Hydraulic power steering (HUR) is a system that makes driving a car comfortable, reducing the force required to turn the wheels. The key parameter of its work is work pressure, created by the pump and supported in the circuit. It is on this indicator that the ease of rotation of the steering wheel and the absence of extraneous sounds during maneuvers depend.
Many car owners wonder what pressure in the GUR system is considered normal when the steering wheel begins to "heavy". The answer cannot be a single number, since the parameters depend on the design of the particular car, the type of pump and the engine mode. In this article, we will discuss the technical nuances, diagnostic methods and ways to eliminate pressure problems.
Disturbance of the pressure balance is often the first bell about the upcoming breakdown. If you ignore the symptoms, you can go to expensive repair of the rack or replacement of the pump. Understanding the physical processes inside the hydraulics will help you notice the deviations in time.
The principle of operation and the role of pressure in the circuit
The main task of the system is to transfer the force from the steering wheel to the wheels using a liquid. GUR pump pumps fluid, creating excess pressure that affects the pistons in the steering mechanism. At rest, when the steering wheel is not rotating, the liquid circulates in a small circle or is discharged through the bypass valve back into the tank.
At the time of the start of the rotation of the steering wheel, the pressure in the system increases sharply. Reduction valveThe slat, built into the pump or rail, regulates this flow, preventing the hose rupture and excessive load on the drive belt. Pressure can reach tens of atmospheres, which requires high tightness of all compounds.
It is important to understand that the system is not static. Parameters are constantly changing depending on the frequency of rotation of the crankshaft of the engine. At idle speeds, the pump creates less pressure than when the engine is operating in the 2000-3000 rpm mode.
⚠️ Warning: Exceeding the critical pressure in the GUR system can lead to the extrusion of the glands and rupture of high pressure hoses. Never hold the steering wheel in the extreme position for more than 5 seconds.
What happens when you focus on the extreme situation?
When you turn the steering wheel to the point, the flow of fluid is blocked. The pressure instantly jumps to a maximum, which is limited only by setting the bypass valve. At this point, the pump is working with maximum load, and the liquid in the tank can boil due to a sharp increase in temperature.
Normal pressure indicators for different systems
There is no single standard for all vehicles. Engineers design systems for a specific vehicle weight and steering gear ratio. For passenger cars with rack type Danfoss or ZF The performance will be different from the cargo systems.
Typically, the operating pressure at the pump outlet varies from 60 to 100 bar (atmospheres) in idling mode when turning the steering wheel. When blocking the flow (stress) it can reach 120-140 bar. However, these figures are relevant only with a serviceable system and warmed liquid.
Below is a table with indicative pressure values for different types of cars. Remember that accurate data should always be searched for in the service documentation for your model.
| Type of vehicle | Idle pressure (bar) | Maximum pressure (bar) | Volume of tank (l) |
|---|---|---|---|
| Small hatchback | 40–60 | 80–90 | 0.6–0.8 |
| Middle class (sedan) | 60–80 | 100–110 | 0.8–1.0 |
| Off-roader/Crossover | 80–100 | 120–140 | 1.0–1.2 |
| Light commercial transport | 90–110 | 130–150 | 1.2–1.5 |
It is worth noting that cold liquid has a higher viscosity, which can temporarily increase resistance in the system. Warming to operating temperature 50–80°C It normalizes the metrics.
Symptoms of insufficient or excessive pressure
Diagnostics of the GUR system often begins not with a pressure gauge, but with an analysis of the driver's sensations. If the pressure drops below normal, you will immediately feel an increase in the steering effort. This can happen constantly or only in certain modes.
Signs of low blood pressure:
- 🚗 The steering wheel rotates hard, especially at low speeds.
- 💧 The appearance of foam in the tank, indicating suffocation and a drop in efficiency.
- 📉 Instability of effort: it is tight, then easy.
On the other hand, excessive pressure or its jumps also have their manifestations. Most often they are associated with a malfunction of the valves, which can not relieve the excess load.
Signs of problems with pressure regulation:
- 🔊 Loud howling or pump hum, especially in extreme positions.
