Patent Publication Number: US-2021179218-A1

Title: Linear actuator system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. Non-Provisional patent application Ser. No. 16/373,601, filed on Apr. 2, 2019, which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 62/651,379, filed on Apr. 2, 2018, each of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This instant specification relates to telescopic linear actuators with self-bleeding hydraulics. This instant specification relates to a balanced, direct-actuation, spool-type flow control valve used in a linear actuator. 
     BACKGROUND 
     Pneumo-hydraulic linear actuators rely on gas and liquids to operate. The liquid is generally used to provide an incompressible column of fluid in which to support a load. The gas is generally used to provide a bias force which can be used to automatically extend (or retract) the linear actuator. Most pneumo-hydraulic linear actuators utilize an internal floating piston (IFP) to maintain separation of the gas from the liquid in a reservoir that contains both liquid and gas. 
     These types of linear actuators suffer when gas unintentionally enters the fluid column. The liquid commonly used in these linear actuators, in itself, can be considered relatively incompressible, however when gas is mixed with the liquid, the fluid becomes compressible. This result is usually undesirable, especially when the linear actuator&#39;s purpose is to securely maintain position. Gas can enter the fluid column by a variety of means; most commonly by leaking seals either in the IFP or in the piston seal. Leaking seals is virtually unavoidable, especially with wear of the system over time. Therefore, the fluid column should eventually be purged of the gas. This is typically done by disassembly of the system, manually bleeding the gas through a bleed port, or manually opening a secondary valve specific to bleeding gas from the column. Because of this, many manufacturers seek to minimize leakage of gas into the fluid column in order to extend the service life. However, eventually the system will need to be bled. This type of service is disruptive, causes downtime of equipment, and can be expensive. 
     Most hydraulic seatposts utilize a poppet valve. Poppet valves are affected by the pressure acting upon them. System pressures can also act upon the poppet to move them. If a poppet is configured to open into (to the inside) a high-pressure cylinder, the pressure of the cylinder will help hold the valve closed. If the pressure increases significantly, the force required to open the valve also increases. In some cases, this force can become too high and the valve cannot be easily opened. A rider applying body weight to a seatpost is enough to make a poppet valve difficult to open. Many times, the rider first removes his/her weight from the saddle and then actuates it. This extra step can disrupt the riding position and balance of the bike. 
     However, if the poppet is configured to open away (to the outside) from the cylinder, the pressure in the cylinder will act upon the poppet to open it. To keep the valve closed in this configuration a spring bias is used. The spring should be strong enough to overcome the force applied by the pressure inside the cylinder. However, if this force is great enough, the ability to actuate the valve by hand becomes too difficult. 
     In either case, the direct effect of the pressure on the valve changes the actuation force required to operate the actuator. This variable force is undesirable. 
     Also, most hydraulic seatposts up until this point have used a “push” force to open the valve. For seatposts that are cable controlled, this force is converted to a pull motion. A variety of means to achieve this have been developed by various manufacturers, but most commonly a lever or cam device to convert pull to push is invoked. Other solutions may utilize hydraulic means of converting pull to push. 
     SUMMARY 
     In general, this document describes telescopic linear actuators. Namely, linear actuators that automatically and continuously bleeds itself—maintaining an incompressible fluid column and extending the service life of the linear actuator. 
     The systems and techniques described here may provide one or more of the following advantages. First, the system provides a way for gas to be automatically purged from the fluid column. Second, the system eliminates the need for an IFP. Third, the purge architecture has no extra moving parts. Fourth, the simple design provides for significant weight savings. Fifth, the purge system can be incorporated into various linear actuator architectures. 
     In general, this document describes a balanced (e.g., remains substantially unaffected by pressure changes in the actuator), direct-actuation, inverse spool-type flow control valve. An inverse spool-type control valve includes an outside that moves relative to an inside, as described herein the outside may generally be referred to as an “actuator” and the inside may generally be referred to as a “core.” In a non-inverse spool-type control valve the core/spool (inside component) is what moves. 
     The systems and techniques described here may provide one or more of the following advantages. First, low actuation force. Second, pressure balanced valve with little to no pressure bias on the actuator. Third, direct pull actuation. Fourth, simple control cable attachment/detachment. Fifth, flow modulation. Sixth, alternate unbalanced configuration that produces a bias force in place of the spring. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a section view of an example of a linear actuator in accordance with the present disclosure including a detailed component overview, with the linear actuator fully extended, locked. 
         FIGS. 2A, 2B, 2C, 2D  illustrate section views of examples of four embodiments of a linear actuator in accordance with the present disclosure, respectively, with the linear actuators fully extended, locked (gas and liquid shown). 
         FIGS. 3A, 3B, 3C, 3D  illustrate section views of the examples of the four embodiments of the linear actuators of  FIGS. 2A, 2B, 2C, 2D , respectively, with the linear actuators fully compressed, locked (gas and liquid shown). 
         FIGS. 4A, 4B  illustrate an example of a linear actuator in accordance with the present disclosure including illustrations of Volume A and Volume B using the first embodiment of the linear actuator of  FIGS. 2A, 3A , with  FIG. 4A  illustrating the linear actuator fully extended, and  FIG. 4B  illustrating the linear actuator fully retracted. 
         FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G  illustrate an example of a first embodiment of a linear actuator in accordance with the present disclosure illustrating compression flow with gas purge. 
         FIGS. 6A, 6B, 6C, 6D, 6E, 6F  illustrate an example of the first embodiment of a linear actuator in accordance with the present disclosure illustrating extension flow after gas purge. 
         FIGS. 7A, 7B, 7C, 7D, 7E, 7F, 7G  illustrate an example of a second embodiment of a linear actuator in accordance with the present disclosure illustrating compression flow with gas purge. 
         FIGS. 8A, 8B, 8C, 8D, 8E, 8F  illustrate an example of the second embodiment of a linear actuator in accordance with the present disclosure illustrating extension flow after gas purge. 
         FIGS. 9A, 9B, 9C, 9D, 9E, 9F, 9G  illustrate an example of a third embodiment of a linear actuator in accordance with the present disclosure illustrating compression flow with gas purge. 
         FIGS. 10A, 10B, 10C, 10D, 10E, 10F  illustrate an example of the third embodiment of a linear actuator in accordance with the present disclosure illustrating extension flow after gas purge. 
         FIGS. 11A, 11B, 11C, 11D, 11E, 11F, 11G  illustrate an example of a fourth embodiment of a linear actuator in accordance with the present disclosure illustrating compression flow with gas purge. 
         FIGS. 12A, 12B, 12C, 12D, 12E, 12F  illustrate an example of the fourth embodiment of a linear actuator in accordance with the present disclosure illustrating extension flow after gas purge. 
         FIGS. 13A, 13B, 13C, 13D, 13E  illustrate section views of examples of five configurations of a spool valve in accordance with the present disclosure, with the configuration of  FIG. 13A  (Configuration 1) being balanced, the configuration of  FIG. 13B  (Configuration 2) being unbalanced with inward bias, the configuration of  FIG. 13C  (Configuration 3) being unbalanced with outward bias, the configuration of  FIG. 13D  (Configuration 4) being unbalanced with inward bias, and the configuration of  FIG. 13E  (Configuration 5) being balanced with seal redundancy. 
         FIG. 14  illustrates an example of a balanced, direct-pull, inverse spool valve in accordance with the present disclosure—in situ (installed in a pneumo-hydraulic linear actuator). 
         FIG. 15  illustrates an example of a balanced, direct-pull, inverse spool valve in accordance with the present disclosure—in situ (equal cross-sectional areas balance forces at seals, diameters A=B, C=D). 
