1. A welding helmet comprising:
a housing comprising a pivotal head band, a forward window, and a shield disposed on the window and including an opening being forwardly of the window; and
a visor comprising a frame secured to the housing, an upper tinted lens disposed on the frame, a lower predetermined lens disposed on the frame, the lower predetermined lens being at an angle with respect to the upper tinted lens, and a pivotal panel disposed between two sides of the shield to separate the opening into two parts.
2. The welding helmet of claim 1, wherein the lower predetermined lens is a transparent lens.
3. The welding helmet of claim 1, wherein the lower predetermined lens is a filter lens.
4. The welding helmet of claim 1, wherein the shield further comprises two holes on front surfaces of both sides respectively, and wherein the pivotal panel comprises two pivotal pins on both ends of a rear edge respectively, the pivotal pins being inserted into the holes to pivotably secure the pivotal panel to the shield.
5. A welding helmet comprising:
a housing comprising a pivotal head band, a forward window, and a shield disposed on the window and including an opening being forwardly of the window; and
a visor comprising a frame secured to the housing, an upper predetermined lens disposed on the frame, a lower tinted lens disposed on the frame, the upper predetermined lens being at an angle with respect to the lower tinted lens, and a pivotal panel disposed between two sides of the shield to separate the opening into two parts.
6. The welding helmet of claim 5, wherein the upper predetermined lens is a transparent lens.
7. The welding helmet of claim 5, wherein the upper predetermined lens is a filter lens.
8. The welding helmet of claim 5, wherein the shield further comprises two holes on front surfaces of both sides respectively, and wherein the pivotal panel comprises two pivotal pins on both ends of a rear edge respectively, the pivotal pins being inserted into the holes to pivotably secure the pivotal panel to the shield.
9. A welding helmet comprising:
a housing comprising a pivotal head band, a forward window, and a shield disposed on the window and including an opening being forwardly of the window; and
a visor comprising a frame secured to the housing, an upper predetermined lens disposed on the frame, a lower tinted lens disposed on the frame, the upper predetermined lens being at an angle with respect to the lower tinted lens, and a panel disposed between two sides of the shield to separate the opening into two parts.
10. The welding helmet of claim 9, wherein the upper predetermined lens is a transparent lens.
11. The welding helmet of claim 9, wherein the upper predetermined lens is a filter lens.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A valve assembly forming a bridge circuit and being fluidly connectable between a fluid source and a fluid drain, the valve assembly comprising:
at least one first valve fluidly connected between the fluid source and a first diagonal point of the bridge circuit, said at least one first valve being a valve which is normally open in a de-energized state, at least in a direction from the fluid source towards the first diagonal point,
at least one second valve fluidly connected between the fluid source and a second diagonal point of the bridge circuit, said at least one second valve being a valve which is normally open in a de-energized state, at least in a direction from the fluid source towards the second diagonal point,
at least one third valve fluidly connected between the first diagonal point of the bridge circuit and the fluid drain, said at least one third valve being a valve which is normally closed in a de-energized state, and
at least one fourth valve fluidly connected between the second diagonal point of the bridge circuit and the fluid drain, said at least one fourth valve being a valve which is normally closed in a de-energized state.
2. The valve assembly according to claim 1, wherein at least one of the valves is an electrically operable valve.
3. The valve assembly according to claim 1, further comprising a hydraulic servomotor comprising a first chamber arranged fluidly connected to the first diagonal point of the bridge circuit and a second chamber arranged fluidly connected to the second diagonal point of the bridge circuit.
4. The valve assembly according to claim 3, wherein the valves of the valve assembly are controlled by means of a closed loop control of the hydraulic servomotor.
5. The valve assembly according to claim 4, further comprising at least one sensor, said sensor(s) being adapted to provide an input signal to the closed loop control.
6. The valve assembly according to claim 1, further comprising at least one additional hydraulic servomotor fluidly connected between the first diagonal point of the bridge circuit and the second diagonal point of the bridge circuit.
7. The valve assembly according to claim 1, wherein at least one of the valves of the valve assembly is driven by a pulse train signal.
8. The hydraulic actuator comprising at least one valve assembly according to claim 1.
9. The hydraulic actuator according to claim 8, wherein the valve assemblies are arranged in a modular configuration.
10. The hydraulic actuator according to claim 8 wherein the valve assemblies are arranged in such a manner that redundant control of a hydraulic servomotor driven by the actuator is obtained.
11. Use of a valve assembly according to claim 1 in a hydro-mechanical transmission (HMT).
12. Use of a valve assembly according to claim 1 in an electro hydraulic steering application.
13. Use of a hydraulic actuator according to claim 1 in a hydro-mechanical transmission (HMT).
14. Use of a hydraulic actuator according to claim 1 in an electro hydraulic steering application.