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SFO Expansion Tank

Expansion tanks not only can keep pressure stable in closed system, but also protect tanks, circulating pumps, pipes and some other equipment from damage then extend service life of whole system.
  • SFO005-SFO150


  • Carbon steel+EPDM

  • Keep pressure stable for all inclosed system

  • Gasbag

  • 1 year


1. Product Description

1.1 Product introduction

  • 1st Sunflower's SFO expansion tank is a gasbag structure. Water completely does not touch the inner wall of the tank in operation so no rust and no water quality secondary pollution exist.

  • In closed loop systems such as air conditioners, solar thermal systems, boilers, and floor heating, expansion tank is to absorb the expansion volume of this system due to temperature changes in order to prevent system's pressure from changing rapidly,reduce the number of pressure reliefs of the safety valve and the number of water feeding of filling valve.

  • On water supply systems such as variable frequency and fire protection water supply, the expansion tank is mainly to buffer the start and stop of the pump and the water hammer impact caused by the opening and closing of the system valve,and to ensure that the pump has enough sleep time during the low peak period of water use,not only energy saving, but also extend the pump's service life.

1.2 Structure

  • SFO expansion tank is composed of a tank body, an gasbag, an inlet/outlet and a gas supply port.

  • Tank body is made of carbon steel and the outer layer is an anti-rust painting.

  • Gasbag's material is EPDM rubber; The pre-inflated gas between the gasbag and the tank body is filled at the factory,you don't need to refill by yourself.

2. Working principle

  • As the system pressure is higher than the pressure of the pre-inflated gas inside the tank,there will be some working fluid entering the gasbag until a new balance is reached when the expansion tank works in the system.

  • When the system pressure rises again,there will be some part of working fluid entering the gasbag, compressing the gas between the gasbag and the tank, In this case, the gas is compressed and the pressure is raised, working fluid stops entering when gas pressure is the same as system pressure.

  • On the contrary,when system pressure drops,the pressure of working fluid in the system is lower than gas pressure between the gasbag and tank, water in the gasbag is replenished into the system by extrusion in order to increase system pressure.

  • Until the system working fluid pressure is equal to the gas pressure insde tank, the water in the gasbag is no longer coming out to the pipeline, maintaining a dynamic balance.

3. Specifications and parameters

Expansion Tank-Paragraph 4

4. Selection calculation of expansion tank

4.1 Selection calculation of expansion tank

The selection formula for the expansion tank in the thermal system(Boiler, air conditioner, heat pump,solar water heater, etc.) is as follows:


In this formula,

C = Total water capacity in the system(Including boilers, pipes, radiators, etc.)

e = Thermal expansion coefficient of waterwater expansion rate at the highest water temperature during boiler operation minus water expansion rate of water temperature at system cooling ,see the table below),in standard equipment,e=0.035990℃)

P1=Precharge pressure of the expansion tankAbsolute pressure

P2=The max pressure of system operation(Absolute pressure)

V = Volume of expansion tank

Expansion Tank-Paragraph 5.1

4.2 Selection calculation of expansion tank in constant pressure system

To avoid pump start frequently,the adjustment volume of the expansion tank should meet the pump flow for a certain period of timeL/min.In a constant pressure system,the formula for calculating the expansion tank is as follows:


In this formula,
K = Pump operating coefficient ,it varies with pump power,see the table below for details:

expansion tank-5.2

Amax = Maximum flow of pumpL/min

Pmax = Maximum working pressure of pumpSystem pressure when pump is stopped,the pressure is absolute

Pmin = Minimum working pressure of pump System pressure when pump is started the pressure is absolute
Ppre = Pressure tank pre-charge pressure the pressure is absolute
V = Volume of the pressure tank
Among them, 1HP= 0.75KW

5. Product installation

  • In a solar pressure circulating system, expansion tank shoud be installed near the inlet of the water pump.

  • In the water supply system,expansion tank shoud be installed at the outlet of the water pump.

  • In thermal systems (such as air conditioners, boilers, heat pumps, solar water heaters, etc.), expansion tanks are generally installed at the return end of the system.

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