Zilmet CAL-PRO Heating Expansion Vessel | 4-35L | 3/4in G Type A

Description

The Zilmet CAL-PRO Heating Expansion Vessel is a maintenance-free pressure vessel designed to absorb the increase in water volume that occurs as a sealed central heating system heats up. Manufactured with a synthetic SBR diaphragm and a durable epoxy-polyester powder-coated carbon steel shell, it protects the boiler, pipework and radiators from the pressure spikes that would otherwise build up in a closed circuit.

The CAL-PRO range spans 4 to 35 litre capacities on a consistent 3/4″ G connection, with the vessel's inlet connection on the underside (Type A) for direct mounting onto system pipework. Every vessel is 100% factory tested before despatch, giving confidence the diaphragm and shell are leak-free from the moment of installation.

SBR

Diaphragm Material

99°C

Max Working Temp

3/4″ G

Connection Size

100%

Factory Tested

Type A

Bottom-Mount Style

6 Sizes

4-35 Litre Range

Please Note

Sources disagree on the maximum working pressure for this range. Zilmet's own CAL-PRO documentation states a maximum working pressure of 5 bar for the 4-8 litre sizes and 4 bar for the 12-35 litre sizes. Some UK retail listings for this product instead quote a flat 10 bar rating across the whole range, which matches the specification of a different Zilmet product line rather than CAL-PRO. Given this conflict, please confirm the maximum working pressure on the vessel's own identification label, or with Zilmet directly, before finalising system design.

Important Safety Information

The system in which this vessel is installed must include a pressure-limiting device such as a pressure relief valve, and sizing calculations must be carried out by a competent heating engineer. This vessel is designed for heating systems only and is not intended for potable (drinking) water use.

Good to Know

The Type A design places the connection on the underside of the vessel, allowing it to be mounted directly onto system pipework rather than requiring a separate wall bracket for the smaller sizes.

Factory Pressure-Tested

Every vessel is 100% factory tested before it leaves production, checking the shell and diaphragm are leak-free from day one on site.

SBR Diaphragm

A synthetic SBR membrane, sized to each vessel's capacity, separates the system water from the air cushion to maximise the vessel's usable drawdown.

Durable Powder-Coated Finish

A long-lasting epoxy-polyester powder coating resists corrosion in damp plant rooms and airing cupboards, and gives a neat, professional appearance.

Direct Pipework Mounting (Type A)

The bottom-mounted connection lets the vessel be fitted directly onto system pipework, simplifying installation in the smaller sizes.

Consistent Connection Size

A 3/4″ G connection is used across the whole range, keeping fitting requirements consistent whichever capacity is selected.

Wide Sizing Range

Available across 4, 8, 12, 18, 24 and 35 litre capacities, covering everything from compact systems to larger domestic heating installations.

Vessel Specification

Manufacturer

Zilmet (CAL-PRO range)

Application

Sealed central heating systems (not potable water)

Max. working temperature

-10°C to +99°C

Connection

3/4″ G

Mounting style

Type A (bottom connection, direct pipework mount)

Diaphragm

Synthetic SBR

Shell

Carbon steel, epoxy-polyester powder coated

Compliance

Manufactured to CE norm 97/23 (Pressure Equipment Directive)

Capacity

Manufacturer Code

Connection

4 Litre

4669-060

3/4″ G

8 Litre

4669-061

3/4″ G

12 Litre

4669-062

3/4″ G

18 Litre

4669-063

3/4″ G

24 Litre

4669-064

3/4″ G

35 Litre

4669-065

3/4″ G

What is the maximum working pressure of this vessel?

Manufacturer documentation for the CAL-PRO range states 5 bar for the 4-8 litre sizes and 4 bar for the 12-35 litre sizes. As some listings for this product quote a different figure, please confirm the rating on the vessel's own label or with Zilmet before finalising system design.

Is this vessel suitable for potable hot water use?

No. This is a heating-only expansion vessel and is not intended for potable water systems. A dedicated potable expansion vessel should be used for unvented hot water cylinders.

What size vessel do I need for my system?

Vessel sizing depends on total system water content, boiler output, and the working pressures of the system and safety relief valve. This calculation should always be carried out by a qualified heating engineer rather than selected by system type alone.

What does 'Type A' mean?

Type A refers to the vessel's connection being on the underside, allowing it to be mounted directly onto pipework rather than requiring a separate wall bracket.

How is the vessel maintained after installation?

The pre-charge pressure should be checked periodically against the value on the vessel's label, and the outer casing can be cleaned using water and mild soap only.

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Room Dimensions

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Width (in m):

Height (in m):

Room Type

Living Room

Bedroom

Kitchen

Bathroom

Conservatory

Hallway

Glazing Type

Single Glazed

Double Glazed

Triple Glazed

External Walls

0 Wall

1 Wall

2 Walls

3 Walls

4 Walls

Insulation Level

Poor

Average

Good (New Build)

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