BACKGROUND This patent document relates generally to safety improvements in the function and operation of progressive cavity pumps. Such pumps have become widely used in many industries including the production of crude oil. These progressive cavity pumps are also well known in the oil industry as Moineau pumps, “screw pumps” and PC pumps. This patent document addresses what is known as an over speed backspin. Over speed backspins occur when the weight of a fluid column (oil, water and sand) above a pump causes the rotor, driveshaft and driveline components to accelerate in a reverse direction to dangerously high RPM. Excessive RPM can create numerous safety hazards, including flying debris if the surface drive equipment disintegrates and is damaged during excessive RPM. Flying debris has been known to damage motor vehicles, surface buildings and equipment, as well as cause severe injury to oil well operators and maintenance personnel. Additionally, the resulting damage to the pump and driveline often requires that the pump and tube string be extracted from the well for service and/or replacement. Over speed backspins can and do occur when the normal above ground braking mechanism fails or when a drive belt, cogwheel or pulley located on the surface drive fails, allowing the fluid column to reverse direction and accelerate downward, causing the remaining driveline to over speed backspin in a reverse rotation. Also, most backspin devices, for example those including a hinged flapper or sliding poppet, may only function reliably in a vertical orientation. Sand buildup and bridging of the intakes of progressive cavity oil pumps is a significant cause of production downtime and servicing. There is a need to effectively clear the intake of the pump of any sand bridging without extracting any of the pumping equipment from the oil well. Also, flushing of the annulus area outside of the tube string has previously required the use of flushing operations by special surface equipment. There is a need for downhole devices that attach below the pump intake that allow a controlled rate of backspin from gravity induced reverse flow, and that, by design, generate expanding vortices to clear the intake of sand bridging at the same time. Existing braking mechanisms in use on progressive cavity oil pumps are surface mounted devices and are usually associated with the drive unit. SUMMARY In view of the foregoing safety problems arising from over speed back spins it is an object to improve the safety of progressive cavity pumps. More particularly, it is an object to automatically control the backspin of any progressive cavity pump equipped with a safe backspin device the instant any reverse flow occurs. It is an object to provide a safe backspin device that requires no modification to current progressive cavity oil pumps, is extremely reliable yet simple and is easy to install. In an embodiment there is a safe backspin device in combination with a progressive cavity pump having an intake end and a discharge end. The safe backspin device has a body attached to the intake end of the progressive cavity pump, a bore within the body, and a valve seat within the bore. A valve member is movably housed in the bore. The valve member is movable, by fluid flow, away from the valve seat when fluid flow is in a normal flow direction and is movable, by fluid flow, into engagement with the valve seat when fluid flow is in a reverse flow direction. A bypass port in the body permits a restricted flow of fluid in the reverse flow direction past the valve member when the valve member is in engagement with the valve seat. In an embodiment there is a method for controlling the backspin of a progressive cavity pump having an intake end and a discharge end. The safe backspin device is attached to the intake end of the progressive cavity pump. The method comprises the steps of firstly, providing a check valve that permits a fluid flow to pass through the safe backspin device and the progressive cavity pump when the fluid flow is in a normal flow direction. Secondly, the check valve restricts the fluid flow passing through the safe backspin device and the progressive cavity pump when the fluid flow is reversed relative to the normal flow direction, while permitting a reduced fluid flow to pass through the safe backspin device and the progressive cavity pump when the fluid flow is reversed relative to the normal flow direction. In an embodiment there is a safe backspin device in combination with a progressive cavity pump having an intake end and a discharge end. The safe backspin device has a check valve attached to the intake end of the progressive cavity pump, in which the check valve is oriented to restrict flow when the flow is reversed. The flow is reversed when the flow is from the intake end of the progressive cavity pump and towards the check valve. The check valve is provided with bypass ports for allowing a reduced fluid flow when the direction of flow is reversed. These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which: FIG. 1 is an assembly view of an embodiment of a safe backspin device; FIG. 2 is a partial section view of an embodiment of the safe backspin device in a normal pumping mode; FIG. 