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Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 4679
Experience:  17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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I have a 420 D cat backhoe steers good without a load in the

Customer Question

I have a 420 D cat backhoe steers good without a load in the bucket . When you get a load on the bucket with main hyd. valve in neutral position steering quits. Move any hyd spool steers good . I think Hyd. pressures are low but do not know what they should be .
Submitted: 7 months ago.
Category: Construction and Road Equipment
Expert:  Dan replied 7 months ago.

Hi Jimmy, My name is***** is your machine serial number?

Customer: replied 7 months ago.
7bj53353
Expert:  Dan replied 6 months ago.

Hi Jimmy, I hope you had a great weekend. Check your resolver network and flow compensator valves as mentioned below. Let me know

The signal network can be easily checked. Install one 6V-4143 Coupler Assembly to each end of the(###) ###-####Hose Assembly . Install the 8T-0860 Gauge with a range of 0 to 40000 kPa (0 to 5800 psi) to the coupler assembly. Install(###) ###-####Hose Assembly to signal pressure tap. (On compensator valve)

Start the engine and warm up the hydraulic oil to the operating temperature. Run the engine at LOW idle. Operate each hydraulic control in the following order.

Auxiliary for the loader (if equipped)

Loader bucket tilt

Lift control for the loader

Steering

Right side stabilizer

Left side stabilizer

Extendable stick (if equipped)

Stick

Backhoe bucket

Swing

Boom

Auxiliary for the backhoe (if equipped)

Stall each circuit. The following tables contain the signal pressures for the hydraulic circuits.

Hydraulic Circuit420D, 428D, 430D, 432D, 438D and 442D416D and 424D

STICK OUT
22800 ± 700 kPa (3300 ± 100 psi)
20700 ± 700 kPa (3000 ± 100 psi)

STICK IN

STICK EXTEND (if equipped)

STICK RETRACT (if equipped)

Auxiliary (if equipped)

SWING

Backhoe BUCKET DUMP

Backhoe BUCKET CLOSE

BOOM RAISE

Front wheel steering
17250 ± 700 kPa (2500 ± 100 psi)

All Wheel Steering
22800 ± 700 kPa (3300 ± 100 psi)Not applicable

BUCKET DUMP (parallel lift machines)
16200 ± 700 kPa (2350 ± 100 psi)

RACK BACK (parallel lift machines)
22800 ± 700 kPa (3300 ± 100 psi)

BUCKET DUMP and RACK BACK for (S/N: FDP1-7198, BNK1-2501)

BUCKET DUMP and RACK BACK for (S/N: FDP7199-UP, BNK2502-UP)
14900 ± 700 kPa (2150 ± 100 psi)

DUMP and RACK BACK (all other machines)
22800 ± 700 kPa (3300 ± 100 psi)
20700 ± 700 kPa (3000 ± 100 psi)

LIFT

Secondary Resolvers with Two or More Valve Sections

If two or more of the control valves in series fail to work properly, the problem may be in the secondary resolver of an upstream implement control valve. The first control valve receives the pump supply oil first. If the secondary resolver for the control valve does not work properly, the secondary resolver may allow signal pressure from any control valve that is further from the pump supply to leak back to the tank.

This leakage may be caused by a resolver ball that is not seating or by a resolver ball that is blocking the signal oil to the drain. Signal oil from a downstream control valve may be at a higher pressure than a control valve that is closer to the pump. However, the faulty resolver will not allow the downstream valve to function properly.

A leakage in the resolver may be caused by a missing resolver ball, debris that prevents the resolver ball from properly seating, a missing seal or a leaking seal. When multiple control valves malfunction, first operate the malfunctioning valve that is farthest from the pump. Operate the other control valves, while you operate the control valve that is farthest from the pump. Operate the other control valves one at a time until a control valve operates both implements.

This is the control valve with the bad secondary resolver. The farthest control valve is sending a signal and the control valve with the faulty secondary resolver is also sending a signal. Because the control valve with the bad secondary resolver has a leak, the signal from the farthest control valve cannot flow to the pump controller until the control valve with the faulty resolver is operated.

Primary Resolver Versus Secondary Resolver

For control valves with a flow control spool, if one control valve section fails to work properly in one or both directions, the primary resolver or the secondary resolver in that control valve may be faulty. In order to determine the faulty resolver, perform the following check.

Stall an implement control valve downstream from the malfunctioning valve. This will force the malfunctioning valve's secondary resolver ball to move away from the seat on the drain end.

This eliminates the possibility of a leak on the drain end of this secondary resolver. While you stall the downstream control valve, operate the malfunctioning control valve. If the control valve is still operating improperly in one or both directions, then the primary resolver may be faulty.

When the primary resolver is faulty, the faulty resolver bleeds off the pressure, which affects the operation of the flow control spool. The combined force of the signal oil pressure and the flow control spring is not enough to move the spool. This prevents additional oil to flow to the cylinder. The load on the cylinder is greater than the amount of oil that is flowing to the cylinder, which causes the implement to have a slower response.

