#### msoultan

##### New Member

Hi,

In our community we have two large water storage tanks (80k gallons each) that gravity feed all of the homes. For the most part everyone has good water pressure, but there are four homes that aren't much lower than the storage tanks and end up in the 20-40 PSI range with low flow rates (due to small pipes). We would like to increase the water pressure and flow rate to all four homes, so I was hoping for some advice. Here's what I think I figured out...

For the four houses, we're going to make the assumption that we want to be able to handle a peak demand of 50 GPM - this is probably on the high side, but we'd rather over-design the system than under-design it. Next, we'd like to make sure each of the homes has at least 50+ PSI. Obviously pipe size to the homes will affect this and we can up-size the piping if the increase in pressure doesn't fix the issues.

Here is what I think we need, but I'm wondering if I'm getting this correct - I'm thinking that we would want to have a pump that can supply that peak demand of 50 GPM. We would get a 30/50 PSI pressure switch which, in conjunction with a Flexcon 119 gallon pressure tanks, for example, would give us a drawdown capacity of 40.6 gallons per tank:

I was thinking that realistically we'd only need to handle a 40 GPM peak, so we could get a 50 GPM pump and throttle it down to 40 GPM - and if I'm understanding minimum runtimes and drawdown capacity, we would want at least an 81.2 gallon drawdown which would be two tanks. At a minimum we would have an additional 30 PSI per home.

I was thinking that we would design the system such that in the event we needed to handle more peak flow, we would already have the tank manifold set up to accept a third tank, and we could also bump up the pump GPM.

We have considered an in-tank pump, but we'd much rather have an external pump unless it's ridiculously more cost-effective to go with an in-tank pump.

It would seem like when searching for these pumps, they don't list the PSI output of the pump, but how many feet they can pump, so I'm assuming if I want to use 30/50 PSI setpoints, then I'd probably want to have a pump that can do 55 PSI, or a pump that can pump 50 GPM at 127.05 ft (2.31 ft/PSI * 55 PSI).

ADDITIONAL DETAILS:

- Max water level in the main tank is 19.1ft

- The proposed location for the pump is next to the tank because the water company owns the land and there is electricity nearby.

- If the pump is placed at the base of the tank, it would already have 19.1 ft of head, or 8.29 PSI - tank level usually hovers around 18.7ish ft, so le's say 8.1 PSI pump inlet pressure.

- There is a 2" pipe that runs to the four water meters, and the pressure at the meters is around 20 PSI, so that's about a 27.5ft elevation drop from the base of the tank.

- The water meters are located a couple hundred feet from the tanks and there is no power there.

So here are my questions:

- Am I calculating this stuff correctly?

- How do you go about calculating these peak usage values - in some regards I'm wondering if we'll ever even hit that peak water usage, but I also don't want to end up on the other end where it's under-designed. I was hoping for some real-world advice on sizing these kinds of systems.

- Should the pump be sized to match the peak demand, or should there just be enough pressure tanks to handle the theoretical peak demand for some given amount of time? So in the case of two 119 gallon tanks, we'd be able to provide 40 GPM for 2 minutes (assuming the pump wasn't helping), correct? Granted, once the tanks drained down and the pressure switch kicked on, the pump would be handling the entire load, and if the demand is higher than the pump's output, there will be a drop in pressure.

- If I am getting this correct and I need a 50 GPM pump that can push up to at least 127 ft (or 55 PSI), are there pumps that will provide this flow at the pressure we're looking for? If so, does anyone have any pump recommendations?

- What type of pump would we look for? Centrifugal seems to be a popular one, but I'm not sure if that's appropriate. I've also seen jet pumps and multi-stage pumps.

Thanks!!

Mike

In our community we have two large water storage tanks (80k gallons each) that gravity feed all of the homes. For the most part everyone has good water pressure, but there are four homes that aren't much lower than the storage tanks and end up in the 20-40 PSI range with low flow rates (due to small pipes). We would like to increase the water pressure and flow rate to all four homes, so I was hoping for some advice. Here's what I think I figured out...

For the four houses, we're going to make the assumption that we want to be able to handle a peak demand of 50 GPM - this is probably on the high side, but we'd rather over-design the system than under-design it. Next, we'd like to make sure each of the homes has at least 50+ PSI. Obviously pipe size to the homes will affect this and we can up-size the piping if the increase in pressure doesn't fix the issues.

Here is what I think we need, but I'm wondering if I'm getting this correct - I'm thinking that we would want to have a pump that can supply that peak demand of 50 GPM. We would get a 30/50 PSI pressure switch which, in conjunction with a Flexcon 119 gallon pressure tanks, for example, would give us a drawdown capacity of 40.6 gallons per tank:

I was thinking that realistically we'd only need to handle a 40 GPM peak, so we could get a 50 GPM pump and throttle it down to 40 GPM - and if I'm understanding minimum runtimes and drawdown capacity, we would want at least an 81.2 gallon drawdown which would be two tanks. At a minimum we would have an additional 30 PSI per home.

I was thinking that we would design the system such that in the event we needed to handle more peak flow, we would already have the tank manifold set up to accept a third tank, and we could also bump up the pump GPM.

We have considered an in-tank pump, but we'd much rather have an external pump unless it's ridiculously more cost-effective to go with an in-tank pump.

It would seem like when searching for these pumps, they don't list the PSI output of the pump, but how many feet they can pump, so I'm assuming if I want to use 30/50 PSI setpoints, then I'd probably want to have a pump that can do 55 PSI, or a pump that can pump 50 GPM at 127.05 ft (2.31 ft/PSI * 55 PSI).

ADDITIONAL DETAILS:

- Max water level in the main tank is 19.1ft

- The proposed location for the pump is next to the tank because the water company owns the land and there is electricity nearby.

- If the pump is placed at the base of the tank, it would already have 19.1 ft of head, or 8.29 PSI - tank level usually hovers around 18.7ish ft, so le's say 8.1 PSI pump inlet pressure.

- There is a 2" pipe that runs to the four water meters, and the pressure at the meters is around 20 PSI, so that's about a 27.5ft elevation drop from the base of the tank.

- The water meters are located a couple hundred feet from the tanks and there is no power there.

So here are my questions:

- Am I calculating this stuff correctly?

- How do you go about calculating these peak usage values - in some regards I'm wondering if we'll ever even hit that peak water usage, but I also don't want to end up on the other end where it's under-designed. I was hoping for some real-world advice on sizing these kinds of systems.

- Should the pump be sized to match the peak demand, or should there just be enough pressure tanks to handle the theoretical peak demand for some given amount of time? So in the case of two 119 gallon tanks, we'd be able to provide 40 GPM for 2 minutes (assuming the pump wasn't helping), correct? Granted, once the tanks drained down and the pressure switch kicked on, the pump would be handling the entire load, and if the demand is higher than the pump's output, there will be a drop in pressure.

- If I am getting this correct and I need a 50 GPM pump that can push up to at least 127 ft (or 55 PSI), are there pumps that will provide this flow at the pressure we're looking for? If so, does anyone have any pump recommendations?

- What type of pump would we look for? Centrifugal seems to be a popular one, but I'm not sure if that's appropriate. I've also seen jet pumps and multi-stage pumps.

Thanks!!

Mike

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