booster pump stations

[civileng061960]

A small water company recently purchased another water company and wants to connect the two systems. The exiting system has a water tank at elevation 8176 and the dead end pipe is at elevation 7971 with 60 psi. The purchased system has a water tank at elevation 8380 and an 6-inch pipe rated for 165 psi. I think i need to put in two booster pumps in order to keep the pressure below 165 psi. the total friction loss in the system is 140 feet. The tank at 8380 feeds two systems and the pressure needs to be a minimum of 45 psi to feed the west system. The 1st BPS will be located at Elev 7971, the 2nd at 8280. My question is static lift. Will the first BPS be lifting from 8176 to 8280 and the second BPS lifting from 8280 to 8380? The actual elevation of BPS is irrelevant correct?

 

[coloeng]

It appears that under existing conditions you have 67 ft of headloss between the tank at elev 8176 and the dead end at elev 7971. If you have increase flow through the pipe to the dead end you will also have increased headloss. Therefore, you need to determine what the existing flow in the piping is that gives you 67 feet of headloss and what the new flow and subsequent headloss will be so that you know what your hydraulic grade line will be at your pump station. The same will be true between the two booster pump stations, you need to calculate the hydraulic grade line based on your anticipated flows. So long as the suction side of the pump station has positive pressure, the actual elevation isn't too important (I wouldn't say irrelevant).

 

[civileng061960]

They opened a hydrant and measured flow at the dead end at 1000 gpm and 60 psi. I only need to pump 560 up the hill.

 

[bimr]

The location of the pumps is irrelevant. You need to add 205 feet of static lift plus the friction loss.

It seems like it would make more sense to just pump it to the top of the hill and serve the streets by gravity. If you pump from the bottom, you will have to put PRV's at each service to drop the pressure. The two PRV's in the distribution system will have to be removed.

 

[civileng061960]

Thank you both. This is an unfortunate situations. If I just put in one BPS, the existing pipe will be above it's rated pressure. They only want to pump to the top of the hill if the storage tank is out of service for any reason. It would be better to have a transmission main up to the top of the hill and then feed the exiting pipe by gravity. I haven't figured out the logistics yet for control. I will have to make sure that the elevated tank doesn't overfill the lower elevation tank. AND the system will have to pump around the existing PRVs. Again thank you for the input.

 

[bimr]

You would not have to connect at the top of the slope. What about connection to the water system just upstream of the PRV's?

If you connect at that point, you would not have to make any significant change to the water system.

 

[civileng061960]

The new pipeline does connect downstream of the PRVs, but I have to be able to get water to the top of the system when the tank is out of service. The existing well, there is only one, does not have the capacity to provide fire flow. It currently fills up the tank at night. Your response did make me think though. If it can provide part of the fire flow, then I won't have to move as much water up the the hill. But then if the one well goes down, they are in the same situation. I thought it would be less costly to just build another storage tank and put the out of service well back on line. The records show that it is a good well. It would cost less than a mile of pipe and the booster pump stations.