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Cashco — 3000 Series Models Pressure and/or Vacuum Relief Vents

3000 Series Models

Pressure and/or Vacuum Relief Vents

SECTION I

I. DESCRIPTION AND SCOPE

The 3000 Series Pressure and/or Vacuum Relief
Vents are weight loaded devices used on atmospheric
and low-pressure storage tanks, vapor recovery and
process systems to relieve excess internal pressure
and/or vacuum.


  Tank protection is the primary function of the 3000
Series Pressure and/or Vacuum Relief Vent. It
must be considered first when selecting, sizing,
setting and maintaining any of these units. Unless
adequate provision is made for the intake of air
and the discharge of vapors while the tank is being
emptied or filled and/or when the internal tank
pressure changes due to product/vapor expansion
or contraction because of temperature changes,
the tank could collapse or the tank could rupture.
These conditions are considered “normal” operating
conditions. OSHA 1910.106 state that these venting
devices shall be sized according to API 2000.


     Besides protecting the tank for normal operating
conditions as stated above the 3000 series Pressure
Relief Vents can also be sized n accordance with API
2000 for emergency venting. Emergency venting
is required when an abnormal condition, such as
ruptured internal heating coils or an external fire,
exists either inside or outside of the tank.
A secondary function of the 3000 Series Pressure
and/or Vacuum Relief Vent is the conservation of
product. The evaporation loses can be minimized by
the proper sizing and maintaining of the vents.

The maintenance of low pressure relief valve
should only be done by qualified technicians. It is
important that the technician be familiar with the API
and corporate standards, corporate safety policies
and the relief vent manufacturer requirements.
When repair services are performed by an outside
company, the company needs to be a Cashco
factory authorized repair center which specializes in
low pressure venting devices.
For information on repair centers in your area, please
contact:

Cashco, Inc.
607 West 15th Street
Ellsworth, KS 67439-0006
(785) 472-4461 (Phone)
(785) 472-3539 (Fax)
The table below shows the nine different Models
covered in this manual and indicates their Pressure
(P) and/or Vacuum (V) relief capabilities.

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SECTION II

II. VALVE DESIGN AND FUNCTION

Typical tank appurtenances used to protect an atmospheric or low-pressure storage tank from over or under
pressure and emergency conditions are:


Model 3200 Pressure/Vacuum Weight Load Relief Vent
Model 1078 Pilot Operated Nitrogen Blanketing Valve
Model 3700 Emergency Relief Manhole Cover Vent


The Model 3100 thru 3600 Pressure and /or Vacuum
Vents are used for the normal venting requirements.
Normal venting is defined as venting required
because of operational requirements (i.e. filling and
emptying the tank) or atmospheric changes. The
Model 3700 thru 3900 Emergency Relief Vents are
used to meet venting required when an abnormal
condition, such as an external fire or such as ruptured
internal heating coils, exist either outside or inside
the tank. The Model 1078 Nitrogen Blanketing Valve
is used to apply a cover of gas in the vapor space of
the tank. This is done for various reasons, such as,
product integrity, dilute toxic vapors for safe emission
levels, prevent internal tank corrosion by keeping
out air and moisture or to keep the vapors out of the
flammable range.


All of these devices are sized in accordance with API
Standard 2000, improperly specified relief vents may
result in structural damage to the tank or system, and
can cause severe personal injury or death.
Figure 1 illustrates the operation of the Pressure/
Vacuum Relief Vent under overpressure conditions.

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As the tank pressure increases as a result of product
being pumped into the tank and/or because of thermal
expansion of the product and vapors the pressure
pallet remains closed until the set pressure of the
vent is reached. When the tank pressure reaches the
pressure setting of the vent, the pressure pallet lifts
allowing the tank pressure to bleed off.
Figure 2 illustrates the operation of the Pressure/
Vacuum Relief Vent under vacuum conditions. As the
tank pressure decreases as a result of product being
pumped out of the tank and/or because of thermal
contraction of the product and vapors the vacuum
pallet remains closed until the set vacuum of the
vent is reached. When the tank vacuum reaches the
vacuum setting of the vent, the vacuum pallet lifts
allowing air to be drawn into the tank.


