The minimum flow rate is determined at engine idle, again only after the system has reached operating temperature (refer to the pump relief pressure test).

Raise the engine to 3000 rpm, in the case of a petrol engine, or maximum governed rpm in the case of a diesel. Checking the flow rate at high rpm checks if the pump flow control circuit is operating satisfactorily. If there is no specification for the maximum flow rate you can use a rule of thumb rate of not more than 20% of the minimum idle flow rate.

If the flow rates are out of specification then dismantle the pump and check the condition of the pumping element and make sure that the flow control spool is free to move in the pump housing.

An idea of pump condition can be had by looking at the flow rate while pressure is raised by slowly closing off the test valve. The pump should maintain a steady flow rate up to about half the pump relief pressure. The pump flow may slowly decline after that point but at least 75% of the specified flow rate must be produced at 80% of the relief pressure.

Internal leakage within the steering gear is leakage past seals and valve sealing edges. An amount of leakage is acceptable and this test is to determine if the steering gear is serviceable. It should be conducted on all steering gear prior to pull down so that minor bore scoring, if present, can be evaluated.

The pump pressure relief test and flow test must be conducted prior to commencing this test. Make a note of the pump relief pressure. If the pump minimum flow rate is not up to specification this test can not be conducted.

It is required to stall the steering gear just prior to full left and full right locks and a safe way should be used to block front wheel movement. Some steering gears are fitted with adjustable lock limiting valves which dump hydraulic pressure just prior to the lock stops being engaged. An aluminium block of about 13 mm (1/2") thickness can be placed between the lock stops of the left or right wheel, this will ensure that the lock limiting valves, if fitted, do not dump pressure. Have someone rotate the steering wheel right until the block is sandwiched between the lock stops. Make sure that sufficient torque is applied to the steering wheel to ensure that the power steering valve is fully closed. Read the system pressure and it should be the same as was recorded during the pump relief pressure test. If it is lower then excessive internal leakage is indicated.

Incorrect column universal joint phasing will cause a rise and fall in steering wheel torque as the steering is rotated lock to lock. Couple the torque wrench to the steering column nut and rotate the steering wheel, lock to lock, reading the torque required. A variation of more than 2.5 Nm (20 in/lbs.) may cause concern.

If there is a significant variation, inspect the column, particularly splined couplings, for evidence of misalignment alignment marks. If there are no alignment marks to work from uncouple the splined joint and re couple after rotating one shaft 1 to 2 splines. Re conduct the test. Repeat this procedure until the lowest torque variation is recorded.

Valve bias is where the valve is not in it's central position when no input torque is applied to the steering gear. If the valve is biased then the vehicle may pull to one side. An easy check is to remove the drag link from the steering gear and remove the steering column from the input shaft. Start the engine and if the steering gear does not rotate then the valve bias is not making the vehicle pull left of right. A more accurate check is to apply, say, 6 Nm (50 in/lbs.) torque to the steering gear input shaft on one lock. Read the system pressure. Apply a similar torque to the opposite lock, and again read the system pressure. Compare both readings, they should be the same for a correctly centred valve.