Water Pressure

[davek78063]

Trying to see if there is anyone knows of any information or has any experience designing/building water distribution systems.

Background
I live in a neighborhood that has a common water system that is owned collectively. Their are approximately 50 lots in the neighborhood with about 30 current residents. My understanding is there is a 4 inch main that runs through the neighborhood. Half of the neighborhood is approx 75 feet above the well according to google earth. Up until a couple years ago there were < 20 residents mostly on the lower section. Over the past couple years there have been a number of houses built and the pressure to the upper sections has gradually reduced. It now fluctuates from 30 psi to 50 psi. On the surface it appears there may be an issue, but they have literally spent a few months arguing about the issues claiming that residents should build their own storage tanks. They have had "experts" come out but they have failed to find the silver bullet that ultimately resolves the issue. Typically they get the pressure up to 50 and claim victory.

My question: Is a 4" pipe large enough to serve roughly 20 residents on the upper half of the neighborhood? My guess is that the system has not been designed to adequately take into account the elevation change as well as support all residents. There are about 15 residents that live below the well and they have no issues. I have complained to the state water board with little luck. They came out and put a pressure monitor at the well, but I am not sure that is really worth anything.

Any insight anyone can provide would be helpful. If additional information is needed I may be able to provide just ask and I will do my best. Thanks.

 

[3Ts]

The 75' elevation change will cause a 32 psi drop in pressure. (1 foot of elevation (head) change is .433 psi ) So if you have 50 PSI at the pump 50 - 32 = 18 psi loss assuming no water flow. There is friction loss with the pipe when the water is flowing and depends on the GPM, so the actual loss is even more. So, it sounds to me like the folks at the top only get water (and only a little) when the pump runs it up to the cut-off pressure. When it's down at the cut-in pressure, they have no water. On the other hand, if there is a 75' drop to the folks on the other end, they could have 82 psi (minus the friction loss due to flow rate). You'll probably need a booster pump part way up the hill, or increase the pressure at the well, but then the folks down hill will have to put in a pressure regulator to keep the pressure down. Note: most household plumbing requires a pressure regulator if the pressure is 80 psi or over.

 

[quicksandfarmer]

The pressure drop along a pipe is determined by the flow rate (gallons per minute) and the resistance of the pipe. The resistance of a pipe is determined by its diameter, material, length and straightness. If there is altitude change then that causes a pressure change as well. For a given pipe, the more water flowing through it the lower the pressure at the end. If no water is flowing the pressure is the same everywhere in the pipe (except for altitude changes).

There are calculators where you can put in the parameters of a pipe and a flow rate and it will tell you the pressure drop. Here's a link to one I found: CalcTool: Flow in pressurized pipe calculator . The problem is, what do you use for the flow rate? For a group of houses you could calculate the average use by adding up everyone's monthly water bill, but that doesn't really help. It's no good to have a water supply that is fine on average, but is inadequate when the most people are using it. You need to figure out when the highest total use is and size for that. Is in weekday mornings when everyone is showering, or is it on Saturday when everyone is washing their cars and watering their lawns?

Rather than calculating, you're probably best off just measuring the water pressure at the end of the pipe. They make water pressure loggers that just screw onto a hose bib, your water company might have one. You should also log the water pressure entering your neighborhood to make sure there isn't a problem with the incoming supply, the entering pressure should be relatively constant regardless of use.

The reason your water company doesn't want to talk about it is there aren't any cheap solutions. If the pipe isn't big enough they'd have to dig it up and replace it with a bigger one. Or they might be able to put a pump mid-way on the line to boost pressure to the far end. What they can't do is just boost the incoming pressure, that will cause everyone to have overly high pressure when no one is using water and will damage your plumbing. I have heard stories of water companies doing that to get people to stop complaining.

 

[RNeumann]

All good info above. Their are two pressures that you are working with. The static pressure and the flow pressure. The flow will change depending on how much is getting used. So at 7am when everyone is showering the pressure is theoretically the lowest. Contrast that with say 2am when no water is flowing the pressure should be highest.
The flow per property is different then the flow per house. In general, the yard uses more water than a house. So if these are tiny lots with no yard you will need far different sizing than 2 acre lots that are all landscaped.
Bottom line is 30psi is too low. If you don’t have the pressure you used to and or don’t have at least 40psi to the property you need to take action.
Either add a tank and booster pump or get serious with your water district.
Bottom line is their isn’t enough info to definitely tell you if the piping is the right size. From my training and experience the pipe size is more than enough but the well pump and or well capacity is way too low/small. The tests that have been done are for pressure only. But aren’t giving an accurate pressure with all the added flow of the new houses.....static pressure is near meaningless for your situation.

