Excessive headloss/poor pump application/available head unused/other?? 1

[CrazyHorse81]

Existing duplex, pitless water booster station serves 52 homes. Incoming transmission pipe is 6" PVC and serves about 3 homes along it. Piping thru pump house is 3-inch. Distribution piping consists of 6" PVC loops water mains that fills a stand pipe with dimensions of 14' and 110' tall. See HGL for reference and sketch for configuration.

The original pumps (now sitting on the pump house floor) are Webtrol WS09050 and should operate at about 142' TDH and 87 gpm based my calculations - also attached. These pumps have been barely producing 25 gpm and have burned through more than a few motors over the course of a year. In fact, the operator only filled the tank to ELEV.=1410 to get them to produce flow - again noted as F. on HGL.

The operator replaced them with Webtrol WT4050 submersibles. And based on fill times of the tank they averaged a flow rate of 45-50 gpm. That corresponds to a TDH of 275-300' about double of what I expect!

We stuck a pressure recorder upstream of the BPS and it steadily recorded upstream pressure of 60-65 psi (as expected). We also verified that all downstream valves were OPEN. I am missing something? I would size the pump of a flow rate of 45 gpm at 150' and have a nice day but something is awry.

Can someone chime in please?

 

[ashtree]

Maybe i have missed something but how deep is the well that these pumps are in, and how much water is over the pumps when they are pumping.

Burning submersible motors out normally means one of a couple of things:

1) Not enough flow past the motor: this could be related to low flow(no water in well, too small of pump for the head etc) , or incorrectly shrouded to get the flow past the motor.
2) Motor sitting in mud.
3) Wrong motor for the pump.
4) Too many starts per hour.

In this case it sounds like low flow which would link to your problem regarding the motor.



Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[CrazyHorse81]

They are only 10 feet deep. there is essentially 60-65 psi of water above them with the residual system pressure as read by the pressure recorder on the fire hydrant right next to them.

such as these:

http://www.bakermonitor.com/content/pitless-booster-stations

 

[ashtree]

And does it maintain that pressure on the incoming pipe when the pumps are running?
Are the pumps mounted horizontally in a "pipe" with the whole system enclosed?


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[CrazyHorse81]

Yes it does maintain that pressure upstream/incoming pipe. No they are mounted vertically just like a submersible well pumps and yes enclosed system except that it pumps to atmosphere at the tank as shown on the original attachment.

 

[ashtree]

If you have 65psi coming into the pumps why do you need a booster pump at all because you are only getting about 65psi when your standpipe is full. Why not just connect the piping directly into the network and bypass the pumps.
There has to be something else i am missing.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[CrazyHorse81]

Please look at the HGL figure. It tells you why they need boosting. One could argue this should have been installed downstream at a higher elevation but that isn't the concern or issue. Boosting pressure is boosting pressure no matter the location.

 

[bimr]

Submersible pumps like this will burn out if the pumps dead head. Usually a recirculation loop will be provided so the pump does not dead head.

 

[coloeng]

Either your headlosses are higher than you have estimated or the flow is greater than you calculated. If the flow is accurate, based on the pump curve it indicates that you have zero head at the pump inlet. Are there any partially closed valves or restrictions between the fire hydrant and pump station on the upstream side that could cause this?

I would recommend getting a strap-on ultrasonic flow meter and do a flow test. In the past I have been able to rent them from a meter supply company (20 years ago). Is it possible that there is additional usage besides what is going into the standpipe? Is there possibly a leak in the system. Just trying to think of things that might cause this.

 

[bimr]

What is the discharge pressure of the BPS?

Is there a bypass check valve as per the installation sheet? Is so, is the check valve leaking?

http://www.bakermonitor.com/content/pitless-booster-installation

 

[CrazyHorse81]

118 psi. I haven't confirmed the existence or leaking of a check valve, though normally they ARE installed as standard not optional.

 

[bimr]

Here are some things to check:

1. Check the rotation of the pump motor.
2. Check the pump motor voltage.
3. Check the slope of the 6-Inch pipes. The velocity of the water is low and there may be air trapped at high spots.
4. Install a flow meter on the pump. Pump to waste and verify that the pump is operating on the pump performance curve. If you verify the pump capacity, that points to a problem with the 6-Inch main.

 

[CrazyHorse81]

Good thought on the air; sneaky lil culprit air can be. We did a flow test to waste on the pumps - though at the time we thought the original pumps were in use. So the analysis made no sense whatsoever. Now that we verified that they'd been swapped with another pump I yet need to plot and analyze vs the new pumps.

 

[CrazyHorse81]

Update - we flushed all of the lines at about 7.5 fps. Air came out of three fire hydrants - a lot of air in fact. Trending data now shows that the pumps increased flow by 21 gpm (45 gpm pre and 66 gpm post flush). Based on the pump curve, the difference in head is about 150 feet. This makes sense based on my design calculations. Eureka!

We may install a few ARV pits and/or just stress to the utility that flushing this system is critical to keeping their pumps alive.