Backpressure issue
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If the pump stops operating, is the inlet pressure high or the outlet pressure high? Why is that? What happens if there is a certain level of liquid at the inlet? I hope everyone can help me understand this
I’d like to share my personal opinion: when stopping the pump, the inlet pressure should be higher than the outlet pressure. The outlet pressure is reduced due to the pressure losses within the pump itself, so it’s lower. At the same pressure, if there is a certain liquid level at the inlet, then the combined effect of the liquid’s own weight and the external pressure should result in a higher total pressure. Check below~~~~~~~~:lol
I thought the same thing today, but it’s because someone said that the pressure at the outlet is higher than that at the inlet? I don’t know how to respond. Logically, this should be the case after the pump stops, but I’m not sure if what others are considering is the pressure caused by the liquid level height after the outlet
It mainly depends on whether it is a high-pressure area or normal pressure after the pump. If it is normal pressure, then there is no distinction between high and low pressure since the fluid does not flow. If it is a high-pressure area, backflow is possible, and definitely the outlet pressure will be higher than the inlet pressure. If the pump stops and there is a certain level of liquid at the inlet, it can be said that the liquid at the inlet has a certain amount of static pressure energy, but this is relative to the pump itself; in other words, as long as the fluid does not flow, it only exerts static pressure energy on the pump itself and has no effect on what lies downstream
After the pump is stopped, in most cases the outlet pressure is higher than the inlet pressure, as the pressure in the container or pipeline at the pump’s outlet is much higher than that at the inlet; otherwise, the flow would occur due to natural pressure alone, and no pump would be necessary； After the pump is stopped, the pump outlet is connected to the back pressure; the pressure at the pump outlet is therefore the pressure of the back pressure system, which is higher than the inlet pressure.
Pumps are used for increasing pressure; theoretically, when one pump stops operating, the backup pump takes over, and the fluid will flow in reverse direction, so the outlet pressure is definitely higher than the inlet pressure. In other words, even in the absence of a backup pump, or if the backup pump is not operating, the pressure downstream in the process is generally higher than the inlet pressure; therefore, the outlet pressure is also higher than the inlet pressure.
If the pump stops operating, is the inlet pressure higher or the outlet pressure higher? Why is that? What happens if there is a certain level of liquid at the inlet? In principle, they are the same height, as they are connected to each other. The pump has stopped operating. If the outlet valve is not closed, the system does not come to a halt; the inlet pressure is slightly lower than the outlet pressure, as there is pressure in the system that is higher than the inlet pressure. If the outlet valve is closed, the inlet pressure is slightly lower than the outlet pressure; since there is a certain height of liquid at the inlet, the hydrostatic pressure helps to keep the outlet pressure higher than the inlet pressure.
It depends on the specific conditions at the outlet. If the fluid is being sent to a high-pressure area and the system is relatively sealed, then when the pump stops, the pressure at the outlet remains high. That’s why a check valve is usually installed at the pump outlet; even if there is a certain level of liquid at the inlet, the resulting pressure should not be higher than the pressure in the outlet system. Otherwise, the purpose of having a pump would be diminished. If the sealing is not good enough and the inlet and outlet are connected, then even if the pressure at the outlet is high right after the pump stops, it will eventually become the same as the pressure elsewhere. There’s one thing I don’t understand: why did the original poster ask this question? Last edited by FloatHead on 2009-3-9 17:18]
I still agree with what was said upstairs; the check valve provides a very good explanation for this phenomenon, and it is related to the liquid level in the feed tank at the pump inlet as well as the pressure of the fluid at the pump outlet； Under normal circumstances, the pressure at the pump outlet is high (especially in cases where there is a mixture of oil and gas). It should be noted that the question raised by the original poster has practical significance: for example, in the event of a pump shutdown, to prevent the gases exiting the pump from flowing back, it is necessary to close both the check valve connected to the pump and the valve at the pump outlet ；
A check valve is installed on the pump outlet pipeline to prevent the liquid from flowing back into the pump and to avoid the pump from reversing direction. There are two types of check valves: one is the lift-type check valve, suitable for horizontal installation on pipelines, and the other is the swing-type check valve, which can be installed on pipelines that are horizontal, vertical, or inclined. If installed on a vertical pipeline, the flow direction of the medium should be from bottom to top.
Who can explain what the pump pressure on the following pump is? What is backpressure? Is the “pressure” by which we say a pump increases the pressure of a fluid the same as the fluid’s “static pressure energy”? :funk:
In a refining unit, the inlet pressure is high, and check valves are present at the outlets to prevent the fluid from flowing back. If the pump stops, then there is no outlet pressure anymore.
This issue depends on the circumstances; for example, in the case of loading at a tank farm, the inlet pressure is higher than the outlet pressure after the pump is stopped
Each issue should be analyzed on a case-by-case basis; different operating conditions result in different phenomena, and the fellow upstairs has basically listed several such situations.