Introduction to Regulators
Type 1098-EGR
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Instrument engineers agree that the simpler a system is the
better it is, as long as it provides adequate control. In general,
regulators are simpler devices than control valves. Regulators are
self-contained, direct-operated control devices which use energy
from the controlled system to operate whereas control valves
require external power sources, transmitting instruments, and
control instruments.
Specific Regulator Types
Within the broad categories of direct-operated and pilotoperated regulators fall virtually all of the general regulator
designs, including:
• Pressure reducing regulators
• Backpressure regulators
• Pressure relief valves
• Pressure switching valves
• Vacuum regulators and breakers
Pressure Reducing Regulators
A pressure reducing regulator maintains a desired reduced outlet
pressure while providing the required uid ow to satisfy a
downstream demand. The pressure which the regulator maintains
is the outlet pressure setting (setpoint) of the regulator.
Direct-Operated (Self-Operated) Regulators
Direct-operated regulators are the simplest style of regulators. At
low set pressures, typically below 1 psig (0,07 bar), they can have
very accurate (±1%) control. At high control pressures, up to
500 psig (34,5 bar), 10 to 20% control is typical.
In operation, a direct-operated, pressure reducing regulator
senses the downstream pressure through either internal pressure
registration or an external control line. This downstream pressure
opposes a spring which moves the diaphragm and valve plug to
change the size of the ow path through the regulator.
Pilot-Operated Regulators
Pilot-operated regulators are preferred for high ow rates or where
precise pressure control is required. A popular type of pilotoperated system uses two-path control. In two-path control, the
main valve diaphragm responds quickly to downstream pressure
Types of Pressure Reducing Regulators
This section describes the various types of regulators. All
regulators t into one of the following two categories:
1. Direct-Operated (also sometimes called Self-Operated)
2. Pilot-Operated
W4793
Figure 1. Type 627 Direct-Operated Regulator and Operational Schematic
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
A6557
W6956
INLET PRESSURE
OUTLET PRESSURE
LOADING PRESSURE
ATMOSPHERIC PRESSURE
A6563
Figure 2. Type 1098-EGR Pilot-Operated Regulator and Operational Schematic
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Introduction to Regulators
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changes, causing an immediate correction in the main valve plug
position. At the same time, the pilot diaphragm diverts some
of the reduced inlet pressure to the other side of the main valve
diaphragm to control the nal positioning of the main valve plug.
Two-path control results in fast response and accurate control.
Backpressure Regulators and Pressure Relief Valves
A backpressure regulator maintains a desired upstream pressure
by varying the ow in response to changes in upstream pressure.
A pressure relief valve limits pressure build-up (prevents
overpressure) at its location in a pressure system. The relief valve
opens to prevent a rise of internal pressure in excess of a specied
value. The pressure at which the relief valve begins to open
pressure is the relief pressure setting.
Relief valves and backpressure regulators are the same devices.
The name is determined by the application. Fisher® relief valves
are not ASME safety relief valves.
VACUUM
B2582
PUMP
VACUUM
B2583
HIGHER
VACUUM SOURCE
TYPE Y695VR
PUMP
TYPE Y690VB
VACUUM
BEING CONTROLLED
VACUUM
BEING LIMITED
INLET PRESSURE
CONTROL PRESSURE (VACUUM)
ATMOSPHERIC PRESSURE
INLET PRESSURE
OUTLET PRESSURE
ATMOSPHERIC PRESSURE
LOADING PRESSURE
A6929
Figure 3. Type 63EG Backpressure Regulator/Relief Valve
Operational Schematic
Pressure Switching Valves
Pressure switching valves are used in pneumatic logic systems. These
valves are for either two-way or three-way switching. Two-way
switching valves are used for on/off service in pneumatic systems.
Three-way switching valves direct inlet pressure from one outlet
port to another whenever the sensed pressure exceeds or drops
below a preset limit.
Figure 4. Type Y690VB Vacuum Breaker and Type V695VR Vacuum Regulator
Operational Schematics
Vacuum Regulators and Breakers
Vacuum regulators and vacuum breakers are devices used to
control vacuum. A vacuum regulator maintains a constant vacuum
at the regulator inlet with a higher vacuum connected to the outlet.
During operation, a vacuum regulator remains closed until a
vacuum decrease (a rise in absolute pressure) exceeds the spring
setting and opens the valve disk. A vacuum breaker prevents a
vacuum from exceeding a specied value. During operation, a
vacuum breaker remains closed until an increase in vacuum
(a decrease in absolute pressure) exceeds the spring setting and
opens the valve disk.
Regulator Selection Criteria
This section describes the procedure normally used to select
regulators for various applications. For most applications, there
is generally a wide choice of regulators that will accomplish the
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