For any pump test at a given rpm, the pump flow at 690 kPa (100 psi) will be larger than the pump flow at 6900 kPa (1000 psi).
The difference between the pump flow of the two operating pressures is the flow loss.
Flow loss is used as a measure of pump performance when the flow loss is expressed as a percent of pump flow.
| Percent of flow loss | |
|---|---|
| [(A - B) ÷ C] × 100 = D | |
| A | Pump flow at 690 kPa (100 psi) |
| B | Pump flow at 6900 kPa (1000 psi) |
| C | Pump flow at 690 kPa (100 psi) |
| D | Percent flow loss |
| Example | |
| [(A - B) ÷ C] × 100 = D | |
| A | 217.6 L/min (57.5 US gpm) |
| B | 196.8 L/min (52.0 US gpm) |
| C | 217.6 L/min (57.5 US gpm) |
| D | Percent of flow loss |
| [(217.6 L/min (57.5 US gpm) - 196.8 L/min (52. US gpm)) ÷ 217.6 L/min (57.5 US gpm)] × 100 = D | |
| D = 9.6 percent | |
If the percent of loss is more than 10 percent for the machine test or 15 percent for the bench test, the pump performance is not good enough.
Note: The numbers in the formula are only examples. These numbers are not values for any particular pump nor for any particular pump condition. See the Steering System Specifications for the pump flow of a new pump at 690 kPa (100 psi) and at 6900 kPa (1000 psi).
Machine Test
- Install a 4C-9437 Hydraulic Flow Meter .
- Start the engine.
- Run the engine at high idle.
- Measure the pump flow at 690 kPa (100 psi) and 6900 kPa (1000 psi).
- Use the values that were measured in Step 4 in Table 1.
Bench Test
If the bench test can be run at 6900 kPa (1000 psi) and at full rpm, determine the percent flow loss.
If the bench test cannot be run at 6900 kPa (1000 psi) and at full rpm, use the following procedure:
- Run the pump shaft at 1000 rpm.
- Measure the pump flow at 690 kPa (100 psi) and 6900 kPa (1000 psi).
- Use the measurements from Step 2 for the values of A and B in Table 1.
- To determine the value of C, use Steps 4.a through 4.b.
- Run the pump shaft at 2000 rpm.
- Measure the pump flow at 690 kPa (100 psi).
- Use the measurement from Step 4.b for the value of C in Table 1.
Leakage
A leakage oil test for the condition of the steering pump is made on a hydraulic test bench. The Leakage Oil Chart has the information that is needed for the test.
The steering pump has too much wear if the leakage oil is more than the value found on the Leakage Oil Chart and the pump output is less than the value found on the Leakage Oil Chart.
| Leakage Oil Chart | |||
| Hydraulic Oil Temperature 63° to 68°C (145° to 155°F) |
|||
| Pump rpm | Approximate Oil Pressure | Pump Output | Leakage Oil |
| 1900 | 3450 kPa (500 psi) |
128 L/min (34 US gpm) |
8.4 L/min (2.22 US gpm) |
| 1900 | 10300 kPa (1494 psi) |
124 L/min (33 US gpm) |
11.0 L/min (2.91 US gpm) |
| 1900 | 15900 kPa (2306 psi) |
120 L/min (32 US gpm) |
13.6 L/min (3.59 US gpm) |
| 1900 | 17200 kPa (2495 psi) |
0 L/min (0 US gpm) |
14.0 L/min (3.70 US gpm) |