What are Expansion Vessels
An expansion vessel is a small tank installed in closed water heating or plumbing systems to maintain safe water pressure by absorbing excess water pressure caused by thermal expansion.
When water is heated, it expands in volume. In a closed system like a residential water heater or boiler, that expanding water has nowhere to go, so it creates a rapid pressure buildup unless there is an expansion vessel.
The expansion vessel contains a bladder inside that is pre-pressurized with air on one side and connected to the water system on the other. As the water pressure rises due to thermal expansion, it compresses the air pocket, giving the expanding water a space to move into while maintaining optimal system pressure. This prevents pressure relief valves from leaking and protects plumbing and valves from excessive strain and damage.
So in summary, expansion vessels are essential components in closed hydronic heating and domestic hot water systems to maintain safe pressure levels by absorbing the volume increase that occurs when water is heated. They allow the system pressure to fluctuate within a safe range rather than building to dangerous levels or being released through leaks.
How Do Expansion Vessels Work?
Expansion vessels are designed to regulate water pressure in a closed heating or plumbing system. Here is how they work:
When water is heated, it naturally expands in volume. In a closed system like a residential hot water heater, this expansion causes an increase in water pressure due to the fixed volume of the pipes and tank. If the pressure gets too high, it can damage plumbing fixtures, joints, and valves.
Expansion vessels counteract this pressure increase by providing space for the expanded water to go. An expansion vessel is a small tank, usually with an internal bladder or diaphragm. It is installed on the water supply line. As the system pressure rises from heated water expansion, the increased pressure pushes water from the system into the expansion vessel. This regulates the pressure, preventing it from getting dangerously high.
When the system starts to cool and water contracts, the pressure drops. The bladder or diaphragm inside the expansion vessel then pushes the stored water back into the system to maintain optimal pressure. This process repeats in cycles as the system heats and cools.
By giving heated water a space to expand into, the expansion vessel smooths out pressure fluctuations. This protects the plumbing system from damage and keeps water pressure consistent for proper performance of fixtures and appliances.
Why are Expansion Vessels Important?
Expansion vessels play a critical role in maintaining proper water pressure within a plumbing system. Without an expansion vessel, a number of problems can occur:
- **Damage to plumbing components**: When water is heated, it expands in volume. In a closed system like plumbing, this expanding water has nowhere to go and exerts tremendous outward pressure on pipes, joints, valves and more. Over time, this pressure can cause leaks, cracks and complete component failure. An expansion vessel provides space for the expanded water to move into, preventing damage.
- **Premature pump failure**: Pumps have to work harder when pressure builds, putting extra strain on their motors and seals. Constant pressure spikes lead to faster wear and tear, reducing a pump's lifespan. Expansion vessels alleviate the pressure placed on pumps.
- **Thermal shock**: Sudden surges in water pressure from expansion can literally shock the system. The abrupt on-and-off hammering can weaken infrastructure and loosen sediment, clogging pipes. Expansion vessels cushion the system from these shocks.
- **Excessive noise**: Pressure spikes also create loud banging sounds from pipes and components. This bothersome noise indicates issues occurring within the plumbing. Expansion vessels muffle these noises by regulating pressure.
- **Temperature fluctuations**: Pressure fluctuations lead to unstable hot water temperatures. Expansion vessels enable consistent pressure for steady hot water delivery.
- **Higher utility bills**: All these pressure-related problems tax water heaters, pumps and infrastructure. More energy is consumed to compensate. Expansion vessels optimize system operation and efficiency.
- **Flooding risk**: Extreme pressure may unseat joints and valves, leading to leaks and water damage. Expansion tanks prevent hazardous pressure levels.
Expansion Vessel Location
When installing an expansion vessel in a plumbing system, the most important factor is locating it on the inlet side of the circulator pump. This placement allows the expansion vessel to properly absorb the increased water pressure caused when water expands as it heats up.
Specifically, the expansion vessel should be installed on the suction side of the circulator pump after any shut-off valves or check valves in the supply line. This location ensures the expansion vessel can regulate system pressure before the circulator pump.
Installing the expansion vessel on the return side or after the circulator pump would mean expanded water under high pressure could potentially bypass the vessel and cause damage elsewhere in the system. The vessel must be positioned to receive water from the boiler before it is pumped into heating zones.
