Power steering: device, diagram and principle of operation

Power steering (power steering) is a system that makes driving easy and comfortable even with minimal effort on the steering wheel. Without it, parking or maneuvering at low speeds would turn into a real struggle with the steering wheel, especially on heavy vehicles. But how exactly does this mechanism work? What components does it consist of, and why does it sometimes start to “leak” or “buzz”?

In this article we will analyze the structure of the power steering down to the smallest detail: from the pump and working fluid to the distributor and actuator. You will learn how fluid circulates in the system, what forces make the wheels turn almost effortlessly, and what happens when they break down. And also - What signs indicate a power steering failure? and is it possible to travel with them further?

The material will be useful both to beginners who are just learning the basics of car repair, and to experienced drivers who want to better understand the operation of one of the key components of the car. Don't switch - there are diagrams, tables and practical tips ahead!

1. Main components of power steering

The power steering consists of several key elements, each of which performs its own function. If even one of them fails, the system will either stop working or begin to behave unpredictably. Let's look at the main components:

• 🔧 Power steering pump - creates fluid pressure. Typically driven by a belt from the engine crankshaft.
• 🛢️ Liquid reservoir - a reservoir for storing and cooling the working fluid (most often ATF or PSF).
• 🔄 Distributor (spool mechanism) — directs the fluid flow in the desired direction depending on the steering wheel rotation.
• 🚗 Actuator - a hydraulic cylinder or rack with a piston that directly turns the wheels.
• 🔗 Connecting hoses and tubes - high and low pressure through which the liquid circulates.

Most modern cars use power steering rack, where all components are compactly combined in one block. However, in older models (e.g. Volvo 240 or Mercedes W123) you can find a system with a separate hydraulic cylinder connected to the steering mechanism.

It is important to understand that The power steering fluid not only acts as a force transmitter, but also lubricates parts, prevents corrosion and removes heat.. Therefore, its level and condition directly affect the resource of the entire system.

2. Operating principle: how force is transmitted to the wheels

The operation of power steering is based on the laws of hydraulics. When you turn the steering wheel, the following happens:

1. The steering wheel rotates through a shaft distribution mechanism (spool).
2. The spool opens a channel for supplying liquid under pressure into one of the cavities slave cylinder (or slats).
3. The pressurized fluid pushes against the piston, which moves and helps turn the wheels.
4. The waste liquid returns to the tank via the return line.

The more you turn the steering wheel, the more the channel in the distributor opens - and the more fluid enters the cylinder. This ensures smooth and measured effort. At the same time the pump runs constantly, even when the steering wheel is stationary: the fluid simply circulates in a “small circle” (reservoir → pump → distributor → reservoir).

Fun fact: some sports cars (eg. Porsche 911 classic models), the power steering was adjusted so that at high speeds it barely worked. This was done for better “feedback” with the road. Today, such solutions are rare - modern power steering is adaptive and changes the force automatically depending on the speed.

Why is power steering "tight" when cold?

When cold, the fluid in the system becomes more viscous, which increases resistance during circulation. Additionally, if there is air in the system or worn out seals, the problem becomes worse. Usually, after the engine (and power steering fluid) warms up, the force returns to normal. If not, diagnostics is required.

3. Types of power steering pumps: which one is better?

The pump is the “heart” of the hydraulic booster. Its type and condition determine how smoothly and reliably the system will operate. There are three main types of pumps:

Pump type	Operating principle	Pros	Cons
Bladed	Uses movable blades that are pressed against the rotor by centrifugal force	Reliable, durable, repairable	Sensitive to fluid quality, may “buzz” when worn
Gear	Two gears (drive and driven) pump fluid	Simple design, cheap to manufacture	Lower efficiency, wears out faster
Lamellar	Movable plates slide on an eccentric rotor	High efficiency, quiet operation	Difficult repair, expensive

Most production cars are equipped vane pumps — they are optimally balanced in terms of price and reliability. Gear drives are more common in budget models (for example, Daewoo Matiz or Cherry Amulet), and plate ones - in premium cars (BMW 5-series, Audi A6).

