SC By SCWS Team | February 2, 2026 | 12 min read
How Well Pressure Tanks Work
Your well pressure tank is more important than you might think. This cylindrical tank sitting near your well pump does far more than just store water—it maintains pressure, protects your pump from premature failure, and ensures you have instant water flow whenever you need it. Understanding how it works helps you maintain it properly and recognize problems before they become expensive repairs.
đź’ˇ Key Facts About Pressure Tanks
- • Pressure tanks use compressed air to push water through your pipes
- • They prevent your pump from cycling on/off with every water use
- • Modern tanks use bladders or diaphragms to separate air from water
- • Proper air charge is essential—check quarterly
- • A failed bladder leads to "waterlogging" and rapid pump cycling
The Basic Principle: Air Pressure Pushing Water
A pressure tank works on a simple principle: compressed air pushes water. When your well pump runs, it fills the tank with water. This water compresses the air inside, storing energy like a spring. When you open a faucet, that compressed air pushes the water out—no pump needed, at least for a while.
Think of it like an inflated balloon filled with water. The air inside the balloon wants to expand, so it pushes the water out. Your pressure tank works the same way, just on a larger, more controlled scale.
This stored energy (called "drawdown") provides several critical benefits:
- Instant water: Water flows immediately when you turn on a faucet—no waiting for the pump to start
- Consistent pressure: Pressure stays relatively stable as you use water
- Pump protection: The pump doesn't have to start and stop constantly
- Energy savings: Fewer pump starts means less electricity used
Types of Pressure Tanks
There are three main types of pressure tanks, each using a different method to keep air and water separated:
🛢️ Pressure Tank Types Compared
Modern Standard
Bladder Tank
Balloon-like bladder holds water, air surrounds it. Most common in new installations. Easy to check air pressure.
Alternative Design
Diaphragm Tank
Flexible rubber divider separates air and water sections. Similar function to bladder, different construction.
Older Style
Air-Over-Water
No separation—air and water in direct contact. Requires air volume control. Mostly obsolete.
Bladder Tanks: How They Work
Bladder tanks are the most common type in modern well systems. Here's how they operate:
- At rest (empty): The tank contains only air at pre-set pressure (typically 2 PSI below cut-in). The bladder is collapsed.
- Pump starts: When pressure drops to the cut-in point (e.g., 40 PSI), the pump activates and pushes water into the bladder.
- Tank fills: As water enters, the bladder expands and compresses the air in the tank. Pressure rises.
- Pump stops: When pressure reaches cut-out (e.g., 60 PSI), the pump shuts off. The tank is now "charged."
- Water used: When you open a faucet, compressed air pushes against the bladder, forcing water out.
- Cycle repeats: When pressure drops back to cut-in, the pump starts again.
The bladder keeps water and air completely separated, which prevents air from dissolving into the water (which would reduce tank capacity over time) and protects the tank from interior corrosion.
Diaphragm Tanks: Similar but Different
Diaphragm tanks work almost identically to bladder tanks, but instead of a balloon-like bladder, they use a flat rubber diaphragm that divides the tank into two sections—air on top, water on bottom. As water fills the tank, it pushes the diaphragm upward, compressing the air.
For a detailed comparison, see our guide on bladder tanks vs diaphragm tanks.
Old-Style Air-Over-Water Tanks
Older galvanized steel tanks don't have a bladder or diaphragm—air and water are in direct contact. These tanks require additional components:
- Air volume control: A device that adds air to the tank because air gradually dissolves into the water
- More maintenance: Air charge needs regular attention
- Shorter life: Interior corrosion from water-air contact
If you have an old galvanized tank, upgrading to a modern bladder tank is usually worthwhile. See our pressure tank replacement cost guide for details.
Why Pressure Tanks Are Essential
Without a pressure tank, your well pump would have to start every single time you used water—washing hands, flushing toilets, running the dishwasher. Here's why that's a problem:
⚡ Motor Damage
Electric motors draw high current at startup. Frequent starts cause overheating and premature failure.
