Pump pressure/outlet pressure
Pump pressure/outlet pressure
(OP)
Dear All,
Small brain cramp today... This will seem obvious to many of you but it is not clear for me.
So, the components to determine the pump required pressure (for a given flow rate) is:
- static head
- friction (pipe & fitting)
- velocity head (ignored on my case)
But do I need to add the required pressure at the outlet of the discharge pipe? For instance, if this is a fire hydrant and that I want the water to flow at a pressure of say 5 barg, shall I add 5 barg to the pump pressure required by friction and head?
It seems logical but then I am afraid that the pump will only incease the flow rate to match its curve (for a pressure only equal to head + friction, without the 5 barg).
Hope I am clear enough (hard to explain clearly sompething while being confused). Thanks by advance, Vincent
Small brain cramp today... This will seem obvious to many of you but it is not clear for me.
So, the components to determine the pump required pressure (for a given flow rate) is:
- static head
- friction (pipe & fitting)
- velocity head (ignored on my case)
But do I need to add the required pressure at the outlet of the discharge pipe? For instance, if this is a fire hydrant and that I want the water to flow at a pressure of say 5 barg, shall I add 5 barg to the pump pressure required by friction and head?
It seems logical but then I am afraid that the pump will only incease the flow rate to match its curve (for a pressure only equal to head + friction, without the 5 barg).
Hope I am clear enough (hard to explain clearly sompething while being confused). Thanks by advance, Vincent





RE: Pump pressure/outlet pressure
RE: Pump pressure/outlet pressure
Thanks for this but by answering a question, you have raised another one... What do you mean by "something to create this pressure".Is this supposed to be the fitting at the outlet of the pipe? Does this mean that an open pipe alone is not suffcient to build-up the pressure?
Thanks again, vincent
RE: Pump pressure/outlet pressure
RE: Pump pressure/outlet pressure
RE: Pump pressure/outlet pressure
yes.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Pump pressure/outlet pressure
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Pump pressure/outlet pressure
So to sum it up, in a classic system, where a pump discharges a fluid at a given static head to a given flow rate, the pressure at the open end of the pipe (no fittings, restrictions, etc.) will be the atmospheric pressure.
In the case of a water monitor, the pump is sized for the required pressure given by the monitor supplier to reach the required dsitace but if one takes the monitor out and runs the system, the flow rate will be huge but the pressure at the monitor flange will still be atmospheric.
What about a tap in my house? What happens in the case where the static head is negative (ie the outlet is below the tank). If there is a pump on this system, will the head pressure be present at the outlet of an open pipe or will it still be atmospheric pressure?
Sorry for this (and any reading recommendations will be apprciated) even if it all takes shape in my head. Being a self learner is great but it has its drawback when things are confusing...
RE: Pump pressure/outlet pressure
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Pump pressure/outlet pressure
Regarding your example of the domestic tap with a pump and a negative static head - the answer was given by Artisi. You are likely to over-run the pump and burn it out.
Katmar Software - Uconeer 3.0
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Pump pressure/outlet pressure
RE: Pump pressure/outlet pressure
Thanks for this.
Katmar, I went through this post from you (at the bottom):
http://www.eng-tips.com/viewthread.cfm?qid=128047
It has clarified everything.
I have developped a small application for pump sizing/pipe losses (not as deep as the one on your website but same approach) and will, from now on, include the velocity head into my calculations.
So Total head:
- Static head
- Friction head
- Velocity head
And in the case where it is not an open pipe outlet (like on a fire system for instance, where the supplier requires "X" bar to be discharged into a fitting), then the residual head (of "X" bar) has to be added.
Thank you all for clarifying this. Have a nice day, Vincent