Patent Publication Number: US-2022228640-A1

Title: Stroke cushioning in piston and cylinder devices

Description:
FIELD 
     This application relates to piston and cylinder devices, more particularly to cushioning an end stroke movement of a piston and cylinder device. 
     BACKGROUND 
     It is common practice to utilize cushioning devices in a piston and cylinder device (e.g. a hydraulic cylinder, hydraulic jack and the like) to prevent high velocity contact of the piston and cylinder head. Such cushioning devices may utilize a cushion sleeve, which restricts the passage of fluid into an exit port. Such restriction causes back pressure on the piston, thereby slowing the piston at the end of the piston&#39;s stroke. However, such cushioning devices provide deceleration only until the piston has traveled to within a very short distance of the cylinder head and may not dissipate enough of the velocity of the piston before reaching the cylinder head 
     Attempts to improve the cushioning of the piston have been made in the art. For example, U.S. Pat. No. 3,964,370 describes a cushioning arrangement in which a rod spud is provided with steps to periodically reduce the diameter of the spud. However, such an arrangement does not provide an ideal cushioning, rather results in step-wise pressure changes during cushioning of the piston as the piston approaches the end of the stroke. 
     There remains a need for cushioning the end stroke of a piston and cylinder device in such a way to better control and complete deceleration of the piston at the very end of the stroke. 
     SUMMARY 
     In one aspect, there is provided a piston and cylinder device comprising: a barrel having a base end and a flange end opposite the base end; a base mounted on the base end of the barrel, the base comprising a base end hydraulic fluid port permitting flow of a hydraulic fluid into and out of the barrel from and to a hydraulic fluid circuit; a gland mounted on the flange end of the barrel, the gland comprising a gland end hydraulic fluid port permitting flow of the hydraulic fluid into and out of the barrel from and to the hydraulic fluid circuit; and, a piston assembly situated inside the barrel, the piston assembly comprising a piston mounted on a piston rod, the piston assembly moveable along a longitudinal axis of the barrel under hydraulic fluid pressure in the barrel to permit piston strokes between the base and the gland, wherein the piston rod comprises a rod spud, and the base comprises a base end cushion sleeve for receiving the rod spud as the piston assembly approaches an end of the piston stroke at the base, wherein the rod spud comprises a proximal end and a distal end, the proximal end situated closer to the piston than the distal end, wherein the rod spud comprises an external tapered portion having a taper length of at least 25% of a length of the rod spud such that the rod spud continuously and gradually narrows proximally to distally over the taper length and the base end cushion sleeve comprises a continuously and gradually narrowing internal tapered portion complementary to the external tapered portion of the rod spud, wherein the rod spud comprises an outer surface and the base end cushion sleeve comprises an inner surface, the outer surface of the rod spud and the inner surface of the base end cushion sleeve defining an annular orifice between an internal volume of the barrel and an interior of the base cushion sleeve, the annular orifice having a cross-sectional area that dynamically, continuously and gradually decreases as the external tapered portion of the rod spud moves through the internal tapered portion of the base end cushion sleeve to the end of the piston stroke at the base, the annular orifice having a length that dynamically, continuously and gradually increases as the external tapered portion of the rod spud moves through the external tapered portion of the base end cushion sleeve to the end of the piston stroke at the base. 
     In another aspect, there is provided a piston and cylinder device comprising a barrel and a piston assembly situated inside the barrel, the piston assembly comprising a piston mounted on a piston rod, the piston assembly moveable along a longitudinal axis of the barrel under hydraulic fluid pressure in the barrel to permit piston strokes in the barrel, the barrel fluidly connectable to a hydraulic fluid reservoir for supplying hydraulic fluid to the device, wherein the piston rod comprises a rod spud or a rod collar and an end of the barrel comprises a cushion sleeve for receiving the rod spud or rod collar as the piston assembly approaches an end the piston stroke at the end of the barrel, the cushion sleeve having an inner surface comprising a resiliently deformable material that is more deformable under load than a spud or collar material of which the rod spud or rod collar is comprised, whereby the resiliently deformable material is deformable to assist with alignment of the rod spud or rod collar in the cushion sleeve. 