The pump is driven by a belt from the crankshaft, so its performance depends on engine speed. At idle the pressure is minimum, and at high speeds it is maximum. To smooth out this effect, the system provides pressure regulator (valve) that dumps excess fluid back into the reservoir.

⚠️ Attention: If the power steering pump begins to “whine” when you turn the steering wheel, this is a sign of wear on the bearings or blades. Ignoring the problem will lead to complete failure of the pump and the need for towing - the steering wheel will become incredibly heavy!

4. Power steering fluid: what to fill and when to change

The working fluid in the hydraulic booster is not just “oil”, but a special composition with additives, which should:

• 🔥 Withstand high temperatures (up to 120°C and above).
• 🛡️ Protect parts from corrosion and wear.
• 🧴 Maintain stable viscosity over a wide temperature range.
• 🔄 Do not foam with intense circulation.

The most common types of liquids:

• 🟢 ATF (Automatic Transmission Fluid) - universal fluid for automatic transmission and power steering (for example, Dexron II/III).
• 🔴 PSF (Power Steering Fluid) - specialized fluid for power steering (for example, Pentosin CHF 11S).
• 🟡 Universal synthetic fluids (for example, Motul Multi ATF or Liqui Moly ATF 1100).

Important: You cannot mix different types of liquids! For example, Dexron and Pentosin have different chemical bases, and mixing them will lead to the formation of sediment that clogs the channels of the system.

When to change the fluid? Manufacturers often claim that it is “filled for life”, but in practice it is recommended:

• Check the fluid level and condition every 15–20 thousand km.
• Completely replace every 60–100 thousand km (or once every 2-3 years).
• Signs for urgent replacement: darkening of the fluid, burning smell, foam on the dipstick.

Darkening or cloudiness of the fluid|Appearance of a burning smell|Foam on the dipstick or in the reservoir|Increased effort on the steering wheel|Extraordinary noise when turning the steering wheel-->

⚠️ Attention: If the fluid in the power steering reservoir is milky in color, this is a sign of water entering (for example, through a crack in the reservoir or condensation). This fluid needs to be replaced urgently, otherwise corrosion of metal parts will begin!

5. Common power steering malfunctions and their causes

Power steering is a reliable system, but it also breaks down. Here are the most common problems and their possible causes:

Symptom	Possible reason	What to do
Heavy steering, uneven force	Low fluid level, air in the system, pump wear	Check the level, bleed the system, replace the fluid
Rumbling or squealing noise when turning the steering wheel	Worn pump bearing, loose drive belt	Tighten the belt, replace the pump or bearing
Leaks under the car (red liquid)	Damaged hoses, rack or pump seals	Replace seals or hoses, add fluid
The steering wheel "twitches" or bites	Fluid contamination, distributor or rack wear	Flush the system, replace the fluid, diagnose the rack

One of the most insidious malfunctions is air entering the system. This occurs due to leaks or incorrect fluid replacement. The air makes the fluid compressible, causing the steering wheel to become “wobbly” and the force to be unpredictable. To remove air, the system must pump up:

1. Add liquid to the maximum.
2. Raise the front of the car (or hang up the wheels).
3. Turn the steering wheel from lock to lock 10–15 times.
4. Check the fluid level and repeat the procedure if necessary.

If bleeding does not help, the problem is more serious (for example, wear of the rack seals). In this case, disassembly and repair will be required.

6. Power steering vs electric power steering: which is better and why they still use hydraulics

With the advent of electric power steering (EPS), many are asking the question: why are power steering still installed on new cars? Each type has its pros and cons:

• ⚡ EUR:
  • ✅ More economical (does not take power away from the engine).
  • ✅ More compact and lighter.
  • ✅ You can adjust the force programmatically.
  • ❌ More expensive to repair (electronics).
  • ❌ Less “feedback” from the road.
• 💧 Power steering:
  • ✅ More reliable and easier to repair.
  • ✅ Better conveys the “feeling” of the wheels.
  • ✅ Cheaper to maintain.
  • ❌ Requires regular fluid replacement.
  • ❌ Subtracts up to 5–10 hp at the engine.

Hydraulic boosters are still used in:

• 🚛 Trucks and SUVs - due to high loads on the steering.
• 🏎️ Sports and premium cars - for better feedback.
• 💰 Budget models - due to low production costs.

