Introduction to Regulators
Type 1098-EGR
Te c h n i c a l
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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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
Introduction to Regulators
585
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required function. The vendor and the customer, working together,
have the task of deciding which of the available regulators is best
suited for the job at hand. The selection procedure is essentially a
process of elimination wherein the answers to a series of questions
narrow the choice down to a specic regulator.
Control Application
To begin the selection procedure, it’s necessary to dene what
the regulator is going to do. In other words, what is the control
application? The answer to this question will determine the general
type of regulator required, such as:
• Pressure reducing regulators
• Backpressure regulators
• Pressure relief valves
• Vacuum regulators
• Vacuum breaker
The selection criteria used in selecting each of these general regulator
types is described in greater detail in the following subsections.
Pressure Reducing Regulator Selection
The majority of applications require a pressure reducing regulator.
Assuming the application calls for a pressure reducing regulator,
the following parameters must be determined:
• Outlet pressure to be controlled
• Inlet pressure to the regulator
• Capacity required
• Shutoff capability required
• Process uid
• Process uid temperature
• Accuracy required
• Pipe size required
• End connection style
• Material requirements
• Control line needed
• Overpressure protection
Outlet Pressure to be Controlled
For a pressure reducing regulator, the rst parameter to determine
is the required outlet pressure. When the outlet pressure is known,
it helps determine:
• Spring requirements
• Casing pressure rating
• Body outlet rating
• Orice rating and size
• Regulator size
Inlet Pressure of the Regulator
The next parameter is the inlet pressure. The inlet pressure
(minimum and maximum) determines the:
• Pressure rating for the body inlet
• Orice pressure rating and size
• Main spring (in a pilot-operated regulator)
• Regulator size
If the inlet pressure varies signicantly, it can have an effect on:
• Accuracy of the controlled pressure
• Capacity of the regulator
• Regulator style (two-stage or unloading)
Capacity Required
The required ow capacity inuences the following decisions:
• Size of the regulator
• Orice size
• Style of regulator (direct-operated or pilot-operated)
Shutoff Capability
The required shutoff capability determines the type of
disk material:
• Standard disk materials are Nitrile (NBR) and Neoprene (CR),
these materials provide the tightest shutoff.
• Other materials, such as Nylon (PA), Polytetrauoroethylene
(PTFE), Fluoroelastomer (FKM), and Ethylenepropylene
(EPDM), are used when standard material cannot be used.
• Metal disks are used in high temperatures and when
elastomers are not compatible with the process uid;
however, tight shutoff is typically not achieved.
Process Fluid
Each process uid has its own set of unique characteristics in
terms of its chemical composition, corrosive properties, impurities,
ammability, hazardous nature, toxic effect, explosive limits, and
molecular structure. In some cases special care must be taken
to select the proper materials that will come in contact with the
process uid.
Process Fluid Temperature
Fluid temperature might determine the materials used in the
regulator. Standard regulators use Steel and Nitrile (NBR) or
Neoprene (CR) elastomers that are good for a temperature range
of -40° to 180°F (-40° to 82°C). Temperatures above and below
this range may require other materials, such as Stainless steel,
Ethylenepropylene (EPDM), or Peruoroelastomer (FFKM).
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Accuracy Required
The accuracy requirement of the process determines the acceptable
droop (also called proportional band or offset). Regulators fall into
the following groups as far as droop is concerned:
• Rough-cut Group— This group generally includes many
rst-stage, rough-cut direct-operated regulators. This group
usually has the highest amount of droop. However, some
designs are very accurate, especially the low-pressure gas or
air types, such as house service regulators, which incorporate
a relatively large diaphragm casing.
• Close-control Group— This group usually includes pilot-
operated regulators. They provide high accuracy over a
large range of ows. Applications that require close control
include these examples:
• Burner control where the fuel/air ratio is critical to
burner efciency and the gas pressure has a signicant
effect on the fuel/air ratio.
