residual head on pump-system curve

[mechanicaldup]

Hi every one!
Could some one perhaps explain to me how to indicate the residual head at the pipe exit (for example fire hydrants) on the system curve. As far as I understand it the system curve stop at the end of the pipe. Your advice would be appreciated.

have a nice day

 

[TD2K]

I would calculate the head produced by my firewater pumps for the flow in question using their pump curve (or curves if you have more than one pump operating in parallel). Then calculate the line losses from the pump to the hydrant which will depend on the line ID, the length and number of fittings and subtract this from the pump discharge pressure.

The pressure you get (which I think you call residual pressure) is what is available at the hydrant.

 

[rzrbk]

To show this on a system curve, I believe you would add the desired residual pressure to the friction curve, similar to the way you would treat static head.

The raised curve would show the 'residual pressure' when flow was zero. This would give the pump head required at any given flow to provide the desired residual pressure at the hydrant.

 

[BRIS]

The response from rzrbk gives you the stadard solution - treat the required hydrant pressure as a static head.

Usually you are looking to meet a specified flow and pressure at the hydrant(s) and this is your boundary condition. other points on the system curve are derived from additional flows from other uncontrolled system demands and it is necessary to include maximum and minimum anticipated flows to draw a system envelope.

There is no reason to stop your system curve at the hydrant. If you really require a "comprehensive" solution including losses through the hydrant and connected downstream pipework system then you can continue the system curve through to the point of downstream control - i.e to the downstream boundary where there is a defined relationship between pressure and flow.