Well Water Pressure Tanks

Constant Pressure Well Water Systems: How They Work, What They Cost, and Who Should Get One

A constant pressure system is a variable speed well pump, an electronic controller on the wall and a pressure tank about the size of a basketball. I have spent 32 years around well systems, first as a service company and now shipping tanks and treatment equipment nationwide, and I tell callers the difference between constant pressure and a standard tank is night and day. It also costs a lot more. This is how the systems work, what the Cycle Stop Valve does differently, and what plumbers actually charge. It also covers what we used to sell and no longer do, and how to put an iron filter or softener on one without wrecking the pressure you paid for.

What constant pressure is, and what a standard tank does instead

A standard well system stores water in a pressure tank and runs the pump flat out between two switch points, most often on at 40 psi and off at 60. Pressure at your shower slides from 60 down to 40 as the tank empties, jumps back up when the pump starts, and repeats. A constant pressure system does away with the swing by running the pump at whatever speed keeps the pressure at one setpoint for as long as water is flowing.

The 20 psi swing is the whole complaint. Nobody notices it with one faucet open, because the tank drains slowly and the pump catches up fast. Open a second shower or start the washer during that draw and you reach the 40 psi bottom sooner, and you feel it as the shower going soft for a minute before the pump brings it back. In the complete pressure tank guide I explain the switch settings and what a tank actually stores. The short of it is that a tank is a buffer, not a pressure source. The pump makes the pressure. The tank just decides how often the pump has to run.

A lot of the people who call me about this moved onto a well from city water for the first time. City water sits at one pressure all day because the utility is holding it there. A constant pressure system is the way to get that on a private well. Here is the way I put it in the pressure tank video, at the 2:28 mark:

How a variable speed constant pressure system works

Three parts: a variable speed submersible pump in the well, a controller (variable frequency drive) mounted on the wall near where the well line comes in, and a small diaphragm tank of 2 to 20 gallons with a pressure sensor plumbed near it. The controller reads the sensor, compares it to the pressure you set (the setpoint), and speeds the pump up or slows it down to hold that number.

Here is what that means at the tap. Open a faucet and the pressure in the little tank starts to fall. For a dripping faucet or an ice maker, the tank handles it on its own. Anything more starts the pump right away, and from then on the controller is adjusting speed to hold the number. Close the last tap and it tops the tank off and shuts down. The residential packages I see are made by Grundfos, Franklin Electric and Goulds; the well contractor picks the one that matches the pump, and the model details are in the FAQ.

Two things worth knowing as the owner. The little tank has its own air-charge rule that is different from a standard tank (the installer sets it; the number is in the FAQ). And the setpoint is a knob or a button. That convenience is also the trap, which I get to under who should get one.

What you feel at the fixtures is what the chart at the top shows. One shower running: pressure stays at 60. Someone starts the washer: the pump speeds up and the shower does not change. That is the "night and day" I tell callers about. It is also why the tank can be small. The tank is no longer storing your shower; the pump is supplying it in real time. The tank only has to smooth out the tiny draws so the pump is not starting for every ice cube.

The Cycle Stop Valve: constant pressure without electronics

A Cycle Stop Valve is a spring-loaded stainless valve installed between the well line and the pressure tank. The pump runs at full speed behind it; the valve opens and closes to pass only as much water as the house is using, holding the downstream pressure at its setting (50 psi is typical) for as long as demand is above 1 gallon a minute. The CSV1A model handles 1 to 25 gpm, adjusts from 15 to 150 psi and sells for $224 direct from Cycle Stop Valves in Lubbock, Texas.

You keep your standard pressure switch, set higher than the valve. Say the switch is 40/60 and the valve is set at 50. Open a shower and the tank drains from 60 down to 40 like it always did, the pump starts, and instead of the pressure climbing back to 60 while you shower, the valve holds it at 50 for as long as water is running. Shut the water off and the valve lets a trickle through, so the tank fills slowly to 60 and the switch turns the pump off. That slow fill is why the maker says you can use a smaller tank than a standard system needs.

The trade-offs are also plain. The pressure is only constant while water is running; the first drawdown from 60 to 40 still happens every time the system has been sitting, which you can see in the middle panel of the chart. The pump runs at full speed against a partly closed valve for the whole shower. Cycle Stop Valves says a throttled pump draws less current than one running wide open; the drive manufacturers say a pump running at reduced speed uses less power still. I have not put a meter on either one, so I am not going to pick a winner on electricity. And the pressure switch cut-out must always be above the valve setting, or the pump will never shut off.