- 🛑 Ugs when the steering wheel is rotated, a feeling of "biting".
- 🌡️ Rapid overheating of the liquid and the appearance of the smell of burning.
If you notice that the steering wheel only becomes heavy when the engine warms up, this may indicate wear on the pump rotor plates or contamination of the system.
Instrumental pressure check with a manometer
For accurate diagnosis, a special pressure tester GUR should be used. This device is a pressure gauge with a shut-off crane and a set of adapters. Connection is made in the break of the high pressure line between the pump and the rack.
The verification process is as follows:
- Warm up the engine to operating temperature.
- Connect the pressure gauge according to the instructions to the device.
- Start the engine and let it work at idle speeds.
- Make a few full turns with the steering wheel to remove air.
Next, the pressure is measured in two modes: free circulation and with a closed crane (imitation of the stop). The indications are compared with the factory specifications for the car.
⚠️ Warning: Do not keep the shut-off tap of the tester closed for longer than 5-10 seconds! This will cause a sharp jump in temperature and can damage the pump's ossicles.
☑️ Preparation for pressure measurement
Adjustment and adjustment of the reduction valve
In some pump designs, it is possible to adjust the pressure using a screw or replacing the spring in the pump. reduction valve. However, in most modern cars, the pumps are maintenance-free and adjustment is only possible by replacing the internal components or the entire unit.
If your system allows adjustment, it is performed by selecting washers or twisting a pressure screw. This requires high qualification, as an error in setting at 5-10 bar can lead to incorrect operation of the amplifier.
Often the problem is solved not by adjustment, but by replacing worn-out parts. Plates, rotor, pump body and sealing rings all affect the ability to create the necessary pressure.
Effect of fluid quality on system performance
A liquid GUR (ATF or special hydraulic fluid) is the working body of a system. From its properties directly depends on the pressure and service life of the components. Using the wrong liquid or mixing different types can lead to foaming and pressure drops.
Over time, the liquid loses its properties: it is oxidized, saturated with moisture and wear products. It changes her viscosity. Too thick liquid creates resistance at the entrance to the pump (cavitation), and too liquid does not ensure proper tightness of gaps, pressure drop.
It is recommended to change the liquid in the GUR system every 60-80 thousand kilometers or once every 3-4 years. When replacing, be sure to use the liquid specified by the manufacturer in the service book.
Frequent errors in service:
- ❌ The liquid supplementation "by eye" without diagnosis of the causes decreased.
- ❌ Use of transmission oil instead of ATF where prohibited.
- ❌ Ignoring the color of the liquid: blackening indicates overheating and destruction of rubber bands.
Can I mix different colors of GUR liquids?
It is strongly recommended not to mix liquids of different colors and manufacturers, even if they seem similar. Red usually means a mineral base (often Dexron) and green means synthetic. Their mixing leads to the formation of sediment, which clogs the valves and destroys the omentums.
Why does the GUR pump howl after fluid replacement?
Howling after replacement often indicates suffocation of the system. It is necessary to smoothly twist the steering wheel from stop to stop with the engine running (without delaying at the extreme points) to expel air. Also, the cause may be in poor-quality liquid or incompatibility with the seal material.
How often should I check the pressure in the GUR?
A routine pressure check with a pressure gauge is not required unless there are complaints about the steering wheel. It is enough to visually monitor the level and condition of the liquid at each TO. Diagnosis with a manometer is carried out only when symptoms of malfunction appear: howl, steering wheel weight or jerks.
Does belt tension affect the pressure in the system?
Yes, the tension of the drive belt directly affects the pump performance. A weak belt will slip under load, especially when turning the steering wheel, which will lead to a drop in pressure and a characteristic screech. Testing tension is the first step in diagnosing GUR problems.
What if the pressure is normal but the steering wheel is tight?
If the pump creates normal pressure but the steering wheel rotates heavily, the problem is most likely in the steering rack itself (biting teeth, wearing a val-rail pair) or in the suspension elements (ball supports, steering tips). It is also worth checking the pressure in the tires.