         FIGS. 16A, 16B  illustrate an example of a balanced, direct-pull, inverse spool valve in accordance with the present disclosure, with  FIG. 16A  illustrating the valve in a closed position and  FIG. 16B  illustrating the valve in an open position, with the valve including a spring bias to the closed position. 
         FIG. 17  illustrates views of an example of a linear actuator including a spool valve in accordance with the present disclosure including illustration of cable attachment and a detachment pocket in the actuator. 
         FIG. 18  illustrates views of an example of a linear actuator including a spool valve in accordance with the present disclosure including illustration of an actuator cable pocket, actuator, housing mount, cable and cable housing. 
         FIG. 19  illustrates an example of assembly/disassembly of a cartridge assembly within a shell of a dropper seatpost including an example of a linear actuator in accordance with the present disclosure. 
         FIG. 20  illustrates an exploded view of the cartridge assembly of  FIG. 19  including an example of a linear actuator in accordance with the present disclosure. 
         FIGS. 21A, 21B  illustrate section views of an example of a first embodiment of a dropper seatpost including an example of a linear actuator in accordance with the present disclosure. 
         FIG. 22  illustrates a section view of an example of a second embodiment of a dropper seatpost including an example of a linear actuator in accordance with the present disclosure. 
         FIGS. 23A, 23B  illustrate section views of an example of a third embodiment of a dropper seatpost including an example of a linear actuator in accordance with the present disclosure. 
         FIG. 24  illustrates a section view of an example of a fourth embodiment of a dropper seatpost including an example of a linear actuator in accordance with the present disclosure. 
         FIG. 25  illustrates an example of assembly/disassembly of a cartridge assembly within a shell of the fourth embodiment of a dropper seatpost including an example of a linear actuator in accordance with the present disclosure. 
         FIG. 26  illustrates an exploded view of the cartridge assembly of  FIG. 25  including an example of a linear actuator in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. 
     Telescopic Linear Actuator with Self-Bleeding Hydraulics 
     With reference to  FIG. 1 ,  FIGS. 2A, 2B, 2C, 2D ,  FIGS. 3A, 3B, 3C, 3D ,  FIGS. 4A, 4B ,  FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G ,  FIGS. 6A, 6B, 6C, 6D, 6E, 6F ,  FIGS. 7A, 7B, 7C, 7D, 7E, 7F, 7G ,  FIGS. 8A, 8B, 8C, 8D, 8E, 8F ,  FIGS. 9A, 9B, 9C, 9D, 9E, 9F, 9G , FIGS.  10 A,  10 B,  10 C,  10 D,  10 E,  10 F,  FIGS. 11A, 11B, 11C, 11D, 11E, 11F, 11G ,  FIGS. 12A, 12B, 12C, 12D, 12E, 12F , examples of a telescopic linear actuator with self-bleeding hydraulics are described. With specific reference to  FIG. 15 , while there is a step down shown from A/B to C/D, such a configuration may vary. For example, A/B can equal C/D (e.g., A=B=C=D). 
     Valve 
     The configuration of the valve  20  can vary. Two valve types, poppet and spool, are shown in the embodiments but valve types are not limited to only these. The embodiments show a variety of valve  20  configurations, but do not show every type of valve  20  configuration (for example, the fourth embodiment ( FIGS. 11A-11G, 12A-12F ) can utilize a poppet valve instead of a spool valve, and the third embodiment ( FIGS. 9A-9G, 10A-10F ) can utilize a spool valve instead of a poppet valve). 
     The valve  20  typically can be configured to have at least two positions: opened and closed. In the open configuration, the valve  20  allows fluid to flow through a fluid pathway, the first fluid pathway  23 . In the closed configuration, the valve  20  blocks flow through the fluid pathway. The valve  20  can also be partially opened or closed, “throttling” fluid flow. A valve  20  with more than two positions may also be used. 
     In most configurations, flow is allowed through the first fluid pathway  23  when the valve actuator  10  is moved in one direction and blocked when the valve actuator  10  returns to the original unactuated position via the valve spring  19 . 
     The first fluid pathway  23  is a major component of the valve  20  and connects two volumes: Volume A and Volume B. The fluid port in communication with Volume A is the first fluid port  13 , the fluid port in communication with Volume B is the second fluid port  15 . 
     Volume A (e.g., a Fluid Column) 
     Volume A is known as the “fluid column” and may be filled with only liquid to remain incompressible. 
     Volume A is defined in large part by the piston cylinder  25 . At one end of the piston cylinder  25  is a movable piston  7  with attached piston rod  3 . The piston  7  and piston rod  3  are telescopically allowed to slide within the piston cylinder  25 . Located at the other end of the piston cylinder  25  is either a valve  20  (as in the first embodiment ( FIGS. 5A-5G, 6A-6F ), second embodiment ( FIGS. 7A-7G, 8A-8F ), and fourth embodiment ( FIGS. 11A-11G, 12A-12F )) or capped off (as in the third embodiment ( FIGS. 9A-9G, 10A-10F )). If the end of the piston cylinder  25  is capped off, the valve  20  is typically part of the piston  7  (as in the third embodiment ( FIGS. 9A-9G, 10A-10F )). These parts (the piston cylinder  25 , piston  7 , and cylinder cap  27 /valve  20 ) enclose Volume A. 
     Since the piston  7  can telescopically slide within the piston cylinder  25 , Volume A is a variable volume depending on the position of the piston  7  with respect to the rest of the components. 
     Volume B (e.g., a Reservoir) 
     Volume B is known as the “reservoir” and is filled with reserve liquid and gas. 
     Volume B is defined by the volume inside the reservoir tube  26 , the volume behind the piston  7 , and the volume inside the piston rod  3 . Note: In the embodiments shown, Volume B is currently shown as concentrically located around Volume A, however this volume can exist separately. Therefore, Volume A has not been used to define Volume B&#39;s perimeter. 
     Volume B is a non-separator type accumulator in which both gas and liquid exist but there is no physical separator between the two—in contrast to a separator type accumulator in which an internal floating piston (IFP) separates the gas from the liquid. In a separator type accumulator with an IFP, the liquid side of the accumulator can be defined as “Volume C” and the gas side of the accumulator can be defined as “Volume D”. 
     In the embodiments shown, Volume B is located concentrically around the piston cylinder  25 . When this configuration is the case, the liquid side of Volume B is located on the same side as the valve  20  side of Volume A (the bottom of the linear actuator). However, in other embodiments, Volume B is not located concentrically around the piston cylinder  25 . In addition, in other embodiments, the piston cylinder  25  does not lie within the reservoir, but rather, in a seat post configuration. Such a configuration may provide a compact configuration. 
     As configured, Volume B is a variable volume depending on the position of the piston  7  (and piston rod  3 ) with respect to the rest of the components. Volume B can be a fixed volume, such as in a case where the Reservoir and Fluid Column are separate. 
     Volume B can be pressurized to provide a bias force. This bias force can be used to automatically extend (or, in some instances, retract) the linear actuator when the valve  20  is opened. Volume B can also be open to the atmosphere and provide no bias force. 
     Bleed Components (Needle, Receptacle, Funnel) 
     The needle  12  is hollow and slides axially within the receptacle  30 , creating a tube-within-a-tube overlap. An optional bleed seal  14  may be incorporated to close the gap between the two parts. A needle-guide may also be used to help guide the needle  12  into the receptacle  30 . 
     The second fluid pathway  24  can be defined as having a third fluid port  16  and fourth fluid port  17 . The third fluid port  16  is located at the top of Volume A and the top of the second fluid pathway  24 . The fourth fluid port  17  is located at the bottom of the second fluid pathway  24 . 
     The funnel  11  is located at the top of Volume A and helps channel rising gas bubbles  22  into the third fluid port  16  and top of the second fluid pathway  24 , minimizing dead volume for gas bubbles  22  to get trapped. 
     Standard Linear Actuator Operation 
     Start with a fully-extended linear actuator, a closed valve  20 , Volume A filled with non-compressible liquid. Liquid with a dissolved gas can be considered a single-phase fluid, liquid. Volume A should only have liquid in it for proper operation. Volume B filled with a liquid and a pressurized gas. Volume B contains two distinct fluid phases, gas and liquid (even though the liquid may also contain dissolved gas). As long as the valve  20  is closed, liquid cannot be transferred from Volume A to Volume B. Because the liquid is incompressible, Volume A cannot be reduced, and the linear actuator cannot be compressed. The piston  7  and piston rod  3  cannot be extended due to a hard stop at the end of its fully-extended stroke. In this configuration, the linear actuator may generally be described as “locked” in position. 
