referring now to the drawings wherein like reference numerals correspond to the same or similar parts throughout the drawings , the present invention includes a system for suspending rake wheels 6 from a tool bar 7 using hydraulic cylinders 14 and an accumulator 40 rake wheels 6 . in fig1 and 2 , a fixed - frame , towed rake 1 is equipped with one - way hydraulic suspension cylinders 14 located at the outer edges of the frame 10 and supporting the rake wheels 6 via pivoting links 13 . the hydraulic cylinder 14 controls the orientation of the rake wheels 6 in relation to the ground . the tool bar 7 is attached to a rake frame 10 having a tongue 11 on the front end thereof , but the details of how the tool bar 7 is attached to the frame 10 forms no part of this invention . fig3 illustrates the hydraulic circuit , including a tractor remote valve 87 , and the circuit for controlling hydraulic suspension cylinders 14 . flotation is provided by a hydro - pneumatic accumulator 40 used to exchange volumes of hydraulic fluid with the lift / flotation cylinders 14 . this function is necessary when the rake wheels 6 are lowered , to allow the rake wheels 6 to follow the terrain , which occurs when the lift / flotation cylinders 14 are “ floating ”, wherein they cooperate with the accumulator 40 . an upper pressurized gas chamber of the hydro - pneumatic accumulator 40 is under pressure . the pressure is shared with a lower chamber of the hydro - pneumatic accumulator 40 , open to the hydraulic system . the rake wheel circuit also includes a take - up cylinder 41 and a valve 39 . the take - up cylinder 41 controls the oil volume displaced for lifting and lowering the rake wheels . the valve 39 may be a manually operated ball valve that can be opened to allow flow , or closed to block flow . the valve 39 may alternatively be a solenoid operated valve capable of allowing flow when a solenoid is energized , and blocking flow then a solenoid is de - energized . however , the present invention is not limited to these types of valves . the functions of the valve 39 are described below . in operation the towed rake 1 is hydraulically connected to a tractor ( not shown ) via valve 87 which provides a source of oil and is used to pump oil into the hydraulic systems of fig3 to perform a variety of functions including : 1 ) to control the position of the rake wheels 6 relative to the ground , the tractor remote valve 87 is moved to one extreme position which will cause the rake wheels 6 to lift , and when moved to the other extreme position will cause the rake wheels 6 to lower , and when left in the middle position will hold the rake wheels 6 in a set position ; and 2 ) charging the lift / flotation circuit . charging of the lift / flotation circuit of fig3 is necessary in order to insure that the take - up cylinder 41 , a component of the hydraulic system , yet not strictly speaking a part of the suspension system , is properly filled with oil . the lift / flotation cylinders 14 and the tractor remote valve 87 can be directly connected or isolated by use of the valve 39 . as illustrated in fig3 , the valve 39 is set in a manifold at the base of the take - up cylinder 41 . charging is completed by allowing oil to flow through the valve 39 , when opened , through the lines to the take - up cylinder 41 , while first allowing air to escape at the take - up cylinder 41 , and then to fully extend that cylinder 41 , while also purging air out of the lines between the valve 39 and the lift / flotation cylinders 14 . the tractor remote valve 87 is held in the position to force oil to the circuit until the lift / flotation cylinders 14 are in the extended position , and the rake wheels 6 are lifted to the transport position shown in fig6 b . after this first step of the charging procedure , the valve 39 is locked , isolating the lift / flotation cylinders 14 from direct connection to the tractor hydraulics . in the present embodiment for a fixed - frame rake 1 as shown in fig1 and 2 , the accumulator 40 is biased so as to act like a compressive spring by plumbing it to the extend port of the lift / flotation cylinders 14 , most clearly shown in fig3 . thus , during this first step of the charging procedure , the tractor lifts the rake wheels 6 and pressurizes the accumulator 40 . to complete the charging procedure the tractor remote valve 87 is opened to the tractor hydraulic fluid reservoir so that it does not force oil through the remote valve 87 . this allows the oil to flow from the take - up cylinder 41 to the tractor hydraulic reservoir . then the valve 39 is opened , either manually or electronically by the operator , to allow gravity to work against the accumulator 40 to lower the rake wheels 6 to the ground . the hydraulic system pressure can be viewed on a pressure gauge ( not shown ) so that the operator can bleed the valve 39 to allow rake wheels 6 to press against the ground with appropriate pressure . this is done by pre - determining rake model - specific values for hydraulic