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| Illustration 1 | g01881138 |
The hydraulic cylinder that operates the jaw is equipped with speed control valve (1). The speed control valve is used to adjust the cylinder for use with maximum power or for use in high speed. The resistance that acts against the cylinder will determine the proper mode of operation. Speed control valve (1) is mounted directly to the head end of the cylinder.
Closing the Jaw (High Speed Operation)
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| Illustration 2 | g02127434 |
(2) Auxiliary control valve (3) Check valve (4) Main valve (5) Pilot valve (6) Check valve | |
When the hydraulic cylinder closes the jaw under little resistance, the speed control valve will shift the cylinder into high speed.
When the operator closes the jaw, auxiliary control valve (2) directs oil flow from the host machine to the speed control valve and to the head end of the cylinder. The pressure on the piston causes the cylinder to extend. As the cylinder extends, the jaw closes. Simultaneously, oil flows to main valve (4), and pilot valve (5). Oil flows to left side of pilot valve (5). Spring force keeps the pilot valve shifted to the left. Oil also flows through the orifice to the left end of main valve (4). The pressure at the left side of the valve causes the valve to shift to the right. When the main valve is shifted to the right, oil from the rod end flows to the head end of the cylinder. High-pressure oil is at both sides of the piston, but the extra surface area at the head end causes the piston to move to the right. The extra flow that is supplied to the head end causes an increase in speed. The increase in speed results in a decrease in closing time.
Closing the Jaw (Maximum Force)
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| Illustration 3 | g02128393 |
(2) Auxiliary control valve (3) Check valve (4) Main valve (5) Pilot valve (6) Check valve | |
When the hydraulic cylinder closes the jaw under high resistance, the speed control valve will shift the cylinder into maximum force.
When the operator closes the jaw, auxiliary control valve (2) shifts to the left. When auxiliary control valve (2) is shifted to the left, the valve directs oil flow from the host machine to the speed control valve and to the head end of the cylinder. The pressure on the piston causes the cylinder to extend and the jaws close. Simultaneously, oil flows to pilot valve (5), and main valve (4). When the work tool cuts material, the resistance that is sensed in the speed control valve may increase. Oil flows to the right side of pilot valve (5). When the pressure exceeds 27000 kPa (3915 psi), pilot valve (5) shifts to the right. This allows oil from the left side of valve (4) to return to the hydraulic tank. Oil is also directed through check valve (6) to the right end of main valve (4). The main valve moves to the left and oil is directed from the rod end of the cylinder back to the hydraulic tank. The direction of the oil flow to the tank causes the speed of the jaw to decrease and the force of the jaw to increase.
Retraction of the Jaw
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| Illustration 4 | g02128614 |
(2) Auxiliary control valve (3) Check valve (4) Main valve (5) Pilot valve (6) Check valve | |
When the operator opens the jaw, auxiliary control valve (2) shifts to the right. The auxiliary valve directs oil flow from the host machine to the speed control valve.
The oil flows to the right side of pilot valve (5). The pressure of the spring holds the valve to the left. Simultaneously, the oil flows to the right side of main valve (4). This causes the valve to shift to the left. This creates a path for oil to flow through the valve to the rod side of the cylinder. The oil pressure that acts on the rod side of the piston retracts the cylinder, and the jaw opens. Oil from the head end of the cylinder returns to the hydraulic tank.