Simulation analysis of the effects of friction on the performance of pressure regulator for drip tape

Abstract

Pressure regulators (PRs) are critical equipment to ensure the safety and uniformity of irrigation systems, and their performance and stability are affected by the friction produced by the seal rings. This paper addresses the effects of friction on the performance of a drip tape inlet PR sealed by an O-ring. A dynamic numerical model considering the friction force was developed. The performance of the PR and characteristics of motion of the internal moving parts under different friction levels, inlet pressures, and flow conditions were calculated and analyzed. The results show that the simulated precision for outlet pressure is improved by considering the friction and depends on the magnitude of the friction force and working stages of the PR. Compared with a corresponding model where the friction is neglected, for friction levels of 2.5 N and 5 N, the normalized root mean square error (nRMSE) of the outlet pressure decreases by 3.8% and 6.9% in the transition stage and by 0.8% and 4% in the regulating stage, respectively. According to the response characteristics of the displacement curve of the regulating cup with respect to the variation in the regulation performance curve, the performance curve can be divided into three stages: the pressure raising stage, the transition stage and the regulating stage. Friction causes obvious outlet pressure fluctuations in the latter two stages by affecting the displacement increments of the moving parts, especially in the transition stage. Greater friction corresponds to greater fluctuations (expressed in terms of the variation coefficient of outlet pressure, CV) in the regulation performance curve, and the fluctuation amplitude increases with increasing flow rate. A PR with greater friction has a smaller applicable flow rate range to remain below a certain CV limit. When the friction is less than 7.5 N, the PR is suitable for a flow range of 400–1000 L/h. The rate of variation in the outlet pressure (δPout) increases as the friction increment and flow rate increase and the inlet pressure decreases. δPout can be greater than 20%, mainly in the transition stage and when the friction increment is greater than 7.5 N. Considering the changes in outlet pressure caused by the lubricant loss and O-ring aging during long-term use of PRs, regular inspection and maintenance are recommended for PRs installed downstream of a submain, especially ones with long drip tapes.