Principle Of Operation; Maintenance - Fisher EHD Instruction Manual

EH Valves (NPS 8 through 14)
2. Clean out all pipelines to remove scale, welding
slag, and other foreign materials before installing the
valve.
If installing a valve with small internal
flow passages, such as with Whisper
Trim III or Cavitrolr III cages, consider
installing an upstream strainer to
prevent the lodging of particles in
these passages. This is especially
important if the pipeline cannot be
thoroughly cleaned or if the flowing
medium is not clean.
3. Install the control valve with the valve body in a
horizontal pipeline and the actuator vertical above
the valve. Other orientations may result in shortened
trim life and difficulty with field maintenance. Flow
through the valve body must be in the direction
indicated by the flow arrow (key 15, figure 12 or 13)
on the valve body.
CAUTION
Depending on valve body materials
used, post-weld heat treating might be
needed. Post-weld heat treatment can
damage internal elastomeric, plastic,
and metal parts. Shrink-fit pieces and
threaded connections might also
loosen. In general, if post-weld heat
treating is needed, remove all trim
parts. Contact your Emerson Process
Management sales office for additional
information.
4. Use accepted piping and welding practices when
installing the valve in the line. For flanged valve
bodies, use suitable gaskets between the valve body
flanges and pipeline flanges.
5. Install a three-valve bypass around the control
valve if continuous operation is required during

maintenance.

6. If the actuator and valve are shipped separately,
see the Actuator Mounting procedure.
WARNING
Personal injury could result from
packing leakage. Valve packing was
tightened prior to shipment; however
4
Note
some readjustment will be required to
meet specific service conditions.
7. If the valve was shipped without packing installed
in the packing box, install the packing prior to putting
the valve into service. Refer to instructions given in
the Packing Maintenance section of this manual.

Principle of Operation

Key numbers referenced in this section are shown in
figure 12 for the EHD valve and in figure 13 for the
EHT valve.
EHD and EHT valves are balanced designs. When
they are opening or closing, pressure registers on
top of the valve plug (key 3) through the registration
holes in the plug. The force of the pressure on top of
the plug balances the force of the pressure on the
bottom of the plug to reduce the actuator force
required.
Maintenance
Valve parts are subject to normal wear and must be
inspected and replaced as necessary. Inspection
and maintenance frequency depends on the severity
of service conditions. This section includes
instructions for packing lubrication and maintenance,
trim maintenance, and lapping of metal seats. All
maintenance operations can be performed with the
valve in the line.
WARNING
Avoid personal injury from sudden
release of process pressure. Before
performing any maintenance
operations:
D Do not remove the actuator from
the valve while the valve is still
pressurized.
D Always wear protective gloves,
clothing, and eyewear when
performing any maintenance
operations to avoid personal injury.
D Disconnect any operating lines
providing air pressure, electric power,
or a control signal to the actuator. Be
sure the actuator cannot suddenly
open or close the valve.
D Use bypass valves or completely
shut off the process to isolate the
valve from process pressure. Relieve
process pressure on both sides of the
Instruction Manual
April 2009