Expansion Control Valves
Expansion Control Valves (ECVs) are fitted to the cold water inlet to water heater, downstream of the inlet non-return valve. The ECV acts as the relief valve in the system.
The ECV is always selected to be a lower pressure setting than the mandatory P&T Relief valve, so that as the water heater goes through a heating cycle, the ECV relieves the resulting expansion of water to the drain line. As the ECV is fitted to the cold water inlet, the water relived to drain will be cold. If no ECV is fitted, the expansion control is catered for by the P&T Relief valve which relieves hot water to drain. The ECV does not have a temperature probe fitted to it and operates in response to overpressure only.
It is normal for a mains pressure hot water service to relieve several litres of water whilst going through a heating cycle. By relieving pressure at the cold inlet, energy is conserved. Over the course of a year considerable savings can be made by installing a cold water ECV to a water heater system. Additionally, by discharging cold water instead of over-pressure (and possibly over temperature!) heated water, there is a lower risk of scalding at the drain line.
The H50/H75 ECVs are for application on mains pressure heaters. The LV50/LV75 valves are for use on low pressure water heaters. The HPNR valve is a unique model specifically intended for application on heat exchange type water heaters.