This article introduces the pressure control sequence valve setting of Doosan steering gear
Doosan DMS-5 (Doosan Data Monitoring System) Diagnostic Soware V1.6.3
Theory of Operation Oil output from the steering pump flows through the priority valve to both the loader supply line and to the steering circuit. During operation of the steering wheel, the priority valve shifts and supplies pump flow only to the steering circuit. This results in smooth operation of the steering circuit.
At rest, the spool(1, Figure 4) maintains an open path between inlet port P and steering outlet port CF. Port EF is kept closed by the force from spring (2, Figure 4). The spool(1, Figure 4)
contains a drilled passage. The passage is open to port CF and is also open to both ends of the spool. At the neutral position of the steering unit, oil from port P flows through port CF and into the drilled passage in the spool. At this time, oil flowing out of CF is blocked at the control spool of the steering unit. This raises the pressure in port CF. At this time, port LS is open to the chamber on the far right side of the priority valve. Port LS is notopen to the chamber on the far left side of the valve. As oil flows through the drilled passage in the spool, pressure builds on the left side of the spool but pressure is low on the right side of the spool because oil can drain into port LS. When oil pressure on the left side of the spool rises above the force of spring (2, Figure 4), the spool(1, Figure 4) shifts the right. This allows pump flow at port P to flow out both ports CF and EF. Now both the loader supply line and the steering supply line are charged with flow from the steering pump. Whenever the steering wheel is turned, the spool in the steering unit directs some oil flow back to port LS. This equalizes the oil pressure on both ends of thespool(1, Figure 4). The spring now shifts the spool to the left.
This closes off the passage from port P to port EF. This makes all steering pump flow now available only to the steering circuit from port CF.
SPECIAL TOOLS
1. The following tools are necessary to repair the priority valve. See Figure 6.
Open end wrench-27mm Slip joint pliers Nylon rod Allen wrenches-5 mm,8 mm and 10mm
DISASSEMBLY
1.Use open end wrench to loosen PP plug.See Remove O-ring.
2.Use open end wrench to loosen LS plug.See Figure 8.
Remove O-ring.
3.Remove spring.See Figure 9.
4.Use a nylon rod to push spool out of bore.See Figure 10.
5.Use an 8 mm allen wrench to remove plug from pressure relief valve.See Figure 11
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6.Use a 10 mm allen wrench to unscrew pressure relief valve from its bore.See Figure
7.Hold pressure relief valve with a pliers and use a 5 mm allen wrench to remove set screw.See Figure 13.
8. The pressure relief valve is composed of a valve housing, valve needle, spring and set screw. See Figure 14.
CLEANING AND INSPECTION
(WEAR LIMITS AND TOLERANCES)
For general cleaning and inspection procedures, refer to
"General Maintenance Procedures"section.
Clean all parts with a nonflammable, nontoxic solvent.
Carefully inspect all parts. Replace all worn or broken parts. Use only new O-rings to assemble the valve.
Cost all parts with oil before assembling them.
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