Performance Testing of Reciprocating (Piston) Water Pumps
From the testing of reciprocating water pumps, which is part of the Bachelor of Engineering curriculum at King Mongkut's University of Technology Thonburi (KMUTT).
VR and UMA Ruang Khao water pumps have been tested according to the reciprocating pump test procedures based on the JIS B standard (Japanese Industrial Standard), which is equivalent to the industrial standards in Thailand.
Abstract:
The performance testing of reciprocating water pumps was conducted by building a test rig and testing according to the industrial standard "Reciprocating pumps — Testing method" JIS B 8311-1991, in order to determine the characteristic curves of the reciprocating water pump. Testing was performed using a DC motor to drive the pump at speeds of 200, 250, 300, and 350 RPM. The following data was recorded: suction-side pressure, discharge-side pressure, water temperature during testing, motor rotational speed, and weight of water entering the weighing tank over a timed interval. Testing was repeated with the discharge valve gradually adjusted to obtain 8 total pressure values before changing the test speed.
From the test results, the water flow rate was found to be relatively constant at each speed and increased as the speed increased. The volumetric efficiency was found to be relatively constant at each speed and decreased slightly at higher speeds. The pump efficiency exhibited similar behavior at all speeds: at low total pressures, the pump efficiency increased rapidly, and as total pressure increased, the pump efficiency rose only slightly and approached a constant value. At 350 RPM, the maximum efficiency was achieved. From the mathematical model created at the suction pipe position, it was found that the pressure changed over time, with the average value being close to the actual measured value.
Discussion and Conclusions
Since reciprocating water pump testing involves torque that varies with the crankshaft angle position — a characteristic unique to reciprocating pumps — it was necessary to install a Flywheel in the test rig to store energy during excess periods and release it when needed. This results in smoother motor torque, enabling accurate torque measurement on the motor. The test results showed that the force readings from the Load Cell were relatively constant, indicating that the Flywheel was designed at an appropriate size for the application.
The Vacuum Gauge at the suction pipe showed some fluctuation but values could still be read. The pressure gauge at the discharge pipe showed greater fluctuation than the suction side, resulting from pressure pulsation similar to the suction side. Data collection for both suction and discharge pressure readings involved recording minimum and maximum values and then calculating the average before computing the Total Pressure.
Motor speed was measured using a Tachometer, which showed speed readings fluctuating within a narrow range. Data was collected by recording minimum and maximum values, then calculating the average.
The pressure wave calculations for the suction pipe showed that the pressure waves continuously oscillated up and down, similar to the test results measured from the Vacuum Gauge at −0.6 meters. Additionally, it was found that the pressure wave oscillation behavior at the specified speed (200 RPM) did not exhibit cavitation, as the predicted minimum pressure was −0.8 meters, which is above the vapor pressure (−0.96 meters).
Conclusions
At constant speed, the reciprocating pump provides a relatively constant flow rate as total pressure increases, and flow rate increases with pump speed.
Volumetric efficiency is constant at each speed and decreases as speed increases.
Pump efficiency increases rapidly as total pressure increases in the low-pressure range (approximately 0–15 meters of water) and gradually levels off at higher total pressures.
Shaft power increases as total pressure increases and also increases with higher speed.
Recommendations for future testing:
Install an Accumulator to enable more accurate pressure readings on the discharge side.
Increase the motor size used to drive the pump, enabling testing at higher pressures.
Install transparent pipes in both the suction and discharge lines to allow visual observation of water flow behavior inside the pipes.
Video Demonstration of Reciprocating Water Pump Testing