     When the valve  20  is opened, the liquid in Volume A can be transferred into Volume B through the first fluid pathway  23 . Therefore, an open valve  20  allows Volume A to vary. Thus, the piston  7  and piston rod  3  can be pushed in and the linear actuator can be compressed. Applying an external force to the piston rod  3 , in the direction of compression, forces fluid from Volume A through the valve  20  and first fluid pathway  23  into Volume B. 
     As the piston  7  moves further, Volume B increases because the back side of the piston  7  moves further into the piston cylinder  25 . This increase in volume is reduced by the piston rod  3 , since more of the piston rod  3  occupies space in Volume B. However, the amount of fluid transferred from Volume A is greater than the Volume B increase. Therefore, the amount of room remaining for the compressed gas in Volume B decreases. Because the amount of gas (moles) is constant, the overall pressure increases (unless this volume is open to atmosphere, but as stated, the starting conditions describe Volume B as filled with a pressurized gas). The gas pressure acts upon the fluid in Volume B. 
     The pressure in the linear actuator also acts upon the cross-section of the piston rod  3 , trying to push it out of the linear actuator. As long as the compressive external force applied to the piston rod  3  is greater than the extensive force caused by the pressure in the linear actuator, the piston  7  and piston rod  3  will continue to be pushed/compressed into the linear actuator. The piston  7  and piston rod  3  will continue to move until either they reach the end of their stroke (hard stop) or the valve  20  is closed (creating an incompressible column of liquid in which they cannot move against). 
     The piston  7  can be stopped in place with the close of the valve  20 . With the valve  20  closed, the piston  7  will not be able to be compressed further. As mentioned previously, there is an extension force acting upon the piston rod  3 . When the valve  20  is closed, the piston rod  3  extension force is overcome by a compression force acting upon the back side of the piston  7 . This force comes from the pressure in Volume B being greater than the pressure in Volume A. 
     Recall that when the valve  20  is open, the pressure in Volume A is equal to the pressure in Volume B. But when the valve  20  is closed, the pressure in Volume A becomes independent of Volume B. If Volume A increases by extension of the piston  7 , the pressure will drop (assuming constant temperature). This is because the moles of liquid (and any gas entrapped) is constant. If the piston  7  is extended, Volume B will decrease, and the pressure will increase. The increase in pressure of Volume B increases the compressive force acting upon the back side of the piston  7 . However, there is still pressure inside Volume A acting in the extension direction, on the face of the piston  7 . The further the piston  7  travels in the extension direction, the greater the backside compression force and the less the front side extension force. The net force becomes a compressive force. This net compressive force is enough to overcome the extension force on the piston rod  3 . This force holds the piston  7  against the fluid column. 
     It is possible to add an external extension force to the piston rod  3  simply by pulling on the piston rod  3 . This force can be enough to overcome the net compressive force and allow the piston  7  to move. Because movement of the piston  7  reduces the pressure inside Volume A, any dissolved gasses bubble out. Since there is gas in Volume A, the piston  7  can move as the gas is expanded. Releasing the external extension force increases Volume A pressure and the gas dissolves back into the liquid. 
     If the compressive external force is released from the piston rod  3  and the valve  20  is opened, allowing fluid to flow from Volume B to Volume A, the linear actuator will extend. This is because the internal pressure acts upon the surface area of the piston rod  3 , forcing it outward. Upon opening the valve  20 , the pressures in Volume A and Volume B equalize making the previous net compressive force zero. However, there is still an expansion force on the piston rod  3  due to the pressure difference inside the linear actuator vs outside (the atmospheric pressure). As the piston rod  3  is forced outward, it moves the piston  7  with it. As the piston  7  moves outward, Volume A increase and the pressure inside decreases compared to the pressure in Volume B. This pressure differential forces fluid to flow from Volume B, back through the valve  20  (first fluid pathway  23 ), and into Volume A. 
     The piston  7  and piston rod  3  will continue to move until either they reach the end of their stroke (hard stop) or the valve  20  is closed. If the valve  20  is closed midway through extension, the piston  7  and piston rod  3  will stop extending. This is because of the same reason as mentioned previously: the internal pressure acts upon the back side of the piston  7  holding it against the fluid column with a net compressive force. Likewise, the piston  7  and piston rod  3  cannot be compressed because of the fluid column beneath them. In this configuration, the linear actuator may generally be described as “locked”. 
     Note: As long as the linear actuator is held upright or substantially upright and there is sufficient liquid in Volume B, the second fluid port  15  of the first fluid pathway  23  is submerged under liquid in Volume B. The angle of which the linear actuator can be tilted is a function of the liquid level in Volume B. Tilting the linear actuator far enough to where the second fluid port  15  is no longer submerged may allow gas to be drawn into Volume A upon opening the valve  20  and the extension of the linear actuator. 
     Compromised Linear Actuator Operation 
     A linear actuator with a non-separator type accumulator is simple, but its operation can be easily compromised. During operation, gas can unintentionally infiltrate Volume A (as is the case with hydraulic linear actuators—separator and non-separator types alike). Gas can enter Volume A either by leaking past the piston seal  8 , leaking past valve  20  seal(s), or by being drawn in from Volume B through the valve  20 . In a non-separator type accumulator, the gas and liquid are not physically separated. If the linear actuator is tilted so that the second fluid port  15  is not submerged in liquid, as the linear actuator is extended, gas can be drawn in. The separator type accumulator configuration in which there is an internal floating piston (“IFP”) can also be compromised if the IFP seals leak. Leakage of the IFP allows gas to reside on the liquid side of the IFP (Volume C), and able to be drawn in through the valve  20 . If gas becomes trapped in Volume C, there is no easy way for it to return to Volume D. 
     Note: without a way to purge gas from Volume A, the chances of a non-separator type accumulator being compromised is much greater than a separator type accumulator. In the past, this purge operation involved manually addressing the issue (through disassembly, a bleed screw, or a secondary purge valve. Therefore, it was best practice to architect separator type accumulators and not obvious to architect a non-separator type accumulator unless one incorporates some sort of bleed mechanism (as described later). But as described previously, this arrangement is not infallible, the IFP seals can leak. The seals in the IFP also greatly increase the running friction of the linear actuator—requiring greater actuation forces and pressures. 
     Gas in Volume A is compressible; therefore, the piston  7  and piston rod  3  will be allowed to move even if the valve  20  is closed. This is considered a compromised system because the piston  7  and piston rod  3  are no longer able to hold position when the linear actuator is in the locked configuration. Hydraulic linear actuators will eventually become compromised due to gas entering Volume A. However, if this gas can be quickly and easily purged from Volume A, the linear actuator can continue in service. 
     Until now, it has not been easy to automatically purge gas from Volume A without disassembly or a separate valve (either a manual purge valve or a bleed screw). This is because gas rises to the top of the fluid column. Separator type accumulators can be inverted, allowing the valve  20  to be at the top of the fluid column, forcing fluid through the valve  20  would carry the gas with it and out of Volume A. However, bleeding air out of the valve  20  only transfers it to the wrong side of the IFP (volume C) where the gas does not belong, enabling it to be drawn back into the fluid column. Non-separator type accumulators suffer from a different problem. They utilize the valve  20  on the bottom of the fluid column so liquid can be drawn through the valve  20  and not gas (e.g., unless a fluid path were made from the valve  20  to the liquid side of the reservoir, such as coiled tubing). Because the entrapped gas is at the top of the fluid column and the valve  20  at the bottom, the only way to purge the gas is to move the top of the fluid column close to the valve  20  (as in moving the piston  7  closer to the valve  20 , or if the piston  7  is the valve  20 , the piston  7  closer to the cap of the fluid column) so the gas can be drawn through the valve  20 . However, there is typically dead volume at the bottom of the stroke and in the valve  20  and it becomes impossible to remove the last remaining amount of gas. Since the gas does not reach the valve  20  until the end of the stroke, there is not enough fluid to drive the gas the rest of the way through the valve  20  and out into the reservoir. 
