12 | BHGE
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Inlet pressure, identified as P
1
, enters the main valve at “A”,
flows through the sensing tube “B” and through the clearance
formed by the sensing tube and the floating washer on the
main valve disc to pressurize chamber “C”. Additional flow
occurs between the top of the sensing tube and the pilot disc,
down into chamber “C” through an annular region formed by
the sensing tube and pilot base. Pressure in chamber “C” will
now be designated P
2
.
When the set pressure is reached and the pilot opens,
pressure is exhausted through tube “D” into the main valve
outlet “E” or is exhausted directly into the atmosphere
depending on if the pilot valve outlet is equipped with a
discharge tube. Flow past the pilot seat will allow the P
2
pressure to exhaust and reduce to a value of approximately
58% of P
1
, producing a lifting force on the main disc causing
it to open.
X. Operating Principles
D
E
A
B
C
C
Figure 3: Valve Flow Diagram
