Caleffi 3 Bar Safety Valve 1/2" O-Ring Push Fit | A312438 CST

Description

The Caleffi A312438 CST is a 3 bar safety relief valve from the Caleffi 312 series, supplied with a 1/2 inch O-ring push-fit connection and a 1/2 inch BSP threaded connection. It protects hot water cylinders in domestic hot water systems and boilers and other heating components by opening and discharging to atmosphere before pressure reaches a dangerous level.

Built with a brass body and cover, an EPDM diaphragm and a stainless steel spring, it handles water and air from 5 to 110 °C with a maximum static pressure of 10 bar. The valve is WRAS approved, CE marked and classified PED category IV, making it a dependable like-for-like replacement for installers who need a certified 3 bar valve.

3 bar

Set pressure

5-110 °C

Temperature range

10 bar

Max static pressure

1/2 in

Push-fit and BSP

WRAS

Approved product

PED IV

CE marked

Safety and installation

Safety relief valves are safety-critical devices. On unvented hot water systems, installation must be by a G3 qualified installer in line with Building Regulations Part G. The outlet must be piped to a safe, visible discharge point and never capped, plugged or restricted. Do not use the valve to control system pressure and do not fit it with any isolating valve between it and the protected system.

Check the connection type before ordering

This valve has a 1/2 inch O-ring push-fit connection on one end and a 1/2 inch BSP thread on the other. Manufacturer information for this part number describes the thread end as female, whereas some trade listings describe it as male. Check which thread you need against your fitting before ordering.

Match the set pressure to your system

The valve is factory set to 3 bar. The set pressure must be at or below the lowest rated pressure of any component it protects, so confirm the maximum working pressure of your boiler, cylinder or heating components before fitting.

How it works

As pressure rises to the 3.6 bar discharge pressure, the diaphragm valve opens and discharges to atmosphere. It then re-seats at 2.4 bar, closing again once pressure has dropped back to a safe level.

Key features

3 bar set pressure

Factory set to 3 bar for typical domestic heating and hot water protection duties.

Cylinder and boiler protection

Protects hot water storage cylinders and boilers and other heating components from dangerous overpressure.

O-ring push-fit connection

The 1/2 inch O-ring push-fit end allows quick, tool-light connection where a push-fit port is specified.

Brass body, EPDM diaphragm

Brass body and cover, EPDM diaphragm, brass stem and stainless steel spring for long service life.

Water and air

Suitable for water and air across a 5 to 110 °C temperature range.

Certified product

WRAS approved, CE marked and classified PED category IV.

Technical specification

General

Brand

Caleffi

Manufacturer part number

A312438 CST

Series

312 safety relief valve

Valve type

Diaphragm safety relief valve

Medium

Water and air

Connections

Size

1/2 inch

Connection types

O-ring push fit and BSP thread

Performance (series 312, 3 bar rating)

Set pressure

3 bar

Discharge pressure

3.6 bar

Re-seating pressure

2.4 bar

Maximum flow rate

142.1 kg/hr

Maximum boiler rating

82.5 kW

Temperature range

5 to 110 °C

Maximum static pressure

10 bar

Nominal pressure

PN 10

Materials

Body and cover

Brass, BS EN 12165 CW617N

Stem

Brass, BS EN 12164 CW614N

Diaphragm

EPDM

Spring

Stainless steel

Control knob

ABS polymer

Approvals

Certification

WRAS approved, CE marked

PED category

IV

Installation notes

Isolate and drain the system before replacing a valve. Use the correct sealing method for each connection: the push-fit end relies on its O-ring seal and must be fully seated, while the BSP thread needs suitable jointing compound. Fit the valve in line with the manufacturer installation instructions, run the discharge pipework to a safe location and test the system for leaks. Confirm the valve is not installed where it can be isolated from the equipment it protects.

Frequently asked questions

What does the Caleffi A312438 CST do?

It is a 3 bar safety relief valve that opens to discharge water or air if pressure in a hot water or heating system rises too high, protecting cylinders, boilers and other components.

What connections does it have?

A 1/2 inch O-ring push-fit connection and a 1/2 inch BSP thread. Check the thread type against your fitting before ordering, as trade listings differ on whether it is male or female.

At what pressure does it open?

It is set at 3 bar. In the manufacturer series 312 data for a 3 bar valve, it discharges at 3.6 bar and re-seats at 2.4 bar.

What temperature and pressure can it handle?

5 to 110 °C with a maximum static pressure of 10 bar, for water and air.

Can I fit it myself?

Safety relief valves are safety-critical. On unvented hot water systems the work must be carried out by a G3 qualified installer, with the outlet piped to a safe discharge point.

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