For a hot water heating system, install the expansion tank on the cold water line before the water heater. The same logic applies - the expansion tank needs to be on the inlet side of the water pump to properly regulate expanded water volume and control pressure spikes.
Proper positioning of the expansion vessel is critical for it to protect the plumbing system. Make sure it is installed on the supply or inlet side before the circulator pump or valves. This allows it to absorb expanded water volume and stabilize pressure, avoiding potential damage from pressure spikes.
Sizing Expansion Vessels
Properly sizing an expansion vessel is crucial to maintain optimal water pressure in your plumbing system. The size required depends on the volume of water in your system and the temperature variance your system experiences.
To calculate the required size:
1. Determine the total volume of water in your plumbing system in liters. Include water in pipes, heaters, boilers, radiators, etc.
2. Identify the maximum temperature variance your system experiences in degrees Celsius. This is the difference between the lowest and highest temperatures.
3. Use this formula:
Expansion vessel size (liters) = Total system volume (liters) x Temperature variance (Celsius) x 0.00027
For example:
- Total system volume: 300 liters
- Temperature variance: 70°C
- Expansion vessel size = 300 x 70 x 0.00027 = 5.67 liters
The result is the minimum size expansion vessel needed for your system, in liters. Round up to the nearest common vessel size.
Properly sizing your expansion vessel prevents pressure from exceeding safe levels as water expands with heating. This protects your plumbing system and maintains optimal water pressure. Consult a professional if unsure about sizing.
Installing Expansion Vessels
Installing an expansion vessel is a straightforward process that can typically be done by a handy homeowner. Here is a step-by-step guide:
1. Turn off the water supply and drain the system. This allows you to work on the system without water pouring out.
2. Locate an appropriate location for the expansion vessel. It should be installed on the suction side of the circulator pump. Make sure it is easily accessible for future maintenance.
3. The expansion vessel will have a 3/4" or 1" threaded connection. Install a tee fitting on the pipe where you want to locate the expansion vessel. Apply thread sealant tape.
4. Screw the expansion vessel into the tee fitting. Use two wrenches to tighten - one to hold the tee fitting and one to turn the expansion vessel. Do not over tighten.
5. Install an isolation valve before the expansion vessel. This allows you to easily detach the expansion vessel for maintenance.
6. Install a pressure reducing valve after the expansion vessel to protect the vessel from excessive pressure. Set it to 2-3 psi below the tank pre-charge pressure.
7. Re-pressurize the system once all connections are made. Check for leaks during initial operation.
8. Set the tank pre-charge pressure to match the incoming water pressure. This is crucial for proper operation.
9. Insulate the expansion vessel if located in an unheated space to prevent freezing.
Follow the manufacturer's instructions for specific details on installing your expansion vessel model. Take care to properly size, locate, and adjust the vessel so it can effectively maintain optimal pressure.
Maintenance
Proper maintenance is critical to ensure expansion vessels continue functioning properly over time. Here are some key maintenance tips:
Inspecting the Expansion Vessel
- Visually inspect the expansion vessel annually. Look for any signs of corrosion, damage, or leakage.
- Check that the pre-charge pressure is still optimal. This can be tested with a pressure gauge. The optimal pressure level will be printed on the vessel or in its manual.
- Confirm the air pocket inside still contains air. Over time, air can dissolve into the water, reducing the air cushion.
- Ensure all connections to the vessel are still tight and secure.
Testing the Expansion Vessel
- Shut off the water supply and drain the system to lower the pressure.
- Watch to see if the pressure gauge on the vessel drops. If it does, that indicates air has leaked out of the vessel.
- Turn the water supply back on. The pressure should rise again as the vessel rebounds. No change indicates a problem.
Replacing Expansion Vessels
- Expansion vessels may need replacement every 5-10 years. Signs include inability to maintain system pressure, slow filling, frequent pressure fluctuations, or failure in testing.
- Choose a replacement with equal or larger capacity than the original vessel.
- Follow manufacturer instructions to remove the old vessel and install the new one.
- Repressurize the system and perform tests to ensure optimal function.
Regular inspection, testing, and replacement of expansion vessels is key to identifying issues before they cause major system problems. Contact a professional for assistance in monitoring your expansion vessel over time.
