A dome pressure maintaining valve and circuit for maintaining dome fluid pressure in a pilot operated relief valve is presented wherein the dome pressure in the relief valve is prevented from dropping below a preset value even when inlet pressure at the relief valve drops to zero. The dome pressure maintaining valve incorporates a compact check valve and a back flow relief valve with the two components integrated into one piston embodiment, the valve having in communication with a body bore inlet and an outlet. The circuit provides inlet fluid flow in communication with a piston valve chamber through a passage from the inlet port through the piston under the poppet check valve and through multiport and exterior piston valve ring groove means to the outlet port when the inlet fluid pressure is greater than the outlet fluid pressure. However, when the outlet fluid pressure is greater, the poppet check valve is in a check position within the piston valve chamber and the integrated embodiment provides outlet back flow relief which is due to the greater exposed surface area to the outlet pressure above the outlet port within the piston valve chamber creating an upward force on the piston valve. The force differential provides an upward lift of the integrated piston valve with the lift movement establishing a communication passage between the outlet port and the inlet port as a result of the uplift movement of the piston valve away from the piston valve seat and body bore below the piston valve.
A "V" rake is provided that comprises: a first rigid support frame; a second articulated frame sliding on the first frame, made up of a plurality of mobile arms hinged to each other and to the first frame; at least one joint to slide the second frame on the first frame for opening and closing of said arms; a plurality of fingered wheels arranged on the plurality of mobile arms; and a plurality of bearing wheels for transport of the rake; in which said joint comprises: support elements for sliding of the second frame on the first frame, constituted of: anti-friction support plates made of a material with a low friction coefficient; and bolts and relative spacer sleeves to position and contain the anti-friction support plates on said support elements.
