Honeywell - Diaphragm Expansion Tanks

Honeywell - 4.4G Diaphragm Expansion Tank
Honeywell - Diaphragm Expansion Tanks
Honeywell - Diaphragm Expansion TanksHoneywell - Diaphragm Expansion TankHoneywell - Diaphragm Expansion Tank Installation Diagram
Product Dimensions: 
11 × 11 × 15.5 in
Product Weight: 
8.2 lb
Product Family: 


The Honeywell diaphragm expansion tank is designed to provide for the expansion of water in a closed hot water heating or solar system in order to manage system pressure. Maximum operating temperature is 240F (116C); maximum operating pressure is 100 psi (689 kPa). The tank is precharged at 12 psi (83 kPa). The diaphragm separates the air cushion from the water and prevents absorption of the air cushion by water, thus avoiding water logging. The Honeywell expansion tank maintains pressure in the system and utilizes the smallest possible space.

Honeywell recommends installing the expansion tank by screwing it into the 1/2 in. connection on the bottom of a Honeywell Air Eliminator or Air purger located on the main hot water supply pipe close to the boiler. The installation of a Honeywell Air Eliminator assures automatic removal of all air and microbubbles from the system. However, the Honeywell expansion tanks may also be screwed into any convenient connection. The tank should be installed in a vertical position. Series XPS tanks are provided with a stand for floor mounting. Pipe the tank connection to the inlet side of the circulating pump.

After the Honeywell expansion tank is installed on the system, fill the system and establish circulation, the Honeywell Air Eliminator will automatically vent the air from the system. Operate the boiler to bring the system temperature up to the high-limit shut-off temperature, observe the system pressure to assure that it does not exceed the relief valve setting. If the system pressure is too high, reduce to the desired pressure by drawing a small amount of water from the system or by installing the next larger Honeywell expansion tank. Do not release air from the tank. Air charge in tank should equal the setting of the reducing valve, 12 psi (83 kPa) standard.

If the system pressure is too high, check the pressure reducing valve (fill valve) for a malfunction (i.e. dirt on the valve seat). Check to see if the Honeywell expansion tank has lost air by reducing the system pressure to zero and reading the tank pressure with a tire gage. Check for possible tankless heater leak by shutting off water supply to fill valve, reducing system pressure and observing pressure increase which would indicate a leak. If the relief valve drips water after excess system pressure condition has been corrected, flush relief valve by quickly raising the lever several times. If dipping continues after flushing replace relief valve.


  • Honeywell Heating Expansion Tank, 1/2" NPT, 4.4 gal
  • Butyl diaphragm
  • Deep-drawn Welded Steel Tank
  • Pre-pressurized at 12 PSI
  • Resists: Waterlogging, Loss of Pressure, and BTU's
  • Total Volume: 4.4 Gallons
  • Usable Volume: 2.5 Gallons
  • Connection: 1/2" NPT
  • 100% Factory Tested!

The Honeywell TK300-30 Heating Expansion Tank is designed to absorb hot water expansion in closed heating systems. It is equipped with a butyl diaphragm to separate the air from the system water (glycol). The tanks are a welded, not clamped design. Pre-pressurized at 12 PSI, the tanks keeps fluid circulating and maintains minimum system pressure. Honeywell tanks resist waterlogging, loss of pressure through relief valve spills, loss of BTUs and reduce circulator running time. Use the super efficient Honeywell PowerVent or air vents to remove air and micro-bubbles from the system for maximum performance. The Honeywell TK300-30 Heating Expansion Tank has a volume of 4.4 gallons and maximum acceptance volume of 2.5 gallons. The Honeywell TK300-30 Heating Expansion Tank has a 0.5 inch NPT connection.



Honeywell Controls

With a rich history stretching all the way back to 1885, Honeywell is perhaps the most trusted provider of mission critical control systems for thermostatic and industrial process controls. Honeywell products run the gamut from simple solenoid devices, to medical diagnostic and computerized control equipment. So, whether you need to pop valves on your HVAC manifold, or monitor and control life giving medical equipment, Honeywell has a solution!

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