Fisher Vacuum Control Manuals & Guides

Vacuum Control

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Vacuum Applications

Vacuum regulators and vacuum breakers are widely used in process
plants. Conventional regulators and relief valves might be suitable
for vacuum service if applied correctly. This section provides
fundamentals and examples.

Vacuum Control Devices

Just like there are pressure reducing regulators and pressure relief
valves for positive pressure service, there are also two basic
types of valves for vacuum service. The terms used for each are
sometimes confusing. Therefore, it is sometimes necessary to ask
further questions to determine the required function of the valve.
The terms vacuum regulator and vacuum breaker will be used in
these pages to differentiate between the two types.

Vacuum Regulators

Vacuum regulators maintain a constant vacuum at the regulator
inlet. A loss of this vacuum (increase in absolute pressure) beyond
setpoint registers on the diaphragm and opens the disk. It depends
on the valve as to which side of the diaphragm control pressure is
measured. Opening the valve plug permits a downstream vacuum
of lower absolute pressure than the controlled vacuum to restore
the upstream vacuum to its original setting.

Besides the typical vacuum regulator, a conventional regulator can
be suitable if applied correctly. Any pressure reducing regulator
(spring to open device) that has an external control line connection
and an O-ring stem seal can be used as a vacuum regulator.
Installation requires a control line to connect the vacuum being
controlled and the spring case. The regulator spring range is now a

negative pressure range and the body ow direction is the same as

in conventional pressure reducing service.

Vacuum Breakers (Relief Valves)

Vacuum breakers are used in applications where an increase in
vacuum must be limited. An increase in vacuum (decrease in
absolute pressure) beyond a certain value causes the diaphragm to
move and open the disk. This permits atmospheric pressure or a
positive pressure, or an upstream vacuum that has higher absolute
pressure than the downstream vacuum, to enter the system and
restore the controlled vacuum to its original pressure setting.

A vacuum breaker is a spring-to-close device, meaning that if there
is no pressure on the valve the spring will push the valve plug into
its seat. There are various Fisher® brand products to handle this
application. Some valves are designed as vacuum breakers.
Fisher brand relief valves can also be used as vacuum breakers.

ABSOLUTE

ZERO

-14.7 PSIG (-1,01 bar g),
0 PSIA (0 bar a)

ATMOSPHERIC

5 PSIG (0,34 bar g) VACUUM,

-5 PSIG (-0,34 bar g),

9.7 PSIA (0,67 bar a)

0 PSIG (0 bar g),

14.7 PSIA (1,01 bar a)

5 PSIG (0,34 bar g),

19.7 PSIA (1,36 bar a)

POSITIVE PRESSURE

VACUUM

1 PSIG (0,069 bar) = 27.7-INCHES OF WATER (69 mbar) = 2.036-INCHES OF MERCURY

1kg/cm2 = 10.01 METERS OF WATER = 0.7355 METERS OF MERCURY

Figure 1. Vacuum Terminology

Vacuum Terminology

Engineers use a variety of terms to describe vacuum, which
can cause some confusion. Determine whether the units are in
absolute pressure or gauge pressure (0 psi gauge (0 bar gauge) is
atmospheric pressure).

  •  5 psig (0,34 bar g) vacuum is 5 psi (0,34 bar) below

atmospheric pressure.

  •  -5 psig (-0,34 bar g) is 5 psi (0,34 bar) below

atmospheric pressure.

  •  9.7 psia (0,67 bar a) is 9.7 psi (0,67 bar) above absolute zero

or 5 psi (0,34 bar) below atmospheric pressure
(14.7 psia - 5 psi = 9.7 psia (1,01 bar a - 0,34 bar = 0,67 bar a)).

Vacuum Control

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A conventional relief valve can be used as a vacuum breaker, as
long as it has a threaded spring case vent so a control line can be
attached. If inlet pressure is atmospheric air, then the internal
pressure registration from body inlet to lower casing admits
atmospheric pressure to the lower casing. If inlet pressure is not
atmospheric, a relief valve in which the lower casing can be vented
to atmosphere when the body inlet is pressurized must be chosen.
In this case, the terminology “blocked throat” and “external
registration with O-ring stem seal” are used for clarity.

UNAVOIDABLE

LEAKAGE

TYPE Y695VR VACUUM REGULATOR

POSITIVE PRESSURE OR

ATMOSPHERE, OR A LESSER VACUUM

THAN THE VACUUM BEING LIMITED

TYPE Y690VB VACUUM BREAKER

Figure 3. Typical Vacuum Breaker

Figure 2. Typical Vacuum Regulator

INLET PRESSURE
CONTROL PRESSURE (VACUUM)
ATMOSPHERIC PRESSURE

A spring that normally has a range of 6 to 11-inches w.c. (15 to 27 mbar)
positive pressure will now have a range of 6 to 11-inches w.c.
(15 to 27 mbar) vacuum (negative pressure). It may be expedient to
bench set the vacuum breaker if the type chosen uses a spring case
closing cap. Removing the closing cap to gain access to the adjusting
screw will admit air into the spring case when in vacuum service.