2A is a partial section view of the safe backspin device in a normal pumping mode; FIG. 3 is a partial section view of the safe backspin device in a safe backspin/reverse flow mode; FIG. 3A is a partial section view of the safe backspin device in a safe backspin/reverse flow mode; FIG. 4 is a partial section view of the safe backspin device having a body with single threaded end and four helical internal bypass ports; FIG. 5 is a partial section view of the safe backspin device having a body with double threaded ends and four helical internal bypass ports; FIG. 6 is a partial section view of the safe backspin device having external bypass ports; FIG. 7 and FIG. 7A are partial section views of the safe backspin device having helical internal bypass ports and angled external bypass ports; FIG. 8 is a partial section view of the safe backspin device with one helical internal bypass port; FIG. 9 is a partial section view of the safe backspin device with one helical internal bypass port of a different size than in FIG. 8; FIGS. 10 and 10A are partial section views of the safe backspin device with two helical internal bypass ports; FIGS. 11 and 11A are partial section views of the safe backspin device with four helical internal bypass ports; FIGS. 12 and 12A are partial section views of the safe backspin device with eight helical internal bypass ports; FIG. 13 is a partial section view of the safe backspin device with helical internal bypass ports and a flapper; and FIGS. 14 and 14A are partial section views of the safe backspin device with helical flapper bypass ports and no retainer. DETAILED DESCRIPTION In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite article “a” before a claim feature does not exclude more than one of the feature being present. A safe backspin device 10 is shown in FIGS. 1 to 14A. As shown in FIG. 2, the safe backspin device 10 is used in combination with a progressive cavity pump 12. The progressive cavity pump 12, during normal operation, has an intake end 14 and a discharge end 16. The safe backspin device 10 has a body 18 attached to the intake end 14 of the progressive cavity pump 12. A bore 20 lies within the body 18 and a valve seat 22 lies within the bore 20. A valve member, for example ball 24 in the embodiments of FIGS. 1-12A, is movably housed in the bore 20 and the valve member is movable, by fluid flow, away from the valve seat 22 when fluid flow is in a normal flow direction. In FIG. 2A, the ball 24 is shown in an open position 28, in which the ball lies away from the valve seat 22. The valve member is movable, by fluid flow, into engagement with the valve seat 22 when fluid flow is in a reverse flow direction. In FIG. 3A, the ball 24 is shown in a closed position 26, in which the ball 24 is in engagement with the valve seat 22. At least one bypass port in the body 18 permits a restricted flow of fluid past the valve member when the valve member is in the closed position 26. For example, internal helical bypass ports 30 are shown in the embodiment of FIGS. 2A-5. The collection of the body 18, the valve seat 22 and the valve member together function as a check valve. In operation, the safe backspin device 10 as shown in FIG. 2 is attached to the intake end 14 of the progressive cavity pump 12. A female threaded collar 38 may be used to connect the intake end 14 of the progressive cavity pump 12 with the safe backspin device 10. The safe backspin device 10 acts as a check valve that permits a fluid flow to pass through the safe backspin device 10 and the progressive cavity pump 12 when the fluid flow is in a normal flow direction. The normal flow direction of the fluid flow is for fluid to flow into the intake end 14 and out of the discharge end 16 of the progressive cavity pump 12. The check valve restricts the fluid flow passing through the safe backspin device 10 and the progressive cavity pump 12 when the fluid flow is reversed relative to the normal flow direction. The check valve permits a reduced fluid flow to pass through the safe backspin device 10 and the progressive cavity pump 12 when the fluid flow is reversed relative to the normal flow direction. The bypass ports, being angled, curved, straight or helical bypass ports, are machined into the valve seat 22 of the body 18. When for any reason the fluid column is allowed to flow in a reverse direction to the normal flow direction the safe backspin device 10 restricts flow to the bypass ports. The bypass ports cause the oil/fluid column to generate vortices when in reverse flow/safe backspin mode. These vortices expand along an intake end 58 (FIG. 3A) of the bore 20 on the opposite side of the valve seat 22 from the progressive cavity pump 12 to effectively clear the intake end 58 (FIG. 3A) of any sand bridging. The intake end 58 (FIG. 3A) may be partially conical or tapered to allow expansion of the generated vortices. Generating vortices when in reverse flow/safe backspin mode reduces frequency of oil well maintenance and/or eliminates the need for flush by operations and or pump extractions. Additionally or alternatively, the reverse flow through the bypass ports may be directed toward an annulus area (not shown) between the safe backspin device 10 and an oil well