How a Pressure Tank Works in a Well Water System

Every rural Manitoba home on a private well has a pressure tank — the large, typically cylindrical tank in the mechanical room near the water entry point. Many homeowners don't know what it does or how to check if it's working correctly. A failed or undersized pressure tank is one of the most common causes of premature well pump failure — so understanding it is worth your time.

What a Pressure Tank Does

The pressure tank stores a quantity of pressurized water so the pump doesn't have to start every time you open a tap. Without a pressure tank, the pump would run continuously during use and cycle on and off many times per minute — which would destroy it quickly. The tank acts as a buffer, allowing the pump to run in longer, less frequent cycles.

Here's the sequence of normal operation:

1. The pump runs until tank pressure reaches the cut-out pressure (typically 50–60 psi)
2. The pressure switch turns the pump off
3. You draw water — pressure drops as water leaves the tank
4. When pressure drops to the cut-in pressure (typically 30–40 psi), the pressure switch turns the pump back on
5. Cycle repeats

A properly sized and functioning pressure tank allows the pump to run for 1–2 minutes or more per cycle. A waterlogged tank (see below) causes the pump to start every few seconds — a condition that rapidly destroys the pump motor from repeated hard starts.

Bladder vs. Diaphragm vs. Air-Over-Water Tanks

Bladder Tank (Most Common Modern Design)

A bladder tank contains a rubber bladder inside the steel shell. Water fills the inside of the bladder; compressed air fills the space between the bladder and the tank shell. The air pre-charge provides the spring effect that maintains pressure. When the bladder fails, water contacts the tank shell — leading to waterlogging.

Most residential tanks installed in the last 20 years are bladder tanks. They're effective and low-maintenance, but the bladder is subject to wear and failure over time — typically 10–15 years.

Diaphragm Tank

Similar to a bladder tank but uses a flat diaphragm that separates the water and air chambers instead of a balloon-type bladder. Generally more robust than bladder tanks and found in some commercial and higher-end residential applications.

Air-Over-Water (Captive Air) Tanks — Older Design

Older properties may have traditional steel tanks with no internal separation between the water and air charge. Over time, the water absorbs the air charge (waterlogging), requiring periodic air recharging via an air valve on the tank. These tanks are largely obsolete in new installations but still found in older rural Manitoba properties.

Understanding Waterlogging

Waterlogging occurs when the air pre-charge in the tank is lost — either because the bladder has ruptured (in bladder tanks) or because the air charge has been absorbed (in older tanks). When waterlogged, the tank is full of water with no air cushion. There's virtually no stored volume between cut-in and cut-out pressure, so the pump starts almost immediately every time any water is drawn.

Signs of a waterlogged pressure tank:

• Pump starts every few seconds when water is running
• Pressure gauge cycles rapidly between cut-in and cut-out pressure
• Tank feels heavy (full of water) when knocked — should have a hollow sound in the upper portion when properly charged
• No water from the pressure relief valve on the tank when the pump cycles (this is a diagnostic check, not a DIY test to do regularly)

How to Check Your Pressure Tank's Pre-Charge

Bladder tanks have a Schrader valve (like a tire valve) on the air side — typically at the top of the tank. You can check the pre-charge pressure with a standard tire gauge:

1. Turn off power to the pump
2. Open a tap to drain all pressure from the system (pressure gauge should read zero)
3. Check the pre-charge pressure at the Schrader valve
4. The correct pre-charge is 2 psi below the cut-in pressure — so for a 30/50 system, pre-charge should be 28 psi

If you get water from the Schrader valve (not just air), the bladder has ruptured and the tank needs replacement. If the pre-charge is low (air present but pressure under spec), the bladder may be intact and you can recharge with a standard tire pump or air compressor — but investigate why air was lost.

Pressure Tank Sizing

An undersized pressure tank is nearly as problematic as a failed one. A tank that's too small doesn't store enough water between pump cycles, causing excessive short-cycling. Tank sizing is based on:

• Pump flow rate (gallons per minute)
• Pressure switch differential (cut-in to cut-out range)
• Minimum pump cycle time (we target at least 1–2 minutes per cycle)

A common residential rural Manitoba installation uses a 40–60 gallon bladder tank with a 30/50 pressure switch. Homes with higher demand (large families, irrigation, livestock watering) need larger tanks. When replacing a failed pump, it's worth evaluating whether the existing tank size is appropriate for the application — installing a new pump on an undersized tank just repeats the problem.

When to Replace a Pressure Tank

• Bladder failure: Water from the Schrader valve confirms the bladder has ruptured. The tank must be replaced.
• External corrosion: Significant rust on the tank exterior, especially at the base, indicates the shell is compromised and the tank should be replaced preventively.
• Age: Bladder tanks over 15 years old that show any symptoms should be replaced — the cost of a new tank is much less than the cost of a pump destroyed by short-cycling.
• Undersizing: If the pump is cycling too frequently even with a tank in good condition, the tank may simply be too small for the current demand.

See our post on submersible vs. jet well pump types for the pump side of this equation, and our full guide to diagnosing low water pressure from a well pump. Our well pump and pressure system service covers pressure tank replacement and complete system assessments throughout the Interlake.

Frequently Asked Questions

How long do pressure tanks last?

Modern bladder tanks typically last 10–15 years in residential service. Longevity depends on water quality (corrosive water shortens life), operating pressure, and cycle frequency. Older air-over-water tanks can last 20+ years if properly maintained — but they require periodic air recharging and are prone to waterlogging. When replacing a pump, it's worth inspecting the pressure tank condition and replacing it proactively if it's 10+ years old.

What pressure should my well system run at?

The most common residential setting is a 30/50 pressure switch — the pump turns on at 30 psi and off at 50 psi. Some homes run 40/60, which provides better pressure at fixtures but puts more stress on the pump and plumbing. The pre-charge on a bladder tank should be set 2 psi below the cut-in: 28 psi for a 30/50 system, 38 psi for a 40/60 system.

My pump runs constantly and never shuts off. Is that the pressure tank?

Not necessarily. A pump that runs continuously without reaching cut-out pressure usually indicates the pump can't build pressure — pointing to pump failure (worn impellers, seized motor), a broken drop pipe (water not reaching the surface), or a pressure switch stuck in the "on" position. A waterlogged tank causes very rapid short-cycling, not continuous running. Both conditions need immediate attention to avoid destroying the pump.

Can I replace a pressure tank myself?

A pressure tank replacement itself is a plumbing task — isolating the water supply, draining pressure, disconnecting the old tank, and installing the new one. A capable DIYer with plumbing experience can do it, but it requires proper connection to the existing plumbing, correct pre-charge setting, and confirmation that the pressure switch and gauge are functioning correctly. In Manitoba, any work connecting to the well system should comply with provincial well construction standards. Many homeowners prefer to have it done by a licensed plumber to ensure proper pressure settings and documentation.