Pump

Centrifugal pump is a multistage pump, containing a selected number (application dependent) of impellers equipped with vanes, inside a closely fitted diffuser,  located in series on an axial shaft, driven by the electric motor.

Centrifugal Pump is a machine that moves fluid by spinning it with a rotating impeller into a diffuser that has a central inlet and a tangential outlet.
The path of the fluid is an increasing spiral from the inlet at the center to the outlet tangent to the diffuser.
The impeller’s job is to transfer energy by rotation to the liquid passing through it, thus raising the kinetic energy.
The diffuser section then converts this energy to potential energy, raising the discharge pressure. From there, the rotation of the high-speed impeller throws the liquid into the diffuser.

There are two types of impellers that determine the amount of flow available for the specific design.
The difference between these two types of designs is described by the pump impeller vane angles and the size and shape of the internal flow passages : Axial (Mixed) Flow and Radial (Pancake) Flow.

A mixed flow impeller has vane angles at close to  45 degrees, and therefore, are usually found in pump ranges for higher flow rates.

A radial flow (pancake) impeller has vane angles at close to 90 degrees, and therefore, are usually found in pump ranges for lower flow rates.

Pump Construction :
There are two types of pump stage construction for ESP oil field applications:

1- Comprssion

2- Floater

In a compression pump, all the impellers are rigidly fixed to the shaft so that if an impeller wants to move up or down, it will take the shaft with it.The impeller is normally sitting down on its lower diffuser during assembly due to gravity.  Because of this, the pump shaft is "raised" with shims in the coupling so that the impeller is not allowed to touch the diffuser after final assembly.  This allows all thrust developed in the pump shaft to be transferred to the protector shaft directly.

Why use Compression Pumps?

• Some stages generate too much thrust to be handled by a thrust washer in the stage.
• Some fluids (e.g. liquid propane) do not have enough lubricity to properly lubricate a thrust washer.
• If abrasives or corrosives are present, it may be beneficial to handle the thrust in an area lubricated by motor oil rather than well fluid.
• Occasionally in very gassy wells, the flow volume changes so drastically within the pump that parts of a floater pump could be in very severe thrust while others are not so a compression pump could be one alternative.
• Since all the thrust is handled in the protector, as long as the protector has a great enough capacity, the pump operating range can be extended over a much wider area without any increased wear or reduced life.

Since a floating impeller is free to move up and down the shaft, the only thing to stop it is either the upper or lower diffuser.  "Thrust washers" are provided at all mating surfaces between the impeller and diffuser to absorb any thrust generated. 

We lose efficiency in the upthrust position because of the fluid's ability to recirculate from the high pressure to low pressure eye area.  In addition to loss in efficiency, this can promote erosion in the diffuser in abrasive fluids.

Why use floater pumps?

• Since each stage handles its own thrust, a very large number of stages can be put in a pump without having to worry about protector bearing capacity.
• Floaters are also very good with mild abrasives since they prevent material from getting into the radial bearing area.
• Floaters are much more forgiving in manufacturing since tolerance stack-up is not a concern.
• Easier field assembly - no shimming required.

Pumps come in several different configurations. Most pumps (especially the smaller diameter ones) come as "center tandems" (or -CT type).  

Other types are "upper tandems" (-UT), "lower tandems" (-LT) and "single" (-S) pumps.

The actual pump stages are no different regardless of what "type" it is. The difference in the pumps depends on what they look like at the ends.

Pump Nomenclature: 

Frequently Used Abbreviations :