EPANET2- Pressure Controlled Pump 1

[AjaxEcthelion]

I'm totally new to EPANET and I'm having trouble figuring some stuff out.

I've modelled a system (A trailer park) where a pump draws water from a well and feeds a number of junctions. I've set the demand at the junctions to fluctuate over 24 hours. However, this causes the pressure in the system to fluctuate by a large amount as well.

I tried to solve this by setting simple controls that turn the pump off when the system is at high pressure and on when the pressure drops down. When I run it, it says the number of trials has been exceeded at hour zero. I'm assuming it turns the pump on, the pressure instantly spikes, it immediately turns the pump off, the pressure instantly drops to zero, it turns the pump on again and so on, rapidly flickering on and off. In real life, shouldn't the pressure gradually rise when the pump is on and gradually fall when it's off?

How should I be modelling this? Can/should I add some sort of pressure tank to balance out the pressure from the pump?

Thanks in advance for the help!

 

[Artisi]

I haven't really analysed your post, but a quick answer seems to be to fit a bladder pressure tank after the pump discharge. Google "Grundfos", they are probably the world leaders in supply of this equipment - usually fitted to their pumps.


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.)

 

[AjaxEcthelion]

Ok, thanks Artisi, that makes sense.

Any idea how to model a bladder pressure tank in EPANET?

 

[Artisi]

Sorry, no I don't.

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.)

 

[AjaxEcthelion]

That's ok.

I'm experimenting with a couple things in EPANET that seem to be working. If I put a small tank between the pump and the system and give it a high elevation to represent pressure, that seems to work- The pressure in the system stays much more steady. Alternately, using a Pressure Control Valve keeps the pressure from spiking in the system when demand is low.

Thanks for the help.

 

[hydrae]

I have modeled a pressure tank with success by making the tank tall and very skinny
pressure tanks typically have a pre charge pressure 2 psi below cut pressure,
this can be modeled by matching the elevation of the bottom of the tank
to get even more fancy you can vary the diameter to account for either isothermal or adiabatic compression of the air

Hydrae