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New Hydraulic Systems

Systems Operation

Valve Operation

Figure IDCS007B is a schematic illustration of a
three section valve, showing the inlet and outlet ports
and the by-pass, pressure and tank passages.
The pressure passage is used to carry fluid to the
cylinder ports when the spools are shifted. The by-
pass passage permits flow directly to the outlet when
the spools are not being operated. The tank passage
also carries fluid to the outlet; either return flow from
the cylinder ports or fluid diverted past the flow
control and relief valve,

The spools are shown in the centered or neutral
position, Under these conditions, fluid in the pressure
passage is blocked from the cylinder ports by the
spool lands. Flow through the valve is through the
by-pass and tank passages to the outlet.

(1) Control Valve Sensing Orifice.
(2) Flow Control And Relief Valve.
(3) Tank Passage.
(4) By-pass Flow Control Orifice.
(5) Cylinder Ports.
(6) Pressure Passage.    (7) By-pass Passage.

IDCS007B

Lift Spool

IN

Pressure to 

B

A

to tank

By-pass blocked

CENTER

A

and 

B

blocked

By-pass open

OUT

B

to tank

A

blocked

By-pass open

Lift spool - used for control of single acting cylinder
applications. It directs flow to only one end of a
cylinder, as in the lift mechanism of a lift truck.
Return flow is from the same end of the cylinder and
relies on gravity or mechanical means to retract.

IDCS008B

IDCS009B

Summary of Contents for D20-2

Page 1: ...Aug 1996 Specifications SystemsOperation Testing Adjusting Disassembly Assembly New Hydraulic Systems D20 25 2 D20 25 30S 2 G20 25 30S 2 G20 25 30S 2 SB2097E00...

Page 2: ...rt symbol is as follows Attention Become Alert Your Safety is Involved The Message that appears under the warning explaining the hazard can be either written or pictorially presented Operations that m...

Page 3: ...lic System D20 25 30S 2 G20 25 30S 2 GC20 25 30S 2 Model 6 Hydraulic System D20 25 2 Model Only 11 Anti Stall And Remote Relief Valve 14 Testing And Adjusting Hydraulic System 23 Flow Control Valve Ad...

Page 4: ...embly 36 5 0 5 N m 320 4 lb in See Folw Control Valve Adjstment in Testing And Adjusting 4 Torque for screws 12 1 5 N m 105 13 lb in 5 of 29 New Hydraulic Systems Specifications CONTROL VALVE TILT Aux...

Page 5: ...3 Sideshift cylinder s if equipped 4 Lowering flow control valve 5 Hydraulic control valve 6 Tilt cylinders 7 Relief valve lift 8 Relief valve tilt and sideshift 9 Hydraulic oil filter 10 Hydraulic oi...

Page 6: ...lve go to lift cylinders 1 and or 19 tilt cylinders 6 or sideshift cylinder s 3 The return hydraulic oil from the cylinders flows through hydraulic control valve 4 line 13 into filter 9 and hydraulic...

Page 7: ...prevent cavitation development of air pockets in tilt cylinders 6 REFERENCE For the Hydraulic Systems Schematics 8 of 29 New Hydraulic Systems Systems Operation Basic Hydraulic Schematic With Standard...

Page 8: ......

Page 9: ...control valve 6 Tilt cylinders 7 Relief valve lift 8 Relief valve tilt and sideshift 9 Hydraulic oil filter 10 Hydraulic oil tank 11 Priority valve 12 Oil line trucks with power brakes only 13 Oil li...

Page 10: ...ses anti stall valve 20 now closes the passage to remote relief valve 18 With remote relief valve 18 blocked normal hydraulic relief pressures are available The control valve levers move the valve spo...

Page 11: ...ilt cylinders 6 REFERENCE For the Hydraulic Systems Schematics 13 of 29 New Hydraulic Systems Systems Operation Basic Hydraulic Schematic With Standard Lift 1 Lift cylinders 2 Excess flow protectors 3...

Page 12: ...stall valve will increase This pressure increase will be limited by the remote relief valve to 8250 kPa 1200 psi 6R7072 Relief Valve This relatively low system pressure allows for a smoother engine i...

Page 13: ......

Page 14: ...e bodies connect each section to the common inlet and tank ports Seal rings between the sections seal the connecting passages Sections are held together by studs and nuts 17 of 29 New Hydraulic System...

Page 15: ...ered or neutral position Under these conditions fluid in the pressure passage is blocked from the cylinder ports by the spool lands Flow through the valve is through the by pass and tank passages to t...

Page 16: ...he counterbalance feature prevents the forks from tilting forward faster than the pump can supply oil preventing tilt IDCS012B Auxiliary Spool IN Pressure to B A to tank By pass blocked CENTER A and B...

Page 17: ...ional secondary relief valve allows the use of lower pressure for tilt and accessory function while higher pressure is provided for the lift function NOTE The secondary relief valve must be set at a l...

Page 18: ...the sensing orifice is great enough to overcome the force of the large spring the valve spool shifts permitting flow to the tank passage Relief valve sub assemblies in the inlet section are pre set an...

Page 19: ...ue nuts to specified ratings Remedy Replace detent barrel Replace detent spring Trouble Detent type spools will not stay in detent position Trouble No motion slow or jerky action of hydraulic system P...

Page 20: ...ngs Group CONTROL VALVE Tilt Auxiliary Relief Valve Pressure 350 kPa 50 psi 15 500 2250 15 500 2250 15 500 2250 Main Relief Valve Pressure 500 kPa 75 psi 18 100 2625 19 500 2825 21 550 3125 Mast Std F...

Page 21: ...low Control Valve Adjustment 1 Flow control valve adjuster 1 Remove the nut from the main hydraulic valve tie bolt stud 2 Remove the stud from the valve 3 Use Hex Wrench 6mm turn the flow control adju...

Page 22: ...r it must be filtered to remove water and other contamination Be sure the unit is not subjected to pressure Disconnect and cap all lines and disconnect linkage to the spool Attaching Parts 1 Remove th...

Page 23: ...ean and free from obstruction Examine all mating surfaces for nicks and burrs Minor nicks and burrs can be removed with a crocus cloth or an India stone 2 Discard all old seals and O rings Wash all pa...

Page 24: ...27 of 29 New Hydraulic Systems Disassembly and Assembly IDCS015B...

Page 25: ...tall the O ring 31 on the relief plug Tighten the plug securely in valve body DO NOT over tighten CAUTION Hex head of relief valve must be face outside of unit Relief Valve 1 Install a new O ring 27 o...

Page 26: ...rings in proper bores of inlet and mid body sections Attaching Parts CAUTION Make sure all mating surfaces of valve bodies are clean and free of burrs 1 Install seals 4 O ring 5 and the retainer 3 in...

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