Control Blocks and Valves

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Legend for illustration (Z 22436):

(1) Control block housing (2) Cab ("A side)

(3) Cap ("B" side)

(4) Solid spool

(5) "B" side service line ports

(6) Centering springs

(7) MRV, main relief valve (8) Port A, to cylinder/motor (9) Port B, to cylinder / motor (10) Fine controlling grooves (11) Port P, from pumps (12) Port T, to tank (13) Load holding valves

Control blocks with "Open Center and Closed Ports".

Control blocks I, II and III are 4 spool blocks and IV is a 1 spool block.

See hydraulic circuit diagram for spool details.

Each spool is provided with "Fine Controlling Grooves" and ring grooves for hydraulically centering of the spool.

Between 8 and 19 bar pilot pressure the spools are moved in their fine control range.

Spool number 4 of block I, 2 of block II and 4 of block III are special

designed, to keep the pressure channel connected to the center channel during the floating function is activated, so that pump flow is available for other functions. This spools are marked in the hydraulic diagram with (# or $) symbol.

The Load Holding Valves are installed inside of the spool, for each port to the cylinder or motor one valve. The hydraulic diagram shows only one.

The MRV is a pilot operated pressure relief valve.

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

6.1.11 Control Blocks and Valves

Legend for illustration (Z 22440):

(1) Main relief valve (MRV)Control block housing (2) Load holding valve

(3) Anti cavitation valve (ACV) (4) Service line relief valve (SRV)

Explanation of the schematic drawing of the control block:

The hydraulic oil flows through the control block from port P to T, if all spools are in neutral position ("pressure-less circuit" or “Free circulation“).

(A) 4 valve block

E.g. the spools moves up when pilot pressure is build up in the control pipe line a1. (Imagine the lower symbol box moves to the center position.) Now pump oil flows through holding valve (2) to the user port A1 because the free flow circulation to the hydraulic reservoir is closed. The main relief valve (1) limits the maximum operation pressure in this circuit. Via port B1 the return oil from the user is flowing back to the hydraulic reservoir.

During down hill travelling motion and stopping procedure (e.g. travel motors) the anti cavitation valves (3) prevents cavitation on the hydraulic motors. Because during these short periods of time the hydraulic motor needs a higher oil supply than the pump can deliver.

E.g. the spool (4) moves up when pilot pressure is build up in the control pipe A4. Now the user port A4 is connected to the pump pressure line and the free circulation to the tank. There is no high pressure build up only 8 bar from the back pressure valve and line resistance. Via port B4 the return oil from the user is flowing back to the hydraulic reservoir. Service line relief valve (4) is additional installed in this circuit to protect the circuit for extreme pressure.

The shortly extreme pressure closes also the holding valve (2) which secures the hydraulic pump from extreme pressure peaks.

The holding valves (2) have also the function of load holding valves because during the fine controlling period all lines are connected together (negative over-lapping). The load pressure is for a moment higher than the pump pressure.

(B) single valve block

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

6.1.11 Control Blocks and Valves

Legend for illustration (Z 22441):

(1) Spool (2) Reset springs (3) Load holding valve

Function:

Reset springs (2) moves the spool (1) in neutral position.

Fine control grooves provide for sensitive controlling, because a motion is started always while the pressure oil and the return oil first passes this fine control grooves before spool (1) is inter connecting the entire groove to the user channel.

In neutral position of spool (1) the pump oil is flowing back via port PU to the tank.

Lower picture:

Example. The spool is moved by pilot pressure on the left spool side to right position: Port PU is closed and the connection through the holding valve (3) to the user (port A) is open. Also the connection from the other user side (port B return)is connected to the port T (return line to tank).

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

6.1.11 Control Blocks and Valves

Legend for illustration (Z 21705):

(01) Service -Line Relief Valve (9) Set screw

MRVs and SRVs are pilot operated relief valves. The MRV limits the max.

Pump supply line pressure. The SRV limits the max. possible pressure peak in the service-line.

The valves have an „opening characteristic“. That means, that in case of contamination after the response procedure no further pressure increasing is possible and damages are avoided.

Function:

The circuit pressure P forces with the force F1 on the piston surface A of the main valve cone (15). Because there is via the jet bore (16) the same pressure on the back side of the main cone, this results together with the spring (14) force in a force F2 that keeps the main cone closed. Via the jet bore (13) the circuit pressure is in front of the poppet (12). Exceeds the circuit pressure the setting value of the spring (11), the poppet opens against the force of the spring (11).

This causes that the force F2 decreases and there is no more balance condition between F1 and F2. Valve cone (15) is moved upwards by the greater force F1.

That means there is now a direct connection from port P to T (tank).

ACVs serve for compensation possible lack of feed when the SRV at the opposite port is actuated (see circuit diagram) and for avoiding cavitation damages. In addition, to supply a user in case it is continuously moved by acceleration forces at zero position of the control spool.

Function:

The circuit pressure inside the spring chamber closes the valve cone (7).

The back pressure of the return line acts on the surface of the valve cone (7).

Whenever the pressure in the service-line is lower than the springs force the valve cone opens by the force of the back pressure and hydraulic oil is additional supplied.

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc

06.10.05 PC5500-6-D_Sec_6-0_rev1.doc