Bell & Gossett Expansion Tanks: Models Overview

Bell and Gossett expansion tanks are one of the most specified products in the hydronic and plumbing systems market. Selecting the right Bell & Gossett expansion tank protects your system from over-pressurization, prevents equipment damage, and ensures long-term operational efficiency.

This guide covers everything you need to know: how expansion tanks work, the three main Bell and Gossett expansion tank product families, how to approach expansion tank sizing using Bell and Gossett's tools, piping diagram considerations, and how to get the right product for your application.

Further, it will complement an older article we posted, which provides additional insights into expansion tanks, including explanations of bladder/diaphragm systems and installation best practices. Feel free to read a bit more about the Bell & Gossett expansion tank features on this link.

What Is a Bell & Gossett Expansion Tank

When a fluid gains energy and its temperature rises, it expands. The expansion tank accommodates the extra volume in the system caused by temperature fluctuations, maintaining pressure within safe operating limits. Without a properly sized and installed expansion tank, system pressure will rise beyond the relief valve setting, leading to nuisance valve discharges, premature pump seal wear, waterlogged piping, or, in extreme cases, permanent equipment failure.

How an expansion tank works
Video credit: Ter-en

The Core Functions of an Expansion Tank

Absorbs volume expansion caused by the thermal variations in the fluid to prevent over-pressurization.
Maintains minimum system pressure to prevent equipment damage.
Reduces cycling of pressure relief valves, extending their service life.

Bell and Gossett Expansion Tank - How It Works
Image credit: Angi

Bell and Gossett Expansion Tank - How It Works
Image credit: Angi

Bell & Gossett Expansion Tank Product Families: The Three Subgroups

The Bell and Gossett expansion tank range is divided into three distinct product families, each engineered and built for specific applications, tailored to their requirements. Understanding the differences is essential for selecting the correct expansion tank type and sizing. Modern expansion tanks use two different material arrangements in their construction, as we will see in the article: Bladder or Diaphragm. We've published an entire article explaining the differences, advantages, and disadvantages of each. It can be found on this link. Below are the Bell & Gossett expansion tank, subgroups as mentioned:

HVAC Tanks - Hydronic Heating and Cooling Systems

Bell and Gossett HVAC expansion tanks are designed for closed hydronic systems, including hot water heating, chilled water, condenser water, and dual-temperature systems. These tanks are the most commonly specified product in commercial and institutional buildings.

HVAC Expansion Tank Usage

Bell and Gossett HVAC tanks family use a pre-charged bladder or diaphragm (both options available) to separate the system fluid from a pressurized air cushion. With the water expansion, it compresses the air charge through the flexible membrane, absorbing the volume change without allowing air to enter the water circuit - a critical advantage over older open-type or compression tanks that allowed oxygen absorption and corrosion.

Bell and Gossett HVAC Tank Models
- Bell and Gossett Plain Steel Compression Tanks (ASME) - with the classic compression tank arrangement, they are designed for smaller systems. Available in standard and ASME-rated (nationally available only) configurations. Compatible with B&G tank fitting accessories for easy connection.
Bell and Gossett Compression Tanks (Plain Steel)
- Bell & Gossett Pre-charged Bladder & Diaphragm Expansion Tanks (ASME) B and D Series - factory pre-charged bladder tanks for hydronic systems. Available in horizontal and vertical configurations, with capacities ranging from small residential to large commercial sizes.
Bell and Gossett Expansion Tanks - B and D Series
- Bell and Gossett Small Diaphragm Tanks (Non-Code) - HFT Series - The Series HFT tank is designed to absorb the extra volume created by the thermal expansion of heating water and maintain proper pressurization in small closed hydronic systems.
Bell and Gossett Small Diaphragm Tanks Non-Code - HFT Series
Plumbing System Potable Water Tanks

As plumbing codes have evolved - particularly with the widespread adoption of backflow preventers, pressure-reducing valves (PRVs), and check valves in domestic water lines - closed plumbing systems have become the norm in commercial and residential construction. A closed plumbing system requires a thermal expansion control tank to prevent pressure buildup from water heater operation. These series are PDA/FDA approved, completely isolating the water from the steel shell (an integrated bladder integrity monitor is included in some models; to be checked), distinguishing them from HVAC expansion tanks, which are not rated for potable water service.

Bell and Gossett Plumbing Potable Water Tank Models
- Bell and Gossett Potable Water Diaphragm Expansion Tanks (ASME) - PTA Series - PTA expansion tanks are ASME-rated, pre-charged diaphragm-type vessels designed to absorb the extra volume of expanding water and protect a potable water system from pressure buildup (FDA Approved).
Bell and Gossett Potable Water Diaphragm Expansion Tanks (ASME) - PTA Series
- Bell & Gossett Potable Water Diaphragm Expansion Tanks (Non-Code) - PT Series - “PT” tank is designed to absorb the extra volume of system-expanding water and protect the domestic water system from pressure buildup (FDA Approved).
Bell and Gossett Potable Water Diaphragm Expansion Tanks (Non-Code) - PT Series
Well Water System Potable Water Tanks

A pre-charged bladder or diaphragm inside the tank separates pressurized air (the air charge) from the well water. When the pump runs, water enters the tank, compressing the air charge. As household fixtures demand water, the stored pressure delivers it without requiring an immediate pump start. The pump only activates when the tank pressure drops to the cut-in setting.

