Abstract: A placement bucket for placing material such as concrete in forms by manipulation of clam shell gates in response to action of a power cylinder makes use of a hydraulic fluid system which prevents opening the gates of a full or partially full bucket of material unless there is a sufficient reserve of pressure and fluid volume to make certain of closing the gates at any time. The system is provided with a precharged fluid supply under pressure into which additional fluid is diverted when generated in a master cylinder by lifting a piston against the weight of the bucket and its contents. A sequence valve prevents flow of fluid to the power cylinder until an optimum amount of fluid pressure and volume is reached. An auxiliary direction valve in a fluid return line can be manipulated to temporarily block return flow of fluid from the exhaust side of the power cylinder to a reservoir, in that way to temporarily fix the partially or full open position of the gates.

Abstract: A control system for opening and closing the clam shell gates of a material placement bucket makes use of a selfcompensating back pressure fluid system with a double-acting cylinder and piston. An air receiver is filled with high pressure air while air at the same pressure is being applied to the piston in a gate opening direction. At the same time, air from the receiver flowing through a pressure regulator and simultaneous exhaust valve at a reduced pressure is applied to the opposite, or reversing, side of the piston, creating back pressure. Hence the differential pressure applicable in the forward acting direction is the gate opening pressure. Closing pressure is the reduced pressure which becomes effective when pressure on the opening side is diverted to exhaust. Speed of closing the gates can be increased by adjusting only the pressure regulator to supply a higher reduced pressure.

Abstract: A fluid power device such, for example, as one for opening and closing clam shell gates is operated by a ram under fluid pressure. A tank is provided for storing fluid under pressure and by a system of valving extension of the ram, as for a gate opening operation, is inhibited until enough fluid under pressure is stored in the tank to assure completion of reverse operation of the ram to close the gates.