311B and 312B Excavators Hydraulic System Caterpillar

Pressure Specifications - 312B and 312B L

Usage:

312B 2NS

Specifications

Note: A New specification is the performance that can be expected for a new machine. A Rebuild specification is the performance that can be expected after rebuilding the components of a system. Performance beyond Service Limit specifications is an indication of these problems: improper adjustment, wear, damage of relief valves and damage of pumps.

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Illustration 1	g00378392
Relief valve locations (A) Main relief valve (B) Boom cylinder line (head end) (C) Boom cylinder line (rod end) (D) Stick cylinder line (head end) (E) Stick cylinder line (rod end) (F) Bucket cylinder line (head end) (G) Bucket cylinder line (rod end) (H) Swing (right) (I) Swing (left) (J) Left travel crossover relief valve for forward travel (lower valve) (K) Left travel crossover relief valve for reverse travel (upper valve) (L) Right travel crossover relief valve for forward travel (lower valve) (M) Right travel crossover relief valve for reverse travel (upper valve) () Pilot relief valve () Main control valve (P) Pilot manifold (Q) Travel motor (right) (R) Travel motor (left) (S) Swing motor (U) Blade control valve (V) Blade control valve relief valve (W) Blade cylinder (head end)

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Table 1
Relief Valve		Specifications			Torque for Locknut
Relief Valve		New	Rebuild	Service Limit	Torque for Locknut
(A) Main relief valve	Implement	29900 ± 490 kPa (4350 ± 72 psi)	29900 ± 490 kPa (4350 ± 72 psi)	27940 to 30390 kPa (4065 to 4422 psi)	29 ± 2 N·m (21 ± 1 lb ft)
(A) Main relief valve	Travel	34300 ± 490 kPa (5000 ± 72 psi)	34300 ± 490 kPa (5000 ± 72 psi)	32340 to 34790 kPa (4715 to 5072 psi)	29 ± 2 N·m (21 ± 1 lb ft)
(B) Boom cylinder line (head end)		31900 ± 1470 kPa (4650 ± 215 psi)	31900 ± 1470 kPa (4650 ± 215 psi)	28950 to 33370 kPa (4200 to 4850 psi)	29 ± 2 N·m (21 ± 1 lb ft)
(C) Boom cylinder line (rod end)
(D) Stick cylinder line (head end)
(E) Stick cylinder line (rod end)
(F) Bucket cylinder line (head end)
(G) Bucket cylinder line (rod end)
(H) Swing relief pressure (right)		24500 ± 980 kPa (3550 ± 140 psi)	24500 ± 980 kPa (3550 ± 140 psi)	22540 to 25480 kPa (3265 to 3690 psi)	155 ± 16 N·m (115 ± 12 lb ft)
(I) Swing relief pressure (left)		24500 ± 980 kPa (3550 ± 140 psi)	24500 ± 980 kPa (3550 ± 140 psi)	22540 to 25480 kPa (3265 to 3690 psi)	155 ± 16 N·m (115 ± 12 lb ft)
(J) Left travel crossover relief valve (forward)		36800 ± 1470 kPa (5350 ± 215 psi)	36800 ± 1470 kPa (5350 ± 215 psi)	33850 to 38270 kPa (4920 to 5565 psi)	34 ± 2 N·m (25 ± 1 lb ft)
(K) Left travel crossover relief valve (reverse)
(L) Right travel crossover relief valve (forward)
(M) Right travel crossover relief valve (reverse)
(N) Pilot relief valve		4100 ± 200 kPa (595 ± 30 psi)	4100 ± 200 kPa (595 ± 30 psi)	4100 ± 200 kPa (595 ± 30 psi)	16 ± 1 N·m (12 ± 1 lb ft)
(V) Blade control valve relief valve		20600 ± 490 kPa (3000 ± 72 psi)	20600 ± 490 kPa (3000 ± 72 psi)	18640 to 21090 kPa (2715 to 3072 psi)	29 ± 2 N·m (21 ± 1 lb ft)
(W) Blade cylinder (head end)		24500 ± 980 kPa (3550 ± 140 psi)	24500 ± 980 kPa (3550 ± 140 psi)	22540 to 25480 kPa (3265 to 3690 psi)

Adjustment Procedures

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Table 2
Required Tools
Part Number	Description	Qty
6V-3121	Multitach group	1
6V-4161	Hydraulic testing group	1
8T-0470	Thermometer group	1

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Table 3
Relief Valves	Pressure change With One Turn Of Adjustment Screw
Main implement valves	17700 kPa (2550 psi)
Main travel valve	17700 kPa (2550 psi)
Line relief valve	17700 kPa (2550 psi)
Travel crossover relief valve	8850 kPa (1275 psi)
Pilot relief valve	690 kPa (100 psi)
Blade control valve relief valve	17800 kPa (2600 psi)
Relief valve for blade cylinder	13500 kPa (1950 psi)

Preparation For Relief Valve Adjustment

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Illustration 2	g00379594
Pump compartment (1) Pressure tap (power shift pressure) (2) Pressure tap (rear pump delivery pressure) (3) Pressure tap (front pump delivery pressure)

Position the machine on level ground.
Stop the engine.
Release the pressure in the hydraulic system. Refer to Testing And Adjusting, "Hydraulic System Pressure - Release".
Connect a 60000 kPa (8700 psi) pressure gauge to pressure tap (2). Connect a 60000 kPa (8700 psi) pressure gauge to pressure tap (3).
Connect a 6000 kPa (870 psi) pressure gauge to pressure tap (1).
Start the engine.
Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).
Place the machine controls at the following settings: Power Mode, engine speed dial "10" and AEC switch OFF.

Reference: Refer to Testing And Adjusting, "Operational Checks" for engine rpm settings.

Note: Normal operations of the engine and pumps are necessary for the pressure adjustments. If the results of the pressure adjustment are not correct, then the engine and the pump characteristic curve needs to be checked. Slow output flow from the pump is an indication of air in the hydraulic system. Make sure that no air is present in the hydraulic system. Refer to Testing And Adjusting, "Hydraulic System Pressure - Release".

Temporary Setting Of The Main Relief Valve

Note: A temporary setting of the main relief valve is required before any line relief valve can be adjusted.

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Illustration 3	g00379596
Top of main control valve (4) Adjustment screw (5) Locknut (6) Adjuster nut (7) Locknut (8) Main relief valve

Open the bucket until the bucket cylinder rod is at the full retraction.
Be sure that the main relief valve pressure is set at 29900 ± 490 kPa (4350 ± 72 psi).
Note: Always make final pressure adjustments on pressure rise.
Loosen locknut (5). Turn adjustment screw (4) clockwise for one full turn. Tighten locknut (5).
Loosen locknut (7). Turn adjuster nut (6) clockwise for one quarter turn. Tighten locknut (7).