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2.2.1 Overpressure protection
(see figure 2 / figure 3)
When the pressure Pa in pressure converter D is higher than the threshold value set
by compression springs V1 and V2, diaphragm C is pressed down and handle H turns
around pivoting point O1. Pin N is pushed upwards, so that balance jaw P turns to the
right past pivoting point O2. Because of this, the balance jaw will no longer support
the downward pointing switch rod M of the switch handle, so that it rotates around its
axle. This axle partly has a crescent-shaped section. This is the point of support of
the valve, and for HON HSVS the point of support of rod L, which releases the
"second-stage handle" H2. When the switch handle (K) has made a quarter-turn,
valve (S) closes by means of handle arm (R) fitted in the valve body. Because of the
pressure exchange at the outlet side of the installation, a pressure difference usually
occurs at valve (S), so that it is pushed further into the valve seat.
Continued for 16" and larger.
When switch handle K has made a quarter-turn, handle H2 can move downwards
(due to the force executed by the valve). This will switch on the valve or the second
stage. Switching on the second stage: see chapter 4.1.
The safety device is now locked. Even when pressure Pa drops below the threshold
value, valve (S) remains shut.
2.2.2 Underpressure protection
When pressure Pa of pressure converter D is lower than the set threshold value of
spring V1, diaphragm C moves upwards. The top of V2, by means of the spring seat,
now presses against the housing of the control and switch mechanism and no longer
against the diaphragm disc of the pressure converter. Because of this, the threshold
value is determined by spring V1 only. Handle H is now going to push down pin Q, so
that balance jaw P (just as with overpressure) turns to the right.
The working principle of switch handle K, valve (S) and valve shaft L, which releases
the valve or the "second-stage handle" H2, is identical to the one of overpressure.
2.2.3 Operation of the emergency button
When the emergency button (red button) is pressed (not indicated in figure 2),
balance jaw P turns to the right. This will make switch handle K turn at least a quarter.
For 16" and larger, shaft L of the "second-stage handle" H2 touches on the crescent-
shaped point of support and the second stage is switched on. The position of handle
H, diaphragm C and the minimum and maximum springs is not changed. The valve
shaft passes the crescent-shaped point of support and the valve is shut.
© 2017 Honeywell International Inc
Operation and maintenance manual HON HSV086
12
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