D6N Track-Type Tractor Hydraulic System Caterpillar

Introduction

This test will determine if a resolver is bad. A resolver is a check valve. The resolver compares two pressures. The lower pressure of the two pressures is blocked. The higher pressure or the higher signal goes to the next component in the resolver network.

Each implement control valve has a resolver. The resolver compares the signal in one control valve to the signal in the other control valves. The signal resolver network is arranged in a series. The series stops at the pump compensator valve.

This procedure includes the following test:

• "Test Procedure (Primary Resolver)"

• "Test Procedure (Secondary Resolver)"

Required Tools

Illustration 1	g01291479

Test Procedure (Primary Resolver)

1. Start the engine.

2. Warm up the hydraulic oil.

3. Run the engine at LOW IDLE.

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Illustration 2	g01318344

4. Attach the tetragauge (A) to signal line pressure tap (1) .

5. Operate each control lever in the following order:
   • Ripper

   • Angle

   • Tilt

   • Lift

6. Put each cylinder into a fully stalled condition.

7. Maximum system pressure of 25000 ± 500 kPa (3626 ± 75 psi) should be seen for all circuits.

   Note: Do not keep any cylinder in a stalled condition for more than 10 seconds. Do not return any cylinder to a stalled condition within 30 seconds of the prior stalled condition.

Test Procedure (Secondary Resolver)

If two or more control valves next to each other fail to work normally, the problem may be in the secondary resolver of the malfunctioning control valve that is closest to the pump supply. The secondary resolver of this control valve is allowing signal pressure from any other control valve to leak through a signal passage to the tank.

One of the following conditions could also cause one of the control valves to fail:

• the ball is missing.

• there is debris that is preventing the ball from seating properly.

• the ball is damaged or the seat is damaged.

Operate the valves in order to determine the malfunctioning valve that is closest to the pump. The following list proceeds from the valve that is farthest from the pump to the valve that is closest to the pump:

• Ripper

• Angle

• Tilt

• Lift

Primary Resolver versus Secondary Resolver

If a valve section fails to work in at least one direction, the primary resolver or the secondary resolver in that control valve may be bad. To locate the bad resolver, perform the following test.

Stall the attachment that is farthest away from the pump. This will force the ball in the secondary resolver of the suspect valve to seat on the side away from the drain. This eliminates the possibility of a leak on the drain side of the secondary resolver. At the same time, operate the suspect valve. If the problem is not corrected in the suspect valve, the primary resolver may be bad.

If the primary resolver is bad, the pressure loss is affecting the operation of the flow control spool in the valve body. The force that is needed to open the valve completely is insufficient. Therefore, the attachment has a slower response.

Normally, if an attachment is slow in both directions, the problem is in the secondary resolver. If an attachment is slow in one direction, the problem is typically caused by a bad primary resolver.

A malfunctioning valve section might be caused by one of the following items:

• valve spring that is worn or broken

• incorrectly installed flow control spool

• bad line relief valve or makeup valve

Note: If there is debris in the system, the system should be flushed by removing the balls from the secondary resolvers and operating the equipment. Enough flow will be supplied in order to flush the debris into the hydraulic tank.