     Automatic Gas Purging Architecture 
     The solution to automatically purging gas from Volume A is to transfer the liquid/gas from the top of Volume A during the stroke, through the first fluid port  13  of the valve  20 , and out the second fluid port  15  into Volume B of a non-separator type accumulator where the liquid/gas will naturally become re-separated in Volume B due to their density/weight difference. The second fluid port  15  of the valve  20  should be located at the bottom of Volume B so that only liquid is transferred back into Volume A on the return stroke. Because the distance between the top of Volume A and bottom of Volume B is variable depending on the linear actuator&#39;s extension, the mechanism of transfer should accommodate this variation. 
     To accommodate the distance variation, a novel telescopic needle  12  and receptacle  30  architecture has been developed. The needle  12  and receptacle  30  form a telescopic fluid pathway that can vary in length with the stroke of the linear actuator LA. The telescopic fluid pathway can be defined as having a first fluid pathway  23  and a second fluid pathway  24 . The first fluid pathway  23  can take the form of either the needle  12  or the receptacle  30 . Likewise, the second fluid pathway  24  can take the form of either the needle  12  or the receptacle  30 . In other words, the configuration of the telescopic fluid pathway can vary—with either the needle  12  or receptacle  30  on top. The first fluid pathway  23  has the same structure as previously described, with a first fluid port  13 , valve  20 , and a second fluid port  15 . The second fluid pathway  24  can be defined as having a third fluid port  16  and fourth fluid port  17 . The third fluid port  16  is located at the top of Volume A and the top of the second fluid pathway  24 . The fourth fluid port  17  is located at the bottom of the second fluid pathway  24 . In examples, the first fluid pathway  23  and second fluid pathway  24  telescopically overlap. In other examples, as will be later described, the first fluid pathway  23  and second fluid pathway  24  do not telescopically overlap. When telescopically overlapped, the first fluid pathway  23  communicates with the second fluid pathway  24  at the first fluid port  13  and fourth fluid port  17 . The second fluid pathway  24  extends the first fluid pathway  23  so that the fluid intake of the first fluid port  13  is replaced by the fluid intake of the third fluid port  16 . Therefore, fluid can be transferred from the top of Volume A. 
     Depending on the orientation of the third fluid port  16  with respect to the very top of Volume A, a funnel  11  may be provided. Without a funnel  11 , if the linear actuator LA is titled so that the third fluid port  16  is below the upper part of Volume A, a gas pocket may form preventing gas from being drawn into the second fluid pathway  24 . The funnel  11  helps channel rising gas bubbles  22  into the third fluid port  16  and top of the second fluid pathway  24 , minimizing dead volume for gas bubbles  22  to get trapped. 
     The needle  12  is hollow and slides axially within the receptacle  30 , creating a tube-within-a-tube overlap. To allow the needle  12  to slide within the receptacle  30  and to account for manufacturing tolerances and misalignment in the assembly, there is a gap. The gap should be sealed with a bleed seal  14  or the gap should be small enough to generate high resistance to fluid flow through it. Not enough resistance to fluid flow through this gap will allow too much fluid to flow through the overlap, bypassing the second fluid pathway  24 . The needle  12  and receptacle  30  can be integrated into the valve  20 , piston  7  or cylinder cap  27  depending on the desired configuration. 
     The needle  12  and receptacle  30  can overlap during the entire stroke of the linear actuator LA (full-time telescopic fluid pathway) or only during a portion of it (part-time telescopic fluid pathway). In examples, in the case of a full-time telescopic fluid pathway, the first fluid pathway  23  and second fluid pathway  24  are always in communication with each other and telescopically overlapped. Therefore, the second fluid pathway  24  can be considered always active. This means that when fluid flows, it will always flow through the first fluid pathway  23  and second fluid pathway  24 . In examples, in the case of a part-time telescopic fluid pathway, during part of the linear actuator stroke, the first fluid pathway  23  and second fluid pathway  24  do not overlap and are therefore not in communication with each other. Because of this, the second fluid pathway  24  can be considered inactive during this portion of the linear actuator stroke (the first fluid pathway  23  remains active). The second fluid pathway  24  becomes active as soon as the first fluid pathway  23  and second fluid pathway  24  overlap and either a) form a seal with the bleed seal  14  or b) close the gap enough to where the resistance to fluid flow through the gap is greater than fluid flow through the second fluid pathway  24 . 
     The operation of the part-time gas purging architecture will now be explained in detail. Starting with the linear actuator LA fully extended, the needle  12  and receptacle  30  are separated. Because there is no telescopic overlap with the first fluid pathway  23 , the second fluid pathway  24  is inactive, meaning fluid is not actively being force through it. This is because the pressure acting on the third fluid port  16  is the same as the fourth fluid port  17  and there is no bias acting to move fluid through the fluid pathway. As the linear actuator LA is compressed (valve  20  open), fluid flows through the first fluid pathway  23  by entering the first fluid port  13 , passing through the valve  20 , and out into Volume B through the second fluid port  15 . Any gas in Volume A has been accumulated at the third fluid port  16  and top of the second fluid pathway  24 . However, since the second fluid pathway  24  is inactive and there is no fluid flow, the gas bubbles  22  remain in place and are not purged out of Volume A. 
     As the linear actuator LA is compressed further (valve  20  open), the first fluid pathway  23  and second fluid pathway  24  will overlap, activating the second fluid pathway  24 . As fluid begins to flow through the second fluid pathway  24  it carries the entrapped gas bubbles  22  with it. The second fluid pathway  24  is restricted enough (in cross sectional area) that the fluid cannot easily bypass the gas bubbles  22  and the gas bubbles  22  cannot easily slip out of the fluid stream. The fluid sweeps the gas bubbles  22  through the second fluid pathway  24 , into the first fluid pathway  23 , and then out into the Volume B. 
     Once the gas bubbles  22  enter Volume B, the gas separates from the liquid naturally, due to density differences and gravity. Because of the orientation of the second fluid port  15  with respect to the Volume B (i.e. the second fluid port  15  is located at the bottom of the volume where the liquid lies), the gas bubbles  22  rise away from the second fluid port  15  and the second fluid port  15  remains submerged under liquid. This creates a one-way passage of gas into Volume B from Volume A where the gas then naturally separates from the liquid. 
     Gas will continue to be purged as long as there is fluid flow. Fluid will flow through the fluid pathways until the linear actuator LA is fully compressed. Depending on the entrapped volume of gas, Volume A may not be completely purged and another actuation cycle may be needed. Because the purge happens every cycle, if any gas enters between cycles, it will be purged from Volume A in the next stroke. The volume of gas purged depends on the geometry of the needle  12 , receptacle  30 , piston cylinder  25  and active length of stroke. The embodiments shown have been designed to purge a relatively large volume of gas. The needle  12  and receptacle  30  can be shorter, making the active length of stroke shorter, purging less volume of gas. 