     In another aspect, there is provided a piston and cylinder device comprising a barrel, a base mounted on a base end of the barrel and a gland mounted on a flange end of the barrel opposite the base end, and a piston assembly situated inside the barrel, the piston assembly comprising a piston mounted on a piston rod, the piston assembly moveable along a longitudinal axis of the barrel under hydraulic fluid pressure in the barrel to permit piston strokes in the barrel between the gland and the base, the barrel fluidly connectable to a hydraulic fluid reservoir for supplying hydraulic fluid to the device, wherein the piston rod comprises a rod collar, and the gland comprises a gland throat for receiving the rod collar as the piston assembly approaches an end of the piston stroke at the gland, wherein the rod collar comprises a proximal end and a distal end, the proximal end situated closer to the piston than the distal end, wherein the rod collar comprises an outer surface and the gland throat comprises an inner surface, the outer surface of the rod collar comprising at least one whistle notch situated at the distal end of the rod collar, whereby the outer surface of the rod collar and the inner surface of the gland throat substantially prevent the hydraulic fluid from flowing therebetween except at the at least one whistle notch when the rod collar moves through the gland throat, wherein the outer surface of the rod collar in the at least one whistle notch and the inner surface of the gland throat form a collar orifice therebetween, and the outer surface of the rod collar in the at least one whistle notch tapers longitudinally along the outer surface of the rod collar such that the collar orifice has a cross-sectional diameter that dynamically, continuously and gradually decreases as the rod collar moves through the gland throat to the end of the piston stroke at the gland. 
     In another aspect, there is provided a piston and cylinder device comprising a barrel, a base mounted on a base end of the barrel and a gland mounted on a gland end of the barrel opposite the base end, and a piston assembly situated inside the barrel, the piston assembly comprising a piston mounted on a piston rod, the piston assembly moveable along a longitudinal axis of the barrel under hydraulic fluid pressure in the barrel to permit piston strokes in the barrel between the gland and the base, the barrel fluidly connectable to a hydraulic fluid reservoir for supplying hydraulic fluid to the device through a base end hydraulic fluid port in the base and a gland end hydraulic fluid port in the gland, wherein the gland comprises a gland end relief valve connecting the gland end hydraulic fluid port to the barrel on a gland side of the piston as the piston moves toward an end of the piston stroke at the gland, wherein the gland end relief valve opens if the hydraulic fluid pressure at the flange end exceeds a flange end safety pressure limit to permit the hydraulic fluid to flow past the gland end relief valve into the gland end hydraulic fluid port to relieve the hydraulic fluid pressure at the flange end, and wherein the base comprises a base end check and relief valve connecting the base end hydraulic fluid port to the barrel on a base side of the piston as the piston moves toward an end of the piston stroke at the base, wherein the base end check and relief valve opens if the hydraulic fluid pressure at the base end exceeds a base end safety pressure limit to permit the hydraulic fluid to flow past the base end check and relief valve into the base end hydraulic fluid port to relieve the hydraulic fluid pressure at the base end. 
     In certain aspects of the present invention, at least one cushion sleeve is utilized to restrict passage of hydraulic fluid into a hydraulic fluid port at an end of the device as the piston approaches an end of the piston stroke at that end of the device. The cushion sleeve may be at one or both ends of the device. The restriction causes back pressure on the piston thereby slowing the piston as the piston approaches the end of the piston stroke. The restriction is provided by an outer surface region of the piston rod and an inner surface region of the cushion sleeve forming an orifice between an interior of the cushion sleeve and the internal volume of the barrel when the outer surface region of the piston rod first enters the cushion sleeve at the inner surface region. The orifice is narrowed in comparison to a diameter or cross-sectional area of the cushion sleeve, and even more narrowed in comparison to a diameter or cross-sectional area of the internal volume of the barrel. Hydraulic fluid flow from the internal volume of the barrel into the hydraulic fluid port is thereby restricted because the hydraulic fluid is only able to reach the hydraulic fluid port through the narrowed orifice, because the hydraulic fluid port is in fluid communication with the internal volume of the barrel through the cushion sleeve. 
     When the outer surface region of the piston rod first enters the cushion sleeve at the inner surface region, there is an abrupt increase in the hydraulic fluid back pressure between the piston and the end of the barrel toward which the piston is moving. To provide a substantially constant hydraulic fluid back pressure as the outer surface region of the piston rod moves through the cushion sleeve and to prevent or at least mitigate sudden piston acceleration at the very end of the piston stroke, the orifice formed between the outer surface region of the piston rod and the inner surface region of the cushion sleeve dynamically, continuously and gradually closes. To dynamically, continuously and gradually close, the orifice is designed to provide one or more of the following dynamic, continuous and gradual changes as the outer surface region of the piston rod moves through the inner surface region of the cushion sleeve:
         a dynamically, continuously and gradually decreasing cross-sectional area of the orifice, preferably dynamically, continuously and gradually decreasing quadratically;   a dynamically, continuously and gradually increasing length of the orifice;   a dynamically, continuously and gradually decreasing separation between the outer surface of the piston rod and the inner surface of the cushion sleeve; and,   a dynamically, continuously and gradually decreasing volume of hydraulic fluid in the orifice.       

