Installation manual

34 ©ESP Ltd. Sept 2008
The Temperature & Pressure Relief Valve is the third and final level of protec-
tion. Although this valve does incorporate a pressure relief function, the sole
purpose of this control is to prevent the system water temperature exceeding 99°
C - the pressure relief function is not used.
The Reliance Temperature & Pressure Relief Valves are supplied in two de-
signs, Lever Type or “Twist Top” (Lever Type valves are being phased out)
and, are available in DN15, DN20 and DN25 nominal sizes. These can be sup-
plied with an extended temperature sensor probe, depending on the relevant
manufacturer‟s design and specification.
All Temperature & Pressure Relief Valves should be factory fitted to the Un-
vented unit by the relevant manufacturer.
Lever Type Temperature & Pressure Relief Valve
Originally specified for use with the first generation
systems installed in the UK, these valves incorporate
lever type easing gear. With over 20 Million valves
manufactured and, although still used in Australia and
the Far East, the demands of both the UK and European
manufacturers has seen this valve being replaced by the
“twist-top” version as the standard fitment on today‟s
units.
“Twist-Top” Temperature & Pressure Relief Valve
Developed following the demands of manufacturers for a more aesthetic,
modern design to compliment the “white goods” image of today's unvented
units, the “twist-top” valve is now becoming the standard fitment, superseding
the “old fashioned” lever type valve, and has the added benefit of direct com-
pression connections for the discharge pipework. The twist-top Temperature
& Pressure Relief Valve has also been designed to conform to the require-
ments of the latest European Standard.
Under fault conditions, the Temperature & Pressure
Relief Valve will discharge water to prevent over
temperature of the system. The drain pipework from
the valve must discharge through a Tundish, posi-
tioned within 500mm of the Temperature & Pressure
Relief Valve, to a safe and visible position to alert the
householder of a fault condition with the Unvented
System and to prevent damage to the property.
The drain discharge pipework must comply with the
relevant manufacturer‟s instructions and the require-
ment of Building Regulation G3. The Expansion
Valve will also discharge water under fault conditions
and it is acceptable practice to allow the drain pipe-
work from the Expansion Valve to discharge into the
same Tundish used for the Temperature & Pressure
Relief Valve provided the requirements of both the relevant manufacturer's
instructions and Building Regulation G3 are maintained.
UNVENTED HOT WATER STORAGE SYSTEMS AND CONTROLS