The recognised method of deciding on the number of ring weights re-enired to balance a certain pressure in a dead-weight safety valve, the latter being fixed, is to put all the rings on and, when the water is in the apparatus, to lift one or more rings off until the valve just leaks; then put buck again the ring last removed to stop the leak. Some people, after putting a ring back to stop the leaking, put one more on, to make sure. The rings generally represent a pressure of about 41b. to 61b. per square inch, but this depends on the weight of the ring and the area of the aperture it closes. A 1-lb. ring bearing on an aperture of lsq. in. area would represent 1 lb. per square inch, and the pressure is increased by making the ring heavier and the hole smaller.