 

[oosik]

RNeumann has hit the nail on the head. Get an engineer with a background in water system design. Your system may need both an added storage tank and a booster pump. OR even more extensive modifications. Your system was not adequately designed in the beginning to handle the 50 lots.

You will find - everybody on the system has their own opinion on a solution. That's what probably led to what you have today.

Seek qualified professional help OR continue to throw money at the problem and hope.

Be advised - any smart bank will seek professional advice on the status of this water system when financing new construction or sale of a home.

 

[mcfarmall]

Booster pump that is controlled by a VFD and a pressure transducer. For a system that size you might want to consider what Grundfos has to offer. We have several Grundfos booster skids at work with 2-3 pumps on each skid packaged with the electrical panel, touch screen HMI and everything all included. Just hook up to the flanged connections on each end, supply electricity and away you go.

The pumps will vary in speed according to demand and bring 1,2 or all 3 pumps on line as necessary. We use them as boiler feed pumps, potable city water, and on a few purified water RO skids.

 

[Egon]

What’s the well delivery rate and drawdown?

 

[STx]

The easiest fix is to put a water tower at the top of the hill and pump to that. It'll keep a constant pressure on the entire system. That's how most larger municipal systems maintain their pressure, much less fluctuation from gravity than from a pump.

Most residential use stays at 5GPM or less so, a 4" pipe is within reasonable design standards and well above it if it's looped. If it's not looped, maxed out at a flow of 250 GPM, you're at 6.4fps, we like to stay below 5fps but this isn't enough over to be a deal breaker, and friction loss is only 1.2psi per 100'. Keep in mind that every time the water passes a house in this scenario, 5GPM peels off and those numbers all go down. Again, if that main line is looped around the neighborhood, these numbers will be substantially lower, less than 1/2, so your pipe size isn't the problem, it's the elevation.

If I was in charge of the water department and on a tight budget, I'd go to the highest elevation spot in the neighborhood and install a 15,000 gallon or larger storage tank and it would help a lot. If I had a big budget, I'd install a 100,000 gallon elevated water tower and the problem would be gone forever.

If neither of those are possibilities and I was a homeowner on top of the hill, I'd install an RPZ backflow valve at my water meter, a booster pump where the water comes into the house and an expansion tank by my water heater. I'd set the pump to 60 PSI and have better pressure than anyone else in the neighborhood.

 

[davek78063]

Thank you for all the quick replies. The water supply is a local well. There is no connection to city water. I don't know the draw downs of the well but I don't think that is the issue. We do have a large storage tank; I believe like 20,000 gal. It is The lots are all 3-5+ acres in a rural community with only a couple sprinkler systems. We also have a couple pumps that have been increased in size over the years. I don't remember the size but they were several 1000s of dollars each. It is frustrating because I have been calling for a licensed engineer to come analyze our system for years because we have literally changed out every major component at least once but all i was able to get was a buddy of someone looked at some drawings.

One of my main concerns is that the 4" pipe is undersized. The problem has gotten worse over the past couple years with increased development in the neighborhood.
I recently discovered that every house has varying size pipes running from the meter to their house. I have 1 1/4" pipe feeding my house but another neighbor only has 3/4 or 1" and he is the one with the sprinkler system. He says I have much better pressure/volume coming out of my hose bib than he does but his pressure is ~20 psi higher than mine. The large fluctuations(20-30 psi) also lead me to believe this as well. As had been stated I don't think these issues are cheap or easy to resolve and so far only the people on the high side of the neighborhood are complaining. The ones who are have been here for a while notice the changes, the new ones just think that is normal.

 

[Gary Fowler]

First off, 50 PSI water pressure in a housing development supply line is way too low, especially if there are houses 75 feet elevation above the well. Each house must have a pressure regulator installed and the well pressure should be in the 75-100 psi (100 psi for cutoff, 75 psi for the pump to start up). MCFARMALL's suggestion for installing a skid mounted jockey pump installation might be your cheapest solution. Building large elevated storage tanks would be best, but most likely also be the most expensive. However once completed, they last almost forever and require no maintenance other than painting every 15-20 years if painted correctly when installed and an epoxy painted interior(special paint is made just for potable water tank interiors) .