What happens to a pump's pressure gauge if you disconnect a hose line

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SUMMARY

When a hoseline is disconnected from a pump, the pressure gauge reflects the static (deadhead) pressure of the pump rather than dropping to zero. In the discussed scenario, with the pump set at 800 kPa and experiencing a 100 kPa loss due to friction, the gauge would indicate the static pressure, which remains at 800 kPa. The removal of the hose line eliminates resistance, leading to an increase in water flow, but does not reduce the gauge reading to atmospheric pressure.

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David43214
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New user has been reminded not to try to use AI chatbots as references in the PF technical forums
TL;DR
Would the pressure go up or down?
Imagine a firetruck with a hoseline attached to the pump. The pump is set to 800kpa with 100kpa loss due to friction in the 30m hoseline so you have 700kpa at the nozzle.

What would the pump's gauge read if you disconnected the hoseline?

I thought since there is no more resistance, the pressure gauge would show a much lower reading, maybe 0 because the pump's outlet is now at atmospheric pressure.
However, ChatGPT was telling me the gauge jumps to the static (deadhead) pressure of the pump.
 
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David43214 said:
I thought since there is no more resistance, the pressure gauge would show a much lower reading, maybe 0 because the pump's outlet is now at atmospheric pressure.
I believe that you are correct: the gauge pressure would go down, while the waterflow would increase.
A chart for that particular pump should tell you what the manufacturer has recorded from the tests completed for different conditions.
 
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David43214 said:
However, ChatGPT was telling me the gauge jumps to the static (deadhead) pressure of the pump.
Please keep in mind that AI chatbots are not considered valid references in the technical PF forums. Thanks.
 
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Will the flow increase or decrease?
If the flow increases, does that mean the pressure falls?
Does it depend on the type of pump being used?
Does removal of the hose and nozzle restriction, connect the pump output with the gauge, directly to atmospheric pressure?
 
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