Horizontal Expansion Vessel

Product Overview

The Horizontal Expansion Vessel is a pre-charged bladder-type pressure vessel designed for installation in closed-loop heating, chilled water, and cooling systems. Its horizontal, floor-standing configuration makes it ideal for plant rooms and equipment spaces where vertical clearance is limited. Available in capacities from 8 to 5,000 litres, the vessel accommodates a wide range of system sizes — from small commercial installations to large industrial plants.

How Bladder Expansion Vessels Work

In a closed-loop hydronic system, water expands as it is heated and contracts as it cools. Without a means of accommodating this volume change, pressure within the pipework would fluctuate dangerously. The bladder expansion vessel addresses this by housing a flexible EPDM bladder that separates the system water from a pre-charged nitrogen gas cushion. As system water volume increases, it compresses the nitrogen through the bladder, absorbing the pressure rise. When the system cools and water contracts, the nitrogen expands to maintain a stable minimum pressure. This process protects pumps, boilers, chillers, and pipework from damaging pressure swings.

Construction and Materials

The vessel shell is manufactured from carbon steel, providing robust structural integrity and long service life. The internal bladder is made from EPDM (Ethylene Propylene Diene Monomer) rubber, which offers excellent resistance to water, heat, and the chemicals commonly found in heating and cooling system fluids. The nitrogen pre-charge is factory-set to suit standard system requirements and can be adjusted on site via the Schrader valve. BSP threaded connections ranging from 3/4" to 2" ensure compatibility with standard pipework across the full capacity range. The vessel is rated to a maximum working pressure of 10 bar.

Compliance and Standards

All vessels in this range are manufactured and tested in accordance with BS EN 13831, the European standard for closed expansion vessels with an internal diaphragm for installation in water installations. Compliance with this standard ensures the vessel meets rigorous safety, performance, and quality requirements, and supports straightforward approval by building services engineers and inspectors.

Typical Applications

Horizontal expansion vessels are widely used across commercial and industrial building services, including central heating systems, underfloor heating circuits, chilled water distribution networks, and process cooling loops. Their horizontal orientation and broad capacity range make them a versatile solution wherever space constraints or system volume demands require an alternative to conventional vertical vessels.