casing, for example tube string (not shown), to cause expanding vortices and a swirling pattern in the annulus area to clear any sand bridging. The safe backspin device 10 is assembled by placing the ball 24 into the body 18 and threading the retainer 34 into the body 18 in the bore 20 opposite to the intake end 58 of the bore 20. The retainer 34 may be held in place by torque. In addition to the threading, the retainer 34 may be welded to the body 18 for extra security. Alternatively, the retainer 34 may be press fit and welded or shrink fit and welded to the body 18. Alternatively, a breech lug interface may be used. In the case of the embodiments shown in FIGS. 13, 14 and 14A with a flapper 32, the safe backspin device 10 is assembled by placing the flapper 32 into the valve seat 22 of the body 18 while aligning a hinge 54 with suitable holes in the body 18 and then subsequently inserting a hinge pin 56. When the safe backspin device 10 is installed into the progressive cavity pump 12 (FIG. 2) the hinge pin 56 is held by a female threaded body of the intake end 14 (FIG. 2) of the progressive cavity pump 12 (FIG. 2), or by the female threaded collar 38 (FIG. 2). The safe backspin device 10 as shown in FIG. 2 attaches to a progressive cavity pump 12 by the use of standard existing threads onto the intake end 14 of the progressive cavity pump 12. The safe backspin device 10 can be used as a tag bar (to gauge the rotor position) or can be attached below a standard tag bar 36 and/or tube anchor (not shown). The safe backspin device 10 may also have a tube anchor attached below it in some variations. The safe backspin device 10 does not stop the backspin, but redirects the path of fluid at the intake end 14 of the progressive cavity pump 12 and controls the rate at which the fluid can flow in the reverse flow direction in the tube string (not shown) and therefore prevents an over speed RPM from developing. This in effect provides safe and automatic back flushing of the pump tube any time a reverse flow is allowed to occur either intentionally, accidentally or by failure of the drive or surface brake. At the same time, this safe backspin device 10 allows unrestricted intake and production of oil when the progressive cavity pump 12 is operating in the normal operating direction. The progressive cavity pump 12 is shown in FIGS. 2 and 2A in normal pumping mode. As the progressive cavity pump 12 is drawing fluid through the safe backspin device 10, the ball 24 is raised above the valve seat 22 and internal helical bypass ports 30 by the flow of the fluid. During normal pumping mode the flow of fluid is pulled through the safe backspin device 10 in the normal flow direction as shown by the arrows in FIGS. 2 and 2A. A retainer 34 prevents the ball 24 from escaping from the body 18. During normal pumping mode the flow is unrestricted through the safe backspin device 10. The progressive cavity pump 12 and safe backspin device 10 are shown with fluid flow reversed from the normal flow direction in FIG. 3 and FIG. 3A. The ball 24 seats on the valve seat 22 to form one side of the internal helical bypass ports 30 through which fluid may flow. The other sides of the helical bypass port are formed by cutouts in the body 18. The internal helical bypass ports 30 permit a slow and safe let down of the fluid column and a slow, controlled and safe backspin results. In the embodiments shown in FIG. 4 and FIG. 5, each body 18 has four internal helical bypass ports 30. The internal helical bypass ports 30 are at an angle from the longitudinal centerline, or central axis, of the safe backspin device 10. In an embodiment for example, the internal helical ports may form an approximate 35 degree helix angle measured from the longitudinal centerline and may have a total combined cross-sectional area of approximately 0.25 inches squared. In different embodiments, the helix angle may range from 1 degree to 75 degrees. Pump flow rate capacities vary widely and as such the bypass port cross-sectional areas of some embodiments of the safe backspin device 10 may vary from approximately 0.09 inches squared to larger than 1.1 inches squared. The cross-sectional area of the bypass ports will determine the RPM backspin speed of a specific size and model of progressive cavity pump 12. FIG. 4 discloses an embodiment of this safe backspin device 10 that has only one external end threaded 40. This feature makes the safe backspin device 10 functionally impossible for operators to install backwards. FIG. 5 discloses an embodiment of this safe backspin device 10 that has both external ends threaded 42 in order to attach devices such as a tube anchor (not shown) below the safe backspin device 10. FIG. 6 discloses an embodiment that has external bypass ports 44 that force bypassing fluid to the outside of the pump tube string (not shown). This causes flushing of the annulus area outside of the tube string (not shown). FIGS. 7 and 7A show an embodiment of the safe backspin device 10 that has both internal helical bypass ports 30 and external bypass ports 44. This embodiment has the advantage of flushing both the intake end 58 of the bore 20, and the annulus area outside of body 18 and tube string at the same time. FIG. 7A