Problem of decreasing pump outlet pressure reading
Thread Content
The medium inside the pump is water, and the water temperature rises to around 80°C during operation. What could be the reason for the significant drop in the pressure at the pump’s outlet? Since the water level is higher than that of the pump, cavitation at the pump’s inlet should not be an issue.
The water temperature is already 80°C, and at this temperature the density of water decreases significantly (according to tables, the density at 80°C is 0.971)； At 25°C, it is 0.997); the pump’s outlet pressure = pump head * fluid density + pump inlet pressure (estimated formula), so the pump’s outlet pressure decreases. As long as the pump is fine, there’s no need to worry about it. If cavitation occurs in the pump, you can try cooling it by spraying coolant on the pump body.
Cavitation can also occur if the water tank is not much higher than the pump; for example, the deaerator tank must be at least 10 meters higher than the boiler feed pump in order to function properly
The normal boiling point of water is 100°. Although the water tank is at a higher level than the pump inlet, the pressure at the pump inlet may not reach atmospheric pressure; instead, it is under negative pressure, and the fluid has already begun to vaporize. So to cause the phenomenon you mentioned, try starting the pump by spraying cold water at its inlet.
This post was last edited by xlxuiin on 2016-3-25 09:20. What are the inlet and outlet pressures? Density changes as water temperature rises
Cavitation is more likely to occur at a water temperature of 80°C.
The focus should still be on identifying the causes related to cavitation; at 80 degrees Celsius, the net positive suction head required by the pump is much higher, and moreover, an inlet water level that is only slightly higher than that of the pump is definitely not sufficient.
Reasons for low pressure at the water pump outlet: 1. Low inlet pressure (low liquid level in the inlet tank, pressure drop)； 2. The inlet filter is clogged.