     A parameter that changes dynamically, continuously and gradually is a parameter that does not retain the same value over time and does not exhibit a change in the rate of change over that time. The dynamic, continuous and gradual change creates a period of substantially constant hydraulic fluid back pressure from a time just after the abrupt pressure increase in back pressure when the outer surface region of the piston rod first enters the inner surface region of the cushion sleeve to a time just before the end of the stroke. At the end of the stroke, the hydraulic fluid back pressure abruptly decreases without abrupt piston acceleration, thereby preventing the piston from slamming against the end of the barrel. 
     The one or more dynamic, continuous and gradual changes may be accomplished by any one of a number of different embodiments, including providing the piston rod with a continuously and gradually tapered outer surface region, providing the cushion sleeve with a continuously and gradually tapered inner surface region, or providing the outer surface region of the piston rod and the inner surface region of the cushion sleeve with complementary continuous and gradual tapers. Both the flange end and the base end may utilize the same embodiment, or may utilize different embodiments to accomplish the one or more dynamic, continuous and gradual changes. 
     The orifice formed between the outer surface region of the piston rod and the inner surface region of the cushion sleeve is sized from when the outer surface region of the piston rod first enters the cushion sleeve at the inner surface region to the end of the stroke to provide sufficient back pressure of hydraulic fluid for a cushioning effect without preventing hydraulic fluid from moving through the orifice at all (at least until the end of the stroke) or increasing the back pressure beyond safety tolerances for the device. For example, the separation between the outer surface of the piston rod and the inner surface of the cushion sleeve from beginning to end may be set to provide a desired back pressure for cushioning, and the length of the inner surface of the cushion sleeve may be adjusted to dissipate more or less kinetic energy of the piston depending on the desired back pressure. Where a higher back pressure is desired, the separation between the outer surface of the piston rod and the inner surface of the cushion sleeve may be smaller while the length of the cushion sleeve may be longer. 
     In certain aspects of the present invention, at least a portion of the inner surface region of the cushion sleeve may comprise a resiliently deformable material that is more deformable under load than a material of which the outer surface of the piston rod is comprised. The resiliently deformable material is deformable to assist with alignment of the piston rod in the cushion sleeve. The resiliently deformable material also assists with ensuring that the size of the orifice remains its intended size despite a misalignment of the piston rod in the cushion sleeve, especially as the outer surface of the piston rod first enters the cushion sleeve at the inner surface region. In particularly preferred embodiments, the resiliently deformable material is bronze, especially SAE 660 bronze. 
     In certain aspects of the present invention, both the base and the gland may comprise relief valves that open and close fluid connections between the internal volume of the barrel and the respective base and gland end hydraulic ports. When the hydraulic fluid pressure at the base or flange end exceeds a respective safety pressure limit, the relief valve at that end opens to permit the hydraulic fluid to flow from the barrel past the relief valve into the hydraulic fluid port to relieve the hydraulic fluid pressure at that end. The relief valve at the base end may also be a check valve that can open to permit flow of hydraulic fluid from the base end hydraulic fluid port to a base end face of the piston to start an extension stroke after the piston rod assembly reaches the end of a retraction stroke at the base end. 
     Preferably, the piston and cylinder device is a hydraulic cylinder, hydraulic jack or the like. 
     Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  depicts a side cross-sectional view of a hydraulic cylinder in accordance with one embodiment of the invention; 
         FIG. 2A  depicts a magnified view of a side cross-sectional view of a cap end of the hydraulic cylinder of  FIG. 1  with a rod spud entering a base end cushion sleeve; 
         FIG. 2B  depicts the view of  FIG. 2A  with half of the rod spud having moved into the cushion sleeve; 
         FIG. 3  depicts a series of side-cross-sectional views of a base end of the hydraulic cylinder of  FIG. 1  as a piston rod assembly completes a retraction stroke, with a graph of hydraulic fluid back pressure (P) vs. time series (t) showing how the hydraulic fluid back pressure changes as the retraction stroke is completed; 
         FIG. 4A  depicts a side cross-sectional view of a gland of the hydraulic cylinder of  FIG. 1 , 
         FIG. 4B  depicts a side view of a rod collar for a rod for the hydraulic cylinder of  FIG. 1 ; 
         FIG. 4C  depicts a schematic drawing of a cross-sectional end view at a circular opening to a gland throat when the rod collar of  FIG. 4B  first enters the gland throat; 
         FIG. 4D  depicts a schematic drawing of the cross-sectional view of  FIG. 4C  after the rod collar has moved part of the way through the gland throat; 
         FIG. 5  depicts the gland of  FIG. 4A  rotated 90-degrees about a longitudinal axis through a center of the gland; 
         FIG. 6  depicts a perspective view of the rod collar of  FIG. 4B ; and, 
         FIG. 7  depicts an exploded side cross-sectional view of a gland end of the hydraulic cylinder of  FIG. 1  showing the gland separated from a flange end of a barrel of the hydraulic cylinder. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the Figures, a hydraulic cylinder  1  comprises a barrel  2  having a base end  20  and a flange end  50  opposite the base end  20 . The hydraulic cylinder  1  further comprises a base  21  mounted on the base end  20  of the barrel  2 , and a gland  51  mounted on the flange end  50  of the barrel  2 . The hydraulic cylinder  1  further comprises a piston assembly  80  situated in a cylindrical internal volume  3  of the barrel  2 . 
     The base  21  comprises a base end hydraulic fluid port  22  in fluid communication with the barrel  2  and an external hydraulic fluid circuit (not shown) permitting flow of a hydraulic fluid into and out of the barrel  2  from and to the hydraulic fluid circuit. The base end hydraulic fluid port  22  is located proximate an end of a spud receiver  24 . 
     The gland  51  comprises a gland end hydraulic fluid port  52  in fluid communication with barrel  2  and the external hydraulic fluid circuit permitting flow of a hydraulic fluid into and out of the barrel  2  from and to the hydraulic fluid circuit. 
     The piston assembly  80  comprises a piston  81  mounted around a cylindrical piston rod  82 , the piston assembly  80  moveable in the internal volume  3  along a longitudinal axis of the barrel  2  under hydraulic fluid pressure in the barrel  2  to permit piston strokes between the base  21  and the gland  51 . In operation, hydraulic fluid from the hydraulic fluid circuit enters the internal volume  3  of the barrel  2  through the base end hydraulic fluid port  22  at a base side of the piston  81  to push the piston  81  thereby extending the piston rod  82 . While the piston rod  82  extends, hydraulic fluid on a gland side of the piston  81  is pushed out the gland end hydraulic fluid port  52  into the hydraulic circuit. When the piston  81  reaches the end of an extension stroke, the flow of hydraulic fluid in the hydraulic circuit is reversed so that hydraulic fluid from the hydraulic fluid circuit enters the internal volume  3  of the barrel  2  through the gland end hydraulic fluid port  52  at a gland side of the piston  81  to push the piston  81  thereby retracting the piston rod  82 . While the piston rod  82  retracts, hydraulic fluid on the base side of the piston  81  is pushed out the base end hydraulic fluid port  22  into the hydraulic circuit. When the piston  81  reaches the end of a retraction stroke, the flow of hydraulic fluid in the hydraulic circuit is reversed thereby repeating the extension stroke. Seals around the piston  81  prevent hydraulic fluid from passing passed the piston  81  between the base side and gland side of the piston. In this manner, the hydraulic cylinder  1  can operate continuously in a cyclical manner. 
     To help cushion the ends of the retraction and extension strokes, the base  21  and gland  51  are provided with a base end cushion sleeve  23  and a gland throat  53 , respectively, and the piston rod  82  comprises a rod spud  83  and a rod collar  84 , which are received by the base end cushion sleeve  23  and gland throat  53 , respectively, as the piston rod  82  approaches the ends of the retraction and extension strokes, respectively. The gland throat  53  acts as a cushion sleeve in the gland  51 . In both the base and the gland, the formation of orifices between inner surface regions of the cushion sleeves  23 ,  53  and outer surface regions of the rod spud  83  and rod collar  84 , respectively, when the outer surface regions first meet the respective inner surface regions as the rod spud  83  and rod collar  84  move through the respective cushion sleeves  23 ,  53 , causes an abrupt increase in hydraulic fluid pressure, which slows the piston assembly  80  as the piston  81  nears the end of the stroke. 
     Details at a cap end of the hydraulic cylinder  1  are shown in  FIG. 2A ,  FIG. 2B  and  FIG. 3 . In  FIG. 2A , the rod spud  83  is shown having entered the base end cushion sleeve  23  as the piston assembly  80  approaches the end of the retraction stroke. In  FIG. 2B , half of the rod spud  83  has moved into the base end cushion sleeve  23  as the piston assembly  80  approaches the end of the retraction stroke. 
