What caused the pump to stop?
Thread Content
In the heat transfer oil system, there is a flow control valve between the supply and return lines (which is now required by regulations). I’m encountering a problem at the moment: during debugging, the control valve is not open while the bypass is fully open; the system operates normally and the pump flow rate is normal. Once the control valve was set to automatic mode, the pump inlet began to make a buzzing sound, similar to that of cavitation; the pressure at the pump outlet dropped rapidly, and eventually the pump stopped delivering any flow. The flow sequence without considering external oil-using equipment is: pump outlet → control valve assembly → oil-gas separator → pump inlet. Theoretically, even if it is the control valve that causes gas to be generated, the oil-gas separator should separate out the gas phase, so that it does not reach the pump inlet. But if it’s not cavitation, what could be causing the automatic pump to stop as soon as it starts operating?
As a clarification, what was described just now isn’t quite correct; the pump didn’t stop working, but it failed to generate pressure.
Preliminary analysis indicates that the valve size was too large, resulting in a short circuit and oil flowing into the external piping
It would be clearer if a diagram could be drawn. Was the control valve bypass enabled during debugging? Where is the oil-gas separation tank located? Is it at the top of the system? The control valve is installed between the supply pipe and the return pipe; how does the oil coming out of the control valve flow directly into the oil-gas separation tank? It is likely that the air before and after the control valve has not been properly removed, or that solid particles from around the control valve have entered the pre-pump filter.
The oil inlet pipe of the pump is located above the pump; before starting the pump, open the inlet and outlet valves first to remove air from the pump chamber
The bypass pipe has a small control valve while the main pipe has a large one; when switching to the control valve, it’s as if the outlet is widened, and if the pump’s flow rate cannot keep up, the pressure at the outlet decreases.
The previous description of the process omitted the heat transfer oil furnace; during debugging, external oil-using equipment should be isolated. The process flow is: pump outlet → heat transfer oil furnace → control valve assembly → oil-gas separator → pump inlet. Additionally, here are answers to the questions that were unclear: 1. The pump inlet is at the lowest point in the system, while the oil-gas separator is at the higher point (below the expansion tank). 2. The pipeline containing the control valve has a diameter of DN80; the control valve itself also has a diameter of DN80. A shut-off valve is installed in the bypass line, which has a diameter of DN125. 3. When the control valve is not opened and operation proceeds entirely through the bypass, the pump runs normally, with no issues regarding flow rate or pressure. As soon as the gate valve in front of the control valve is opened, the pump outlet pressure drops rapidly.
Are there any issues with the liquid levels in the high and low tanks of the heat transfer oil system?
1) It’s also possible that the safety valve has been adjusted. Observe carefully. 2) What pump? 3) No pictures, no truth.
It is clearly a problem with the control valve assembly; first, check whether the gate valve’s core has fallen out, and second, verify the selection and calculation for the control valve.