Dynamic compression compensator for submersible pumps

Description

FIELD OF THE INVENTION

This invention relates to a variable compression methodology to aid in the prevention of diffuser spinning, overheating. and destruction of downhole submersible pumps.

BACKGROUND

In current designs, reference FIG. 1 submersible pumps are an assembly of diffusers 5 and impellers 3 contained within the pump housing 4, with a shall 2 powered by an external motor (not shown) to supply the rotational power for the impellers 3 which are keyed to the shaft 2. The impellers 3 provide the lift for the well fluids in order to move the fluids to the surface. The forces associated with the impeller 3 rotation and fluid lift will, at times, cause associated diffusers 5 to rotate inside the housing 4 when they should not. The diffuser 5 rotation generates considerable heat, and can cause housing 4 and/or adjacent stage failures.

To prevent the diffusers 5 from spinning due to the hydraulic reaction of the impellers 3, the diffuser stack, the common reference to all of the diffuser/impeller pairs in the pump, is pre-loaded against the housing 4. This is achieved by attempting to force an oversize diffuser stack into the pump housing.

The diffuser stack is made too long using a filler tube that is commonly called the compression tube 1 (also referenced as the compression ring). When the stack is captured in the housing 4, the housing 4 is placed in tension while the stack is compressed. The resulting normal force between diffusers 5 and the compression tube 1 is applied at the common interface point 6, and is enough to generate sufficient friction force to keep the diffusers 5 from spinning. The compression ring 1 is simply a tube of metal, where steel or stainless steel being typical materials used although others may be selected depending on well conditions expected to be encountered or other design considerations.

Typical problems that arise with this arrangement include the following:

• • compression ring 1 variability, ring cut too short—allows diffusers 5 to move and can lead to diffuser 5 spin, housing 4 overheating, and eventual destruction of the pump.
  • compression ring 1 variability, ring cut too long—places stress on diffuser 5 side walls which can lead to side wall collapse and eventual pump failure through reduced output or overheating.
  • compression ring 1 variability, ring cut too long—normal operation, but when internal pump parts are heated by normal operation, thermal expansion may create unusual pressures on the diffusers 5, again leading to side wall collapse and eventual pump failure through reduced output or overheating.

The variability in the length of the compression ring 1 can be attributed due to human error during measurements, human error during length calculations. human error during cutting of the ring itself, relaxation of the diffuser/impeller stack after the hydraulic pressure is removed, as well as other related assembly items that could affect the total assembly. Compound the possible human errors with normal expansion characteristics of the material being used and pump failure can occur.

SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention is the design and implementation of a variable compression device to relieve precise measurement errors during the assembly of downhole submersible pumps. The invention provides a flexible compression component, expanding to provide the necessary compression if the metallic compression tube is cut short, and compressing to provide the necessary compression if the metallic compression tube is cut too long. The invention allows for variable compression caused by normal operational heating of the impellers/diffusers stack within the submersible pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical submersible pump assembly configuration, with the current compression ring assembly method.

FIG. 2 is a typical submersible pump assembly configuration, with the variable compression ring added to the assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Given the problems noted in the current technology, some type of dynamic adjustment is needed to provide both constant pressure and pressure relief to the diffuser/impeller stack during pump operation.

Such a compensator would allow for compression tube 1 short cuts, providing the necessary expandability to adjust for the short cut, and compensate fur long cuts and thermal growth of other pump components with the ability to compress and maintain the pressure desired on the diffuser/impeller stack. Such an arrangement is illustrated in FIG. 2. In the preferred embodiment, the variable compression ring 7, 8 is a ring of hard rubber, plastic, or suitable material (AFLAS, etc.), with a hardness of durometer 90 (an approximate number), where the material 8 provides both compression and elastic properties to accommodate the variation in the compression ring 1 pressure. The new dynamic adjustment is provided structural support with a thin metal insert 7, primarily to provide stability and a metallic interface 6 to the diffuser/impeller stack.

During assembly, the compression ring 1 length is calculated taking into account the addition of the variable compression ring 7,8 which is compressed to approximately 60% of the unit width, thus providing some pre-loading to the stack. If, in the final assembly, the compression ring 1 is cut too short, the variable compression ring 7,8 will expand toward its original width, thus maintaining the required pressure on the diffuser/impeller stack. If the compression ring 1 is cut too long, the variable compression ring 7,8 would compress further, again adjusting to provide the pressure desired. During operation, the variable compression ring 7,8 would also allow thermal growth of the diffuser/impeller stack, thus preventing undue pressures being applied to the diffuser 3 sidewalls.