🔄 Switch Wear
Pressure switches are rated for a limited number of cycles. Rapid cycling wears them out quickly.
đź’¸ Higher Energy Bills
Startup current is 3-5 times higher than running current. More starts = more electricity.
đźšż Pressure Surges
Without the buffer, pressure would spike and drop constantly, causing inconsistent flow.
A properly sized and functioning pressure tank ensures your pump runs for 1-2 minutes per cycle, allowing adequate cooling and dramatically extending pump life.
Understanding Drawdown Capacity
"Drawdown" is the amount of water a tank can deliver between pump cycles. It's always less than the tank's total gallon rating because the tank is never completely filled with water—there's always compressed air taking up space.
| Tank Size (gallons) | Approximate Drawdown (30/50) | Approximate Drawdown (40/60) |
|---|---|---|
| 20 gallon | 5-6 gallons | 5-6 gallons |
| 32 gallon | 8-10 gallons | 8-10 gallons |
| 44 gallon | 12-14 gallons | 12-14 gallons |
| 62 gallon | 16-19 gallons | 16-19 gallons |
| 86 gallon | 24-28 gallons | 24-28 gallons |
| 119 gallon | 34-40 gallons | 34-40 gallons |
The exact drawdown depends on your pressure settings and the tank's acceptance factor (how much of its volume can fill with water). Manufacturers provide specific charts, but the rule of thumb is about 25-30% of tank volume for common pressure ranges.
The Air Charge: Critical for Proper Operation
The pre-charge—the air pressure in the tank when empty—is critical to proper operation. Here's how to set it correctly:
🎯 Air Charge Rule of Thumb
Set air pressure 2 PSI below your cut-in pressure:
- • 30/50 system → 28 PSI air charge
- • 40/60 system → 38 PSI air charge
- • 50/70 system → 48 PSI air charge
Why 2 PSI Below?
If the air charge equals or exceeds the cut-in pressure, the bladder can never fully expand to maximum capacity. Setting it 2 PSI below ensures:
- Maximum drawdown capacity
- Bladder doesn't get stressed by over-expansion
- System operates efficiently within designed parameters
How to Check and Adjust Air Pressure
- Turn off power to the pump at the electrical breaker
- Drain all water from the tank by opening a faucet and letting it run until flow stops and pressure gauge reads zero
- Locate the air valve on top of the tank (looks like a tire valve, usually under a plastic cap)
- Check pressure with a tire gauge—use a quality gauge for accuracy
- Add air if needed using a bicycle pump, air compressor, or tire inflator
- Restore power and let the system refill
⚠️ Important
Only check air pressure when the tank is completely empty. Checking with water pressure in the tank gives false readings—you're reading a combination of water pressure and air charge, not just the air.
Signs of a Failing Pressure Tank
Pressure tank failure is one of the most common well system problems. Here's what to watch for:
🔄 Rapid Pump Cycling (Short Cycling)
The most common symptom. If your pump turns on and off every few seconds or minutes when water is running, the tank is likely waterlogged (bladder failed).
Learn more: Well Pump Short Cycling Causes
🎵 Tank Sounds Solid When Tapped
A healthy tank sounds hollow at the top (air) and solid at the bottom (water). If the entire tank sounds solid/full, it's waterlogged—no air cushion remaining.
đź’¨ Water Sprays from Air Valve
If water comes out when you press the air valve, the bladder has ruptured. Water has entered the air side of the tank.
📉 Pressure Fluctuates Rapidly
With no drawdown capacity, pressure swings wildly as the pump kicks on and off. You may notice water pressure pulsing at fixtures.
Learn more: Why Well Water Pressure Fluctuates
🦠Rust or Visible Corrosion
External rust, especially at seams or the base, indicates potential internal problems. Heavy corrosion means replacement time.
