Overpressure Protection - Fisher 67CF Instruction Manual

Month Year
Type XXXX
W8442
Type 67C oR 67CS
InleT pReSSuRe
ouTleT pReSSuRe
aTMoSpheRIC pReSSuRe
INLET PRESSURE
OUTLET PRESSURE
principle of operation
ATMOSPHERIC PRESSURE
LOADING PRESSURE
Downstream pressure is registered internally on the
INTERMEDIATE PRESSURE
lower side of the diaphragm. When the downstream
PILOT SUPPLY PRESSURE
pressure is at or above the set pressure, the valve plug
is held against the orifice and there is no flow through
the regulator. When demand increases, downstream
pressure drops slightly allowing the spring to extend,
moving the stem down and the valve plug away from
the orifice. This allows flow through the regulator.
Internal Relief (Types 67CR, 67CSR,
67CFR, and 67CFSR)
If for some reason, outside of normal operating
conditions, the downstream pressure exceeds the
setpoint of the regulator, the force created by the
downstream pressure will lift the diaphragm until the
diaphragm is lifted off the relief seat. This allows flow
through the token relief. The relief valve on the
Type 67CR, 67CSR, 67CFR, or 67CFSR is an
elastomer plug that prevents leakage of air from the
downstream to atmosphere during normal operation,
thereby conserving plant air.
Type 67CR oR 67CSR
Figure 2. 67C Series Operational Schematics
W7433
Type 67CFR oR 67CFSR
Smart Bleed™ Airset
In some cases, it is desired to exhaust downstream
pressure if inlet pressure is lost or drops below the
setpoint of the regulator. For example, if the regulator
is installed on equipment that at times has no flow
demand but is expected to backflow on loss of inlet
pressure. The Types 67CFR and 67CFSR can be
ordered with the Smart Bleed™ option which includes
an internal check valve for this application. During
operation, if inlet pressure is lost, or decreases below
the setpoint of the regulator, the downstream pressure
will back flow upstream through the regulator and check
valve. This option eliminates the need for a fixed bleed
downstream of the regulator, thereby conserving
plant air.

overpressure protection

The 67C Series regulators have maximum outlet
pressure ratings that are lower than their maximum
inlet pressure ratings. A pressure relieving or pressure
limiting device is needed if inlet pressure can exceed
the maximum outlet pressure rating.
67C Series
Type 67CF oR 67CFS
SMaRT BleeD™ opTIon
TypeS 67CFR anD 67CFSR
3