Abstract:
A switching valve which directs pressurized fluid through alternating pathways in the valve&#39;s body is provided, controlled by the cycling of a set of seals between positions, each position providing an alternate fluid pathway. The seals&#39; position during operation is constrained by having the force moving the seals overcome the force of a cam follower on a cam profile to keep the valve from stalling at an equilibrium point.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/545,483, filed Feb. 19, 2004, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a system for ensuring accurate stroke length of a spool in a differential pilot-operated switching valve in a closed well-head power system, independent of variations in differential pressures, and the avoidance of stalling the spool&#39;s movement at an equilibrium pressure at a particular point in the spool&#39;s travel.  
         [0003]     In particular, the present invention relates to the field of providing gas drive to mechanical devices such as pumps and injectors at well-heads, using pressurized gas in a pipeline system to power the mechanical device without flaring or venting “spent” gas.  
         [0004]     The present invention has particular application (but is not thereby limited) in the field of gas production in the oil and gas industry, where it is often useful to provide power to energize well production equipment without resorting to externally (or remotely) supplied energy sources such as electrical power, and without using produced gas in internal combustion or other power-generating engines where waste products, heat, and maintenance are issues. The gas used is recirculated to the production line; the system is in that way a closed system.  
       BACKGROUND OF THE INVENTION  
       [0005]     It is well known to provide for generation of mechanical power (such as powered reciprocal motion by reciprocating piston/cylinder/valve means or rotary motion by turbine, fan, or combined reciprocal piston/crank means) utilizing pressure differentials between produced well-head gas pressure and atmosphere; likewise between produced well-head gas pressures and sales line pressures. Engines in which power is derived from partially expanding pressurized fluid to drive an output shaft are generally preferred over internal combustion. See Patents U.S. Pat. No. 3,801,230, U.S. Pat. No. 4,369,373, U.S. Pat. No. 4,896,505, and U.S. Pat. No. 6,113,357, which each provide means of harnessing either fluid flow or differential pressure to provide mechanically available power for other purposes.  
         [0006]     The use of valves and pistons in combination with a fluid operated pressure-powered system is also known. See Patents U.S. Pat. No. 4,439,114 and U.S. Pat. No. 4,616,981, which describe the use of pistons in combination with valves and fluid pressure in a pumping system.  
         [0007]     It is also well known to provide for the injection of chemicals into a well bore to assist in the production of desired hydrocarbons or the protection of the well&#39;s equipment. See, for example, Patents U.S. Pat. No. 3,901,313 and U.S. Pat. No. 4,776,775. Of course, the injection of material into a well (which is typically at higher than atmospheric pressure) requires the use of mechanical or pressure-providing power sources.  
         [0008]     It is known in the art that such power sources may be provided by the use of pressure-differential between well-head produced gas pressures and atmosphere, with the spent gas (that is, once it is relieved to atmospheric pressures after powering the devices required) being released to atmosphere or flared. At current prices for hydrocarbons, in particular natural gases, and with current constraints on pollution of the atmosphere, these techniques are not ideally suited for today&#39;s use.  
         [0009]     Engines that derive power from partially expanding pressurized fluid to drive equipment are preferred over internal combustion engines because of the absence of the involvement of volatile combustible fluids and the resulting exhaust gas which gives rise to pollution and safety concerns.  
         [0010]     Several innovations have arisen due to those problems, such as the devices offered for sale and installation by ABI Oil Tools e-tronics Corp. under the trade name “Zero Emission Blair Air System”, which powers a traditional venting glycol pump replacement with a closed-loop system in a containment device, depending upon the differential between well-head pressures and sales line pressures, which may be very high pressures, and may be very different pressures, and may be pressurized gases including corrosive or dangerous substances the release of which at high pressures could be problematic.  
         [0011]     U.S. Pat. No. 6,694,858 describes a system for directing pressurized gas from a pipeline through a switching valve, to drive a power unit with a reciprocating piston. The power unit piston, in turn, operates a pump or other mechanical device to be powered. The switching valve may include a spool movable in linear fashion within a chamber. Two sets of cavities are formed continuous with the chamber, and the spool also includes sealing means to permit or prevent communication between chamber cavities depending on the position of the spool within the chamber. For example, when the switching valve&#39;s spool is moved to one extreme, high pressure pipeline gas will flow through the conduit formed between one set of communicating chamber cavities, and through to the power unit, driving the power unit&#39;s piston completely in one direction, while another pathway will be isolated by the sealing means for exhausting spent low pressure gas from the opposite side of the power unit&#39;s piston. When the piston has been maximally driven in one direction, pressure builds within the conduit such that a flow control valve is opened, allowing the high pressure gas to provide back pressure to the spool, driving it in the opposite direction. The spool will be driven into a position such that a conduit is formed between an alternate set of chamber cavities, allowing high pressure pipeline gas to flow through to the opposite side of the power unit, thereby driving the piston of the power unit in the opposite direction, with the gas on the previously driven side of the piston being exhausted through an alternate conduit now isolated by the spool sealing means.  
