Description
Valve 91 is a load sensing pressure compensated control valve, a so-called closed-centre valve. This means that each valve function delivers an oil flow directly proportional to control lever movement as long as pump flow is sufficient. The flow is completely independent of load even when several valve functions are used simultaneously. Valve 91 can be used together with a variable pump. However, we recommend a constant displacement pump for HIAB cranes. Except 6 valve functions there is in the valve block, a shunt function, the duty of which is to direct pump oil to tank and further to maintain a certain pressure in the pump line.
The valve block can be fitted with a solenoid valve, which controls the shunt function, e g when using remote control. There are no separate port relief valves in valve 91. These relief valves have instead been moved out to the load-holding valves for inner and outer boom cylinders, for the slew function to the crossover valve. For the extension a special spool with built-in signal pressure relief for side A or B is available.
The load-holding valve LHV-91 has been specially developed to be used in the inner and outer boom functions together with valve 91.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
Connections
P1 = Pressure connection from pump (R 3/4”)
P2 = Pressure outlet for pressure reduction filter (R 1/4”) (CombiDrive)
P3 = Serial outlet to stabiliser valve. Serial connection plug necessary (R3/4”) T1 = Tank connection (R 3/4”)
T2 = Return from pressure reduction filter (R 1/4”) (CombiDrive)
T3 = Return from load-holding valve 91 (R 1/2”)
S1 = Gauge connection for signal pressure/ signal connection to variable pump (R 1/4”) S2 = Signal pressure connection from following closed centre valve (R 3/8”)
There are also casting marks for side A and B, P-connections, T-connections, S-connections, and section numbers.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
H002-2
fig.2
Spools
Description
The spools are adapted to suit crane size and function by means of shaping metering slits for a predetermined and approved speed.
Each spool is coded. In this first case 14B which means 63-63-35-35. In more detail 63 1/mm to piston side and 35 1/min out from rod side. From the other direction, 35 1/min into rod side and 63 1/mm out from piston side.
It is about time to make acquaintance with the new valve symbol. Ports A and B are closed which is similar to D-spools but we now have a “closed centre”, i e closed throughput in neutral position. Instead we find here an S connected to T for tank. This S means signal line. Let’s take a closer look at the symbol figures when describing the lifting and lowering functions.
The spool in the centre is a DM-spool, which as previously means motor spool. The code 84A means 50 L/min out as well as in. As you can see from the symbol the DM-spool has ports A and B connected to tank in neutral position.
The exterior of the bottom spool looks like the topmost spool, but there is a in–built signal pressure relief valve. This is set at a fixed pressure, in this case 140 bar above port A. A spool of this kind can be used for an extension function, because the 91-valve has a common signal pressure relief for ports A and B and the port relief (shock) valves are fitted in the load holding valves. Normally there are no load-holding valves on the extension cylinder and therefore pressure limiting for extension out is solved in this fashion.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
H003-2
fig.3
Description
This is a cross-section of the connection end of valve 91 showing both dump valve and shunt. The shunt housing at SI with shunt spring and shunt piston. The dump valve consists of the vertical cartridge in the top left corner. This version is used for manual operation. For remote control a solenoid valve (dotted line) is added. Shown also is the pump connection P1, the CombiDrive oil supply P2 and the oil supply P3 to the stabiliser valve e g. The blue field in a diagonal pattern is a chamber behind connecting all tank connections such as T1 to tank. Other tank connections include T2 (return from CombiDrive), T3 (port relief oil from and reference pressure to the load-holding valve).
Function
In this case the dump valve is closed. When used for manual operation this means that a plug closes connection between top and bottom side of the dump piston. For remote control with a voltage over the solenoid the connection channel is also closed. Pump pressure having been transmitted up through the dump piston into the spring housing becomes locked in and gives hydraulic balance to the dump piston. The spring keeps the piston closed against releasing pump pressure to tank. The pressure level 13 bar is determined by the shunt spring.
continued on page 6
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
Notes
Conclusion
When used for manual operation or remote control with voltage over the dump solenoid (emergency button pulled out) the closed dump valve means full standby pressure 13 bar to the valve. Pressure is determined by the shunt.
We can follow this in fig.3: The shunt to the left admits oil to tank while the dump valve to the right is closed. The plug below T2 is the serial plug used for a separate stabiliser valve connected to P3. The plug below T3 is the plug seen to the left in the cross-section
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
H004-2
fig.4
Description
The open dump valve is seen here. For opening a solenoid valve the same as used for remote control is necessary.
Function
Voltage over the solenoid valve is OV, i e the emergency button is pushed in. A poppet opens connection to tank whereby the locked in pressure behind the dump piston is released. The piston moves up and is balanced only by the weak spring corresponding to 3 bar. The shunt spring closes the shunt and circulation pressure is reduced to 3 bar with the shunt open.
Conclusion
Pushing in the emergency button will reduce circulation pressure from 13 bar to 3 bar which means reduced heat generation.The hydraulic diagram shows that the plug below T3 has been replaced by a two-position valve open/closed. With the valve open counter pressure will be drained and pump oil dumped to tank.
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
fig. 5
HYDRAULIC CONTROL SYSTEMS
HYDRAULIC CONTROL SYSTEMS
Idling
Description
This is the valve when idling, i.e. no lever has been moved. Fig.5 shows a valve cross-section at different levels. Far left the ground floor is seen with shunt, pressure compensator, and signal system including signal pressure relief valves. Further to the right at the 3rd up to the 5th function we are moving upward to the spool floor. Of course there are pressure compensators and signal systems under the spools as well. At the 6th function we have moved down to the bottom floor again. Pressure compensator and pressure relief belonging to this function are seen. It is to be noted that the signal system is equipped with balls on every function except the last one. The reason for this being that the pressure must be drained when the lever is released.
Function
The pump is supplying oil at 120 l/min. Since the valve is a so-called closed-centre valve there is no other exit for the oil than passage through the shunt back to tank. Since signal pressure is 0 bar and the signal pressure spring puts up a resistance corresponding to 13 bar, this will be the circulation pressure.
The colours also make clear that the pressure compensator of each function reduces pressure down to 8 bar above signal pressure which in this case was 0 bar. Seen also is the pressure gauge connection on the shunt cover. It will indicate pressure in the signal pressure system. When idling full flow goes to tank over the shunt.