Hydraulic Bump Stops

Hydraulic Bump Stop

MICHAEL FROM SUPERIOR ENGINEERING SHOWS US JUST HOW MUCH YOU CAN ACHIEVE BY INSTALLING THE RIGHT BUMP-STOPS!

Bang! If that sound is coming from your suspension at full compression, it means you probably need a reminder on the value of bump-stops. While the most common types of bump-stops found on production vehicles are made of rubber or urethane, they don't often feature enough length or void area to adequately dampen impacts.

Hydraulic bump-stops (often called air bumps) are a great solution for vehicles that experience suspension bottoming at high speeds or when heavily loaded and are chasing the ultimate in bump-stop technology. These bump-stop units consist of a short stroke pressurised emulsion shock that is velocity sensitive. This allows the bump to effectively dampen, or slow, the suspension movement through the final few inches of travel.

As the suspension reaches maximum compression, this secondary 'air-shock' progressively increases damping resistance for increased impact control. As a result, the vehicle and occupants are protected from high stress loads. Suspension using air bumps can often run a softer spring rate so the ride is smoother under normal driving conditions, allowing the air bumps to provide a progressive end of travel force to supplement the main spring rate.

MAIN BUMP COMPONENTS

Piston Rods

With rod sizes that range from 28mm diameter up to 50mm, air bump main shafts are designed for maximum strength and durability when absorbing heavy impact loads. The rod diameter determines the amount of pressure or force that can be exerted once the bump is pressurised, as this becomes the theoretical 'piston area' where the force is focused. The internal gas pressure pushes against this rod and forces it to extend out from the main body.

PISTON

The main piston can be machined or cast from either alloy or steel depending on application, and has a series of ports or passages in both faces. The piston will also have a wide wear band to reduce the friction and prevent metal to metal contact with the main tube under offset loading during compression.

SHIM STACK

On both faces of the piston are a series of round thin valve shims or discs. These shims are arranged in a pyramid type stack decreasing in diameter. The larger diameter shims closest to the piston face control low velocity, the smaller shims at the outsides handle high speed.

SHAFT SPACER

A cylindrical tube or spacer is often fitted internally to the rod, just below the piston to set or reduce travel.

STRIKER PAD

At the end of the piston rod a replaceable rubber or nylon domed section is held captive by an aluminum housing. This Striker is the part of the air bump that makes contact with the mating plate or pad on the differential.

HOW THEY WORK

Air bumps are completely self-contained. They typically come in 2.0in & 2.5in diameters and travel lengths from 2-4in are most common. In basic terms they are considered a high-pressure emulsion shock. In the compressed position, shock oil is used to fill the Bump and allow a void for the Nitrogen to be added.

The level of oil must always cover the piston shims during operation otherwise dampening will not occur. Adding more oil will reduce the void and the room to add nitrogen – this changes the force of the bump as it approaches fully compressed. Too much oil and the bump will 'hydraulic' which is where the bump stroke cannot close due to oil taking up too much void inside the body. This can be used as a tuning function if a reduction in stroke is required.

Inside the bump

On either side of the piston you have valve stacks that control how fast or slow the shock cycles/reacts. The compression stack adds resistance to bump by metering the oil as it is being compressed. This force is velocity dependent due to the 'tapering' of the shim stacks that are closing off the piston ports. That means that the faster the bump is compressed the greater the additional resistance applied by the oil. The rebound stack is ideally tuned slow enough to allow the suspension to drop away without pushing it away or making the vehicle 'buck' or skip. Having two separate valve stacks allows you to truly fine tune your setup.

Air bumps generally use nitrogen

(N2) to fill the void in the bump body. The amount of pressure at extension provides the initial force the bump can produce, the size of the void (how much N2) set by the oil level and the amount of stroke contributes to the maximum force of the bump at full compression. All of these characteristics can be fully tuned to suit your requirements.

Another useful feature

In setting up air bumps on your rig is the introduction of the threaded-body air bump. Superior Engineering have the Profender range of air/hydraulic bump-stops available, that feature a threaded outer main body to allow easy adjustment of where the bump makes contact.

The ability to adjust the height of the bump is ideal when changes in ride height or dampening position is changed. Other fitting options are available to suit and include both clamp, and retaining-bolt style mounting cans to be welded to the chassis. Contact Superior Engineering for more information or help selecting from our extensive range of hydraulic bump-stops, mounting components and specialist 4WD suspension products.