Principle Of Operation; Maintenance - Fisher EHD series Instruction Manual

Instruction Manual
D100392X012

Principle of Operation

Key numbers referenced in this section are shown in figure 12 for the EHD valve and in figure 14 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 valve. Drain the process media from both sides of the valve.
D Vent the power actuator loading pressure and relieve any actuator spring precompression.
D Use lock‐out procedures to be sure that the above measures stay in effect while you work on the equipment.
D The valve packing box may contain process fluids that are pressurized, even when the valve has been removed from the
pipeline. Process fluids may spray out under pressure when removing the packing hardware or packing rings, or when
loosening the packing box pipe plug.
D Check with your process or safety engineer for any additional measures that must be taken to protect against process
media.
WARNING
Refer to table 4 for valve assembly weights and the appropriate actuator instruction manual for actuator assembly weights.
Due to the size and weight of the valve and actuator assembly, be sure adequately sized hoists and chains or slings are used
to handle it. Also, take proper precautions to prevent personnel from being injured if the hoist or rigging slips
unexpectedly.
Note
Whenever a gasket seal is disturbed by removing or shifting gasketed parts, install a new gasket upon reassembly. This is necessary
to ensure a good gasket seal.
EH Valves NPS 8 through 14
June 2017
5