• Metering devices, such as gas meters, which require
constant input pressures to ensure accurate measurement.
Pipe Size Required
If the pipe size is known, it gives the specier of a new regulator
a more dened starting point. If, after making an initial selection
of a regulator, the regulator is larger than the pipe size, it usually
means that an error has been made either in selecting the pipe size
or the regulator, or in determining the original parameters (such
as pressure or ow) required for regulator selection. In many
cases, the outlet piping needs to be larger than the regulator for the
regulator to reach full capacity.
End Connection Style
Special materials required by the process can have an effect on the
type of regulator that can be used. Oxygen service, for example,
requires special materials, requires special cleaning preparation,
and requires that no oil or grease be in the regulator.
Control Lines
For pressure registration, control lines are connected downstream
of a pressure reducing regulator, and upstream of a backpressure
regulator. Typically large direct-operated regulators have
external control lines, and small direct-operated regulators have
internal registration instead of a control line. Most pilot-operated
regulators have external control lines, but this should be conrmed
for each regulator type considered.
Stroking Speed
Stroking speed is often an important selection criteria. Directoperated regulators are very fast, and pilot-operated regulators
are slightly slower. Both types are faster than most control valves.
When speed is critical, techniques can be used to decrease
stroking time.
Overpressure Protection
The need for overpressure protection should always be considered.
Overpressure protection is generally provided by an external relief
valve, or in some regulators, by an internal relief valve. Internal
relief is an option that you must choose at the time of purchase.
The capacity of internal relief is usually limited in comparison with
a separate relief valve. Other methods such as shutoff valves or
monitor regulators can also be used.
In general, the following end connections are available for the
indicated regulator sizes:
• Pipe threads or socket weld: 2-inch (DN 50) and smaller
• Flanged: 1-inch (DN 25) and larger
• Butt weld: 1-inch (DN 25) and larger
Note: Not all end connections are available for all regulators.
Required Materials
The regulator construction materials are generally dictated by the
application. Standard materials are:
• Aluminum
• Cast iron or Ductile iron
• Steel
• Bronze and Brass
• Stainless steel
Regulator Replacement
When a regulator is being selected to replace an existing regulator,
the existing regulator can provide the following information:
• Style of regulator
• Size of regulator
• Type number of the regulator
• Special requirements for the regulator, such as downstream
pressure sensing through a control line versus internal
pressure registration.
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Regulator Price
The price of a regulator is only a part of the cost of ownership.
Additional costs include installation and maintenance. In selecting
a regulator, you should consider all of the costs that will accrue over
the life of the regulator. The regulator with a low initial cost might
not be the most economical in the long run. For example, a directoperated regulator is generally less expensive, but a pilot-operated
regulator might provide more capacity for the initial investment.
To illustrate, a 2-inch (DN 50) pilot-operated regulator can have
the same capacity and a lower price than a 3-inch (DN 80), direct-
operated regulator.
NONRESTRICTIVE
VENTS AND PIPING
ALTERNATE PILOT
EXHAUST PIPING
MAIN VALVE
VENT VALVE B
BLOCK VALVE A
30B8289_A
MAIN PRESSURE LINE
RELIEF PRESSURE CONTROL AT RELIEF VALVE INLET BACKPRESSURE CONTROL
PILOT
CONTROL LINE
Backpressure Regulator Selection
Backpressure regulators control the inlet pressure rather than the
outlet pressure. The selection criteria for a backpressure regulator
the same as for a pressure reducing regulator.
Relief Valve Selection
An external relief valve is a form of backpressure regulator. A
relief valve opens when the inlet pressure exceeds a set value.
Relief is generally to atmosphere. The selection criteria is the same
as for a pressure reducing regulator.
VENT VALVE C
CONTROL LINE
BLOCK VALVE A
PILOT
30B8288_A
VENT VALVE B
MAIN VALVE
ALTERNATE PILOT
EXHAUST PIPING
VENT VALVE D
Figure 5. Backpressure Regulator/Relief Valve Applications
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