Linde H 50 D, Обучение по обслуживанию

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Service Training Section
4.7
Page
3
4.7.1.1 EXPLANATION OF THE WORKING HYDRAULICS
When the control levers are in the neutral position and the pump output is nill, way valves (2), (4), (6) and
(7) and also the pressure balance (9) are closed. Port P1 is connected via the pressure-reducing valve (8)
to port VS.
When the engine is running, oil coming from the pump (27) enters the valve block at port P1 and opens the
pressure balance (9) against the force of the spring, thus making the oil circuit pressureless. The spring
pressure exerted on the pressure balance and the pressure applied at port P1 are in balance with a
differential pressure of approx. 5 bar. The oil pressure existing at port M goes to inlet M of the emergency
valve, while port HB is connected to outlet HB of the emergency valve.
Operating one of the control levers lets the load pressure go through a special control oil passage in the
control spool of the way valve in question and via the shuttle valves (3) and restrictor (10a) to the shock
valve (10) and into the spring chamber of the pressure balance (9). Due to the change in the balance of
pressure, the pressure balance closes just enough so that oil flows through the way valve to the load. The
volume of the oil flow depends on how far the way valve spool is shifted. The pressure balance lets the
excess oil go directly to port T3.
When the set pressure of the safety valve (10) is reached, the maximum pressure valve opens and lets oil
flow to port T3. Due to the differential pressure resulting at restrictor (10a), the load pressure becomes
greater than the response pressure of the maximum pressure valve and the pressure balance is modulated
so that only so much oil flows as is required for the maintenance of the differential pressure at restrictor
(10a). Any excess oil is diverted to port T3 by the pressure balance (10).
SPEED CONTROL
The inlet of the pressure-reducing valve (8) is connected to oil passage P1 and the outlet to the engine
speed control unit via port VS. The actual value signal is connected to the tank via the restrictor passage
(8a)-(8b). When the valve spool for lifting is not operated, restrictor (8b) is closed. The actual value for the
pressure-reducing valve is therefore taken between restrictors (8b) and (8a). When the way valve for tilting
(6) or auxiliary hydraulics (2) or (4) is activated, the pressure-reducing valve lowers the pressure on the
outlet side to approx. 7 bar, letting the engine speed rise to approx. 1200 rpm.
When the way valve (7) for lifting is operated, restrictor (8b) is opened more and more, depending on the
setting of spool (7), and thus connecting it to the tank. This creates a differential pressure, whose size
depends on the setting of spool (7), between the signal for increasing speed and the actual value pick-up.
The engine control pressure will increase so much that the engine will accelerate to top speed. As no
pressure builds at port P1 during lowering, the engine speed is not increased then.