Where the CSV earns a place: you have a good conventional pump you do not want to replace, you can do your own plumbing or you have a plumber who can, and you want steady shower pressure for a few hundred dollars instead of a few thousand. It is also the only one of the three approaches you could reasonably call a weekend job on an existing system.

Is there such a thing as a constant pressure tank?

No. A tank stores water; it cannot regulate pressure. Amtrol did sell a product called the Well-X-Trol WX1 constant pressure system, and we carried the WX1-250 for a while, but it was a tank with a digital pump controller mounted on it, not a tank that made pressure constant by itself. We no longer stock it. If you read anywhere, including an older version of this page, that a specially designed bladder tank holds pressure within a few psi with no electronics, that is wrong.

I want to be direct about this because we got it wrong here before. The controller mounted on that tank was the part doing the work, and I am not aware of a tank-only product from anyone that does what our old copy claimed.

What a bigger tank does do is lengthen the cycle. A WX-250 at 40/60 gives you 11.8 gallons between pump starts; a WX-203 gives you 8.6. That is a real improvement if your problem is the pump clicking on every time somebody flushes, and it is the fix for a lot of the "low pressure" calls I get, because the actual issue turns out to be a waterlogged or undersized tank. But the pressure still goes from 60 to 40 and back. The sizes article has every Well-X-Trol drawdown number at both switch settings.

Side by side: variable speed vs Cycle Stop Valve vs bigger tank

The variable speed system is the only one that holds pressure at one number from the moment a tap opens. The Cycle Stop Valve holds it after one drawdown. The bigger tank holds nothing steady; it just cycles slower. Here is how they compare on the things people actually ask me about.

What a constant pressure system costs installed

The number I give callers is $3,500 to $4,000 installed for a variable speed constant pressure system, and that assumes the well pump is coming out anyway. Plumbers around Maryland were charging about $3,600 for the same job when I was still in the field. A Cycle Stop Valve is $224 plus the plumbing. A bigger Well-X-Trol is $1,695 to $2,195 plus a tank swap.

Why the variable speed number is what it is: the controller cannot run a standard single-speed pump. You need the matching variable speed submersible, and getting it into the well means pulling the old pump, which on a 200 to 500 foot well is most of the labor. That is also why the timing matters so much. If your pump is 11 or 12 years old and you are pricing a replacement, the constant pressure upgrade is the controller and the small tank on top of a job you were already paying for. If your pump is five years old and fine, you are paying to pull a good pump.

A caller this spring had already done the smart version of this without knowing it. He replaced his pump a year and a half earlier, put in a variable speed unit and had it wired for a controller. When his low-profile plastic tanks started leaking and he asked whether to buy a new tank or go constant pressure, my answer was to hold off on the tank: all he needed was the controller and the expansion tank, and the tank we sell would have been wasted money. We do not sell controllers. That is pump-contractor territory, and I would rather tell you that than sell you a tank you will take out in a year.

One more cost note from the phone. A caller in Maryland with acidic water had two quotes in hand from big service companies, each bundling a constant pressure system with a water softener and a chemical feed system, at hardness of 3 grains. His water needed a sediment filter and an acid neutralizer. He wanted the constant pressure because his pump was 12 years old, which is a fair reason. The softener and the chemical feed were padding. When a treatment quote and a pump quote arrive on the same piece of paper, price them separately, and get the pump side from a well contractor who does pumps all day.

Who should get one, and who should not

Get a variable speed constant pressure system if you are drilling a new well, if your pump is due for replacement, or if you have a large house or irrigation and you have already ruled out a bad tank or a bad switch. Skip it, or start with a Cycle Stop Valve or a bigger tank, if your pump is young and healthy and the complaint is cycling rather than pressure.

New construction

This is the easiest call I make. A caller building on a lot where the driller expected 200 to 500 feet asked whether to buy a big tank or something else. My answer was either a WX-305 or WX-350 from a plumbing supply house, or, if he wanted genuinely good pressure, a Goulds or Grundfos constant pressure system, and to tell the driller so the right pump goes in the hole the first time. On a new well the incremental cost of the drive is small next to the well itself, and you never pay to pull a pump.

Pump replacement

Same logic. If a contractor is quoting a new submersible, ask what the variable speed version plus a controller adds. You are already paying the labor that makes these systems expensive.