     From a fully compressed linear actuator state, as the linear actuator LA extends and Volume A increases, liquid from Volume B is drawn through the first fluid pathway  23 . In the beginning of the stroke, the first fluid pathway  23  and second fluid pathway  24  are overlapping and in communication with each other. Therefore, the fluid flows from the first fluid pathway  23 , through the second fluid pathway  24  and out the third fluid port  16 , refilling Volume A. In a part-time gas purging architecture, the first fluid pathway  23  and second fluid pathway  24  will eventually separate. This deactivates the second fluid pathway  24 . Fluid then flows out the first fluid port  13 , refilling Volume A until the linear actuator LA is fully extended. 
     If un-purged gas remains in the Volume A or purged gas in Volume B is drawn back through the second fluid port  15  (possible to do if the system is actuated fast enough to where the gas bubbles  22  do not have time to rise to the top of Volume B, or if the linear actuator LA is tilted far enough and the second fluid port  15  is exposed to the gas in Volume B), the process repeats itself the next time the linear actuator LA is actuated. The gas bubbles  22  rise to the top, are funneled into the second fluid pathway  24 , and staged for evacuation. 
     Full-time gas purging architecture operates in the same manner; however, in examples, the second fluid pathway  24  is always active due to a constant telescopic overlap at the first fluid port  13  and fourth fluid port  17 . Unlike the part-time purging architecture, gas is purged through the entire stroke of the linear actuator LA. This allows for the maximum volume of gas to be purged. The volume of gas to be purged during normal operation, however, may be small. 
     Balanced, Direct-Pull, Inverse Spool Valve 
     With reference to  FIGS. 13A, 13B, 13C, 13D, 13E ,  FIG. 14 ,  FIG. 15 ,  FIGS. 16A, 16B ,  FIG. 17 ,  FIG. 18 , examples of a balanced, direct-pull, inverse spool valve are described. 
     Inverse Balanced Spool Valve Specifics 
     Spool valve SV subcomponents: valve core SV 2 , valve actuator SV 1 , seals, return bias member (optional) 
     The return bias member for either valve can be a physical spring SV 9  (compression, extension, torsion, leaf, etc.) or gas spring. 
     The valve typically can be configured to have at least two positions: opened and closed. In the open configuration, the valve allows fluid to flow through a fluid pathway, the “first fluid pathway”. In the closed configuration, the valve blocks flow through the fluid pathway. The valve can also be partially opened or closed, “throttling” fluid flow. 
     In most configurations, flow is allowed through the first fluid pathway when the valve is actuated in one direction by applying an external force to the poppet or spool and blocked when the valve returns to the original unactuated position via the return bias member  9 . 
     The first fluid pathway connects two volumes: Volume A SV 17  and Volume B SV 18  of the linear actuator LA described in the “Telescopic Linear Actuator with Self-Bleeding Hydraulics” section above. The fluid port in communication with Volume A SV 17  is the first fluid port SV 5 , and the fluid port in communication with Volume B SV 18  is the second fluid port SV 6 . 
     Variations in pressure in both Volume A SV 17  and Volume B SV 18  should apply no biasing force to the valve actuator SV 1 . In some instances, the valve actuator SV 1  may be designed to be unbalanced in order to provide a bias force in one direction. 
     High pressure seals leak to low pressure reservoir rather than to external atmosphere. 
     Spring SV 9  return bias, gas spring return bias, or combination of both. For example, to reduce weight, a gas spring bias may be utilized. The gas spring bias may be the result of utilizing an unbalanced valve. When an unbalanced valve is used as a gas spring bias, a decrease in gas pressure (e.g., due to a leak) may be detrimental to the performance of the bias. By way of further example, a metal spring SV 9  may be used. However, while a metal spring SV 9  may alleviate concerns relating to a decrease in gas pressure, the use of a metal spring SV 9  may result in increasing the weight. 
     Direct pull, no reversal of actuation direction needed 
     Tool-less and hardware-less cable SV 10  attachment. 
     Balanced, Inverse Spool Valve Architecture 
     The spool valve SV consists of two main components, a valve core SV 2  and valve actuator SV 1 , and is in communication with two chambers, Volume A SV 17  and Volume B SV 18 . The spool valve SV can be integrated into Volume A SV 17  and/or Volume B SV 18  or independent from the two volumes. The valve core SV 2  and chamber(s) can be one piece or separate pieces to aid in manufacturability. 
     The valve core SV 2  contains a first fluid port SV 5  and a second fluid port SV 6 . The first fluid port SV 5  connects to Volume A SV 17 . The second fluid port SV 6  connects to Volume B SV 18 . Two high-pressure seals (inward high-pressure seal SV 7  and outward high-pressure seal SV 8 ) are installed in circumferential grooves around the valve core SV 2  and on either side of the second fluid port SV 6 . 
     The valve actuator SV 1  slides coaxially over the valve core SV 2  and over the high-pressure seals (inward high-pressure seal SV 7  and outward high-pressure seal SV 8 ). The valve is in the “closed” configuration when the valve actuator SV 1  is in sealing contact with both high-pressure seals (inward high-pressure seal SV 7  and outward high-pressure seal SV 8 ). In this configuration, Volume A SV 17  is separated from Volume B SV 18 . The valve is in the “open” configuration as soon as at least one of the high-pressure seals (inward high-pressure seal SV 7  or outward high-pressure seal SV 8 ) loses sealing contact with the valve actuator SV 1 , allowing Volume A SV 17  to communicate with Volume B SV 18 . 
     The valve actuator SV 1  can be axially moved to the open or closed configuration by a bias force. This bias force can come from a spring SV 9 , an externally applied force, a non-contact force (e.g. magnetic force) or a combination of the three. For example, to open the valve, an external pull force can be applied to the valve actuator SV 1 , compressing/extending a spring SV 9  as the valve actuator SV 1  moves toward the open position. When the external pull force is released, the compression/extension force from the spring SV 9  returns the valve actuator SV 1  to the closed position. In another example, the valve actuator SV 1  can be moved by an external pull force in one direction and an external push force in the other direction. In yet another example, the valve actuator SV 1  can be pushed and/or pulled via an electric solenoid or the valve actuator SV 1  may be a component of the solenoid, being pushed and/or pulled with a magnetic field. 
     To apply an external force to the valve actuator SV 1 , one side of the valve actuator SV 1  is exposed to the environment at atmospheric pressure so that an external force can be applied. The other side of the valve actuator SV 1  is exposed to Volumes A and B. Atmospheric pressure is separated from Volume A SV 17  and Volume B SV 18  by the environment seal SV 15 . The atmospheric pressure and pressures within Volume A SV 17  and Volume B SV 18  may all be different. Because of this, a bias force can also result from pressure differences between volumes and/or atmosphere. 
     In a pressure balanced valve configuration, regardless of the differences in pressure between the volumes and/or atmosphere, no net bias force acts upon the valve actuator SV 1  due to pressure. This does not mean that pressures do not apply forces to the valve actuator SV 1 . Any pressure that applies a force to the valve actuator SV 1  in one direction is balanced by pressure applying a force in an opposite direction. The net bias force is zero. 
     Pressure applies forces perpendicular to exposed surfaces. In the case of the valve actuator SV 1 , any force vector component acting along the axis of actuation produces a bias force on the valve actuator SV 1 . The sum of these bias forces should be zero for the valve to be considered balanced. 
     In the configuration shown (Configuration 1), pressure in Volume A SV 17  applies a force only to the exposed surface of the valve actuator SV 1  between the two high pressure seals (inward high-pressure seal SV 7  or outward high-pressure seal SV 8 ). Since this surface is cylindrically parallel to the axis of actuation, the resulting force is perpendicular with no force vector acting in the axis of actuation. Therefore, Volume A SV 17  does not produce a bias force on the valve actuator SV 1 . 
     Pressure from Volume B SV 18  and the environment acts upon the valve actuator SV 1  as well. However, due to the step in the valve actuator SV 1  and a first breathe port SV 13 , the surfaces with a resulting force vector component cancel each other out. In this configuration, the step is designed specifically for this cancellation of forces. In another configuration (Configuration 2), the step can be alternately arranged, so that the resulting forces do not balance each other out and a net bias force is intentionally created. In this configuration, the pressure in Volume B SV 18  is significantly higher than the atmospheric pressure in the environment. The net bias force on the valve actuator SV 1  from Volume B SV 18  acts to draw the valve actuator SV 1  inward. The net bias force on the valve actuator SV 1  from atmospheric pressure acts to draw the valve actuator SV 1  outward. However, because the pressure in Volume B SV 18  is significantly greater than atmospheric pressure, the net bias force is inward. If the atmospheric pressure were greater than the pressure in Volume B SV 18 , the valve actuator SV 1  would be biased outward. 
