Power steering pump for your car

Generating high pressure with the steering pump

A steering pump is one of the central components in a hydraulic system. Its task is generating hydraulic pressure, possibly up to a hundred bar or more. The pressure supplies actuators with the necessary driving power. Examples are the hydraulic cylinder, radial engines and many more.

Different constructions of steering pumps

Six different constructions of steering pumps are common:

• vane pump
• gear pump
• screw pump
• axial piston pump
• radial piston pump
• piston pump

The vane pump consists of a carrier rotating eccentrically in a cylinder. Its blades generate two cells in the cylinder, their volumes constantly changing. The vane pump's advantage is its simple and cheap construction. Its main disadvantage is its high wear. Vane pumps are used in the low-pressure area of 70 – 175 bar. Gear pumps and screw pumps are technically the simplest hydraulic pumps. They consist of two interlocking screws or gear wheels. The pumping performance can be enhanced by lengthening the screw. These devices are simple and cheap in construction, although they score less with respect to size and efficiency. Gear and screw pumps are able to generate up to 300 bar pressure. Axial piston pumps convey hydraulic oil via small pistons mounted to a slanted swashplate. Axial piston pumps are very efficient and able to generate high pressure. Therefore they are often used in building machinery. Particularly interesting of this pump type is the fact that the pressure can be regulated via the slanting angle of the swashplate. Axial piston pumps, however, are expensive in production. Radial piston pumps are equally equipped with small pressure pistons driven by a central disc. Its movement however is transversely to the circular trajectory. The radial piston pump's construction is more compact than the axial piston pump. It can generate equally high pressure. Its intricate construction makes it somewhat more expensive. Piston (reciprocating) pumps are very simple constructions, consisting of a cylinder in which a piston generates vacuum as well as pressure. Reciprocating pumps are often used as manual feed pumps for water wells. Due to their massive construction their use is limited. They are too impractical for mobile use such as in a dredger or a forklift truck. Piston pumps can generate up to 700 bar pressure. Radial piston pump can handle even up to 1000 bar.

Life span of steering pump

The life span of a steering pump greatly depends on its construction. In vane pumps a metal plate is constantly scraping against the inner cylinder, generating wear and destroying the part from the inside. The life span of the vane pump is correspondingly limited. Gear and screw pumps are long-lasting when their threshold value is respected. They run contact-free and are permanently lubricated by hydraulic oil. As long as the oil is kept clean, gear and screw pumps can perform damage-free for years, which makes them particularly suitable for agricultural use. Piston pumps are amazingly durable as well. They can generate high pressure. As its components are correspondingly built to withstand the pressure, piston pumps function reliably and without any problems for many years. The main weak point in a steering pump is its gasket. High hydraulic pressure puts every gasket under constant strain. Fortunately, defective gaskets are easily identified and repaired.

Defective steering pumps

A defect of a hydraulic pump becomes apparent in two ways:

• Hydraulic oil is escaping.
• The pumping performance is deteriorating.

Escaping oil indicates a defective gasket or a fractured housing. Due to the high pressure even a small leak will not remain unnoticed for long. If the pumping function deteriorates, possibly a breach has occurred in the pump's interior. If a tooth of a gear pump breaks off, it can no longer effectively convey oil. The same applies to jamming pistons, breaking con rods or stretching swashplates in axial piston pumps. In any case, only disassembling and repairing a hydraulic pump can restore the desired function. The high strain of a steering pump requires the best possible quality for all its components and its construction. This makes high-grade hydraulic pumps particularly expensive, although they guarantee a maximal pumping performance and long life span.