Lately it has become more and more common hybrid systems, where hydraulics are combined with electronics (e.g. Electro-Hydraulic Power Steering, EHPS). In them, the pump is driven not by a belt, but by an electric motor, which saves fuel.

7. Is it possible to drive with a faulty power steering?

If the power steering fails, the car remains controllable - but The steering force will increase by 3–5 times. This is especially dangerous:

• 🚗 At low speeds (parking, maneuvering).
• 🛣️ When making sharp turns at high speed.
• 🚛 In a loaded car or with a trailer.

Driving with a broken power steering possible, but highly undesirable. Here's why:

• 🔧 Risk of accident: A sudden increase in force can lead to loss of control.
• 🔥 Pump overheating: If the pump seizes, the belt may break or overheat.
• 💸 Expensive repairs: Ignoring fluid leakage will result in wear of the rack or pump.

If the power steering fails on the way:

1. Stop and check the fluid level (if there is a leak, add ATF or, as a last resort, transmission oil).
2. Drive slowly, avoiding sharp turns.
3. Contact service as soon as possible.

⚠️ Attention: If the steering wheel has become heavy due to a broken power steering pump belt, do not try to continue driving for long distances. Without fluid circulation, the pump and rack overheat, which leads to their accelerated wear!

8. How to extend the life of your power steering: maintenance tips

The service life of the power steering depends not only on the quality of the parts, but also on how you operate the car. Here are some practical tips:

• 🔄 Check the fluid level regularly (every 5–10 thousand km).
• 🔧 Monitor the condition of the pump belt - it should be tensioned, without cracks.
• 🚗 Do not hold the steering wheel in the extreme position for more than 5 seconds - this creates maximum load on the pump.
• 🛑 Avoid sharp turns at high speed - this increases rack wear.
• 🧴 Use only recommended fluid (see manual!).

One of the most harmful myths is that the power steering is “maintenance-free.” In fact, even if the manufacturer does not indicate the period for replacing the fluid, you still need to change it. Over time, the fluid loses its properties, accumulates wear products and begins to destroy the seals.

Another important point - warming up power steering in winter. In cold weather, the liquid thickens, and the first turns of the steering wheel are given with effort. To avoid premature wear:

1. After starting the engine, let it run for 1-2 minutes.
2. Smoothly turn the steering wheel left and right several times (without holding it in extreme positions).
3. Only then start moving.

FAQ: Frequently asked questions about power steering

Is it possible to fill the power steering with transmission oil instead of a special fluid?

In extreme cases (for example, if there is a leak on the road), you can add Dexron II/III gear oil, but only if it is compatible with your system. However this cannot be done on an ongoing basis - different fluids have different additives, and mixing them will accelerate the wear of the seals. Flush the system and fill with the recommended fluid as soon as possible.

Why does the power steering hum only when it's cold?

This is normal if the hum disappears after warming up. The reason is that thick liquid when cold creates additional load on the pump. However, if the noise becomes louder or does not go away after warming up, this is a sign:

• Pump bearing wear.
• Low fluid level.
• Air entering the system.

In these cases, diagnosis is required.

What happens if you completely drain the power steering fluid?

If the fluid is drained and you continue to turn the steering wheel, the pump will run dry, resulting in:

• Instant wear of seals and pump blades.
• Overheating and possible jamming.
• Distributor breakdown due to lack of lubrication.

Never start the engine without power steering fluid! If you need to drain the fluid (for example, for repairs), the steering wheel must be locked.

How to check if there is air in the power steering system?

Signs of air in the system:

• The steering wheel "springs" or jerks.
• The effort is uneven (sometimes light, sometimes heavy).
• Foam is visible in the tank.
• The pump makes a "gurgling" sound.

To remove air, you need bleed the system (see section 5).

Is it possible to repair the power steering rack or just replace it?

The rack can be repaired if only the seals or bushings are worn. However, in most cases the repair costs almost the same as a new rack, so it only makes sense for rare or expensive cars. In mass models (for example, VW Golf or Toyota Corolla) usually install restored or new slats.