Control of pumps in a closed potable water distribution network
Control of pumps in a closed potable water distribution network
(OP)
Hi all,
I'm currently working in a closed system of potable water distribution system, pumping directly to consumers, there are no storage tanks that I can use to shut off the pumps when it gets filled, so what is the most common way of controlling the pumps in this case ?
1- Pressure sensors at the furthest hydraulic point in the system ( or even several pressure sensors in several locations ) these will have several set point keep tracking the pressure from a minimum of 2bar to a maximum of 4.0bar.
2- A pressurized tank at the pumping station, is this the same as the hydropnumatic tank ? what is the difference between this and the surge vessels ? will this hydropnumatic tank work for surge protection ? what should it be sized for if it will work for both ?
The pumps will be VFDs. 2 duty and one standby. Pumping 180l/s at peak. 90l/s on average.
Your help is very appreciated.
I'm currently working in a closed system of potable water distribution system, pumping directly to consumers, there are no storage tanks that I can use to shut off the pumps when it gets filled, so what is the most common way of controlling the pumps in this case ?
1- Pressure sensors at the furthest hydraulic point in the system ( or even several pressure sensors in several locations ) these will have several set point keep tracking the pressure from a minimum of 2bar to a maximum of 4.0bar.
2- A pressurized tank at the pumping station, is this the same as the hydropnumatic tank ? what is the difference between this and the surge vessels ? will this hydropnumatic tank work for surge protection ? what should it be sized for if it will work for both ?
The pumps will be VFDs. 2 duty and one standby. Pumping 180l/s at peak. 90l/s on average.
Your help is very appreciated.





RE: Control of pumps in a closed potable water distribution network
RE: Control of pumps in a closed potable water distribution network
As for the pressure, although you do need to control the pressure at a MINIMUM at at the furthest point, the pump control is usually done locally. This is primarily due to safety - so if a valve somewhere is shut off the pumps will not overpressurize the entire system.
RE: Control of pumps in a closed potable water distribution network
I would add that you should do a surge analysis to check for possible water hammer. You should also design the system with a surge relief valve to prevent over pressurization.
RE: Control of pumps in a closed potable water distribution network
RE: Control of pumps in a closed potable water distribution network
I would use vfd's to control the pumps from a transducer located in the pumphouse.
RE: Control of pumps in a closed potable water distribution network
RE: Control of pumps in a closed potable water distribution network
you said system pressure : how do you measure that and where do you measure it and how do you send the signal to your pumps ?
*thewellguy,
"I would use vfd's to control the pumps from a transducer located in the pumphouse"
Can you please explain more, do mean pressure transducer in the discharge line ? I cannot use level transducer cause I have no gravity tanks, even If I do they wouldn't be located in the pumphouse.
the idea of measuring the pressure of the discharge line directly after the pumps seems interesting , I thought about it. would this work ? it is definitely cheaper and easier.
*Cvg,
thanks for your input, I'm now confident that the hydropnumatic tank is not an option since it has to be too big to serve this community.
unfortunately building a gravity tank is not an option.
Guys,
I just need someone to confirm that using pressure sensors in several hydraulic critical points "these could be 2km away from the pumping station" would be a reasonable solution to control the VFD pumps. Please note that these pressure transmitter will be placed on the distribution mains.
Regards.
RE: Control of pumps in a closed potable water distribution network
To answer you other question, yes it is very common in this area to control systems like this.
RE: Control of pumps in a closed potable water distribution network
RE: Control of pumps in a closed potable water distribution network
RE: Control of pumps in a closed potable water distribution network
RE: Control of pumps in a closed potable water distribution network
I’m new in the water distribution network design. There is a senior guy in the office who is convinced that controlling the pumps near consumers “2km away” would give the best indication of system pressure.
I checked the model for severe changes in demand to see how would that affect pressures in the system as overall , I noticed that when pressure was reduced by 50% at 2km away from pumps the discharge pressure just after the pumps was reduced by only 17%. The main reason for this big difference is because there is a relatively larger main feeding the smaller branches where the demand change was assumed to occur. I’ve assumed fixed speed pumps in this scenario to see the direct impact of a huge demand change.
The 50% reduction in pressure was due to a modeled fire incident.
It seems that there is some sense in what my senior guy is saying. Even though the 17% still give enough flexibility to detect the change but smaller demand changes could have much smaller impact at the pump discharge.