Normally if an implement is slow in both directions, the problem is usually in the secondary resolver. If an implement is slow in only one direction, the cause is typically caused by a faulty primary resolver.

The causes for a faulty primary resolver are the same causes for a secondary resolver. A leakage in the resolver may be caused by a missing resolver ball, debris that prevents the resolver ball from properly seating, a missing seal or a leaking seal.

A malfunction in a valve section could be caused by one of the following problems.

A misadjusted linkage

A spring in the flow control valve that is broken

A flow control spool that is incorrectly installed

A faulty line relief valve

A faulty makeup valve

Note: As a recommendation, flush the system if there is debris in the system. Flush the system by removing all of the resolver balls in the secondary resolvers. Then operate the implements. There will be enough oil flow in order to flush the debris to the tank.

Try to find a section that does not work correctly and check that valve's resolvers (bottom) then recheck the network (back-side) resolvers.

Check the inlet section of the loader valve as well. The flow limiter spool to regulate steering pressure can stick causing low pressures.

Flow Compensator adjustments.

(1) Hydraulic pump

(2) Flow compensator valve

(3) Pressure compensator valve

(4) Signal pressure tap

Signal pressure tap (4) is located on hydraulic pump (1) . Flow compensator valve (2) and pressure compensator valve (3) are also located on hydraulic pump (1) . Access is gained from the bottom of the machine or access is gained by removing the floorplate.

The system pressure tap is located on the block for the pump discharge pressure. Access is gained from the bottom of the machine.

Pump discharge pressures are known values. The pump discharge pressures can be tested during two specific conditions.

low pressure standby

high pressure stall

Prior to making any pump adjustments, perform "Low Pressure Standby Test", "Margin Pressure Test" and "High Pressure Stall Test".

Increase the hydraulic oil temperature to the operating temperature by installing the boom lock and stalling the boom down for 60 seconds. Check for leaks.

Low Pressure Standby Test

Start the engine.

Lower the work tool on the front of the machine and the stabilizers to the ground. Engage the parking brake. Stop the engine.

Turn the engine start switch key to the ON position.

Move the hydraulic hand controls to all the positions in order to release system pressure.

Turn the engine start switch key to the OFF position.

Install the 8T-0856 Pressure Gauges with a range of 0 to 6000 kPa (0 to 870 psi) to each hose assembly. Install one hose assembly to the pressure tap (5) for system pressure. Install one hose assembly to the signal pressure tap (4) .
Note: Do not move any hydraulic hand controls or the steering wheel while the 8T-0856 Pressure Gauges are installed. The higher pressure that is created by upstroking the pump will damage the gauges.

Start the engine. Run the engine at HIGH idle. Check for leaks.

Do not move any hydraulic hand controls nor move the steering wheel. The pressure reading on the gauge that is attached to the pressure tap (5) for the system pressure should be 2850 ± 750 kPa (415 ± 110 psi). This pressure is the low pressure standby pressure. For best results, the low standby pressure should be set at approximately 3100 kPa (450 psi).

The pressure reading on the gauge that is attached to the signal pressure tap (4) should be approximately 650 kPa (95 psi). This pressure is the steering signal pressure. The steering signal pressure is not adjustable.
Note: The steering signal pressure will vary with each machine. The steering signal pressure of each machine should remain consistent with the previous readings on that machine.

Stop the engine.

Before continuing to the next test, remove the two 8T-0856 Pressure Gauges from both hose assemblies. Install a 8T-0860 Pressure Gauge with a range of 0 to 40000 kPa (0 to 5800 psi) to the hose assembly that is attached to the pressure tap (5) and to the pressure tap (4) .
Note: Failure to remove the 8T-0856 Pressure Gauges prior to performing the following tests will cause the gauges to be destroyed, when the pump is upstroked.

Margin Pressure Test

Start the engine. Run the engine at HIGH idle.

Engage the boom lock. Stall the boom circuit with a one-third lever movement in the DOWN position.

Subtract the pressure at signal pressure tap (4) from the pressure at system pressure tap (5) . This is the margin pressure. The margin pressure should be 2200 ± 350 kPa (320 ± 50 psi).

Stop the engine.

If margin pressure or standby pressure is not correct, the flow compensator valve must be adjusted.

Do not make adjustments to the flow compensator spool based on the results of this test. Perform the "High Pressure Stall Test" before you make adjustments to the flow compensator spool.

High Pressure Stall Test

Install the swing lock pin and install the boom lock.

Start the engine. Run the engine at LOW idle.

Ensure that the work tool on the front of the machine and the stabilizers are on the ground. Engage the parking brake.

Move the hydraulic hand controls one at a time in order to initiate a stall condition for the circuits in Table 2 (Chart in earlier post). Note the pressure reading at pressure tap (4) for each circuit.

See Table 2 for the proper pressure readings at pressure port (4) .

The larger setscrew is the high pressure setting.

