Running time

[SMIAH]

Wastewater from a new urban developpement will be connected to an existant pumping station (2 small pumps working in alternance with motors = 3600 RPM 4.5 kW).

Reviewing the running time for both pump (2012-2013), they're both running around 5 hours/day with peak around 8 hours/day.
Checking the actual hourly peak flow rate entering the pump station (Qpump/2), I calculate 3 starts/hour (for both).

With this new urban developpment, number of pump starts per hour will decrease but overall running time will increase.
The Q hourly in peak will be > Q pumping capacity (out).

Is there anything wrong with a 3600 RPM motor working around 8 hours a day?
I have yet to talk with the guys in charge of the maintenance but I know they're often working on this pumps.

 

[rotw]

I thought it is the number of start that is a threat for motor life time?

 

[SMIAH]

That's what I think too. Just wondering if there's any other issues.

 

[JJPellin]

The vast majority of my motors run for months at a time in continuous operation. And these tend to be the most reliable motors. The ones that give me trouble are often the ones with lots of starts per day. I would not worry much about the motors’ running hours. On the other hand, if the pumps suffer from erosion damage, run hours will shorten their life in proportion to the extra run time.

Johnny Pellin

 

[SMIAH]

Thanks.

I worry about the fact that Q hourly in peak will be > Q pumping capacity (out) after development.
This is a small pump station and it could lead to more discharge outside of the pumping station.

 

[BigInch]

Motors can be operated for relatively high loads, of they are operated for a short time. Their power rating will be lower for continuous duty. Check what kind of rating your motor has and decide if it is appropriate for your required power level and duty periods.

I hate Windows 8!!!!

 

[LittleInch]

There's a few odd things here. It's a pretty small pump. The two pumps work "alternatively", why?

Flow greater than one pump "discharges out side the pumping station" ?? Why not stay the second one? Is there no holding tank?

You "calculate" number of starts. You really need to know as if this is a system with very small hold up volume it could be much more if incoming flow is less than outflow. More info please.

Motors work better in a continuous manner but a BI says, look at the motor plate or data sheet.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[SMIAH]

They work alternatively because they're designed like that (duplex mode).
Right now, one of them is out for repair and the other one work alone.
The manhole is relatively small (1,83 sq. meter) of area (with start/stop levels V = 0,5 m3)

I did a drop test yesterday to check the flow rate.
Pump installed is a 4,6 L/s for 34,3 m of TDH.
My own calculations = 1,7 L/s for 34,3 m of TDH.
Drop test results = 1,7 L/s.

So there was a mistake with the headloss calculation (geometric head = 33,4 m for a discharge pipe (3 in) of 360 m in CPV). 0.9 m of total head loss...

I'm now planning an upgrade to 6,1 L/s for 44,6 m TDH (new urban developpement) and look for the good pump choice. Right now, KSB and Flygt are around 25% efficiency.

The rising main is a 3'' and the twin pipes in the station are 2'' each (connected to the 3''). Any idea for a selection of pump??