Expansion tanks

Our expansion tanks are designed and manufactured under both the Ad Merkblätter design code and ASME Section VIII, Division I U Stamp.

The normal version of these tanks connects to the heat oil collection tank without pressurization. The volume of these expansion tanks depends on three factors: the type of heat transfer fluid, the temperature of the circuit and the total volume of the system. Consult our engineering department for proper sizing of the tank volume.

Our tanks are provided with a level switch connected to the heater control cabinet which emits a general stop alarm when the level is insufficient. It also has a lateral magnetic sheet visual level easily visible from anywhere.

These tanks also have all the associated instrumentation, valves and tubing and are therefore ready for assembly.

In the absence of nitrogen pressurization, generally we recommend they are installed about 2 meters above the highest point of the facility.

Pirobloc’s expansion tanks also have a safety valve for the discharge leading to the collection tank, a vacuum breaker valve and another drain valve.

The volume of the expansion tank is based on the total volume of the heating
oil circuit, working temperatures and the type of fluid used.


Key features

  • Horizontal design
  • Design pressure: 10 bar
  • Temperature: 260 ° C
  • The construction material of the expansion tanks is ASTM A 516 Gr. 60
  • Total corrosion thickness 3 mm.
  • They have a 150 lb 24” manhole, and nitrogen intake for circuit pressurisation and inertisation.
  • They include all control valves and pressure transmitters for split-range regulation.


  • Pressurization with nitrogen
  • Thermal insulation
  • ATEX version
  • Internal warming
  • Our expansion tanks can be designed and made for locations classified as having an ATEX explosion hazard.
  • They can also include a heating element to prevent the fluid freezing when ambient temperatures are extremely low. In these cases, thermal insulation for the tank and its associated tubing is also included.
  • Our expansion tanks can be supplied mounted on skids with all control instrumentation and safety elements.


Expansion tank level control is carried out by a magnetic reed level transmitter also including a minimum level alarm. This instrument allows the tank’s level to be read easily, regardless of its accessibility. It basically consists of a chamber parallel to the tank, connected to it at two points, in which a float with a magnet moves which shows the position of the fluid level on an external strip with magnetic reeds.

This magnetic reed transmitter reduces to a minimum the risk of leaks due to accidents involving breakages which may occur in other systems which use, e.g., glass or methacrylate in their reading chambers containing the hot oil.

It is vertically mounted on the side of the expansion tank with flanges.
Electrical switch or continuous reading signals are added to complement it.

Profibus or Hart communication can also be provided for integration in distributed control systems (DCS), as well as safety integration levels (SIL) and ATEX area classification.

  • Acceptable temperature range: -200ºC to +400ºC.
  • Optimum viewing without power input.
  • Indication proportional to the depth of the tank’s contents.
  • Simple, robust, solid design, with multiple possible configurations.
  • Pressure separation between the chamber and local indicator.


Expansion tanks are intended to be used in closed circuits of water or other fluids, to allow for their expansion following a temperature increase in the heating fluid.

The Pirobloc DE-2500-V-HP expansion tank is a reservoir suitable for being pressurized, with a diaphragm dividing the tank into two parts (air and fluid). This maintains a constant pre-set pressure by a change in the volume of fluid inside the tank and later, as it is emptied of fluid, of the air inlet without oil via a compressor, until the established or desired working pressure is again reached.

It is therefore responsible for compensating for the increase in fluid volume and preventing the circuit pressure from exceeding the nominal pressure of its components.

General features

The tank, made of steel, is designed and built according to the design code ASME BPVC VIII Div.1 Ed. 2015.

It is of vertical orientation and supported on 4 metal “L-profile” legs welded on 4 base plates with drill holes for fixing in position.

The unit is made up of two KLOPPER type torispherical ends joined together by cylindrical sheet metal, through joints welded by officially approved procedures and personnel, according to the aforementioned design code.

To comply with operation and safety requirements, the tank is equipped with an overpressure safety valve, a socket indicating the pressure in the tank and a fluid inlet and outlet.

The tank contains an EPDM membrane fixed in the bottom of the tank via a flanged connection arranged to allow the entrance of fluid in its interior.
This membrane completely isolates the air inside and provides practically the total capacity of the tank as expansion volume.

The technical features of the expansion vessels are shown on the rating plate: year of manufacture, volume in litres, maximum and minimum admissible temperature (TS), maximum admissible pressure (PS), group to which the fluid belongs (air, water or other fluid), pre-load pressure category to which it belongs and test pressure (PT). The technical features described on the expansion vessel rating plate must be preventively checked to be compatible with those of the facility, as well as checking that the prescribed limits are never exceeded.

The sealing and resistance to pressure of the tank is verified by a hydrostatic test of at least 60 minutes duration. According to the code ASME BPVC VIII Div.1 – UG-99, this test must be at least equal to PS x 1.3 x LSR, where, PS is the equipment design pressure and LSR the stress ratio of the materials the container is constructed with.


The increase in fluid volume as a result of its increase in temperature is driven and directed towards the tank.

As the fluid enters the tank, it does so inside the diaphragm or membrane, which separates the air and fluid. The entry of fluid expands the volume of the membrane, causing a decrease in the initial volume of air contained within the tank and the consequent increase in pressure.


Before installing an expansion tank, a proper dimensioning exercise must be carried out, according to precise calculation rules, by authorized technical personnel following the regulations applicable in the country of destination.

Installing a pressurized device which is not properly dimensioned can cause damage to people, pets or property, as well as the device itself. All pressure devices must be installed and maintained by specialized personnel in accordance with the national regulations of the country in which the device is installed.

Before installation, make sure there is sufficient space for maintenance and disassembly of valves, instrumentation or other parts of the facility.

The equipment must be provided with a suitable tared safety valve at a pressure not exceeding the maximum pressure of the expansion vessel, taking into account the difference in level between the safety valve position and expansion vessel.

  • Check that the tank has not suffered damage during transport or handling. If this happens, it should be repaired.
  • Place the tank on a clean, flat base.
  • The tank must be resting freely on its legs in a vertical position.
  • The proper positioning of the tank and its support must be verified, so it cannot be damaged.
  • Connect the equipment compressor and control panel.

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