fig.6
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
fig.7
Dump valve (closed, work position)
Description
Figure 7 shows the same cross-section but the dump valve is closed.
Function
With 24 V over the dump valve, i.e. emergency button pulled out, the valve needle will close the drain from above the dump piston. Circulation pressure or the pressures generated when a spool is activated will together with the spring produce the force needed to close the dump piston. When the emergency button is pulled out it is possible to feed oil at full working pressure to the cylinder functions.
Inner boom function, all CE-cranes
Description
Figure 8 is a cross-section through the inner boom function of the control valve, valid for all EU cranes. The cross section applies to the outer boom function as well. The A-side has a pressure relief cartridge with suction valve function included the B-side has a plug. There is a separate load-holding valve at the cylinder. In the return line, as seen in the diagram, a one-way restriction valve is fitted. In the figure the spool is pushed in for lifting.
Function
Via the parallel channel pressurised oil (red) is directed to the B-port and further through the check valve of the separate load holding valve to the inner boom cylinder. Return oil (blue) passes through the one-way restriction valve, then via the spool to the return channel. The separate load holding valve in the closed position prevents the crane boom from sinking. The boom cannot be lowered without pump pressure. Coloured channels are pressurised.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
Slew function, small CE-cranes
Description
Figure 9 shows a cross-section of the slew function for small EU-cranes. At first sight the load-holding function looks similar to the one for the V41 although fitted on both A and B-side. This was true for the first generation of valve 50. However, valves from 1997 onward are fitted with a completely new development: a patented flow regulator at the tip of the pressure relief cartridge. This provides the valve function in question with a limited throughput area suitable for the slewing oil flow and a hydraulic filter thereby making it possible to increase the pilot ratio from 2:1 to 8.5:1. As a consequence, driving pressure for the slew function has been reduced radically. It follows that simultaneous operation with a low-pressure function, such as extension has been improved considerably
Function
Pressurised oil (red) is directed via the parallel channel, over the check valve into the slew cylinder. At the same time oil is pushed diagonally left to the flow regulator of the lowering side, which opens a slit for return oil to the tank channel. When slewing downhill the slew cylinder can never be emptied quicker than oil is being replenished on the opposite side. This will prevent hydraulic play. Also, it is not possible to slew without pump pressure. Coloured channels are pressurised.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
Slew function, small CE-cranes (overload)
Description
Figure 10 shows the same cross-section as fig.9 but in an overload situation. The spool is in the neutral position. Pressure is built up in the left slew cylinder.
Function
The check valve closes the channel towards the spool but oil under high-pressure forces the relief valve to open for outlet to the tank channel. At the same time, pressure (green) is created in the right slew cylinder. Therefore, return pressure will lift the check valve allowing the cylinder to be refilled with tank oil. In this mode the flow regulator is inactive. Oil forced out due to over pressure will refill the opposite slew cylinder, thus eliminating hydraulic play. Slewing without pump pressure is not possible. Coloured channels in the small valve picture are pressurised.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
H012-6
Slew function (large CE-cranes)
Description
Figure 11 shows a valve cross-section of the slew function for large EU-cranes the A and B sides have only pressure relief cartridges including suction valve function. Load holding and damping for the slewing motion is taken care of by a separate motion-control valve.
Function
Pressurised oil (red) is directed via the parallel channel to the B-port and further via the one-way restriction valve and the motion-control check valve to the slew cylinder. Return oil (light red) is pressure regulated over the motion-control valve and is flow limited over the one-way restriction valve before it returns to the tank channel under return pressure. When slewing downhill the slew cylinder can never be emptied quicker than oil is being replenished on the opposite side thanks to the separate load holding function. This will prevent hydraulic play. Also, it is not possible to slew without pump pressure. Coloured channels in the small valve picture are pressurised
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
H013-6
Inner boom function (small Non-CE-cranes)
Description
Figure 12 shows a valve cross-section illustrating the inner boom function for small OS-cranes. The
equipment is similar to the old V41 having a pressure relief cartridge including suction valve function on side A, built-in load holding on side B. The outer boom function for small OS-cranes looks alike, the only small difference being that the relief valve has no back-up ring or O-ring in order to create an amount of damping. The lack of spool position indicators should also be noted.
Function
Pressurised oil (red) is directed via the parallel channel and the check valve in the B-port to the bottom of the inner boom cylinder. Since load holding is taken care of by the in-built function in the control valve at the crane base, a separate hose rupture valve close to the cylinder is needed. Return oil (blue) passes through the one-way restriction valve and the pressure relief valve before going to the return channel via the spool. The built-in check valve in the closed position provides the control valve with load holding properties. The crane boom cannot be lowered without pump pressure. Coloured channels are pressurised.
The inner boom function for large OS-cranes is identical to the one for EU-cranes. The only difference is the lack of spool position indicators.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
H014-6