Ramamurthy Narasimhan
Harbison-Fischer, a ChampionX Business Unit
Rod pumps often fail due to gas and solid interference. When the system’s check valves are unable to displace these solids or gas it can cause failure and significant damage to the overall rod pump system, such as intense ball rattling, plugged cages, inefficient pump fillage, and fluid pounding.
Historically, the industry has dealt with these issues by utilizing stellite lined and insert guided cages with alterations for the ball’s clearance. However, these offerings have only provided a linear fluid path through the restricted valve areas. By changing this fluid flow path profile, check valves can improve the valve flow coefficient and more efficiently contains gas and solids in the fluid flow path. Additionally, by optimizing the flow design and creating a shorter ball travel length, Harbison-Fischer’s HFX cage reduces gas and solid interference by lowering the pressure drop during valve actuation, improving the overall run-time and pumping efficiency.
A rod pump’s performance depends on its ability to open and close valves during production operations regardless of the well’s conditions. The HFX cage delivers a higher lifting force that maximizes pump fillage and overall performance.
This white paper aims to define the variables and understand the factors affecting the coefficient of volume (Cv) of a check valve (cage) used in rod lift applications. This understanding will help to predict the pressure losses in different pumping well conditions and help optimize the system’s valve efficiencies. Four variables will be discussed in this paper to identify an improved rod pump cage design: 1) fluid force on a ball type check valve 2) net lifting force and coefficient of lift on ball 3) fluid tracing and untracing on a ball surface 4) changes in ball resistance through the cross-sectional area. These four variables will be explained with either a general engineering equation, a finite element analysis, or a laboratory model with defined test parameters. The finite element analysis is used when general engineering formulas are unable to meet the fluid flow conditions. Similarly, the finite element analysis has few limitations to replicate actual well conditions for this study. It is critical to understand these general engineering and test analyses to understand a check valve’s efficiency & loss.