         [0012]     One potential shortcoming of the above system is the potential for stalling of the spool. During operation, due to the rapid reciprocation of the spool, and given that the gas volumes at either end of the spool act as closed systems, there will always be an abrupt drop in pressure of the higher pressure gas acting on one end of the spool and an abrupt increase in pressure of the lower pressure gas acting on the other end of the spool during spool travel. As the spool reciprocation moderates due to changing input and/or output conditions, the resultant pressure on the high pressure end of the piston and the resultant pressure on the low pressure side can come to an equilibrium of pressure, at which point the piston will stall. Therefore, the pressure at the two end chambers adjacent to the spool will tend to equalize with changing input and/or output conditions, resulting in a decreasing spool stroke length, leading to eventual stall of the spool. Due to the location of the seals along the spool, the decreased stroke length may eventually result in the spool reciprocating minimally between two positions in which neither conduit will be opened, resulting in temporary power failure due to the inability to permit gas flow past the valve. This can mean that when gas pressure differential elevates, the spool will not be re-motivated without manual intervention, and the stall will thus require well-head servicing to resume operation.  
         [0013]     It is therefore desirable to provide a source to energize equipment at the well-head in the form of reciprocating motion without venting or flaring exhaust gas, and with reduced risk of equipment stalling and power failure, even if temporary. The goal of achieving self-maintaining long-term operation is desired.  
       SUMMARY OF THE INVENTION  
       [0014]     It is an object of this invention to overcome the limitations in the prior art. The existing prior art inadequately addresses the need for a recirculating linear gas drive system that utilizes pressurized gas, a simple closed valve and a piston drive system to drive a mechanical device, such as a pump, eliminates the need to routinely flare or release “spent” gas to atmosphere, and is not susceptible to stalling over long periods of continuous use and changing operating conditions.  
         [0015]     The present invention has particular application (but is not thereby limited) in the field of gas production in the oil and gas industry, where it is often useful to provide power to energize well production equipment without resorting to externally (remotely) supplied energy sources such as electrical power, and without using produced gas in internal combustion or other power-generation engines where waste products, heat, and maintenance are issues. The use of pressurized gas with the present invention&#39;s features also assists in preventing the system from stalling and will cure difficulties overcoming the friction of the driver.  
         [0016]     These and other objects and advantages of the present invention are apparent in the following descriptions of the preferred embodiments of the present invention, which are not intended to limit in any way the scope or the claims of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:  
         [0018]      FIG. 1  is a schematic representation of the switching valve system of the present invention, shown driving a power unit;  
         [0019]      FIG. 2   a ,  2   b , and  2   c  are schematic representations of the switching valve with cam profiled detent spool and cam followers, showing the spool in various positions during reciprocation; and  
         [0020]      FIG. 3  is a schematic representation of the cam profile and cam follower, showing the relative relationships of each. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The preferred embodiment of the present invention includes high pressurized gas supplied from a pipeline well-head, pipe, a switching valve complete with manifold system for directing the gas flow and a power unit with piston. The switching valve includes a detent system in which the spool has a cam profile portion  10  for engaging a cam follower  11  to force a full extension of the spool in either direction, or in other words, to keep the spool out of a stalled position of pressure equilibrium. In conditions of low pressure differential (between the two sides of the spool), in which the spool would not be fully reciprocated, the detent system  10  and  11  will prevent spool movement until such time as there is sufficient pressure differential to overcome the cam profile and fully reciprocate the spool, rather than permitting the spool&#39;s seals to partially open both sides, or be caught within a segment of the spool&#39;s operating range when neither high pressure conduit is open to power the piston&#39;s reciprocation.  
