Revalve Control Overview
What is Revalve Control?
Revalve Control (patent pending) is our revolutionary external revalve system. It accomplishes the same thing that a suspension tuner does when he disassembles and revalves your suspension, except Revalve Control does it in a few seconds.
Revalve Control is not a “clicker” like compression or rebound – it is much more powerful. This dyno graph to the right shows the compression damping adjustment range on a stock AER 48 fork. The bottom line is compression fully open, and the top line is compression fully closed. The graph below depicts the same fork equipped with Revalve Control.
Revalve Control is easy to use. Simply turn the Revalve Control adjustment dial to the desired setting. There are five turns of adjustment available.
Kreft Moto provides a settings chart to help you get the most from Revalve Control. The chart provides recommended settings for both fork and shock to adjust for rider ability and terrain. We use the shock’s high speed compression adjuster to balance the chassis when making large Revalve Control adjustments.
This technology makes it possible to use one bike for any type of riding, from technical enduro terrain to motocross, and have suspension that performs well everywhere you go.
Revalve Control also makes it possible to try different valving settings quickly and easily, helping you understand your preferences and zero in on your ideal suspension setup. This is a tremendous advantage that few riders have had the opportunity to experience.
Revalve Control technology is available exclusively through Kreft Moto. We make versions designed forthe WP AER 48 and WP XPlor suspension forks. Click one of the buttons below to learn how Revalve Control works in your fork.
Technical background and explanation of Revalve Control
Suspension system basics
A suspension system is composed of a spring and a damper. The spring supports the load, and the damper dissipates energy from bumps. Modern suspension components generate damping, or resistance to movement, through a system of valves that regulate the flow of oil within the damper. As the suspension compresses and extends, pressure differences between chambers in the damper forces oil to flow through valves from the high pressure chamber to the low pressure chamber. The valves are partially blocked by a stack of flexible steel washers called “shims,” which help maintain the pressure differential, but allow a metered amount of oil to flow through. As pressure differential builds up across the valve, the outer edge of the shims begin to bend away from the valve face, enabling oil to flow through. Oil flow characteristics are determined by the number and shape of ports through the valve bodies, and the stiffness of the shims covering the ports. The greater the restriction to oil flow, the more damping force is generated.
Modern performance suspension dampers can be extremely complex. The paragraph above describes the system at its simplest.
Low-speed damping adjusters
Among the many innovations and improvements to suspension components, various external damping adjusters have been developed. External damping adjustments enable the user to fine-tune the suspension without disassembly. The most common type of damping adjuster is a needle and orifice valve that bypasses the main shim-controlled valve.
These adjusters are often called “clickers” because of the detent mechanism that makes them move in defined increments with a click. When the adjuster is fully closed, the needle shuts off oil flow through the orifice. As the adjuster is opened, the needle backs out the orifice and more oil can flow through.
Clickers change damping force by about the same amount at all suspension velocities. Proportionally speaking, they have a much greater impact on low speed damping because the total damping force is small at low speeds. For example, a two-pound change in damping force created by the adjuster is more significant when total damping force is five pounds rather than fifty pounds. For that reason, clickers are primarily low-speed damping adjusters. They have no direct effect on the main valves.
High speed compression adjusters
The high speed compression adjuster found on rear shock absorbers is a different type of damping adjuster. Rather than regulating the fluid flow bypassing the valve, a high speed adjuster provides a means of externally stiffening a shim stack. A screw or dial mounted externally on the suspension is connected to a spring, which in turn applies pressure to the shim stack via a pressure plate. The pressure plate may press against the outermost shim, or against any of the other shims in the shim stack except for the smallest shim. If it presses against the outermost shim, the spring directly contributes towards resistance to shim-edge lift. If it presses against any smaller diameter shim (except for the smallest shim), the spring force changes to fulcrum point that the other shims bend around, which reduces shim bending leverage and stiffens the shim stack. As the screw is turned in farther, the spring exerts greater force against the shim stack, and the stiffer the valve becomes.
Because the high speed adjuster stiffens the shim stack, it alters the slope of the damping curve (a plot of suspension velocity vs. damping force). This is very different from the vertical shift of the damping curve caused by low-speed adjusters. In practice, high speed adjusters usually affect low-speed damping, high-speed damping, and everything in between.