showing the section D-D of FIG. 7 shows the external bypass ports 44 being offset at a radial angle not in line with the central axis of the safe backspin device 10. The external bypass ports 44, being offset at a radial angle, allow any bypassing fluids to cause a swirling and downward flow to assist clearing any sand buildup in the area. FIGS. 8 and 9 disclose embodiments of the safe backspin device 10 each with a single helical bypass port 46. The single helical bypass port 46 effectively takes the form of a single start thread that runs through the valve seat 22. FIG. 10 and FIG. 10A show an embodiment of the safe backspin device 10 with two helical internal bypass ports 48. FIG. 10A shows the section N-N of FIG. 10. FIG. 11 and FIG. 11A show an embodiment of the safe backspin device 10 with four helical internal bypass ports 30. FIG. 11A showing the section X-X of FIG. 11 also represents the cross-section of the same area of the embodiments shown in FIG. 4 and FIG. 5. The cross-section X-X is taken just above the internal helical bypass ports 30 looking away from the retainer 34 and toward the valve seat 22. FIG. 12 and FIG. 12A show an embodiment of the safe backspin device 10 with eight helical or angled bypass ports 50. FIG. 12A shows the section C-C of FIG. 12. FIG. 13 illustrates an embodiment of the safe backspin device 10 with a valve member in the form of a hinged flapper 32 in place of a ball 24 of the embodiments of FIGS. 3-12A. The design of the body 18 and bypass ports shown in the embodiments of FIGS. 1-12A will function with the flapper 32 by use of a cross-drilled hole and hinge pin 56 to provide a hinge 54 of the flapper 32. The flapper 32 as shown is a circular disc with a spherical segment of the same radius as the ball 24 in the embodiments of FIGS. 1-12A. As a result, the flapper 32 seats in the valve seat 22 as the ball 24 would in the embodiments of FIGS. 1-12A. Also, the retainer 34 may also be introduced in the embodiment of FIG. 13 to serve as a method to use the safe backspin device 10 as a tag bar without damage to the flapper 32. Also the retainer 34 provides a measure of safety for the flapper 32 in the event the safe backspin device 10 is used with a standard tag bar 36 above the safe backspin device 10. FIGS. 14 and 14A illustrate an embodiment of the safe backspin device 10 which feature a body 18 without ports. Bypass is achieved by helical or angled ports 52 on the periphery of the flapper 32. In this embodiment the flapper 32 has a spherical rounded segment to allow the flapper 32 to sit in a rounded valve seat 22. In the closed position 26 the fluid will bypass the flapper 32 and produce swirling, expanding vortices to help clear the intake end 58 of any sand bridging. FIGS. 13, 14 and 14A show a section view of this safe backspin device 10 with a flapper 32 in place of the ball 24 of FIGS. 1-12A. The flapper 32 can be used with any body 18, and any port design and configuration or combination illustrated but not necessarily limited to FIGS. 4 to 13. In different embodiments the body, for example having a single threaded end, a long body or a short body, or a double threaded body to accept a tube anchor or other devices below this device, may be configured with different bypass port designs. In different embodiments, any number of bypass ports, any bypass port helix angle, left hand or right hand, 0 degrees to 89 degrees, and any cross-section shape including, but not necessarily limited to, round or circular segments, internal splines and/or polygonal port shapes are possible. In some embodiments, the safe backspin device 10 having a check valve with a ball 24 allows for reliability in horizontal oil wells. Regardless of pump tube angular rotation, or angular elevation, the smooth radius and inclined shape of the inside of the body 18, together with the ball 24, allows the safe backspin device 10 to operate with reliability in any horizontal oil well. New oil wells can produce as much as 50% sand and 20% water. Older mature wells and new wells in some oil fields can produce virtually clean oil. As such the actual configuration and bypass design and cross-section of the safe backspin device 10 will vary considerably. In some embodiments, components of the safe backspin device 10 may be made from Stainless Steel, Titanium, Alloy Carbon Steel, Cast Iron, Cast Steel, Forged Steel or any other suitable materials or any combination of the above. In alternative embodiments, the ball may be out-of-round to permit fluid flow past the ball in the reverse flow direction when the ball is in engagement with the valve seat. For example, the ball may be potted, drilled or contain cutouts, or may not be perfectly circular. In alternative embodiments of the flapper, the flapper may have bypass ports drilled through the middle of the flapper. In some embodiments, there may be more or less than four bypass ports through the flapper, for example, one or two bypass ports may pass through the flapper. In alternative embodiments, the section of the body between the retainer and the valve seat may not be rounded, for example, the body may have a long taper from the retainer to the valve seat. Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims. |