     In another configuration (Configuration 3), the step can be removed or even reversed. When Volume B SV 18  pressure is greater than atmospheric pressure, the valve actuator SV 1  is biased outward. 
     Configuration 4 lacks the first breathe port SV 13 . Because of this, a vacuum is pulled between the outward high-pressure seal SV 8  and the valve actuator SV 1 . The vacuum can be used as a bias force to hold the valve actuator SV 1  inward. 
     Consider again Configuration 1. High pressure seal leaks can be detrimental to the proper operation of equipment. If the inward high-pressure seal SV 7  leaks, the fluid in Volume A SV 17  leaks to Volume B SV 18 . If the outward high-pressure seal SV 8  leaks, the fluid in Volume A SV 17  leaks to the environment. To prevent the later leak, a low-pressure seal  16  and second breathe port SV 14  can be added (Configuration 5). 
     In this configuration (Configuration 5), if the outward high-pressure seal SV 8  leaks, the fluid leaks into an auxiliary volume between the valve actuator SV 1  and valve core SV 2  and between the outward high-pressure seal SV 8  and the low-pressure seal SV 16 . If this volume was not ported back to Volume B SV 18  by the second breathe port SV 14 , pressure would continue to build as fluid leaks into it. This could cause the low-pressure seal SV 16  to leak as well. Therefore, the second breathe port SV 14  provides a way for the fluid to leak into Volume B SV 18  rather than the environment. Because pressure in the auxiliary volume applies a force only to the exposed surface of the valve actuator SV 1  between the two high pressure seals (inward high-pressure seal SV 7  or outward high-pressure seal SV 8 ), and this surface is cylindrically parallel to the axis of actuation, the resulting force is perpendicular with no force vector acting in the axis of actuation. Therefore, this auxiliary volume, low pressure and second breathe port SV 14  does not add a bias force on the valve actuator SV 1 . 
     In a pressure unbalanced valve, the net bias force can be used as a valve actuator SV 1  return force. For example, consider Configuration 2 with Volume B SV 18  pressure greater than atmospheric pressure. The net bias acts to hold the valve closed. To open the valve, an external pull force greater than the net bias inward force can be applied to the valve actuator SV 1 , moving the valve actuator SV 1  toward the open position. When the external pull force is released, the net bias force takes over and returns the valve actuator SV 1  to the closed position. In another example, the net bias force can act to hold the valve open. When an external push force greater than the bias force is applied to the valve actuator SV 1 , the valve actuator SV 1  will be urged toward the closed direction. When the external force is removed, the valve actuator SV 1  is biased to the open position. 
     A drawback to utilizing a pressure unbalanced valve is pressure can be lost in Volume B SV 18 . A reduction in pressure will reduce the bias force caused by that pressure. A complete loss of pressure in Volume B SV 18  and equalization with the atmospheric pressure would remove all pressure induced bias. 
     Therefore, Configuration 5 may be desirable for linear actuators, and more specifically dropper seat posts, due to reliable valve actuator SV 1  bias (non-pressure biased, pressure balanced, but spring SV 9  bias closed) and seal redundancy. 
     Throttling, Flow Modulation 
     As the valve actuator SV 1  opens, the second fluid port SV 6  becomes more and more unblocked by the valve actuator SV 1 . A partial actuation, where the valve actuator SV 1  partially blocks the second fluid port SV 6 , provides resistance to flow (more than a fully open port). Therefore, the speed of the flow can be modulated. 
     Direct Pull Actuation 
     For remote actuation of the spool valve SV, one method is to attach a control cable SV 10  to the valve actuator SV 1 . Because this architecture pulls outward to open the valve, the cable SV 10  can be attached directly. A poppet valve in place of this valve would rely on push actuation, therefore the cable SV 10  pull would have to be converted to push. Direct pull may simplify parts, may utilize fewer parts, and may be more compact in size. 
     Control Cable Attachment/Detachment 
     A pocket has been machined into the end of the valve actuator SV 1  that allows the cable head SV 11  to be easily inserted and removed, but when tension is applied to the cable SV 10 , the cable head SV 11  may be captive and unable to be removed. A slot in the housing mount SV 3  and in the valve actuator SV 1  allow for cable housing SV 12  to be pulled out of the housing mount SV 3 , the cable SV 10  then to be pulled out of the slots, and then the tension in the cable SV 10  released to free the cable head SV 11  from the valve actuator SV 1 . This solution does not require tools and can provide for simple installation and removal. 
     Example Dropper Post Implementations 
     With reference to  FIG. 19 ,  FIG. 20 ,  FIGS. 21A, 21B ,  FIG. 22 ,  FIGS. 23A, 23B ,  FIG. 24 ,  FIG. 25 ,  FIG. 26 , in implementations, the linear actuator as disclosed herein, including the linear actuator as disclosed herein with the inverse spool valve as disclosed, is included in a height-adjustable seatpost (“dropper post”) for a bicycle. More specifically, in an example, a dropper post is set forth as follows: 
     A. In an example, a dropper post comprises: a linear actuator, the linear actuator including: a fluid chamber; a piston chamber; and an inverse spool valve, the inverse spool valve including: a core, the core including at least one fluid channel having a piston chamber port and a fluid chamber port; and a sleeve, the sleeve extending around at least a portion of a periphery of the core and being movable between an open and a closed position, wherein when the sleeve is in the open position, a fluid path extends from the piston chamber, through the fluid channel, and into the fluid chamber; and when the sleeve is in the closed position, the piston chamber is sealed from the fluid chamber. 
     B. In an example of the dropper post of A, the inverse spool valve is configured such that fluid pressure acting on the inverse spool valve does not substantially bias the sleeve towards the open position or the closed position. 
     C. In an example of the dropper post of A, the inverse spool valve further comprises a biasing mechanism to bias the sleeve towards the open or closed position. 
     D. In an example of the dropper post of C, the biasing mechanism is a spring. 
     E. In an example of the dropper post of C, the biasing mechanism is configured to urge the sleeve towards the open or the closed position using fluid pressure. 
     F. In an example of the dropper post of A, the sleeve includes a sleeve extension, the sleeve extension comprising a first end and a second end disposed opposite the first end, the first end disposed within an outer body of the linear actuator and the second end configured to be disposed external to the outer body. 
     G. In an example of the dropper post of F, the inverse spool valve further comprises a first chamber seal, a second chamber seal, and an environment seal, the first and second chamber seals being disposed on opposing sides of the fluid chamber port of the fluid channel and the environment seal being disposed between the sleeve extension and a portion of the linear actuator. 
     H. In an example of the dropper post of G, the inverse spool valve further comprises a backup seal and, wherein, a separation volume is defined between the backup seal, the second chamber seal, the core, and the sleeve. 
     I. In an example of the dropper post of H, the inverse spool valve further comprises a spool valve port extending through the sleeve, the spool valve port fluidly coupling the separation volume to the fluid chamber. 
     J. In an example of the dropper post of F, the sleeve extension defines a cavity extending from the second end towards the first end, wherein the second end is an open end. 
     K. In an example of the dropper post of J, the sleeve includes a connector for receiving a control cable, the control cable being configured to exert a force on the connector and urge the sleeve toward the open or the closed position. 
     L. In an example of the dropper post of K, the connector and the sleeve are monolithic. 
     M. In an example of the dropper post of L, the dropper post further comprises the control cable, the control cable includes a head and the connector includes a pocket for receiving the head of the control cable, wherein the head of the control cable is retained in the pocket in response to a tension being applied to the control cable. 
     Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. 
     Telescopic Linear Actuator with Self-Bleeding Hydraulics (LA) 
     
