I have low water pressure where I am. If the sprinkler system is turned on, it is difficult to flush the tankless toilets. I filled a 5gal bucket from a 3/4" line in 25seconds, so about 12GPM.

My understanding of fluid flow is based on my understanding of current flow. For a fixed load, increasing pressure (voltage) will increase flow (current). But what I am reading with regards to booster pumps seems to indicate that they only increase pressure, not flow. That does not compute for me. To me it seems that if I increase pressure, that should increase flow as well.

If I'm correct, how much more flow can I expect? If I connected a booster pump to the outlet of that 3/4" line, and it tried to pull more that 12GPM from the line, I assume that creates a vacuum in the line, so I could only increase the flow by that amount which would correspond to an additional 14.7PSI from the source. Is that correct?

 

What is the diameter of your water input line? To the house? Are you on a well?

 

You will be limited to the input diameter and pressure.......unless you install reservoir/pump.

 

People on well water have a pressurized system. The pump pressurizes a tank and water is drawn from the tank as needed. The pressure is adjustable. You could do the same though the source would not be a well. It's not super expensive if you do it yourself.

 

The diameter(and height) is the resistance to flow. You can install larger pipes and a pump......but you will still be limited by the source resistance......which is your input diameter.

 

This is for the building at work. I need 40GPM @ 40PSI (could possibly work with a bit less) for continuous operation over a span of 6 - 8 hours for a test. In the past we have rented 20,000 gallon frac tanks pumped out with a gas pump for this purpose but I am trying to eliminate that cost. It's several thousand dollars for each test. I'm trying to do it with city water supply now. I don't have any numbers to back it up, but I'm almost positive this 3/4" line isn't going to work. Plan B is to tap into the 2" main line to the building, but I'm pretty sure that's still going to require a booster pump as city water supply is low pressure.

 

If the city has any water pressure......2" should be fine.

https://www.hy-techroofdrains.com/water-flow-through-a-pipe/

 

Can you put a figure on "low pressure" (you can McGyver a water pressure gauge from an old tyre pressure gauge)?
Flow rate, for a given pipe diameter and length, is proportional to the pressure difference between the two ends of the pipe. Suppose the inlet of the pipe is at 2 bar pressure and your pump sucks 0.5 bar, then pumped flow rate is unpumped rate x (2.0 + 0.5)/(2.0) = unpumped rate x 1.25. Not as much of an increase as you'd hoped .
A much bigger increase is possible by upping the pipe cross-section, since flow rate is proportional (other factors being equal) to the 4th power of the radius IIRC. So go for the 2" pipe.

 

You would want to put the booster pump right where the tap is connected to the main line.
Could also put the pump in series with the main line.

As a teenager I worked at a local cannery during the summer.
Their water supply was from an artesian well with low pressure.
The had a large centrifugal pump right at the wellhead to increase both the water pressure and flow rate.

 

...I need 40GPM @ 40PSI.... I'm almost positive this 3/4" line isn't going to work.

I agree that 40gpm is not going to happen with just a 3/4" line. I have no idea what pressure would be required but it would probably exceed the safety rating of the piping. Piece of cake with a 2" pipe.

You might consider a water tower approach. Let normal pressures slowly fill a reservoir with adequate volume to supply your tests, and then pump at whatever rate you need out of that reservoir. We used to use empty tanker trucks for chores like this. It doesn't cost a lot to rent one, especially if you borrow it from a trucker you use regularly for shipping.

 

I agree that 40gpm is not going to happen with just a 3/4" line. I have no idea what pressure would be required but it would probably exceed the safety rating of the piping. Piece of cake with a 2" pipe.

You might consider a water tower approach. Let normal pressures slowly fill a reservoir with adequate volume to supply your tests, and then pump at whatever rate you need out of that reservoir. We used to use empty tanker trucks for chores like this. It doesn't cost a lot to rent one, especially if you borrow it from a trucker you use regularly for shipping.

20,000 gallon frac tank is what it takes. It takes several water trucks to fill it for 1 test. Thousands of dollars

 

This is for the building at work. I need 40GPM @ 40PSI (could possibly work with a bit less) for continuous operation over a span of 6 - 8 hours for a test. In the past we have rented 20,000 gallon frac tanks pumped out with a gas pump for this purpose but I am trying to eliminate that cost. It's several thousand dollars for each test. I'm trying to do it with city water supply now. I don't have any numbers to back it up, but I'm almost positive this 3/4" line isn't going to work. Plan B is to tap into the 2" main line to the building, but I'm pretty sure that's still going to require a booster pump as city water supply is low pressure.

You should be able to get about 240 gallons/minute from a 2" pipe. And that flow is cut in (**About**) half for each step down to 1.5" (120 gpm), 1.25" (70 gpm), 1" (40 gpm) and down to about 20 gpm for a 3/4" pipe (at 40 psi).

You should contact the fire department/city water department before implementing this. Taking off more than the system was designed for can cause a few problems.

1) not enough line pressure for the hydrants in case of a fire.
2) Large water hammers if you slam valves open and closed during your tests (and that can trigger alarms in fire suppression systems for a large radius of other customer on the system with water pressure monitoring systems for their own fire alarm systems (especially companies with high level of hazard preparedness - chemical, energy, petroleum, hospitals, ...)
3) Companies relying on high flow of water and under contract with the water company may experience inconsistent flow in violation with their service agreement with the water company. If the water company has service level agreements with their customers, they likely have rules in your water supply contract that prevent large take-offs of water.

Also, the water company may change your meter to a higher flow meter & regulator and increase your supply water pressure (regulator just in front of the meter) - usually at no charge if they can sell more water. They can also increase your water pressure at that regulator.

NOTE: you may want to add some diaphragm tanks to eliminate water hammering in your own building if you are turning the water valves on/off quickly. You can quickly blow out a toilet fitting with a water hammer.

 

You have a very different situation from mine. I made the meter guy let the water blow right out of the meter for 1 minute. 28 gallons per minute from a 40 PSI source a couple of feet away. Then it goes through about 150 feet of 1959 galvanized steel pipe and delivers 7 GPM at my house.
Oh well. Good enough for a residence.