     The rod spud  83  comprises an outer surface  85  having an external tapered portion s 1  that narrows in diameter continuously and gradually from a location a 1  proximate the piston rod  82  to a location a 2  farther toward a chamfered end  86  of the rod spud  83 . The outer surface  85  of the rod spud  83  between the location a 2  and the chamfer at the end  86  is straight without any tapering. The outer surface  85  of the rod spud  83  between the location a 1  and the remainder of the piston rod  82  is also straight. The external tapered portion s 1  tapers at a very slight taper angle relative to a longitudinal axis of the rod spud  83 , the taper angle being less than 1°. The base end cushion sleeve  23  comprises an inner surface  26  having an internal tapered portion s 2  that narrows in diameter continuously and gradually from a location b 1  at a proximal end of the base end cushion sleeve  23  to a location b 1  at a distal end of the base end cushion sleeve  23 . The internal tapered portion s 2  tapers at the same taper angle as the taper angle of the external tapered portion s 1 . 
     As seen in  FIG. 2A , when the external tapered portion s 1  of the rod spud  83  first enters the internal tapered portion s 2  of the base end cushion sleeve  23 , an annular orifice  25  is formed. The annular orifice  25  is defined by the outer surface  85  of the rod spud  83  and the inner surface  26  of the base end cushion sleeve  23 . Total cross-sectional area of the annular orifice  25  is determined by subtracting cross-sectional area of the rod spud  83  from cross-sectional area of the base end cushion sleeve  23  at a given longitudinal location where the rod spud  83  is in the base end cushion sleeve  23 . Outside the base end cushion sleeve  23  in the internal volume  3 , total cross-sectional area of an annular gap in a hydraulic fluid-filled space  6  around the rod spud  83  is determined by subtracting cross-sectional area of the rod spud  83  from cross-sectional area of the internal volume  3  at a given longitudinal location where the rod spud  83  is in the hydraulic fluid-filled space  6 . The total cross-sectional area of the annular orifice  25  is about 1% of the total cross-sectional area of the annular gap when the external tapered portion s 1  of the rod spud  83  first enters the internal tapered portion s 2  of the base end cushion sleeve  23  ( FIG. 2A ). As the rod spud  83  moves through the base end cushion sleeve  23 , the distance between the external tapered portion s 1  and the internal tapered portion s 2  dynamically, continuously and gradually becomes smaller, therefore the total cross-section area of the annular orifice  25  dynamically, continuously and gradually decreases. The area of the annular orifice  25  dynamically, continuously and gradually decreasing quadratically causing a linear increase in resistance at a constant hydraulic fluid back pressure. At the same time, a length of the annular orifice  25  dynamically, continuously and gradually increases, as seen when  FIG. 2A  is compared to  FIG. 2B . In  FIG. 2B , the distance between the external tapered portion s 1  and the internal tapered portion s 2  at locations a 1  and a 2  are the same; therefore, the total cross-sectional area of the annular orifice  25  is the same at locations a 1  and a 2  despite the total cross-sectional area of the annular orifice  25  being smaller in  FIG. 2B  than in  FIG. 2A . Selection of the of orifice size permits tuning the hydraulic fluid back pressure for the particular type of device. For example, gradually decreasing the distance between the external tapered portion s 1  and the internal tapered portion s 2  from 0.010″ to 0.002″ is suitable for many hydraulic cylinder applications. 
     The base end cushion sleeve  23  comprises a bushing composed of a softer material (e.g. SAE 660 bronze) than the material of the rod spud  83 . The base end cushion sleeve  23  is seated in the spud receiver  24 , the spud receiver  24  being a cylindrical cavity in the base  21  having a smaller diameter than the internal volume  3  of the barrel  2  and a larger diameter than the rod spud  83 . The spud receiver  24  receives the rod spud  83  as the rod spud  83  reaches the end of the retraction stroke. The base end cushion sleeve  23  is immovably seated within the spud receiver  24  by threading and crimping. Because the base end cushion sleeve  23  is softer than the rod spud  83 , the base end cushion sleeve  23  is deformable under contact with the rod spud  83  to assist with alignment of the rod spud  83  in the base end cushion sleeve  23  when the rod spud  83  first enters the base end cushion sleeve  23 . Further, deformation of the base end cushion sleeve  23  assists with maintaining a constant annular orifice size as the rod spud  23  moves through the base end cushion sleeve  23 . 
