The Series 61 Booster Relays include the Model 61H and the
Model 61VH. The 61H is a high-capacity booster relay designed
to improve the stroking speed of large diaphragm valves, while
the 61VH is a high-capacity volume booster designed for use
on control valve actuators that require very fast stroking speeds.
Both feature a stabilizing bypass needle valve between the
input and output, which eliminates the need for an externally
piped bypass. Input pressure, acting upon the effective area of
the upper diaphragm, produces a force that is opposed by the
output pressure exerted upon the effective area of the lower
diaphragm. The opposing forces are in a direct 1:1 ratio.
Thus, any increase in the input pressure will depress the
diaphragm assembly, thereby opening the pilot valve to admit
a sufficient supply of air to the output and re-balancing the
input pressure. A decrease in input pressure will cause the
diaphragm assembly to lift off the exhaust port, which reduces
the output and re-balances the input.