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SECTION III

III. SAFETY WARNINGS:


Tank or system protection is the primary function
of the weight loaded Pressure and/or Vacuum
Relief Vent. It must be selected to meet the total
pressure and vacuum flow requirements within the
Maximum Allowable Working Pressure and Vacuum
of the system on which it is installed. Consult API
Standard 2000 for tank protection sizing procedures.
Improperly specified relief vents may result in structural damage to the tank or system, and can
cause severe personal injury or death.


When Pipe-Away relied vents are used, backpressure in the header system will affect the set point of
weight loaded vents by the amount of the header
pressure. Maximum possible header pressure must
be considered when sizing the pressure relief vent.


Certified published relief vent flow data for Valve
Concepts weight loaded vents were determined
according to the requirements of API Standard 2000,
ASME PTC 19.5 and ASME PTC 25. In as such,
additional inlet piping and/or outlet piping must be
taken into account when sizing the pressure and
vacuum relief device.

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SECTION IV

IV. INSPECTION AND STORAGE:


The pressure/vacuum relief vent is carefully packaged
to prevent damage or contamination during shipping.
Inspect the equipment when it is received and report
any damage to the carrier immediately. The vent
should be stored with all the protective flange covers
in place. Make sure that any loading weights that
might have been shipped separately, to protect the
vent during shipping, are accounted for and stored
with the vent. These weights, if required, will be
installed during installation, see section V.


SECTION V

V. INSTALLATION:



All of Valve Concepts weight loaded vents have a
maximum pressure setting of 3 psig and a maximum
vacuum setting of 1 psig. The minimum setting (no
loading weights) for both pressure and vacuum is
0.75 oz/in2. The certified flow data at various set
points for each vent can be found in the Valve
Concepts catalog. API 2000 allows for interpolation
and extrapolation of the data for set points not shown
on the graph.
The Valve Concepts 3000 Series vents designed
to mate with a 150 lb ANSI B16.5 flange. Torque
guidelines are given in Table 1. The vents are NOT
rated for full flange pressure and do not require high

bolting torque.

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The following guidelines should be followed during
installation:
Before installing the 3000 Series Vent remove all
packing materials from inside and outside the vent.
If loading weights were shipped separate from the
vent make sure to install the appropriate pallet.
Inspect the gasket seating surface of the tank nozzle
flange. It must be clean, free of scratches, corrosion,
tool marks and flat.
FRP and Aluminum vents are furnished with flat
faced flanges. It is recommended that they be
installed on mating flat face flanges with a full faced
gasket. If the flat face of the vent is sealing against
a raised face steel flange, a spacer or filler ring must
be used to fill the annular space of the raised face
steel flange.

and is in good condition.
Fiberglass flanges 2 inch to 12 inch require the use
of a full-face 150 lb. gasket. For full face gaskets, we
recommend the use of a 1/8-inch Gortex gasket.
Center the gasket within the bolt circle of the tank
flange.
Carefully set the vent on the flange nozzle and align
the bolt holes.
All stud threads must be lubricated to obtain proper
torque results. A washer should be used under each
stud nut.

Install the studs, washers and nuts and tighten
nuts hand tight. Check proper alignment of flange
faces. Misalignment of flange faces will cause
bending stresses at the flange and flange joint and
damage may result. Correct any misalignment prior
to applying torque to nuts.
All nuts must be torqued in proper sequence
and increment. Proceed through the tightening
sequence and increment until the recommended
torque is attained.
Recheck the torque on each bolt in the same
sequence as bolts previously tightened may have
relaxed through the torque sequence.