     With reference to  FIG. 2A ,  FIG. 2B  and particular reference to  FIG. 3 , in operation, as the piston assembly  80  approaches the end of the retraction stroke, hydraulic fluid is forced out the base end hydraulic fluid port  22 , which is in fluid communication with the barrel  2  through the spud receiver  24 . At t 1 , before the external tapered portion s 1  of the rod spud  83  first enters the internal tapered portion s 2  of the base end cushion sleeve  23 , the hydraulic fluid back pressure P on the base-side of the piston  81  is relatively constant and relatively low because hydraulic fluid can flow freely through the spud receiver  24  to the base end hydraulic fluid port  22 . At t 2 , when the external tapered portion s 1  of the rod spud  83  first enters the internal tapered portion s 2  of the base end cushion sleeve  23 , the hydraulic fluid in the hydraulic fluid-filled space  6  around the rod spud  83  must now flow through the annular orifice  25  to get to the base end hydraulic fluid port  22 . Because the total cross-sectional area of the annular orifice  25  is about 1% of the total cross-sectional area of the annular gap in the hydraulic fluid-filled space  6  at t 2 , there is a spike in hydraulic fluid back pressure P on the base-side of the piston  81 . This spike in hydraulic fluid back pressure P causes the piston assembly  80  to decelerate. During deceleration, the rod spud  83  continues to move through the base end cushion sleeve  23 . At t 3 , half of the rod spud  83  has moved into the base end cushion sleeve  23 . At t 4 , the piston assembly  80  completes the retraction stroke. In the period from t 2  through t 3  to just before t 4 , the annular orifice  25  dynamically, continuously and gradually decreases in cross-sectional area, which equates to a continuous and gradual decrease in the amount of hydraulic fluid in the orifice and a dynamic, continuous and gradual decrease in the distance between the outer surface  85  of the external tapered portion s 1  of the rod spud  83  and the inner surface  26  of the internal tapered portion s 2  of the base end cushion sleeve  23 . The dynamic, continuous and gradual changes keep the hydraulic fluid back pressure P constant during the deceleration of the piston assembly  80  until the end of the retraction stroke at t 4  where the hydraulic fluid back pressure P abruptly drops as the piston assembly  80  stops. Further, there is no, or only an insignificant, spike in hydraulic fluid back pressure P when the piston assembly  80  reaches the end of the retraction stroke. 
     At t 4 , the end  86  of the rod spud  83  abuts or almost abuts the end of the spud receiver  24 , the annular orifice  25  is now too small for hydraulic fluid to flow through and the rod spud  83  blocks hydraulic fluid flow from the base end hydraulic fluid port  22  to the end  86  of the rod spud  83 . It is a particular advantage that the size of the annular orifice  25  can be closed entirely, with the bronze bushing of the base end cushion sleeve  23  deforming to provide a mechanical stop for the piston assembly  80 . In order to be able to start the extension stroke, the base  2  is provided with a base end check and relief valve  27  in a valve conduit  28  that fluidly connects the base end hydraulic fluid port  22  through the spud receiver  24  to the internal volume  3  of the barrel  2  on the base-side of the piston  81 . Hydraulic fluid flowing from the hydraulic circuit into the base end hydraulic fluid port  22  passes around a perimeter of the rod spud  83  into a first portion  28   a  of the valve conduit  28  with sufficient pressure to force the base end check and relief valve  27  open so that hydraulic fluid can flow through a second portion  28   b  of the valve conduit  28  into the internal volume  3  where the hydraulic fluid can exert pressure on the piston  81  to start the extension stroke. Once the extension stroke has started, the hydraulic fluid can flow to exert pressure on the end  86  of the rod spud  83 . 
     During the retraction stroke, hydraulic fluid flows from the internal volume  3  through the second portion  28   b  of the valve conduit  28  to close the base end check and relief valve  27  forcing the hydraulic fluid to flow only through the annular orifice  25  when the external tapered portion s 1  of the rod spud  83  first enters the internal tapered portion s 2  of the base end cushion sleeve  23 . If the hydraulic fluid back pressure P exceeds a pre-determined safety pressure limit during the retraction stroke, the base end check and relief valve  27  opens to permit hydraulic fluid to flow to the base end hydraulic fluid port  22  to relieve the pressure to protect the hydraulic cylinder  1  from damage and to protect any workers in the area. 