system pressure at which the operator can close the valve 39 to maintain . the bias of the accumulator 40 to lift the rake wheels 6 keeps the rake wheels 6 from digging into the surface of the ground , yet is sufficiently small to allow gravity to press the rake wheels 6 against the surface and maintain continuous contact . the rake wheels are able to travel freely through a range of travel , typically starting at a normal operating position where the ground force is adjusted to a desired force , typically approximately 20 pounds . the rake wheels are typically able to move downward from that position approximately 4 inches and upward approximately 8 to 12 inches . oil in the rake hydraulic system will constantly be seeking to occupy volume so as to obtain equilibrium pressures throughout the system . if the take - up cylinder valve 39 is locked , oil flow is restricted to flowing between the suspension cylinders 14 and the accumulator 40 . thus , with the valve 39 locked , the rake wheels 6 cannot be lifted or lowered via the tractor hydraulic system but only by the exchange of oil between the cylinders 14 and accumulator 40 as would be caused by variations in the force the ground exerts on the rake wheels 6 due to ground surface irregularity ( shown in fig1 and 2 ) while raking as the rake 1 passes over uneven ground , the ground exerts changing forces on the rake wheels 6 . the oil can flow between the cylinders 14 and the accumulator 40 to constantly maintain system pressure so that good contact between the rake wheels 6 and the ground is maintained . fig4 through 8 illustrate an individual rake wheel , and flotation system in various positions . fig8 is a representative position that may be observed in an operating position , in a static situation , on level ground . this is the most likely configuration that an operator would use to evaluate and adjust the flotation . once set , fig4 and 5 represent positions that may be encountered during operation , when the wheel encounters a raised portion of the terrain . the rake wheels may be raised , for instance by approx 6 inches as shown in fig4 and by approx 10 inches as shown in fig5 . the advantage of the present invention is that the variation in the ground force will be greatly reduced as compared to prior art rake wheel suspensions . it is desirable to minimize the variation . the preferred embodiment that is illustrated will provide a ground force that is at most 20 % more in the highest operating position , shown in fig5 , as compared to the ground force that was set in the normal operating position , as shown in fig8 . the present invention provides an additional benefit by allowing the rake wheel to move downward , as shown in fig7 , while maintaining a fairly consistent flotation force . the preferred embodiment as illustrated allows the rake wheel to move downward approximately 4 inches , while the ground force will be within 60 % of the ground force in the operating position . the preferred embodiment further relies on the flotation cylinder to serve as a down - stop , when the cylinder is completely extended , the downward movement of the wheel is stopped . in operation this suspension system provides advantages related to the durability of the rake wheels . each rake wheel is comprised of a number to rake tines , typically including a wire rod . these rods are connected together in a variety of ways , but in all known cases the connection of the rake tines are known to be potential sources for failure . when the rake wheels are subjected to varying ground forces , the individual rake tines are also subjected to varying bending loads . the variation of bending loads contributes to the failure of the rake tines , thus a system that minimizes the variation of the ground force will have a beneficial affect on the durability of the rake tines . in addition to the improved tine durability , the capability to provide a consistent ground force through an expanded range of travel , will result in improved raking action . the ground force on the individual rake wheels affects the way the rake tines engage the crop and ground . higher ground forces tend to result in increased contamination of the crop material , as the tines also carry some dirt along with the crop material . thus , a more consistent ground force will provide improved raking function . fig9 and 10 are related to each other and are graph charts showing the estimated approximate ground force verses vertical wheel pressure force to compare the present invention using a hydraulic cylinder as compared to a wheel rake using springs for the rake wheels . the above embodiment is the current preferred embodiment , but this invention is clearly not limited thereto . it is , therefore , apparent that many modifications and variations of the present invention are possible in light of the above teachings . it is , therefore , to be understood that within the scope of the appended claims , the invention may be practiced otherwise than as specifically described .