From HERE
Most instant electric heaters incorporate a means of compensation for the
variations in mains supply pressures to achieve an even flow and thus a
stable showering temperature. The device used may be one of the
following:
i. Flow regulator
ii. Pressure reducing valve
iii. Fully modulating solenoid valve to accurately control the flow as in the Mira
Advance ATL
Instantaneous electric showers should be fitted with a pressure relief device
or some no less effective device. This is a built-in safety feature to prevent
excessive heater tank pressures, which could be caused by either freezing
or a blocked outlet pipe. If a unit is suspected of being frozen it must not
be used and must be allowed to thaw before use.
The regulator regulates the flow of water using a soft rubber ‘O’ ring that
fits over a tapered insert. The water flow squeezes the ring onto the taper
and so reduces the hole size, thus reducing and regulating the flow rate. It
is not too affected by a back pressure change, e.g. raising or lowering the
handset, and requires higher pressures than other devices to make it work
effectively. The regulator can suffer from hysteresis, i.e. it does not always
return to the same flow after a pressure fluctuation, resulting in a slight
change in the shower temperature.
The pressure reducing valve keeps a constant flow by the action of a spring
on a diaphragm. It is affected by back pressure, but recovers well after
supply pressure changes.
Modulating solenoid valve keeps a constant showering temperature by
varying the flow rate of water to accommodate changes in:
iv. The supply pressure
v. The supply temperature of cold water
vi. The mains electrical voltage.
This is achieved by measuring the flow rate, incoming and outgoing
temperatures of the water and computing the correct flow rate for the
conditions.
Most instant electric heaters incorporate a means of compensation for the
variations in mains supply pressures to achieve an even flow and thus a
stable showering temperature. The device used may be one of the
following:
i. Flow regulator
ii. Pressure reducing valve
iii. Fully modulating solenoid valve to accurately control the flow as in the Mira
Advance ATL
Instantaneous electric showers should be fitted with a pressure relief device
or some no less effective device. This is a built-in safety feature to prevent
excessive heater tank pressures, which could be caused by either freezing
or a blocked outlet pipe. If a unit is suspected of being frozen it must not
be used and must be allowed to thaw before use.
The regulator regulates the flow of water using a soft rubber ‘O’ ring that
fits over a tapered insert. The water flow squeezes the ring onto the taper
and so reduces the hole size, thus reducing and regulating the flow rate. It
is not too affected by a back pressure change, e.g. raising or lowering the
handset, and requires higher pressures than other devices to make it work
effectively. The regulator can suffer from hysteresis, i.e. it does not always
return to the same flow after a pressure fluctuation, resulting in a slight
change in the shower temperature.
The pressure reducing valve keeps a constant flow by the action of a spring
on a diaphragm. It is affected by back pressure, but recovers well after
supply pressure changes.
Modulating solenoid valve keeps a constant showering temperature by
varying the flow rate of water to accommodate changes in:
iv. The supply pressure
v. The supply temperature of cold water
vi. The mains electrical voltage.
This is achieved by measuring the flow rate, incoming and outgoing
temperatures of the water and computing the correct flow rate for the
conditions.
