20
Overload protection mechanism
Where pressure higher than the measured pressure is applied from the high-pressure or low-
pressure side, the measuring bellows moves and the movement of the sealing liquid becomes
zero between the inside of the bellows and the high-pressure chamber due to the O-ring
seal. After being sealed off by the O-ring, the over-pressure is received by the whole part of
the center body due to the incompressible nature of the sealing liquid. Consequently, the
measuring bellows etc. are not subjected to unreasonable force.
Structures and operating principles
The structure and operating principles of the meter bodies are covered in this section.
Models 11/12, 33 and 81/82
The high and low process pressures (HP and LP) are fed via diaphragms
and
to the
center section (oil filled section) of the meter body. The HP acts on the differential pressure
detecting bellows from the right hand side
and the LP from the left hand side
. When
a state of equilibrium is reached (zero differential pressure state), identical forces are
exercised on both sides of the differential pressure detecting bellows
.
As the pressure of the HP side rises thereby increasing the differential pressure, the
differential pressure detecting bellows moves leftward. The movement of the bellows is fed
as a torque via the torque arm to the beam of the transmitter.
LP
HP
6
1
8
7
4
3
2 5
HP seal diaphragm
LP seal diaphragm
Liquid fill of PH side
Liquid fill of LP side
Differential pressure detecting bellows
Damping control (Optional)
Torque arm
Torque tube
Fig. 3-4. Operating principle of meter body
