Residual pressure valves

A residual pressure valve (RPV) is an important safety element of electronic suspension systems in vehicles such as all-terrain vehicles and upper- and mid-range saloon cars. It is used for example in the Mercedes Benz S Class, the VW Touareg, Porsche Cayenne and Audi Q7. The valve is installed in each air suspension strut as an integral part. The air suspension strut is part of the pneumatic suspension system, which takes advantage of the compressibility of gases, in particular air.

During normal vehicle travel, the residual pressure valve is open, ensuring free air flow between the air suspension strut and the compressor. In the event of a defect, no matter on which side of the valve, the residual pressure valve closes at a defined residual pressure. The intact side of the valve remains pressurised, providing protection against further damage.

An air spring equipped with a residual pressure valve can be delivered by the manufacturer directly to the OEM customer (original equipment manufacturer) in filled state. No additional blind plugs or special tools are needed. While undergoing repair in the auto repair shop, during which the plastic tubes of the EAS (emergency alert system) have to be removed from a suspension strut, the residual pressure protects the suspension strut.

A small, but important part of the air spring, the RPV has several functions:

• As a filling port
• Protection of the air content during transport to the OEM
• Protects the bellows from rolling up and being destroyed
• Disconnects the air spring from the pneumatic system if a tube is pulled off
• Disconnects the defective air spring from the vehicle’s pneumatic system
• Protects the entire chassis from lowering due to diffusion of the air volume through the rubber bellows if the vehicle is not moved over an extended period
• Electric vehicles also use the air spring to cool the battery. This is achieved by a change in the angle to the road surface. The change of angle increases the air flow at the battery housing, which is located in the vehicle’s underframe assembly

Material
Brass or plastic.

Inquest now

The RPV is always open in normal position. It can be thought of as a piece of pipe. The valve switches only if a difference in pressure occurs between the air spring side and the compressor side.

Transport protection

The air spring is fully assembled before delivery by the system supplier to the auto manufacturer. The spring must be pressurised for transport, to prevent damage to the rubber bellows. When the air spring is filled with compressed air, the compressor exceeds the spring force of the spring so the air can flow into the air spring. When the pressure is withdrawn, the spring presses the seal element against the seal lip to prevent the air from escaping the air spring.

Pressure drop in the pneumatic system

In case of a pressure drop in the vehicle’s pneumatic system, due to leaks or a pulled off tube, the RPV disconnects the air spring. The membrane is pressed by the spring against the pressure ridge.

Pressure drop in the air spring

In case of a pressure drop in the air spring there is an initial drop in pressure in the entire system. This allows the spring to close the valve (spring force > pressure) and protect the remaining system from total decompression, which would cause other defects.

2-sided residual pressure: corresponds to the set pressure of the air spring, if the air spring, which is pressurised to 10 bar absolute, is evacuated by means of the required throttle valve. During evacuation of the suspension strut no air is supplied by the compressor.

1-sided residual pressure: corresponds to the pressure set in the air spring, if the air tube downstream of the residual pressure valve were to burst. In this case there is a rapid pressure drop in the suspension strut. The 1-sided residual pressure is always greater than the 2-sided residual pressure.

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