CONTROL PRESSURE (VACUUM)

OUTLET PRESSURE (VACUUM)

ATMOSPHERIC PRESSURE

VACUUM

BEING CONTROLLED

VACUUM

PUMP

HIGHER

VACUUM SOURCE

VACUUM

PUMP

VACUUM

BEING LIMITED

B2582

B2583

Vacuum Control

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VACUUM BEING CONTROLLED HIGHER VACUUM SOURCE

ATMOSPHERIC

BLEED

VACUUM

PUMP

FIXED

RESTRICTION

TYPE Y695VRM

VACUUM REGULATOR

TYPE 1098-EGR

PRESSURE REDUCING REGULATOR

Figure 5. Type Y695VRM used with Type 1098-EGR in a Vacuum Regulator Installation

Figure 4. Type 133L

VACUUM BEING

REGULATED

VACUUM SOURCE

Vacuum Regulator Installation Examples

CONTROL PRESSURE (VACUUM)

ATMOSPHERIC PRESSURE

OUTLET PRESSURE (VACUUM)

CONTROL PRESSURE (VACUUM)

LOADING PRESSURE

ATMOSPHERIC PRESSURE

OUTLET PRESSURE (VACUUM)

A6555

Vacuum Control

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CONSTANT INLET OR
ATMOSPHERIC PRESSURE

TYPE 1098-EGR

PRESSURE REDUCING REGULATOR

FIXED

RESTRICTION

TYPE Y690VB

VACUUM BREAKER

VACUUM TANK

VACUUM

PUMP

Figure 7. Type Y690VB used with Type 1098-EGR in a Vacuum Breaker Installation. If the positive pressure exceeds the

Type 1098-EGR casing rating, then a Type 67CF with a Type H800 relief valve should be added.

VACUUM TANK

VACUUM

PUMP

ATMOSPHERIC OR
CONSTANT INLET ONLY

Figure 6. Type 1805

Vacuum Breaker Installation Examples

INLET PRESSURE

CONTROL PRESSURE (VACUUM)

INLET PRESSURE

LOADING PRESSURE

ATMOSPHERIC PRESSURE

CONTROL PRESSURE (VACUUM)

VACUUM BEING LIMITED

A6671

Vacuum Control

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M1047

Type 289H

VACUUM TANK

ATMOSPHERIC
INLET ONLY

PITOT TUBE SERVES TO REGISTER
VACUUM ON TOP OF DIAPHRAGM
(NO CONTROL LINE NEEDED)

TYPE 66R

VACUUM

TANK

VACUUM

PUMP

VACUUM

PUMP

ATMOSPHERIC INLET
PRESSURE

Figure 8. Type 289H Relief Valve used in a Vacuum Breaker Installation

If inlet is positive pressure:

• Select balancing diaphragm and tapped lower
casing construction.

• Leave lower casing open to atmospheric pressure.

Figure 10. Type 66RR Relief Valve used in a Vacuum Breaker Installation

VACUUM

TANK

MAIN VALVE
PLUG

TYPE 66RR

LOADING PRESSURE
CONTROLLED PRESSURE (VACUUM)
INLET PRESSURE

MAIN VALVE
DIAPHRAGM

PILOT VALVE DISK

FIXED RESTRICTION

PILOT CONTROL
SPRING

Vacuum Breaker Installation Examples

Figure 9. Type 66R Relief Valve used in a Vacuum Breaker Installation

INLET PRESSURE

CONTROL PRESSURE (VACUUM)

INLET PRESSURE

CONTROL PRESSURE (VACUUM)

M1047

M1041

M1056

Vacuum Control

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Gas Blanketing in Vacuum

When applications arise where the gas blanketing requirements
are in vacuum, a combination of a vacuum breaker and a regulator
may be used. For example, in low inches of water column vacuum,
a Type Y690VB vacuum breaker and a Type 66-112 vacuum
regulator can be used for very precise control.

Vacuum blanketing is useful for vessel leakage to atmosphere
and the material inside the vessel is harmful to the surrounding
environment. If leakage were to occur, only outside air would
enter the vessel because of the pressure differential in the tank.
Therefore, any process vapors in the tank would be contained.

Features of Fisher® Brand Vacuum Regulators
and Breakers

  •  Precision Control of Low Pressure Settings—Large

diaphragm areas provide more accurate control at low
pressure settings. Some of these regulators are used as pilots
on our Tank Blanketing and Vapor Recovery Regulators.
Therefore, they are designed to be highly accurate, usually
within 1-inch w.c. (2 mbar).

Figure 11. Example of Gas Blanketing in Vacuum

20 TO 30 PSIG (1,4 to 2,1 bar)
NITROGEN OR OTHER GAS

VACUUM BREAKER TYPE Y690VB
SET TO OPEN AT

-2-INCHES W.C. (-5 mbar)

TO EXHAUST HEADER

-9-INCHES W.C. (-22 mbar)

VACUUM REGULATOR
TYPE 66-112 SET TO CONTROL
AT -1-INCH W.C. (-2 mbar) VACUUM

CONTROL LINES

TANK — 1-INCH W.C. (2 mbar) VACUUM

  •  Corrosion Resistance—Constructions are available in a

variety of materials for compatibility with corrosive process
gases. Wide selection of elastomers compatible with

owing media.

  •  Rugged Construction—Diaphragm case and internal parts are

designed to withstand vibration and shock.

  •  Wide Product Offering—Fisher

®

brand regulators can be

either direct-operated or pilot-operated regulators.

  •  Fisher Brand Advantage—Widest range of products and

a proven history in the design and manufacture of process
control equipment. A sales channel that offers local stock
and support.

  •  Spare Parts—Low cost parts that are interchangeable with

other Fisher brand in your plant.

  •  Easy Sizing and Selection—Most applications can be

sized utilizing the Fisher brand Sizing Program and

Sizing Coefcients.

BJ9004