Dept. Bull. 1136, U. S. Dept. of Agriculture PLATE 5 
A PRESSURE-REDUCING VALVE FOR STEAM, DESIGNED ESPECIALLY FOR LOW 
REDUCED PRESSURES 
Steam enters at a, is reduced somewhat in pressure by the throttling action of the restricted pas- 
sages while flowing through the valve, and passes out at b, reaching its final pressure value by expan- 
sion in the low-pressure space. ‘The pipe c transmits the reduced pressure to the chamber d, which 
is closed at the bottom by the rubber diaphragm e, to which is attached the valve stem f. The 
pressure on the diaphragm tends to move the valve stem downward, an action that would close the 
valve and shut off the high-pressure steam. ‘This action is resisted by the weights on the arm g, which 
is pivoted at h. When the left-hand weight is placed far out, as is done in practice, its thrust presses 
upward on the stem f, tending to open the valve. When steam is actually flowing through the 
valve, the stem comes to the position that permits a flow just sufficient to produce the pressure on the 
diaphragm required to balance the effect of the weights. Thus the valve adjusts itself as needed 
to maintain the reduced pressure desired, the amount of which is determined by the setting of the 
sliding weights. The pair of equal weights shown reduces chattering more than a single weight 
would; unequal weights, permitting also the convenience of rough and fine adjustment, are supplied 
by some makers. 