Troubleshooting Common Expansion Vessel Problems
Expansion vessels play a critical role in maintaining proper water pressure in your plumbing system. However, they can develop issues over time that lead to pressure fluctuations and other problems. Here are some of the most common expansion vessel troubles and how to address them:
**Loss of Precharge Pressure**
The precharge pressure is the amount of air pressure in the tank when there is no water pressure present. This pressure cushion is what allows the expansion tank to absorb excess water volume. If the precharge pressure drops due to a leak or failure of the tank's bladder, the expansion vessel won't be able to control pressure properly. Checking and adjusting the precharge pressure requires a special pump. Have a plumber assess and restore the proper precharge if you suspect it's low.**Waterlogged Expansion Tank**
If the bladder inside the expansion tank has ruptured or failed, water can enter the precharge chamber. This renders the tank unable to absorb water expansion, leading to pressure spikes. Replacing a waterlogged expansion tank is the only remedy. Make sure to drain the tank fully first.**Undersized Expansion Tank**
An expansion tank that's too small for the volume of water in your system won't be able to properly control pressure fluctuations. This leads to relief valve discharge and other issues. Confirm the right size for your system based on its volume and water heater temperature. Replace with a larger tank if needed.**Faulty Connections**
From loose fittings to leaks, any connection issues can impact expansion tank operation and water pressure control. Inspect all pipes and fittings thoroughly and make any necessary repairs. Pay special attention to the connection point on the water supply line.By identifying and addressing common expansion vessel problems, you can restore proper pressure regulation and prevent plumbing system damage. Don't hesitate to call a professional plumber if issues persist.
Expansion Vessel Alternatives
When an expansion vessel fails or is incorrectly sized, there are some alternative methods to help regulate pressure in a plumbing system. However, expansion vessels remain the recommended method in most cases.
Manual Air Vents
Manual air vents can be installed at high points in the plumbing system to allow air to escape when pressure builds up. This prevents pressure from building excessively. However, the system must be manually vented periodically, which is an inconvenience. Air vents can also allow oxygen into the system, increasing corrosion.
Pressure Relief Valves
Pressure relief valves are designed to open and release water when the pressure exceeds the valve's set point. This prevents unsafe pressure levels. However, water will be released from the valve and may cause flooding. Frequent opening of the valve can also lead to wasting water and energy.
Thermal Expansion Tanks
Small thermal expansion tanks are designed for water heaters. They can help control pressure but have very limited capacity compared to a properly sized expansion vessel for the full plumbing system. Using an undersized expansion tank will result in excessive pressure.
Correctly Sized Piping
Oversized piping can allow water to expand within the pipes themselves when heated, reducing pressure buildup. However, most plumbing systems already use the smallest piping size necessary for adequate flow rates. And relying solely on pipe expansion increases pressure levels throughout the system.
Ultimately, a properly sized bladder or diaphragm expansion vessel is the most effective means of controlling pressure from thermal expansion. Alternatives may provide partial solutions but come with drawbacks. Whenever possible, installing a correctly sized expansion vessel is recommended.
When to Call a Professional
Plumbing issues related to expansion vessels often require the expertise of a professional plumber. Here are some signs it's time to call for help:
- Frequent spikes or drops in water pressure - If you notice your water pressure fluctuating throughout the day, your expansion tank may be failing. This requires replacement by a plumber.
- Knocking pipes - If you hear banging or knocking sounds coming from your pipes when water is run, this could indicate water hammer. Water hammer happens when steam bubbles collapse in your pipes, creating shock waves. It's a sign your expansion tank needs servicing.
- Leaking expansion tank - If you notice water pooling around the expansion tank or connected pipes, the expansion tank likely has a leak. Replacement is required to prevent further water damage.
- Tank corrosion - Over time, minerals in the water can cause corrosion and rust on the expansion tank. If the tank exterior looks corroded, the internals are likely failing too.
- Age of the expansion tank - Expansion tanks typically last 8-12 years before needing replacement. If your tank is over 10 years old, it's a good idea to have it inspected and tested by a plumber.
- Inability to maintain pressure - If your home's water pressure drops below 40 psi despite an expansion tank being installed, the tank may not be working properly. A plumber should check the precharge pressure and tank functioning.
Calling a professional plumber to diagnose and repair expansion tank issues can prevent more serious problems like leaks, water damage, burst pipes, and mold. Don't delay - consult an expert plumber if you notice any of the above signs.