A common high speed adjuster design incorporates both a high speed adjuster and a low speed adjuster into a single valve. The low speed adjuster needle and orifice is located at the center of the valve, with a high speed spring and pressure plate position concentric with the low speed adjuster screw. In the industry, this is called a dual compression control adjuster.
High speed adjusters in use today are always located at the base valve, because the base valve is physically located in a fixed position relative to the external body of the suspension damper.
Types of compression valves
Shock absorbers and many types of suspension forks use two different valves to generate compression damping. The nomenclature varies, but common terms for cartridge forks are “base valve” and “mid-valve.” The base valve controls fluid flow that results from the damping rod entering the cartridge and displacing fluid as the fork compresses. The base valve must pass the volume of displaced fluid, no more and no less. When the fork extends, a check valve on the opposite side of the base valve opens and allows fluid to refill the cartridge with minimum resistance. Thus, the base valve functions only as a compression valve. It is in a fixed position relative to the externally visible parts of a suspension fork. Unsealed “open cartridge” fork designs place the base valve at the bottom of the fork, next to the axle lug, and seal “closed cartridge” fork designs place it at the top of the fork.
The mid-valve is attached to the end of the damping rod, so it cycles back and forth inside the cartridge as the suspension compresses and rebounds. It is a bi-directional valve, generating compression force when the fork is compressed, and rebound force as the fork extends. To accomplish this, the valve body has two sets of ports and two sets of shims oriented in opposite directions. It works differently from the base valve in that fluid flow through the valve is not dependent on displacement of the damping rod. It moves “through” the fluid with suspension movement. A larger volume of oil flows through the mid-valve compared to the base valve, so other factors being equal, it will generate much more damping force.
In traditional configurations, the rebound-side shim stack is fixed securely to the piston face, but the mid-valve shim stack is setup with a “float” distance. Float means the shims can move freely away from the piston face before reaching a hard stop and beginning to provide resistance to fluid flow. Float values are often very small, in the range of 0.5mm, but that gap greatly reduces the compression damping force it generates. With a floating shim stack, the mid-valve produces very little damping force at low velocities, but greater and greater force as velocity increases. The term “mid-valve” was originally “mid-speed-valve,” so called because the valve came into operation at middle suspension velocities.
The floating shim stack technique is used because the mid-valve is extremely sensitive. Because it passes a larger volume of fluid compared with the base valve, it has potential to generate more damping force and have a larger effect on the damping curve overall. In applications were higher damping rates are required, such as rear shock absorbers for motorcycles, the mid-valve shim stack is fixed securely to the piston face.
A low-speed rebound adjuster is a needle and orifice valve located at the mid-valve. Fluid usually flows both direction through the valve, and therefore it affects compression damping as well as rebound damping, but the effect on rebound damping is much more significant. This occurs because the rebound shim stack is clamped solidly against the piston face, so any fluid allowed to bypass the valve has a big impact on damping rates. However, fluid flowing in the compression direction already has a very large bypass in the form of the floating shim stack. Float is like a river of suspension oil; the rebound adjuster is like adding another small stream to that river.
External Mid-Valve Stiffness Adjuster
The overall damping curve is highly sensitive to mid-valve stiffness. Vehicle manufacturers and suspension tuners choose the mid-valve shim setting carefully to yield the desired damping characteristics.
With Revalve Control installed, disassembly is no longer required to adjust mid-valve stiffness. This puts an extremely powerful tuning tool within easy access of the user. The effect of this adjustment on the damping curve is far greater than either low-speed compression adjusters or conventional high-speed compression adjusters. It combines the valve-stiffening system of a high speed compression adjuster with the sensitivity of the mid-valve.
This type of adjuster has not developed previously because it is much more mechanically complex than other types of adjusters. The base valve is usually secured near the end of a fork leg, and attached in a fixed position relative to the external components that surround it, so it is easier to access and has more room to build concentric adjustment systems. The mid-valve is attached to the end of a long slender rod, far from any connection to the structural body of the fork, and it cycles back and forth within the cartridge at high speed. Accessing it is challenging. The problem is further complicated by the fact that the rebound adjuster mechanism resides in the same area, so adding an additional adjustment feature at this location requires a series of long concentric rods that turn inside one another.