Note: There may be air in the signal network, if there is a hesitation before reaching the relief pressure. Purge the signal lines of the air.

In order to check the BOOM LOWER circuit, perform the following procedure.

Engage the boom lock.

For 416D, 420D, 424D and 430D machines, run the engine at 1100 rpm. Activate the BOOM LOWER by pushing the boom control lever fully forward.

For 428D, 432D, 438D and 442D machines, run the engine at 1250 rpm. Activate the BOOM LOWER by pushing the boom control lever fully forward.

Note the pressure reading at pressure tap (4) .

See Table 3 for the proper pressure readings at pressure port (4) .

Table 3

Hydraulic Circuit420D, 428D, 430D, 432D, 438D and 442D416D and 424D

BOOM LOWER
15200 ± 700 kPa (2200 ± 100 psi)
15500 ± 700 kPa (2250 ± 100 psi)

The Relief Valve for the Tilt Cylinder (Bucket Dump and Rackback)
Refer to the following steps in order to check the pressure setting:

Attach 8T-0857 Pressure Gauge to the output pressure port on the hydraulic pump.

Start the machine.

Tilt the bucket to the DUMP position or tilt the bucket to the RACK BACK position. Hold the valve in the open position.
Note: The valve functions when the control spool is actuated.

Read the pressure gauge in order to determine the relief valve setting. See table 2 for the correct pressure for your machine.

Compensator valve (all other machines)

(1) Flow compensator

(3) O-ring

(4) Locknut

(5) Adjustment screw

(6) Cap

(7) Adjustment screw

(8) Cap

(9) Locknut

(10) O-ring

(11) Pressure compensator spool

(12) O-ring

(13) O-ring

Note: If an adjustment is necessary, replace the O-rings (3) , (10) , (12) and (13) . Replacing the O-rings will reduce the possibility of oil leakage after an adjustment to the compensator valve is made.

Flow compensator valve (1) and pressure compensator valve (11) have been tested by running the pump discharge tests.

Adjustment For The Pressure Compensator Spool
Adjustments to the pressure compensator spool can be made on the machine. If the "High Pressure Stall Test" is within the specification, then go to the Flow Compensator Spool Adjustment. If the "High Pressure Stall Test" is not within the specification, then do the following procedure.

Ensure that the work tool on the front of the machine and the stabilizers are on the ground. Engage the parking brake.

Stop the engine.

Turn the engine start switch key to the ON position.

Move all of the hydraulic hand controls to all of the positions. This releases the system pressure.

Turn the engine start switch key to the OFF position.

Remove cap (13) and loosen locknut (14) . Turn adjusting screw (12) clockwise in order to increase the pressure setting. Turn adjusting screw (12) counterclockwise in order to decrease the setting.

Install a 8T-0860 Pressure Gauge with a range of 0 to 40000 kPa (0 to 5800 psi) to system pressure tap (4) .

Repeat the "High Pressure Stall Test" until the system pressure is within the specification.

When the pressure compensator is adjusted correctly, stop the engine. Tighten locknut (14) . Replace cap (13) and remove the gauges.

Flow Compensator Spool Adjustment
Adjustments to the flow compensator spool can be made on the machine. If the Margin Pressure and Low Pressure Standby pressures are within the specifications, then go to the Test and Adjustment for the Torque Limiter. If the Margin Pressure or Low Pressure Standby pressures are not within the specification, then do the following procedure.

Lower the work tool on the front of the machine and the stabilizers to the ground. Engage the parking brake.

Stop the engine.

Turn the engine start switch key to the ON position.

Move all the hydraulic hand controls through all of the positions in order to release pressure in the hydraulic system.

Turn the engine start switch key to the OFF position.

Install two 8T-0856 Pressure Gauges with a range of 0 to 6000 kPa (0 to 870 psi) to the pressure tap (5) for the system pressure and to signal pressure tap (4) .
Note: Do not move any hydraulic hand controls nor move the steering wheel while the 8T-0856 Pressure Gauge is installed. The higher pressure that is created by upstroking the pump will damage the gauge.

Repeat the "Low Pressure Standby Pressure Test".

If the low pressure standby pressure is within the specifications, then go to Step 11. If the low pressure standby pressure is not within the specifications, then remove cap (6) and loosen locknut (9) . Turn adjusting screw (10) clockwise in order to increase the pressure setting. Turn adjusting screw (10) counterclockwise in order to decrease the pressure setting.

Repeat the "Low Pressure Standby Pressure Test" until the low pressure standby pressure is within the specification.

Tighten locknut (9) and replace cap (11) .

Lower the implements to the ground. Stop the engine and engage the parking brake.

Remove all test equipment.

Repeat the "Margin Pressure Test" in order to check that the margin pressure is still within the specification.

If pump has second valve attached to it, it is for torque limiting. Do not adjust the valve. It is to hard to get it in the proper setting without flow meters.

Expert:  Dan replied 6 months ago.

flow compensator

Expert:  Dan replied 6 months ago.

Pressure and flow compensator