Power Steering Pump

The power steering pump serves as the primary hydraulic pressure source in conventional Hydraulic Power Steering (HPS) or Electro-Hydraulic Power Steering (EHPS) systems. Its main function is to convert mechanical energy from the engine (driven via the crankshaft belt) or electrical energy from an electric motor into hydraulic energy, continuously supplying high-pressure steering fluid to the steering rack. When the driver turns the steering wheel, pressurised fluid from the power steering pump precisely acts on the hydraulic piston and control valve, significantly reducing the steering effort required and ensuring light, responsive handling.

Core Construction and Operating Types

Power steering pumps are primarily categorised into two main types based on their design and operating mechanism: mechanical and electro-hydraulic: 

Mechanical Vane Pump: 

Commonly found in conventional internal combustion engine (ICE) vehicles, it is directly driven by the engine crankshaft pulley via an accessory belt to turn an internal eccentric rotor and vanes. As the rotor spins, centrifugal force pushes the vanes outward, drawing in and discharging fluid under high pressure as the pump chamber volume changes. This design is proven and robust, with hydraulic output pressure directly tied to engine RPM (higher revs generate greater steering assist). 

Electro-Hydraulic Power Steering (EHPS) Pump: 

Eliminating the traditional engine belt drive, this setup employs a dedicated onboard DC electric motor to drive the hydraulic pump. Its key advantage is that steering assistance is no longer dictated by engine revs. Instead, it enables speed-sensitive power assistance based on vehicle speed sensors—delivering maximum assist for effortless manoeuvring at parking speeds, and reducing assist at higher speeds for a firmer, more stable steering feel. 

Safety Guidelines and Operating Limits 

Never start the engine or dry-steer (turning the wheel forcefully while stationary) when power steering fluid is critically low, burnt/contaminated, or completely empty (Prohibiting Dry-Running or Operating with Low/Contaminated Fluid):

The precision-machined rotor, vanes, and housing inside the pump rely entirely on power steering fluid (ATF or specified hydraulic fluid) for lubrication and cooling. Running the pump dry or with severely degraded fluid is strictly prohibited. Operating under dry friction generates intense heat within seconds, causing the pump to seize and burn out, while metal shavings will contaminate the entire steering hydraulic circuit.

Never hold the steering wheel at full lock for extended periods when stationary (i.e., cranking the wheel fully to its limit and holding under pressure for more than a few seconds), which causes hydraulic pressure to spike to its maximum limit (Prohibiting Holding Steering Wheel at Full Lock for Extended Periods): 

At full lock, the steering system's pressure relief valve is subjected to maximum working pressure. Holding the wheel against full lock forces the pump into a continuous, overloaded high-pressure bypass state. This rapidly overheats the fluid, induces severe vibration along the high-pressure hoses, accelerates the degradation and cracking of rubber seals, and inevitably leads to major fluid leaks.