Non - contact measurement of outlet flow of reciprocating mud pump
Security Label,Void Pp Label,Pp Void Label,Silver Void Label SOONTOMAX (TAISHAN) LABEL MATERIAL CO.LTD , https://www.stmlabel.com
This paper introduces an indirect method for measuring the flow rate at the pump outlet by monitoring the number of strokes. The principle behind using a revolution sensor to determine the pump stroke is explained, along with the formula used to calculate the pump's outlet flow.
The drilling reciprocating mud pump, often referred to as the "heart" of the drilling process, plays a crucial role in circulating drilling fluid downhole to remove cuttings and power downhole tools. The outlet flow rate is a key parameter that directly impacts drilling efficiency and must be optimized during the drilling process. However, direct measurement of this flow is challenging due to the high pressure (typically 20–25 MPa) and the presence of sand-laden mud, which can lead to issues such as seal failure and clogging of traditional flow meters. As a result, direct measurement becomes complex and unreliable.
Based on the working principle of a reciprocating pump, the theoretical average flow rate (Q) can be calculated using the pump piston cross-sectional area (S), the piston stroke length (L), and the number of strokes per unit time (n). Since S and L are fixed structural parameters, measuring n allows for the accurate calculation of the pump’s outlet flow.
Key words: flow measurement, mud flow, reciprocating pump, indirect measurement
1. Stroke Number Measurement
Since the number of pump strokes is proportional to the speed of the drive shaft, it can be determined by measuring the shaft’s rotational speed. This method avoids the challenges associated with direct flow measurement.
1.1 Working Principle of the Speed Sensor
A Hall effect speed sensor is used to measure the rotational speed of the pump drive shaft. The sensor consists of two windings (A and B) placed perpendicularly, with Hall elements (Ha and Hb) positioned along their center lines. The rotor is a permanent magnet, and the Hall elements are excited by the respective windings. The output signal from the sensor is derived based on the magnetic field variations caused by the rotating rotor.
The Hall electromotive force generated in each element depends on the magnetic flux density, the position of the Hall elements, and the sensitivity of the material. By combining the outputs from both Hall elements, a signal proportional to the rotational speed is obtained.
1.2 On-Site Installation of the Speed Sensor
The speed sensor can be easily installed on the pulley or sprocket of the pump drive shaft. This installation method does not interfere with the normal operation of the pump and ensures reliable data collection.
2. Calculation of Pump Outlet Flow
Once the number of strokes (n) is measured, the theoretical average flow rate (Q) can be calculated based on the pump’s structure and operating mode. For a single-cylinder single-acting pump, the formula is:
Q = Sln (m³/min)
For multi-cylinder single-acting pumps, the formula becomes:
Q = MSln (m³/min)
In the case of multi-cylinder double-acting pumps, where each cylinder delivers liquid twice per stroke, the formula adjusts to:
Q = M(2S - S'')ln (m³/min)
However, in practice, the actual flow rate is often lower than the theoretical value due to factors like valve timing, gas content, and internal leakage. A correction factor (α) is typically applied, with α ranging between 0.85 and 0.95 depending on the pump’s condition.
3. Conclusion
This study presents a practical and efficient method for indirectly measuring the pump outlet flow by counting the number of strokes. This approach avoids the challenges of high-pressure environments and potential corrosion, making it easier to install, maintain, and use. While the method is effective under normal conditions, it may introduce errors when the pump’s fill level is low or inconsistent. Therefore, for high-precision applications, additional non-contact measurement techniques should be considered.