely sealed for operation of the pneumatic discharge system.
Conventional hatches for such storage reservoirs typically provide a cylindrical sleeve defining a cylindrical port at the top of the unit. A hatch cover is pivotally connected to the sleeve for movement between an open position for loading and a closed position for latching, sealing and delivery. The hatch cover generally carries an annular seal that establishes an interface between the sleeve and the hatch cover. A plurality of over-center levers are circumferentially disposed about the sleeve and pivotally connected thereto. The levers include an offset cam surface that engages the top of the cover and upon inward rotation engages the periphery of the cover and downwardly biases the cover to compress the sealing interface. At the delivery site, the above procedure is reversed, the levers being disengaged and the hatch cover pivoted to the open position.
With such hatch cover system, the loader, typically the vehicle driver, must vertically climb a ladder on the reservoir leading to the cover. Oftentimes, such covers are located a substantial distance above ground. Such reservoirs also typically have a curved upper surface adjacent the hatch. Accordingly, the loader must assume a position thereat and exert substantial force to unlock the levers and pivot the cover, which can weigh between 20 to 40 pounds. In addition to the substantial time to accomplish the above activities, the same must be done in precarious positions during various types of inclement weather, excessive heat and cold, rain, snow, sleet and wind.
As should be apparent, conventional hatch cover system require inordinate loading and unloading time and effort and pose substantial risks to the workers under operating conditions. One approach for providing a lower level operator platform for accessing the hatch is disclosed in U.S. Pat. No. 5,538,286 to Hoff wherein a platform is positioned intermediate a pair of pressure vessels and requires that the hatches be offset from the top of the vessels. Such platforms and offset are not usable in conventional bulk transports wherein a single elongated tank is employed and optimum storage capacity obtained with the hatch located at the top of the transport. Accordingly, a need exists for a hatch cover system that decreases the time required for loading the transport units, simplifies the latching procedure and reduces the safety risks to the operator.
The present invention provides a ground level operated load and latch system for mobile and stationary pneumatic storage reservoirs that reduces associated operator filling time and enables the filling of the reservoir under all conditions without the operator risks set forth above.
The present hatch cover system is specifically desireable for dry bulk transports of the type having a upwardly opening hatch communicating with a storage vessel through which the cargo material is loaded. A hatch cover has an upper annular sealing surface for engaging the hatch. The cover is raised and lowered by a lifting pneumatic actuator carried on a support frame that pivots about a vertical axis. A lock bar is shifted by a pneumatic locking actuator between a locked position interposed between the support frame and the cover to maintain a compressive sealing interface for transportation and pressurization of the reservoir. The lock bar is shifted by the locking actuator to an unlocked position to permit raising and lowering of the cover. A pivoting actuator moves the support frame and the cover between the raised position overlying the hatch and an open position remote from the hatch for loading and maintenance. The control system for the actuators is conveniently located at ground level enabling the operator to view easily the operation of the hatch closure system.
Accordingly, it is an object of the present invention to provide an automatic closure system for the hatch of a bulk carrier that can be operated at ground level without requiring the operator to climb atop the carrier body.
Another object of the invention is to provide a hatch closure system for the hatch of a dry bulk transport that can be selectively remotely actuated to provide pressure sealing of the hatch and a fully open position for loading and maintenance.
A further object of the invention is to provide an automatic hatch closure system for a mobile pneumatic bulk carrier wherein the hatch cover may be remotely controlled to provide unobstructed loading of the carrier reservoir and shifted to a securely closed and locked condition for transportation, delivery and maintenance.