Balances pressure fluctuation
Water expands as it heats up; the expansion tank holds this extra volume in the air cushion behind the diaphragm, keeping system pressure within a safe range.
Product group · Pressure Vessels
Expansion Tanks
Expansion tanks absorb the volume increase of heated water through a diaphragm, preventing pressure from rising in the piping. A correctly selected expansion tank keeps the safety relief valve from opening unnecessarily and prevents water loss. At Denfor Endüstriyel, we supply closed-type diaphragm expansion tanks sized to the system volume and working pressure of heating, cooling and domestic water lines.
Volume8 – 3000 L
Working pressure3 – 10 bar
TypeHeating / cooling / domestic water
DiaphragmReplaceable
Why it matters
What does an expansion tank do?
It absorbs the volume increase of heated water, preventing pressure rise and water loss in the closed circuit.
Prevents water loss and relief valve opening
A correctly sized tank keeps the safety relief valve from opening unnecessarily and losing water, reducing the need for frequent top-ups.
Replaceable diaphragm design
The diaphragm can wear out over time; in replaceable-type tanks, only the diaphragm needs renewing rather than the whole shell, so the tank can keep being reused.
Dedicated types for heating, cooling and domestic water
Domestic water tanks are built with a food-grade diaphragm; heating/cooling tanks use a diaphragm suited to the system fluid.
Types
Expansion tank subtypes
All three absorb the volume increase with an air cushion behind the diaphragm; what differs is the circuit type they serve.
Heating circuit expansion tank
The standard solution in boiler and heat pump circuits, absorbing the expansion of closed-circuit water as it heats up.
- Closed heating circuit
- Economical solution
- Wide volume range
Cooling circuit expansion tank
Absorbs the volume difference caused by temperature changes in chiller and cooling circuits, keeping system pressure stable.
- Chiller circuit compatible
- Diaphragm dedicated to cooling systems
- Pressure stability
Domestic water (booster) expansion tank
Built with a food-grade diaphragm; reduces pressure fluctuation on booster pump and hot domestic water lines.
- Food-grade diaphragm
- Suited to booster pump circuits
- Hygienic domestic water
Selection criteria
What data determines the right expansion tank?
Selection cannot be made without the first two items. The rest determine the diaphragm type and fittings.
ParameterWhy it mattersWhat we need from you
System water volume
Tank volume is calculated from the total water volume in the piping.
L
Working pressure and temperature
Safety relief valve opening pressure and maximum operating temperature.
bar / °C
Circuit type
Heating, cooling or domestic water; determines the diaphragm material.
Heating / cooling / domestic water
Pre-charge pressure setting
The tank's air cushion pre-charge pressure is set relative to the system's static pressure.
bar
Diaphragm material
Food-grade for domestic water; standard EPDM for heating/cooling.
Diaphragm type
Connection size and installation point
Inlet port size and installation position (usually pump suction).
DN size + installation point
For a quote, having the following is enough
It's fine if you don't have all of it. We'll fill in the gaps together with you.
Create a quote request- Total system water volume
- Working pressure and temperature
- Circuit type (heating/cooling/domestic water)
- Current static pressure
- Installation point
- Nameplate data of the existing tank (if a replacement)
FAQ
Questions from the field
The questions we encounter most often at the expansion tank quote stage.
How is expansion tank volume calculated?
It is calculated from the total water volume in the system, the maximum operating temperature, the working pressure and the pre-charge pressure; an incomplete calculation causes the relief valve to open unnecessarily.
Why does the pre-charge pressure setting matter?
The tank's air cushion pre-charge pressure must be equal to or slightly below the system's static pressure; an incorrect setting reduces the tank's effective volume.
When does the diaphragm need replacing?
The diaphragm can lose its elasticity or crack over time; if the tank keeps losing air or fails to hold pressure, the diaphragm should be inspected.
Can a heating tank be used for domestic water?
No, domestic water lines require food-grade (WRAS/KTW approved) diaphragm tanks; a standard EPDM diaphragm does not meet drinking-water standards.
Do you only serve Istanbul?
No. While our office is on Istanbul's Anatolian side (Ataşehir), we supply and ship across Istanbul's European side, the surrounding provinces and the Marmara region, and Turkey as a whole — covering your equipment end to end, from a single source.
Next step
Let's clarify your needs together
Share your system water volume and working pressure, and let's work out the right expansion tank for your line together.
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