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SECTION VI


VI. MAINTENANCE:


Tank or system protection is the primary function
of the weight loaded Pressure and/or Vacuum
Relief Vent. As a safety device it is very important
that maintenance/inspection be done on a regular
interval. Maintenance should only be done by a
qualified technician. Valve Concepts recommends
that all service be performed at the factory or a
factory authorized repair center. For information on
repair centers in your area, please contact:
Cashco, Inc.
607 West 15th Street
Ellsworth, KS 67439-0006
(785) 472-4461 (Phone)
(785) 472-3539 (Fax)


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Refer to the Model 3100 Pressure/Vacuum Relief
Valve on page 8 which illustrate a typical pressure/
vacuum valve when disassembing the unitRemove
the weatherhood wing nuts (#7) and lift off weatherhood (#17)and bug screen (#27). Likewise, remove vacuum cover bolts (#22), remove vacuum cover (#2) and vacuum cover gasket (#12).


 Inspect weatherhood, bug screen, and vacuum
cover for corrosion, damage, or product build
up. Replace if necessary or clean with a suitable
solvent. Inspect vacuum cover gasket. If gasket is
damaged or worn replace.


Remove both the pressure and the vacuum pallet
assemblies, including any loading weights that may
be on the pallets. Be sure to identify each assembly
by tagging as “pressure” or “vacuum” as the pallets
are removed from the vent.


Clean and inspect both pallet assemblies.
Inspect the Teflon diaphragm (# 5) and replace if
necessary.
 Inspect and clean pressure and vacuum seats (#
3). Check seats for any nicks, corrosion, pitting or

product build up. Seat surfaces must be clean and
smooth for vent to perform properly.


Inspect and clean pressure and vacuum guides (#16
and #8). Check for any wear, corrosion, and product
build up. Clean or replace if necessary.


Check the inside of the main vent body (#1) for any
corrosion or product build up. Clean if necessary.


Assemble vent in reverse order, making sure that
the pressure and vacuum pallets and loading
weights are in their proper location. When installing
the weatherhood and vacuum cover make sure the
pressure stem (#10) and vacuum stem (#9) are
inserted in the stem guide.
NOTE:
Before reassembling covers we recommend
the use of 5/32-inch diameter Gortex joint sealant be
replaced. All FRP covers should be torqued to 50 in.
- lbs. for full pressure seal.


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SECTION VII


VII. TEST PROCEDURE:


Table shows the pallet weight per unit of pressure or
vacuum setting. The total pallet assembly weight is
determined by multiplying the desired set point (in
the appropriate units) by the incremental weight per
unit listed in Table 5.
For Example:
4” Model 3104 CS - if the desired setting is 5 oz/in2
Table 5 shows that for a 4” vent, the pallet would
weigh 2.05 lb per oz/in2
So the pallet assembly for a 5 oz/in2 setting would
weigh:
2.05 lbs/oz/in2 x 5.0 oz./in2 - 10.25 lbs
Valve Concepts allows a deviation from this
theoretical weight of ± 3.0%.
After both pallets’ weight has been determined and
verified for the required setting, reassemble the vent
and mount on a Tank Vent Test Stand and slowly
raise the pressure at the flow rate of 1.0 SCFH.
ACCEPTANCE CRITERIA: The pressure gauge
shall maintain a pressure equal to or greater than
90% of set pressure for a one minute period while
the specified flow rate is maintained. Note: Valve
Concepts acceptance criteria exceed the requirements
of API. API 2521 states that if the rate of leakage
does not exceed ½ SCFH for 6 inch size and
smaller, or 5 SCFH for 8 inch and larger, at 75% of
set point, then a vent is considered satisfactory for
all practical purposes.
If the vent fails to meet the 90% criteria, it must
be disassembled and the seat, pallet, and or diaphragms
repaired or replaced.
A test report should be completed for each vent. The
report should indicate the total pallet weight and the
pressure achieved at the Test Flow Rate for both
pressure and vacuum. Other general information
such as serial number, model number, material of
construction, set pressure and vacuum, etc. should
be included in the report.
The test report should be kept in the Valve Maintenance
Records.


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