         [0022]      FIG. 1, 2   a ,  2   b  and  2   c  illustrate a preferred embodiment of the present invention comprised of:  
         [0023]     A-switching valve  
         [0024]     B-flow control valve  
         [0025]     C-seals  
         [0026]      1 -higher pressure gas  
         [0027]      2 -power unit  
         [0028]      2   a -power unit piston  
         [0029]      3 -first piston end of spool  
         [0030]      4 -spool  
         [0031]      5 -lower pressure gas  
         [0032]      6 -second piston end of spool  
         [0033]      7 -valve housing  
         [0034]      8 -first end chamber  
         [0035]      9 -second end chamber  
         [0036]      10 -cam-profiled detent portion  
         [0037]      11 -cam follower  
         [0038]     In  FIG. 1 , the higher pressure or produced gas  1  is obtained from a high-pressure gas source, typically a conventional well-head with fittings and valves, and the like.  
         [0039]     The higher pressure or produced gas  1  flows through the switching valve A and is directed by the spool  4 , to one of the sides of the power unit piston  2   a  in the reciprocating power unit  2 .  
         [0040]     The higher pressure or produced gas  1  pushes the power unit piston  2   a  contained within the power unit  2 , transmitting the piston&#39;s powered stroke to a mechanical device requiring power.  
         [0041]     At the same time, spent lower pressure gas  5  on the opposite side of the power unit piston  2   a  and end chamber  8  is exhausted through the switching valve A to pipeline in a closed system.  
         [0042]     During approximately the same time, high-pressure gas  1  flows through the flow control valve B to provide drive-pressure to the spool  4 , to force the cam-profiled detent portion  10  of the spool  4  to overcome the force of the cam follower  11 , pushing the spool  4  toward one end position.  
         [0043]     The spool  4  moves linearly within the switching valve A, closing one flowpath and opening another, and thus reversing the flow of both spent lower pressure gas  5  and high pressure gas  1 .  
         [0044]     Once the flow direction is reversed, the process may be continuously repeated.  
         [0045]     In  FIG. 2   a , the cam follower  11  is engaged with the leftmost cam profile/camface of the detent portion  10 , causing the spool  4  to be in its most extreme right position. As the high-pressure gas  1  applies back pressure to the first piston end  3  of the spool  4 , the pressure of the detent portion  10  against the cam follower  11  will increase until the back pressure of the higher pressure gas  1  overcomes the pressure exerted by the cam follower  11 , causing the spool  4  to be driven leftward. Thus, the rightmost cam profile of the detent portion  10  will now be engaged with the cam follower  11 , as shown in  FIG. 2   b.    
         [0046]     The spool seals C are arranged such that when the cam follower  11  engages either cam profile of the detent potion  10 , a conduit or flowpath will be opened, enabling high pressure gas  1  to pass, and the switching valve A and associated equipment will not stall.  
         [0047]     The speed, power and time delays of the operation are controlled using adjustable flow control valve B and the stroke of the power unit piston  2   a  may be optimized by using variable length piston sleeves.  
         [0048]     Instead of a spool with pistons, the sealing device could be driven by diaphragms or similar pressure-differential driven systems with similar switching valve body and detent system.  
         [0049]     Testing was carried out to determine the preferred relationship between the cam profile  10  and the cam follower  11  release point. It was found that for typical field conditions of input pressure ranging from 12 psi to 5000 psi, with the range of pressure differential (between high pressure supply and pipeline pressure exhaust) being from 12 psi to 75 psi conditions used, the release point is 2/3×cos φ×r=a, where a is the distance from the cam edge as shown in  FIG. 3 . When used in conjunction with the known seal versus port overlap the required center flat b was determined. The same relationships were used to minimize the flat by varying follower size.  
         [0050]     The detent system is preferably made of tungsten carbide or ceramic, but could also be made of any other conventional or known material suitably inert, having suitable compressive strength, and having appropriate hardness at a wide range of temperatures. Further, the material should have a similar expansion coefficient to the surrounding pieces when press-fit together.  
         [0051]     In the foregoing description, the present invention has been described in its preferred embodiments. However, it will be evident that various modifications and changes may be made without departing from the broader scope and spirit of the present invention. Accordingly, the present specifications and embodiments are to be regarded as illustrative rather than restrictive.  
         [0052]     The descriptions here are meant to be exemplary and not limiting. It is to be understood that a reader skilled in the art will derive from this descriptive material the concepts of this Invention, and that there are a variety of other possible implementations; substitution of different specific components for those mentioned here will not be sufficient to differ from the present invention described where the substituted components are functionally equivalent.  
         [0053]     The above-described embodiments of the present invention are intended to be examples of the present invention. Alterations, modifications and variations may be effected the particular embodiments by those of skill in the art, without departing from the scope of the present invention which is defined solely by the claims appended hereto.