Rule.—Divide the length of the lever by the distance from the centre of the valve to the centre of the fulcrum. Multiply by the amount of the weight in lbs., and divide by the area of the valve.

Example.—The area of the valve is 8 inches, the distance from the centre of the fulcrum to the centre of the valve is 4 inches, and the distance from the fulcrum to the point of suspension of the weight 24 inches, the weight is 40 lbs., what pressure will the valve hold?

Length of lever.
From fulcrum to valve, 4 ) 24
6
40 amount of weight.
Area of valve, 8 ) 240
30
Lbs. per square inch the valve will hold = 30.

The philosophy of this is clear enough when we consider that as the weight is six times as far from the fulcrum as the valve is, and each 1 lb. of weight will press with a force of 6 lbs. on the valve, hence the 40 lbs. will press 240 lbs. on the valve, and as the valve has 8 square inches, the 240 becomes 30 lbs. for each inch of area.

Example.—The area of a safety valve is 8 inches, the distance from the fulcrum to the valve is 4 inches, and the weight is 40 lbs., how far must the weight be from the fulcrum to hold in the boiler a pressure of 30 lbs. per square inch?

In lbs.
From fulcrum to valve, 4 ) 40 amount of weight.
10
Area of valve, 8 square inches.
Pressure required, 30
10 ) 240
24
Answer = 24 inches from the fulcrum.

Example.—The diameter of a safety valve is 4 inches, the distance from the centre of the fulcrum to the valve is 3 inches, a 50 lb. weight is 30 inches from the fulcrum, what pressure will the valve hold?

3 diameter of valve.
3
9
.7854
36
45
72
63
7.0686 = area of valve.

3 ) 30
10
50 = weight
10 = leverage of weight.
Area of valve, 7.068 ) 500.000 ( 70.7 = lbs. pressure per sq. in.
49476
52400
49476
2924