     Details at a gland end of the hydraulic cylinder  1  are shown in  FIG. 4A ,  FIG. 4B ,  FIG. 4C ,  FIG. 4D ,  FIG. 5 ,  FIG. 6  and  FIG. 7 .  FIG. 4A  together with  FIG. 4B  illustrate how the gland  51  ( FIG. 4A ) and the rod collar  84  ( FIG. 4B ) line up as the rod collar  84  approaches the gland  51  near the end of the extension stroke of the piston assembly  80 .  FIG. 4C  and  FIG. 4D  show how collar orifices  75  between the rod collar  84  and the gland throat  53  are formed and change as the rod collar  84  moves through the gland throat  53 .  FIG. 5  shows the gland  51  rotated 90-degrees about a longitudinal axis through a center of the gland  51  to show details not seen in  FIG. 4A .  FIG. 6  shows the rod collar  84  in perspective.  FIG. 7  shows how the gland  51  lines up with the barrel  2  of the hydraulic cylinder  1 . 
     The rod collar  84  is cylindrical having a cylindrical cavity  90  through which the piston rod  82  extends when the rod collar  84  is mounted on the piston rod  82  on the gland-side of the piston  81 , as seen in  FIG. 1 . The rod collar  84  has a chamfered distal face  91  facing the gland  51  and two whistle notches  92  inscribed in an outer surface  93  of the rod collar  84 . The unshown whistle notch is the same as the shown whistle notch, and is situated on an opposite side of the rod collar  84 , 180-degrees around the circumference of the cylinder of the rod collar  84 . While two whistle notches  92  are provided in this embodiment, the rod collar may have 1, 2, 3, 4 or more whistle notches. The use of more notches requires a narrower annulus between the outer surface of the rod collar and the inner surface of the gland throat. The whistle notches  92  are grooves in the outer surface  93  of the rod collar  84 , the grooves being wider and deeper at location a 3  proximate the distal face  91  than at location a 4  proximate a proximal end  94  of the rod collar  84 , the proximal end  94  being closer to the piston  81  when the rod collar  84  is mounted on the piston rod  82 . The whistle notch  92  continuously and gradually narrows and becomes shallower from a 3  to a 4  along a length s 3  of the whistle notch  92 . Therefore, the outer surface  93  of the rod collar  84  in the whistle notch  92  continuously and gradually tapers along the length s 3  of the whistle notch  92 . 
     The gland  51  comprises a block  55  that can be securely mounted on the flange end  50  of the barrel  2  (see  FIG. 7 ), for example by bolting. The gland further comprises the gland throat  53 , which forms a cavity  57  in the block  55 , the gland throat  53  having an inner surface  54  extending between a distal location b 3  to a proximal location b 4  over a length s 4 . The gland throat  53  has a circular opening  56  in a proximal face  59  of the block  55  oriented to receive the rod collar  84  as the piston assembly  80  approaches the end of the extension stroke. The inner surface  54  of the gland throat  53  comprises a first portion  54   a  proximate the opening  56  and a second portion  54   b  between the first portion  54   a  and a distal end  58  of the gland throat  53 . 
     During the extension stroke, and before the rod collar  84  reaches the gland throat  53 , the hydraulic fluid in the internal volume  3  of the barrel  2  is able to pass through the full area of the circular opening  56  to be forced out of the hydraulic cylinder  1  through the gland end hydraulic fluid port  52  into the external hydraulic fluid circuit. As seen in  FIG. 4C , when the rod collar  84  first enters the gland throat  53  at the circular opening  56 , the clearance between the outer surface  93  of the rod collar  84  and the inner surface  54  of the gland throat  53  is sufficiently large to permit the rod collar  84  to move through the gland throat  53  and sufficiently small that the outer surface  93  of the rod collar  84  and the inner surface  54  of the gland throat  53  substantially prevent the hydraulic fluid in the internal volume  3  of the barrel  2  around the rod collar  84  from flowing therebetween except at the whistle notches  92  in the rod collar  84 . The outer surface  93  of the rod collar  84  in the whistle notches  92  and the inner surface  54  of the gland throat  53  at the circular opening  56  form collar orifices  75  through which the flow of hydraulic is restricted. As a result, there is an initial abrupt spike in hydraulic fluid back pressure on the gland-side of the piston  81  when the rod collar  84  first enters the gland throat  53 . This spike in hydraulic fluid back pressure causes the piston assembly  80  to decelerate. 