Sizing Your Pressure Tank
Proper sizing ensures your pump doesn't cycle too frequently. The goal is typically a minimum 1-minute run time per pump cycle. Here's how to determine the right size:
Sizing Formula
Required drawdown = Pump GPM Ă— Desired minimum run time (minutes)
For example, a 10 GPM pump with a 1-minute minimum run time needs 10 gallons of drawdown. Looking at the table above, that means at least a 32-44 gallon tank.
General Sizing Guidelines
| Application | Recommended Tank Size |
|---|---|
| 1-2 person household, low demand | 20-32 gallons |
| Average family (3-4 people) | 32-44 gallons |
| Large family or multiple bathrooms | 62-86 gallons |
| Irrigation + household | 86-119 gallons |
| Commercial/agricultural | 119+ gallons or multiple tanks |
đź’ˇ Pro Tip: Bigger Is Better
When in doubt, go larger. A bigger tank means fewer pump cycles, longer pump life, and more stable pressure. The only downsides are higher upfront cost and more space needed.
Pressure Tank Maintenance
Proper maintenance extends tank life and ensures reliable operation:
Maintenance Schedule
- Monthly Listen for short cycling—pump should run 1-2 minutes per cycle, not seconds
- Quarterly Check air pressure (with tank empty) and adjust if needed
- Annually Inspect tank exterior for corrosion, check all fittings for leaks
- Every 5 Years Have system professionally evaluated—consider replacement if over 10-12 years old
When to Replace Your Pressure Tank
Pressure tanks aren't repairable—when the bladder fails, the tank needs replacement. Signs it's time:
- Waterlogged tank (failed bladder) confirmed by testing
- Significant rust or corrosion on exterior
- Tank is over 15 years old (even if currently working)
- Visible damage, cracks, or leaks
- Tank consistently loses air charge despite no apparent leaks
Replacement typically costs $800-$2,500 installed, depending on tank size and accessibility. Learn more in our pressure tank replacement cost guide.
Frequently Asked Questions
What does a well pressure tank do?
A well pressure tank stores pressurized water and maintains system pressure between pump cycles. It provides immediate water flow when you open a faucet (without waiting for the pump), prevents the pump from starting every time you use water, and maintains consistent pressure throughout your home.
How does a bladder pressure tank work?
A bladder tank contains a flexible rubber bladder that separates the water from the air charge. When the pump runs, water fills the bladder and compresses the air outside it. When you use water, the compressed air pushes against the bladder to maintain pressure and push water out. The bladder prevents water-to-air contact.
What should the air pressure be in my well tank?
The air pressure should be set 2 PSI below the pump's cut-in pressure. For a 30/50 system, set tank air to 28 PSI. For a 40/60 system, set it to 38 PSI. Always check and adjust air pressure with the tank empty (no water pressure).
How do I know if my well pressure tank is bad?
Signs of a failing pressure tank include: rapid pump cycling (turning on/off frequently), the tank feels completely full of water when tapped, water spurts then weakens when faucet is opened, pressure gauge fluctuates rapidly, and reduced water pressure. A waterlogged tank means the bladder has failed.
How long do well pressure tanks last?
Quality well pressure tanks typically last 10-15 years with proper maintenance. Factors affecting lifespan include water quality (corrosive water shortens life), proper air charge maintenance, system pressure settings, and tank quality. Galvanized tanks may corrode faster than stainless or composite tanks.
What size pressure tank do I need for my well?
Tank size depends on pump flow rate and desired run time. A general rule: the tank should provide 1 minute of pump run time per cycle. For a 10 GPM pump, this means about 20-30 gallons of drawdown capacity. Larger tanks mean fewer pump cycles and longer pump life, but cost more and take more space.
Need Pressure Tank Service?
Whether you need air charge adjustment, diagnosis of short cycling, or complete tank replacement, our technicians can help. We service and install all major brands of pressure tanks throughout San Diego County.
