Chapter 9 Steering Systems 189
Pressure Regulator
The purpose of the pressure regulator is to bleed off
high pressures that could damage power steering
components. The pressure regulator is a check ball or a
small valve that is held closed by a spring. The pressure
regulator may be built into the pump housing or may be
part of the flow regulator. If system pressure becomes
greater than the spring tension, the ball is pushed away
from its seat. This opens a passage to the reservoir and
allows fluid to return to the reservoir.
The spring holds the valve closed during normal
operation. However, if the steering wheel is turned
completely left or right, fluid cannot flow through the
steering gears and dead ends in the pump. When flow
stops, fluid pressure increases and overcomes valve spring
pressure. The valve opens and fluid is dumped into the
reservoir, reducing the pressure. When pressure returns to
normal, the spring pushes the valve closed.
Power Steering Hoses
Since the power steering pump is installed on the
engine and the power steering gear is mounted on the
vehicle’s frame, there will be relative motion between the
pump and the gear when the engine moves on its mounts.
To supply the steering gear with fluid, flexible hoses are
needed. The hose that directs the pressurized fluid to the
steering gear is called a high-pressure hose. High-pressure
hoses are made of several layers of reinforced rubber, with
tubing fittings solidly attached to each end. The ends of the
tubing are double-flared fittings or ISO (International
Standards Organization) fittings to withstand high system
pressures. Some high-pressure hoses use banjo-type
fittings. See Figure 9-48.
The return hose is used to return fluid to the reservoir
and is usually a low-pressure hose. Most low-pressure
hoses have much less reinforcement than high pressures.
Instead of using high-pressure threaded fittings, low-
pressure hoses are usually clamped to tubing that is brazed
or threaded into the steering gear and the reservoir cover,
Figure 9-49.
Power Steering Pressure Switch
Some vehicles have a pressure switch installed on the
power steering high pressure hose, Figure 9-50, or on the
gearbox. This on-off–type pressure switch sends signals to
the ECM. This switch and the ECM work together to raise
the engine idle when the power steering system puts an
extra load on the engine. The switch contains a flexible
diaphragm and two electrical contacts. When the wheels
Pressure feed tube
Air control valve
Banjo fitting
Vane pump
assembly
Pulley
Union
bolt
Gasket
Figure 9-48. This high-pressure power steering hose uses a
banjo fitting. The fitting is secured to the pump with a union bolt
(bolt that allows fluid to flow through it) and is sealed with two
gaskets. (Toyota)
High-pressure hose
Outlet pipe
Power steering gear
Frame
Low-pressure hose
Clamp
Pump
Figure 9-49. Power steering system showing both high- and
low-pressure hoses. Note that the low pressure hose is
connected with clamps. (General Motors)
Figure 9-50. The power steering pressure switch tells the ECM
when the steering wheel is locked. The ECM can then increase
engine speed to compensate for the extra load.