Understanding Forces and Accelerations with respect to pump systems

[skiboka33]

I am familiar with the idea of pump head and system pressure losses, pump curves etc.

However, a friend was asking about the relationship between static pressure, force and acceleration.

For example, if the pump supplies a certain pressure (P) at a given flow rate, is there not a force which corresponds to that pressure (similar to P=F/A). The problem is, that if there is a constant force being applied, that would imply a constant acceleration. In reality, most systems have a constant velocity.

I know the logic is wrong, but I am having trouble explaining why, or pinpointing the reason.

Thanks for your help! :thumbs:

 

[russ_watters]

In a closed system, why is a pump needed at all? What is the pump pushing against? Answer that and you'll have your answer.

 

[skiboka33]

Well if, say, the pump is used to pump water out of a lake or a well, would it need to overcome the 'force' of gravity?

I've always thought about it in terms of pressure head and making sure the available head is greater than the potential losses (frictional + elevation changes).

Basically I never really though about pumps/piping systems in terms of forces per se, and I'm having trouble explaining why.

 

[JBA]

The force of gravity is the water head between the pump elevation and the water discharge point. For example: For water, the head pressure is approximately 0.5 psi per ft of lift height; so, if the water discharge height is 50 ft above the pump then the static water back pressure acting upon the pump discharge will be 25 psig.

 

[Evo]

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