       
         
           
               
               
             
               
                   
               
               
                 FIG. Callout 
                 Part/Feature 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Gas Charge Valve 
               
               
                 2 
                 Mount 
               
               
                 3 
                 Piston Rod 
               
               
                 4 
                 Body 
               
               
                 5 
                 Piston Rod Seal 
               
               
                 6 
                 Piston Rod Bushing 
               
               
                 7 
                 Piston 
               
               
                 8 
                 Piston Seal 
               
               
                 9 
                 Backer Ring 
               
               
                 10 
                 Valve Actuator 
               
               
                 11 
                 Funnel 
               
               
                 12 
                 Needle 
               
               
                 13 
                 First Fluid Port 
               
               
                 14 
                 Bleed Seal 
               
               
                 15 
                 Second Fluid Port 
               
               
                 16 
                 Third Fluid Port 
               
               
                 17 
                 Fourth Fluid Port 
               
               
                 18 
                 Gas Charge Port 
               
               
                 19 
                 Valve Spring 
               
               
                 20 
                 Valve 
               
               
                 21 
                 Gas Liquid Interface (Reservoir Volume) 
               
               
                 22 
                 Gas Bubbles 
               
               
                 23 
                 First Fluid Pathway 
               
               
                 24 
                 Second Fluid Pathway 
               
               
                 25 
                 Piston Cylinder 
               
               
                 26 
                 Reservoir Tube 
               
               
                 27 
                 Cylinder Cap 
               
               
                 28 
                 Lower End Cap 
               
               
                 29 
                 Cable Housing Mount 
               
               
                 30 
                 Receptacle 
               
               
                   
               
            
           
         
       
     
     Balanced, Direct-Pull, Inverse Spool Valve (SV) 
       
     
       
         
           
               
               
             
               
                   
               
               
                 FIG. Callout 
                 Part/Feature 
               
               
                   
               
             
            
               
                 SV1 (1)  
                 Valve Actuator 
               
               
                 SV2 (2)  
                 Valve Core 
               
               
                 SV3 (3)  
                 Housing Mount 
               
               
                 SV4 (4)  
                 Lower End Cap (valve body) 
               
               
                 SV5 (5)  
                 First Fluid Port 
               
               
                 SV6 (6)  
                 Second Fluid Port 
               
               
                 SV7 (7)  
                 Inward High-Pressure Seal 
               
               
                 SV8 (8)  
                 Outward High-Pressure Seal 
               
               
                 SV9 (9)  
                 Spring (return bias member) 
               
               
                 SV10 (10) 
                 Cable 
               
               
                 SV11 (11) 
                 Cable Head 
               
               
                 SV12 (12) 
                 Cable Housing 
               
               
                 SV13 (13) 
                 First Breathe Port 
               
               
                 SV14 (14) 
                 Second Breathe Port 
               
               
                 SV15 (15) 
                 Environment Seal 
               
               
                 SV16 (16) 
                 Low-Pressure Seal (backup seal) 
               
               
                 SV17 (17) 
                 Volume A 
               
               
                 SV18 (18) 
                 Volume B 
               
               
                 SV19 (19) 
                 Volume A Bias Force 
               
               
                 SV20 (20) 
                 Volume B Bias Force 
               
               
                 SV21 (21) 
                 Environment Bias Force 
               
               
                   
               
            
           
         
       
     
     Dropper Post, Embodiment 1 (DP1): Balanced Inverse Spool Valve, Lower Receptacle 
       
     
       
         
           
               
               
             
               
                   
               
               
                 FIG. Callout 
                 Part/Feature 
               
               
                   
               
             
            
               
                 100 
                 High Pressure Valve Seal 
               
               
                 101 
                 Actuator Rod Seal (Environmental Seal) 
               
               
                 102 
                 Housing Mount Seal 
               
               
                 103 
                 Reservoir Seal 
               
               
                 104 
                 Valve Actuator 
               
               
                 105 
                 Anti-Rotation Pins 
               
               
                 106 
                 Bleed Seal 
               
               
                 107 
                 Cylinder Cap 
               
               
                 108 
                 Funnel 
               
               
                 109 
                 Gas Charge Valve 
               
               
                 110 
                 Cable Housing Mount 
               
               
                 111 
                 Low Pressure Valve Seal (Backup Seal) 
               
               
                 112 
                 Lower Bushing 
               
               
                 113 
                 Lower End Cap 
               
               
                 114 
                 Lower Retaining Ring 
               
               
                 115 
                 Lower Tube 
               
               
                 116 
                 Needle Guide 
               
               
                 117 
                 Piston 
               
               
                 118 
                 Piston Backer Ring 
               
               
                 119 
                 Piston Cylinder 
               
               
                 120 
                 Piston Cylinder Seal 
               
               
                 121 
                 Piston Rod 
               
               
                 122 
                 Piston Rod Bushing 
               
               
                 123 
                 Piston Seal 
               
               
                 124 
                 Reservoir Tube 
               
               
                 125 
                 Saddle Clamp Post Clamp 
               
               
                 126 
                 Saddle Clamp Rail Clamp 
               
               
                 127 
                 Upper Bushing 
               
               
                 128 
                 Upper End Cap (Mount) 
               
               
                 129 
                 Upper End Cap Seal 
               
               
                 130 
                 Upper Retaining Ring 
               
               
                 131 
                 Upper Tube (Stanchion) 
               
               
                 132 
                 Valve Core 
               
               
                 133 
                 Valve Spring 
               
               
                 134 
                 Wiper 
               
               
                 135 
                 Piston Rod Seal 
               
               
                 136 
                 Saddle Clamp Screw 
               
               
                 137 
                 Needle 
               
               
                 138 
                 Receptacle 
               
               
                 139 
                 First Fluid Port 
               
               
                 140 
                 Second Fluid Port 
               
               
                 141 
                 Third Fluid Port 
               
               
                 142 
                 Fourth Fluid Port 
               
               
                 143 
                 Gas Charge Port 
               
               
                 144 
                 First Fluid Pathway 
               
               
                 145 
                 Second Fluid Pathway 
               
               
                 146 
                 First Breathe Port 
               
               
                 147 
                 Second Breathe Port 
               
               
                   
