pump closed due to its inability to deliver head

[FCJR]

Hi,

Just like to ask why my model is having "WARNING: Pump MNF_PS2_8 closed due to its inability to deliver head at 3:08:21 hrs." and "Pump MNF_PS2_8 open but exceeds maximum flow at 18:18:16 hrs" message. I've checked the report manager and it seems that it's not closing down and flow is not reaching the Design flow that I've specified on my pump Modelling parameters which is 277 lps or 24,001.92 m3/d.

Regarding the first query, I've checked the flow arrows between at 3:00 and 4:00 hour and seems that no reverse flow from other source could've force this pump to shut down. At the same token, the flow being on its normal direction is indicative that my pump isn't really shutting down either. Isn't that correct?

For the second question, I got no idea what's really causing it.

please enlighten me.



Please refer to image below for results i got from my report manager.



Trying to sort out these warning messages because I want to check if this is causing my yellow light on my model run.Report Manager.jpg

T.I.A.

FCJR

[Cliff Dredge]

Hi,

I was just having the exact same issues and Patrick helped me out, so I trust he will verify my response here:

Pump exceeds maximum flow means the pump is trying to operate too far to the right of the curve, either demand is too high or pump undersized. For a test try expanding your pump curve out with another couple of points, just to see if it fixes it.

Pump closed due to inability to deliver head pretty sure it's trying to operate to the far left of the curve, but system resistance is too high to deliver any flow or maybe your demand drops to 0.

Your reporting is set to hourly but I'm assuming your hydraulic time step is lower so maybe flows are higher or lower than you can see in the report.

Hope that helps a bit.

Cliff Dredge.

[FCJR]

Hi Cliff,

Thanks for the response.

I was able to deal with the pump warning. The network that I'm working on has multiple sources on the supplied area. One of the sources has a larger output head and apparently has been pushing water towards the pump that has been acting up(way over its dictated output head setting), shutting it down in the process.

Regarding my problem with flow...; That's the odd thing when it comes to my run report. I've set it to 1 hour interval time step and yet it still gives off warning messages at distinct time periods. Refer to my snapshot below.Simulation Time.JPG

Thaks again!

[Patrick Moore]

Nice response Cliff!

Here are a few other notes.
Pump Warnings (click if need larger image)
Pump Warning messages.jpg

Can't deliver head generally indicates the head gain to get the pump to run is greater than the shutoff head of the pump. Cause is often one of the following:
1) The pump characteristics were poorly chosen. The best rule of thumb I was ever taught was as an initial guess choose tank over flow to tank overflow plus 10 psi as an estimate of design head. This may be just slightly oversized but is a good starting point as a quick check. Receiving tank overflow HGL - suction tank overflow HGL + 10 psi (23.1 ft) = initial guess of pump design head
2) Something is depressing the HGL on the suction side of the pump or raising the HGL on the discharge side. This may occur when an interface between zones is open accidentally. This often occurs when vales are changed to "open" in an initial status or control which rather than make the valve active makes it an open pipe. This can also occur if an isolation valve that is normally closed is accidentally left open. Look for pipes with high headloss or large flows to guide you to the problem area.
3) There are multiple pumps at the station and under low flows the larger pumps have shutoff heads greater than the smaller pump. both pumps generally can run at larger flows but not at lower flow values where the smaller pump would get shut off before the larger pump at low flows.

For the Exceeds maximum flow error this happens when a pump using a multipoint curve flows past the last point on the curve. This issues a warning because this are for most pumps would be a region of operation where the pump has greater potential to have cavitation and damage the pump. But sometimes it occurs because the multi-point pump curve didn't include the full flow region. Generally it is good to check this warnings to see why they occur, but in some cases they are not too worrisome. Basically they often can mean that the system curve requires little head and that the pump may be oversized for the application, or that something is either boosting the suction head higher than it should and/or that the discharge zone HGL is depressed making the pump require less than expected head when it runs.

Hi,

I was just having the exact same issues and Patrick helped me out, so I trust he will verify my response here:

Pump exceeds maximum flow means the pump is trying to operate too far to the right of the curve, either demand is too high or pump undersized. For a test try expanding your pump curve out with another couple of points, just to see if it fixes it.

Pump closed due to inability to deliver head pretty sure it's trying to operate to the far left of the curve, but system resistance is too high to deliver any flow or maybe your demand drops to 0.

Your reporting is set to hourly but I'm assuming your hydraulic time step is lower so maybe flows are higher or lower than you can see in the report.

Hope that helps a bit.

Cliff Dredge.

[Patrick Moore]

Felipe,

It's hard to say exactly what is going on without seeing more information, If you want to submit your question to support@innovyze.com we can take a more in depth look.

However, here are a couple of things we noticed.
1) Time Settings - Generally the rule timestep and quality timestep should be set to 1/10th the hydraulic timestep. So if the hydraulic timestep is 1 hour the rule and quality timestep should be 0.1 hours.
2) If something like a control or a check valve closes an intermediate timestep will be evaluated by the model that are different than your specified report times. This is why you can get warning messages at other time periods.
3) to get the most out of the text status report we recommend these settings:

a) Recommended Simulation Report options (click if need larger image)
reccomended Simulation Report options.jpg

4) Looking at more finer report times. Consider if necessary reducing your hydraulic timestep and report timestep to 15 minutes. This can give you additional data points that you can't see at hour report intervals. You can even make the report time smaller if need be for troubleshooting.
5) Pump warnings are generally always caused by issues with the suction or discharge HGL. Check those when you see warning messages as well to verify something unknown is not causing the error. The HGL plays a big role in water models at all times.

Let us know if you still have further questions. We are always glad to help.

Patrick Moore

Hi Cliff,

Thanks for the response.

I was able to deal with the pump warning. The network that I'm working on has multiple sources on the supplied area. One of the sources has a larger output head and apparently has been pushing water towards the pump that has been acting up(way over its dictated output head setting), shutting it down in the process.

Regarding my problem with flow...; That's the odd thing when it comes to my run report. I've set it to 1 hour interval time step and yet it still gives off warning messages at distinct time periods. Refer to my snapshot below.Simulation Time.JPG

Thaks again!

[FCJR]

Hi Patrick,

Thanks for clearing it out. Regarding the rule and quality timestep, I've altered it on purpose thinking it would show me any difference in the run report. Turns out, this warning messages are because of point 2 you've stated. Point 3 and 5, I've already done, as read from other threads here in this forum. I'll check on regarding the 15 min interval you were saying later on. Seems you've covered enough of my concerns already and my model seems to be fine now...

Thanks as always! this forum is really helpful!

Regards,
FCJR