Submersible well pumping system with an improved...

Wells – With eduction pump or plunger – Having liquid-gas separator

Reexamination Certificate

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C166S065100, C417S368000, C417S414000, C417S473000

Reexamination Certificate

active

06595280

ABSTRACT:

BACKGROUND
1. Technical Field
This invention relates generally to submersible well pumping systems. This invention relates particularly to a positive displacement pumping system enclosed in a housing and comprising a multi-chamber hydraulically driven diaphragm pump, with an improved hydraulically actuated switching mechanism.
2. Description of the Background Art
Hydraulically driven diaphragm pumps are positive displacement pumps which are nearly immune to the effects of sand in the pumped fluid because the pressure generating elements are isolated from the pumped fluid by a flexible diaphragm. In well pump applications, this type of pump is driven by a self contained, closed hydraulic system, activated by an electric or hydraulic motor where the pump, closed hydraulic system, and the motor are enclosed in a common housing and submerged in a well. There are many examples of this type of well pump in the patent literature, but currently none are in use as well pumps because of high cost and/or poor reliability. In well pump applications, the key design feature is the switching mechanism used to redirect or reverse the flow of working fluid from the fluid source, referred to as the auxiliary pump, to the working fluid sub-chambers. The reversal of the flow causes the pumped fluid to move into and out of-pumped fluid sub-chambers through check valves, accomplishing the pumping action.
U.S. Pat. No. 2,435,179 discloses a hydraulically driven diaphragm pump which uses a hydraulically actuated valve to reverse the flow of working fluid. The valve is driven by differential pressure between the fluid inside the working diaphragm (working fluid) and the fluid outside the working diaphragm (pumped fluid). Normally, no differential pressure exists between the two volumes. The pump creates the differential pressure required to reverse the pump by completely filling the diaphragm, causing it to stretch after it is completely full. The amount of pressure generated is limited by the strength of diaphragm material and has the disadvantage of creating diaphragm stress, which can lead to premature diaphragm failure. To maximize diaphragm life, this differential pressure must be limited to the lowest level possible.
The '179 patent uses two sets of diaphragms, one set to control the valve, and the other set to achieve pumping. The pumping diaphragms are located inside the pumping chambers, and the control diaphragms are located between the working fluid inside the pumping chambers and the pump outlet. The external surfaces of the working and control diaphragms are separated by an outlet check valve, creating the possibility that the external pressure would be higher on the control diaphragm due the presence of the checkvalve. If the inlet pressure is higher than the outlet pressure (a common occurrence in well pumps) the pump will not operate and could be damaged. This situation commonly occurs when the pump is installed in a standing fluid column, before fluid has a chance to equalize by flowing through the pump checkvalves. This arrangement also limits the usefulness of the pump by limiting it to use in conjunction with a large diameter liner rather then a more conventional, smaller diameter drop pipe.
A more significant problem occurs in low volume applications. The nature of the pump requires that the hydraulically actuated valve be driven by the same pressure source controlled by the valve, which causes the valve driving force to be released when the valve transverses an intermediate position between states. In low volume applications, this single valve can stop in an intermediate position before it has completely reversed the pump. This can cause the pump to either dither (rapid but incomplete movement of the working fluid in one direction), or go into a mode where half the flow is directed into each chamber or stops, which causes the pump to stop functioning.
Other problems will occur with the valve setup disclosed in the '179 patent. For example, the control diaphragm is acting directly on a tappet, leading to fluid accumulation between the diaphragm and the tappet, which in turn leads to diaphragm failure unless measures are taken to relieve the fluid. For these and other reasons, the pump described in the '179 patent has never been used in a practical application. This patent application addresses those shortcomings and describes a practical well pump with in improved control valve.
U.S. Pat. No. 2,961,966 discloses another method to reverse the flow of working fluid by reversing the direction of rotation of the electric motor driving the auxiliary pump. That patent discloses a method to sense the differential pressure between the working fluid and the pumped fluid to activate the electrical braking and reversal of the electric motor driving the auxiliary pump. That method also leads to diaphragm stress because differential pressure is required across the diaphragm to actuate the sensor. In addition motor reversal requires very complex electronics. Although theoretically possible, in practice the complexity of that method leads to high expense and unreliable operation due to the difficulty of controlling and reversing the electric motor in a downhole environment.
U.S. Pat. No. 6,017,198 discloses another method to reverse the flow of working fluid, namely the use of sensors and electronics to detect the fact that the diaphragm is full, and reverse the direction of flow by using an electrically actuated valve. This method works very well, but requires relatively complex electronics and a connection into the main power cable. Sealing electronics and power cables against high ambient pressure environments found in wells is expensive and can lead to premature failures of the pump due to high ambient pressure related electrical shorts.
Another unexpected problem can occur when pumping in certain environments, namely the accumulation of gas or the corrosion of the internal workings of the pump due to saturation of a corrosive gas through the diaphragm into the pump workings. Loss of working fluid and a related problem of working fluid contamination of the pumped fluid can also be problems, especially in water well applications where oil in the drinking water is not acceptable. This patent application describes two methods to address these problems increasing the applicability of the pump into more restrictive settings.
A pumping system, like the one disclosed herein, which combines the high reliability and ease of installation of a submersible centrifugal pump with the high efficiency in low flow-high pressure applications of a positive displacement pump constitutes a significant advancement in the state of the relevant art.
SUMMARY
The primary pumping system of the invention comprises an axially elongated housing having a diameter less than the bore hole of the well, a pump with a plurality of pumping chambers of fixed volume, each pumping chamber is further subdivided by a flexible diaphragm into two sub-chambers, a working fluid sub-chamber and a pumped fluid sub-chamber, typically made of rubber. Each pumped fluid sub-chamber is connected to the bore hole of the well through a check valve which allows well fluid to flow into the pumped fluid sub-chamber but prevents flow in the reverse direction. Likewise, each pumped fluid sub-chamber is connected through a check valve which allows the well fluid to flow out of the pumped fluid sub-chamber to the pump outlet but prevents flow in the reverse direction. Such an arrangement allows well fluid to flow through the pumped fluid subchambers, thereby moving the pumped fluid from the bore hole of the well to the pump outlet and eventually to the surface. The movement of well fluid into and out of the pumped fluid sub-chambers is caused by the insertion or withdrawal of working fluid into and out of the working fluid sub-chambers. The movement of working fluid is caused by a closed hydraulic system which forces working fluid into one or more working fluid sub-chambers while simultaneously withdrawing working fluid from one or more

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