101
A
i
B
ii
i
B
A
i
A
B
A.0500.251 – IM-TL/13.00 EN (08/2009)
12.2.5 Safety relief valve – Air loaded - air lifted
12.2.5.1 Air loaded
Fig 7 and 8 are showing the design of
the air loaded - air lifted safety relief
valve.
The pressure in the control chamber
(i) is keeping the valve head in
balance with the medium pressure.
If the force created by the medium
pressure becomes higher than the
force created by the control pressure
acting on piston (B), the valve head
(A) starts to move and the valve
opens.
While only part of the valve head (A)
is loaded by the discharge pressure,
the biggest portion of the valve head
(A) is covered by the rotors (front
clearances) or loaded by the
relatively low suction pressure, the
control pressure is working on the
full surface of the control piston. That
implies that the control pressure has
to be set much lower than the
opening pressure of the valve.
Indications of control pressures can
be found on page 103. See table.
Fig. 9 is showing the design of the air
loaded - air lifted safety relief valve
with CIP/SIP valve function.
To operate the CIP/SIP valve function
chamber (ii) must be pressurized.
The pressure is acting on the rear face
of the piston (B). By doing that, valve
head (A) and piston (B) which are
connected to each other, will move
against the force created by the
control pressure inside chamber (i).
If the control pressure is maintained
during the CIP/SIP valve operation,
the pressure needed to open the valve
must be about 0.5 bar higher than the
control pressure in chamber (i). To
resume the safety relief valve
function, chamber (ii) must be
completely relieved.
Fig 9:
Safety relief valve –
Air loaded - air lifted with
CIP/SIP valve function
12.2.5.2 Air loaded - air lifted with CIP/SIP valve function
Fig 7:
Safety relief valve –
Air loaded - air lifted closed
Fig 8:
Safety relief valve –
Air loaded - air lifted partly opened