Large homes, irrigation, more than one building on the well

A house with several bathrooms in use at once, a sprinkler system pulling 10 or 15 gallons a minute while someone showers, or a main house and a boathouse or guest house sharing one well are the situations where the 20 psi swing gets felt every day. One caller runs a variable speed system rated 60 to 70 gpm on an 8 inch well to feed a house and pasture irrigation; another splits his variable speed system at the well to run a boathouse. Constant pressure is the right engineering for those, and a bigger tank would not touch the problem.

Who should not, or not yet

A lot of the "low pressure" calls I get turn out to be the tank: waterlogged, too small from day one, or a switch off its setting. Sometimes it is a clogged sediment cartridge. Those are $50 to $1,300 fixes and the troubleshooting article walks through them in order. Do that first. If the pressure is acceptable and the pump is simply starting too often, a bigger tank is the answer, not a drive. And if your pump is young and you are on a budget, a Cycle Stop Valve gets you most of the steady-shower benefit for a fraction of the money.

Ask Aidan

Not sure if it is the tank, the switch, or time for constant pressure?

Text me a photo of your tank, the gray switch box and the gauge, and how old the pump is. I will tell you whether a tank fixes it or whether you should be calling a well contractor about a drive.

Text Aidan 443-277-2204 Call 800-460-5810

Open seven days. 28 years in the field before we started shipping.

If you would rather not: the bigger tank, honestly

A bigger Well-X-Trol will not give you constant pressure, and I am not going to tell you it will. What it does is stretch the time between pump starts, which fixes short cycling, protects the pump motor and makes the pressure swing slower and less noticeable with one fixture running. If that is your actual problem, it is the cheaper and simpler fix, and it works on the pump you have.

For most households the tank I recommend is still the WX-203 ($1,295, 32 gallons, 8.6 gallons of drawdown at 40/60). If the pump is cycling too often for the house, the WX-250 ($2,195, 44 gallons, 11.8 gallons of drawdown) is the step up, and the WX-205 ($1,695, 34 gallons) is the shorter, wider one for a crawl space. The cost article covers what the packages include and what a tank swap runs. For anything bigger than a 250 on a new build, I send people to a plumbing supply house for a WX-305 or WX-350, or I tell them to price the constant pressure system instead, because at that point the money is close.

The best pressure tank article covers what to look for in the tank itself, whether it is the small one on a variable speed system or a full-size one.

If you also have iron, hardness or acidic water: treatment on a constant pressure system

Every piece of treatment equipment goes after the small tank and the main shutoff, in the same order it would on a standard system: sediment filter, then the iron filter or acid neutralizer, then the softener, with UV last. Nothing goes between the pump and the controller's pressure sensor. A constant pressure system is actually a better partner for backwashing filters than a standard tank, because the backwash sees steady pressure for the whole cycle.

This comes up on the phone every week, usually as "I have a constant pressure system and no big tank, does that change anything?" It does not. Everything goes after the small tank and the main shutoff, same as always, and our residential filters have 1 inch valves and pass plenty of flow for several fixtures at once. If anything it helps: a Texas caller converting to an iron and sulfur filter was worried his constant pressure system was a problem, and it is the opposite, because the filter backwashes at a steady pressure instead of riding a tank from 60 down to 40. The flow requirement does not go away, though: a 2.5 cubic foot iron filter wants about 10 gallons a minute to backwash, and no controller can make a 6 gpm well do that. Match the filter to the pump, not to the pressure.

Three practical notes for anyone plumbing treatment onto one of these:

• Set the pressure for the filters, not the shower. A caller with a large variable speed system was running 45 to 50 psi through his filters even though the pump could do far more, and my advice to him was not to push it higher. Fifty to sixty at the setpoint leaves you 40 or better after a sediment filter and two treatment tanks. Turning it up to 75 to "make up for the filters" is how joints get blown.
• Keep the sensor honest. Grundfos notes that if the pressure sensor is far from the taps, friction losses show up as pressure variation. Put the treatment after the sensor and the tank so the controller is reading system pressure, not the pressure drop across a dirty sediment cartridge.
• If you split at the well, treat each branch after its own pressure point. One caller splits a variable speed system at the wellhead to feed a boathouse. Anything that needs treated water gets its equipment on its own branch, downstream of the split, never on the pump side.

If you are sizing treatment for a well with a constant pressure system, start with a water test. The pressure system tells us nothing about iron, pH or hardness, and those decide what goes on the wall.

Frequently asked questions