This thermostatic radiator valve is designed to be fitted in any orientation & with water flowing in either direction the valve must not be directly exposed to sunlight & curtains or decorative elements must not stop the air from circulating freely. The loose Tap head or return valve (lockshield) must be fitted on the output side of the radiator. This is used to balance the temperature of the whole system & has a loose fitting head which prevents tampering once it has been set.