Condensate enters the tube A and flows out past the valve C. The tube A is made of copper which expands considerably more than the iron body B. When the tube A expands it closes the opening at C by moving towards C. The valve C is pressed towards the tube A by the Spring E. The two nuts D allow adjustment to be made so that the valve shuts tight at any desired temperature. The spring E allows the valve to be pressed back by undue expansion of tube A should the trap be fitted to a line where the temperature is higher than that for which the valve is set, or in case superheated steam reaches the trap