               
            
           
         
       
     
     Dropper Post, Embodiment 2 (DP2): Poppet Valve, Lower Receptacle 
       
     
       
         
           
               
               
             
               
                   
               
               
                 FIG. Callout 
                 Part/Feature 
               
               
                   
               
             
            
               
                 200 
                 High Pressure Valve Seal 
               
               
                 203 
                 Reservoir Seal 
               
               
                 204 
                 Valve Actuator (Poppet) 
               
               
                 205 
                 Anti-Rotation Pins 
               
               
                 206 
                 Bleed Seal 
               
               
                 207 
                 Cylinder Cap 
               
               
                 208 
                 Funnel 
               
               
                 209 
                 Gas Charge Valve 
               
               
                 211 
                 Low Pressure Valve Seal 
               
               
                 212 
                 Lower Bushing 
               
               
                 213 
                 Mount 
               
               
                 214 
                 Lower Retaining Ring 
               
               
                 215 
                 Lower Tube 
               
               
                 217 
                 Piston 
               
               
                 218 
                 Piston Backer Ring 
               
               
                 219 
                 Piston Cylinder 
               
               
                 220 
                 Piston Cylinder Seal 
               
               
                 221 
                 Piston Rod 
               
               
                 222 
                 Piston Rod Bushing 
               
               
                 223 
                 Piston Seal 
               
               
                 224 
                 Reservoir Tube 
               
               
                 225 
                 Saddle Clamp Post Clamp 
               
               
                 226 
                 Saddle Clamp Rail Clamp 
               
               
                 227 
                 Upper Bushing 
               
               
                 228 
                 Upper End Cap 
               
               
                 229 
                 Upper End Cap Seal 
               
               
                 230 
                 Upper Retaining Ring 
               
               
                 231 
                 Upper Tube (Stanchion) 
               
               
                 233 
                 Valve Spring 
               
               
                 234 
                 Wiper 
               
               
                 235 
                 Piston Rod Seal 
               
               
                 236 
                 Saddle Clamp Screw 
               
               
                 237 
                 Needle 
               
               
                 238 
                 Receptacle 
               
               
                 239 
                 First Fluid Port 
               
               
                 240 
                 Second Fluid Port 
               
               
                 241 
                 Third Fluid Port 
               
               
                 242 
                 Fourth Fluid Port 
               
               
                 243 
                 Gas Charge Port 
               
               
                 244 
                 First Fluid Pathway 
               
               
                 245 
                 Second Fluid Pathway 
               
               
                   
               
            
           
         
       
     
     Dropper Post, Embodiment 3 (DP3): Poppet Valve, Lower Receptacle 
       
     
       
         
           
               
               
             
               
                   
               
               
                 FIG. Callout 
                 Part/Feature 
               
               
                   
               
             
            
               
                 300 
                 High Pressure Valve Seal 
               
               
                 303 
                 Reservoir Seal 
               
               
                 304 
                 Valve Actuator (Poppet) 
               
               
                 305 
                 Anti-Rotation Pins 
               
               
                 306 
                 Bleed Seal 
               
               
                 307 
                 Cylinder Cap 
               
               
                 308 
                 Funnel 
               
               
                 309 
                 Gas Charge Valve 
               
               
                 310 
                 Cable Housing Mount 
               
               
                 311 
                 Low Pressure Valve Seal 
               
               
                 312 
                 Lower Bushing 
               
               
                 313 
                 Lower End Cap 
               
               
                 314 
                 Lower Retaining Ring 
               
               
                 315 
                 Lower Tube 
               
               
                 316 
                 Needle Guide 
               
               
                 317 
                 Piston 
               
               
                 318 
                 Piston Backer Ring 
               
               
                 319 
                 Piston Cylinder 
               
               
                 320 
                 Piston Cylinder Seal 
               
               
                 321 
                 Piston Rod 
               
               
                 322 
                 Piston Rod Bushing 
               
               
                 323 
                 Piston Seal 
               
               
                 324 
                 Reservoir Tube 
               
               
                 325 
                 Saddle Clamp Post Clamp 
               
               
                 326 
                 Saddle Clamp Rail Clamp 
               
               
                 327 
                 Upper Bushing 
               
               
                 328 
                 Upper End Cap (Mount) 
               
               
                 329 
                 Upper End Cap Seal 
               
               
                 330 
                 Upper Retaining Ring 
               
               
                 331 
                 Upper Tube (Stanchion) 
               
               
                 334 
                 Wiper 
               
               
                 335 
                 Piston Rod Seal 
               
               
                 336 
                 Saddle Clamp Screw 
               
               
                 337 
                 Needle 
               
               
                 338 
                 Receptacle 
               
               
                 339 
                 First Fluid Port 
               
               
                 340 
                 Second Fluid Port 
               
               
                 341 
                 Third Fluid Port 
               
               
                 342 
                 Fourth Fluid Port 
               
               
                 343 
                 Gas Charge Port 
               
               
                 344 
                 First Fluid Pathway 
               
               
                 345 
                 Second Fluid Pathway 
               
               
                   
               
            
           
         
       
     
     Dropper Post, Embodiment 4 (DP4): Poppet Valve, Upper Receptacle 
       
     
       
         
           
               
               
             
               
                   
               
               
                 FIG. Callout 
                 Part/Feature 
               
               
                   
               
             
            
               
                 400 
                 High Pressure Valve Seal 
               
               
                 402 
                 Housing Mount Seal 
               
               
                 403 
                 Reservoir Seal 
               
               
                 404 
                 Valve Actuator (Poppet) 
               
               
                 405 
                 Anti-Rotation Pins (not shown) 
               
               
                 406 
                 Bleed Seal 
               
               
                 407 
                 Cylinder Cap 
               
               
                 408 
                 Funnel 
               
               
                 409 
                 Gas Charge Valve 
               
               
                 410 
                 Cable Housing Mount 
               
               
                 411 
                 Low Pressure Valve Seal 
               
               
                 412 
                 Lower Bushing 
               
               
                 413 
                 Lower End Cap 
               
               
                 414 
                 Lower Retaining Ring 
               
               
                 415 
                 Lower Tube 
               
               
                 417 
                 Piston 
               
               
                 418 
                 Piston Backer Ring 
               
               
                 419 
                 Piston Cylinder 
               
               
                 420 
                 Piston Cylinder Seal 
               
               
                 421 
                 Piston Rod 
               
               
                 422 
                 Piston Rod Bushing 
               
               
                 423 
                 Piston Seal 
               
               
                 424 
                 Reservoir Tube 
               
               
                 425 
                 Saddle Clamp Post Clamp 
               
               
                 426 
                 Saddle Clamp Rail Clamp 
               
               
                 427 
                 Upper Bushing 
               
               
                 428 
                 Upper End Cap (Mount) 
               
               
                 429 
                 Upper End Cap Seal 
               
               
                 430 
                 Upper Retaining Ring 
               
               
                 431 
                 Upper Tube (Stanchion) 
               
               
                 432 
                 Valve Body 
               
               
                 433 
                 Valve Spring 
               
               
                 434 
                 Wiper 
               
               
                 435 
                 Piston Rod Seal 
               
               
                 436 
                 Saddle Clamp Screw 
               
               
                 437 
                 Needle 
               
               
                 438 
                 Receptacle 
               
               
                 439 
                 First Fluid Port 
               
               
                 440 
                 Second Fluid Port 
               
               
                 441 
                 Third Fluid Port 
               
               
                 442 
                 Fourth Fluid Port 
               
               
                 443 
                 Gas Charge Port 
               
               
                 444 
                 First Fluid Pathway 
               
               
                 445 
                 Second Fluid Pathway