Repair of the pump NSh-32 auto MAZ

Power steering pump for MAZ vehicle with flow and pressure valve

The NSh-32U gear pump consists of a housing 6 (Fig. 1) and two gears placed in it: driving 7 and driven 9, rotating in bronze bushings

These bushings simultaneously provide a mechanical seal for the gears.

The pump is driven from the crankshaft by means of V-belts (T-14x13-1000 GOST 5813-76).

The belt tension is adjusted by a tensioner consisting of a fixed bracket 10 (Fig. 2) and an adjusting screw 9 with a lock nut 8.

The arrangement of the flow and pressure valve is shown in fig. 3.

The flow and pressure valve works as follows.

The working fluid from the pump under pressure enters the vertical channel A and then along the horizontal channel B, through the central hole 3 in the jet 2 to the steering gear distributor.

Since the speed in the central hole 3 of the jet 2 is higher than in the channel B due to the difference in flow sections, the pressure in the cavity D connected to the central hole will be lower than in the channel B, and, therefore, than in the vertical channel A and horizontal channel E.

With an increase in the frequency of rotation of the pump gears, the pressure difference in cavity D and in channels A and E increases and when the pump is fed more than 31-35 l / min, plunger 8 moves to the right, compressing spring 5.

In this case, the working fluid is partially returned from the vertical channel A through the tube 12 (see Fig. ) to the suction pipe 7 of the pump.

There, regardless of the speed of the pump, the flow rate of the working fluid through the distributor will be no more than 31-35 l / min.

When the pressure in channels A and B and cavity D (see Fig. 3) increases to 9810-10790 kPa, ball 9 breaks away from the seat, compressing spring 10.

The working fluid from the cavity D through the throttle channel of the plug 6, through the radial hole 11 in the plunger through the tube enters the drain.

Since the flow sections of the throttle channels 4 and 7 differ slightly, the pressure in cavity D practically does not increase.

The increase in pressure in channel A causes the plunger 8 to move to the right, as a result of which the working fluid from channel A partially enters the suction pipe of the pump through the tube.

In this way, the power steering system is protected from overload.

Power steering pump repair

Removing the pump from the car. To remove the pump, proceed as follows:

• — release the lock nut 8 (see Fig. 2) and unscrew the adjusting screw, loosening the tension of the belts;
• - disconnect the hoses;
• - unscrew the bolts securing the fixed bracket to the engine, remove the pump with the tensioner, after removing the belts.

Pump disassembly. Disassembly order:

1. - fix the pump to the fixed bracket 10 in a vise;
2. —disconnect the oil drain pipe 12 from the flow and pressure valve body;
3. — remove the flow and pressure valve and suction pipe 7 from the pump;
4. - mark the position of the pulley 15 relative to the pump housing;
5. unscrew the nuts and disconnect the pump from the movable bracket 6, noting the position of the splines of the pump shaft relative to the previously made mark on the pump housing;
6. — remove retaining ring 4 and press hub 1 with pulley 15 off bearings 3;
7. - remove retaining ring 2 and then the bearings from the movable bracket;
8. — unscrew plug 12 (see Fig. 3), remove plunger 8 and spring 5 from the body (under the action of spring 5, the plunger should come out of the body freely);
9. — fix the plunger 8 to the non-working surface (it is unacceptable to fasten it along the outer diameter), unscrew the plug 6 and remove the ball 9 and the spring 10 with the guide.

After disassembly, you need to check the condition of the parts.

The end surfaces of the bushings and gears of the pump, the working surface of the plunger 8 should not have noticeable burrs, and the cuff 5 (see Fig. 1), the stuffing box 3 and the seals should not be damaged.

The splines on the pump shaft and in the hub can wear up to 4.0 mm.

Damage of the pulley grooves, cracks on the brackets of the tensioner are not allowed.

Assembly and adjustment of the pump. Assemble the pump in the following order:

• - fix the plunger 8 (see Fig. 3) and reinstall the spring 10 with the guide, ball 9, plug 6 with shims 1;
• —adjust the opening pressure of the ball in the special tool with shims 1.

If before disassembly there was no sharp increase in effort on the steering wheel when turning the track on the spot, then this adjustment can be omitted;

• —replace plunger with spring 5 and screw plug 12;
• - install bearings 3 (see Fig. 2) in the movable bracket 6 and secure with a retaining ring;
• — press the hub 1 with the pulley into the bearings and install the circlip 4;
• — pour 50 cm³ of oil into the movable bracket 6 so that the oil fills the cavity of the hub;
• - connect the pump (aligning the marks made during disassembly) to the movable bracket, after installing the gasket;
• - reinstall the flow and pressure valve and connect the suction pipe 7 to the pump, connect the oil drain pipe 12.

Installing a pump on a car. Install order:

• - put the belts on the drive pulleys of the engine and pump and fix the fixed bracket 10 on the engine;
• —adjust the tension of the belts using the adjusting screw 9.

With the correct tension, the deflection in the middle part of the belt under a force of 39 N should be within 10-15 mm.

After adjustment, tighten the locknut 8 and connect the hoses.