The number of weights, which really means the weight of metal with which the valve is loaded, is controlled hy the pressure of water in the boiler, and not by the size of the range. The customary method, when fixing dead-weight valves, is to have all the weights on when the boiler is firsc charged, and then to lift them off one at a time until water runs from the valve. Immediately water runs, put a weight on to stop the leak, and then put on one more weight - it is usual to put one weight more than is just necessary to prevent the valve leaking. This kind of valve should not be used on an apparatus having plug-cocks, that can be shut suddenly, as the sudden closing causes a shock in the pipes, and this may cause the valve to lift and eject water on each occasion that the tap is used quickly. A 3/4-in. valve is the correct size for all kitchen boilers, and for small independent boilers. A boiler having more than 20 sq. ft. of effective heating surface ought to have one 1-iu. valve or two 3/4-in. valves. The six ring weights on a valve are not always sufficient if the house is a high one, with the cistern at the top and the range at the bottom; in this case lead rings or a solid lead weight are used.

The pressure in feet should be stated when ordering these valves.