     During deceleration, the rod collar  84  continues to move through the gland throat  53 . The inner surface  54  of the gland throat  53  may be straight or tapered away from a central longitudinal axis of the gland  51  (i.e. a reverse taper in comparison to the taper of the whistle notches  92 ). In both situations, as the rod collar  84  continues to move through the gland throat  53 , the collar orifices  75  do not increase in length and remain line orifices at the circular opening  56 , the collar orifices  75  bounded by the inner surface  54  of the gland throat  53  at the circular opening  56  and the outer surfaces  93  of the rod collar  84  in the whistle notches  92  somewhere between locations a 3  and a 4  depending on how far the rod collar  84  has moved through the gland throat  53 . 
     As seen in  FIG. 4D , though the collar orifices  75  do not change in length, because the whistle notches  92  are tapered to continuously and gradually narrow and become shallower from location a 3  to location a 4 , the widths and the cross-sectional areas of the collar orifices  75  dynamically, continuously and gradually decrease, which equates to a continuous and gradual decrease in the amount of hydraulic fluid passing through the collar orifices  75  and a dynamic, continuous and gradual decrease in the distances between the outer surface  93  of the rod collar  84  in the whistle notches  92  and the inner surface  54  of the gland throat  53  at the circular opening  56 . Thus, the outer surface  93  of the rod collar  84  in the whistle notches  92  tapers longitudinally along the rod collar  84  such that the collar orifices  75  have a cross-sectional diameter that dynamically, continuously and gradually decreases as the rod collar  84  moves through the gland throat  53  to the end of the extension stroke in the gland  51 . The dynamic, continuous and gradual changes keep the hydraulic fluid back pressure constant during the deceleration of the piston assembly  80  until the end of the extension stroke at the distal end  58  of the gland throat  53 , where the hydraulic fluid back pressure abruptly drops as the piston assembly  80  stops. Further, there is no, or only an insignificant, spike in hydraulic fluid back pressure when the piston assembly  80  reaches the end of the extension stroke. 
     The gland  51  of the hydraulic cylinder  1  is capable of handling about 15,000 psi of pressure. Because the whistle notches  92  dramatically increase the hydraulic fluid pressure around the rod collar  84  in the barrel  2  at the flange end  50  as the piston assembly  80  approaches the end of the extension stroke, certain measures may be taken to ensure that the gland  51  is not damaged during the extension stroke. 
     With reference to  FIG. 5 , the gland  51  may be machined to include a gland end relief valve  60  in fluid communication through a first conduit  61  with the internal volume  3  of the barrel  2  at the flange end  50  of the barrel  2  even when the rod collar  84  is in the gland throat  53 . The gland end relief valve  60  is also in fluid communication with the gland end hydraulic fluid port  52  through a second conduit  62 . The gland end relief valve  60  prevents hydraulic fluid from flowing from the barrel  2  into the gland end hydraulic fluid port  52  except via the collar orifices  75  while the piston assembly  80  approaches the end of the extension stroke and the rod collar  84  is in the gland throat  53 . The gland end relief valve  60  opens if the hydraulic fluid pressure at the flange end  50  of the barrel  2  exceeds a flange end safety pressure limit to permit the hydraulic fluid to flow past the gland end relief valve  60  into the gland end hydraulic fluid port  52  to relieve the hydraulic fluid pressure at the flange end  50 . 
     With reference to  FIG. 7 , the gland  51  is mounted on the flange end  50  of the barrel  3  by fitting a nose  65  of the gland  51  into a complementary gland seat  7  of the barrel  2 . Once seated, the gland  51  is bolted to the gland seat  7  through a plurality of bolt holes  66  (only one shown) in a flange  69  of the gland  51 . An o-ring  67  and a back-up o-ring  68  mounted around the nose  65  provide a fluid seal between an outer surface of the nose  65  of the gland  51  and an inner surface of the gland seat  7  of the barrel  2 . The dramatic increase in hydraulic fluid pressure at the flange end  50  of the barrel  2  as the piston assembly  80  approaches the end of the extension stroke may cause the o-rings  67 , 68  to blow out due to expansion of the barrel  2  creating a gap between the gland seat  7  and the nose  65 . To prevent the o-rings  67 , 68  from blowing out under the increased pressure, the outer surface of the nose  65  may be tapered to pre-load an outward load on the inner surface of the gland seat  7  at the flange end  50  of the barrel  2  when the gland  51  is bolted to the barrel  2 . Therefore, when the hydraulic fluid pressure in the internal volume  3  of the barrel  2  spikes at the flange end  50  as the rod collar  84  enters the gland throat  53 , the increase in pressure does not cause the barrel  2  to expand, thereby avoiding the creation of a gap between the gland seat  7  and the nose  65 . 
     The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.