Bell and Gossett Well Water System Potable Water Tank Models
- Bell & Gossett Pre-Charged Expansion Tanks for Well Water (ASME) - WTA Series - WTA expansion tanks are ASME-constructed, pre-charged vessels designed for potable well water and booster pump systems. The WTA tanks help protect the pump and other equipment (e.g., pressure switches) against short cycling.
Bell & Gossett Pre-Charged Expansion Tanks for Well Water (ASME) - WTA Series

Choosing the Right Tank for Your Application

The Bell and Gossett expansion tank selection process begins by identifying the system type and fluid.

Use the table below as a quick reference to ensure the correct model selection:

Application	Model
Small HVAC Systems + ASME required	Plain Steel Compression Tank
Small HVAC Systems, no ASME required	HFT Series
Medium/Large HVAC Systems + ASME required	B and D Series
Potable Water System + ASME required	PTA Series
Potable Water System, no ASME required	PT Series
Well Water Systems (ASME required or not)	WTA Series

Note: The information above can be useful as a product guide for quick selections and simulations. For complex projects and arrangements, checkings and validations, don't hesitate to contact the Liberty Supply Sales Team.

Bell & Gossett Expansion Tank Sizing: How to Get It Right

It's important to size the expansion tank according to the correct guidelines to ensure optimized operation; undersized expansion tanks lead to constant pressure relief valve operation, waterlogged bladders, and system pressure complaints. On the other hand, oversized tanks waste money and space. Correct Bell and Gossett expansion tank sizing requires accurate inputs - and the right tool.

The ESP-Systemwize Online Sizing Tool

B&G's ESP-Systemwize platform is the industry-standard digital tool for expansion tank selection. It handles all three tank categories and produces a model recommendation, the required pre-charge pressure, and complete product data with a single click. Access it at esp-systemwize.com under the Expansion Tanks module.

Bell and Gossett - System Syzer Expansion Tank

Manual Sizing: Variables for HVAC Expansion Tanks

For quick manual sizing, usually used a pre-expansion tank selection, the formula below is used and balances the volumetric expansion of system fluid against tank capacity:

Vt = (Vs × e × Pa) / (Pa – Pf)

Vt = Tank Volume
Vs = Total System Volume
e = Fluid Expansion Factor
Pa = Atmospheric Pressure
PF = Minimum Fill Pressure

This calculation must account for glycol concentration if antifreeze is used, as glycol solutions expand at different rates than pure water and have different density-temperature relationships.

Note: If you have any questions or need further information to select the correct expansion tank volume, Liberty's sales team is available to support you. Don't hesitate to give us a shout.

Common Sizing Mistakes to Avoid

Below we are leaving some tips to avoid some common sizing mistakes that can lead to inefficient system operation in the future:

Forgetting to include pipe volume when calculating system volume (Vs).
Using wrong glycol expansion factors - always use the actual solution percentage.
Setting pre-charge pressure incorrectly.
Ignoring MAWP (Maximum Allowable Working Pressure: the tank's maximum working pressure must exceed the relief valve settings.
Specifying an HVAC tank for a potable water application

Frequently Asked Questions

What is the difference between a compression and a bladder expansion tank?

A compression tank is a plain-steel vessel; the water contacts the air cushion directly. A bladder or diaphragm tank uses a flexible membrane to separate the air charge from the water, eliminating air absorption and maintaining a consistent pre-charge pressure. The main difference is the direct contact between air/water.

How do I find the right Bell & Gossett expansion tank size for my system?

Use the ESP-Systemwize online tool at esp-systemwize.com for automated sizing. Enter your system type (HVAC or plumbing), system volume, operating temperatures, fill pressure, and MAWP. The tool returns a recommended tank, pre-charge pressure, and submittal data. For systems with glycol, input the actual solution concentration — glycol significantly increases the expansion factor compared to plain water.

What happens if an expansion tank is too small?

If an expansion tank is undersized, it may not fully accommodate the system's thermal expansion. This can cause pressure relief valves to discharge, system pressure to spike, pump seals to wear prematurely, or the tank bladder to fail earlier than expected.

What happens if an expansion tank is too large?

An oversized expansion tank usually will not damage the system, but it can waste money, take up unnecessary space, and make installation more difficult. Correct sizing is still important because the goal is to provide the required acceptance volume without over-specifying the tank.

B&G Pumps and Tanks Available in Liberty Supply

Check the B&G Tank Ranges Available

Liberty Supply is a customer-centric organization. We focus on hydronic and steam systems for commercial and industrial facilities. As a B2B distributor within the "needs business," our foundational pillars are knowledge, communication, and speed. Relationships are built through hard work and consistent delivery of value. No exceptions. Our team maintains that with each transaction, we start back at zero.