Buckling Pin technology offers an accurate and reliable
means of calibrating pressure relief devices. BS&B has developed the BPRV™
Buckling Pin Relief Valve for in-line pressure or vacuum relief offering quick
and simple external resetting. The BPRV is suitable for both gas and liquid
applications, and provides a full relief opening at a pre-determined set
pressure.
- Simple
in-line installation
- Maximum
relief capacity
- Convenient
external reset
- Set
pressure is unaffected by cycling/pulsating pressures
- Standard
set pressures up to 275 psi
- Set
pressure is unaffected by valve orientation
- The
buckling pin is totally protected with a rugged enclosure
Set Pressure Range—Buckling pin technology is used
for overpressure or vacuum relief at set pressures from a few inches of water
column to over 1000psig.
Size Range—Valves are available for installation between all
international standard flanges.
Temperature—Because the buckling pin mechanism is located in an external
enclosure, the set pressure is unaffected by process temperature; only the
ambient atmospheric temperature needs to be considered.
Operating Ratio—A 90% operating ratio permits process pressures up to
90% of the set pressure.
Service—Suitable for gas or liquid service. The selected seal material
must be compatible with the process fluid.
Vacuum—Valves can be supplied to withstand vacuum. Inverted styles of
the BPRV may be used for vacuum relief.
Pressure Cycling—Accuracy and reliability are maintained under pressure
cycling conditions.
Leak Tight—As the operating pressure increases, the seal is
progressively energized to maintain leak tightness. The seal is bubble-tight
and offers minimal resistance to opening, permitting low set pressures and
tight pressure tolerances.
Specifications
U.S. Patent Number 6,367,498 applies; other international
patents pending.
The Buckling Pin Relief Valve (BPRV™) offers quick and
simple field reset without removal from the piping system.
The Buckling Pin Relief Valve (BPRV™) can improve
productivity within a facility by dramatically reducing the down time that can
be caused with other non-reclosing pressure relief devices.
The BPRV is an in-line pressure relief device which offers
quick and simple field reset without removal from the piping system. This
non-reclosing pressure relief device provides practical technology for the
protection of applications containing one or more of the following conditions:
Continuous Processing (fast reset in the line)
- Hazardous
Service (limits operator exposure)
- Large
Line Size (convenient reset in the Line)
- Inaccessible
Location (external reset in the line)
- Frequent
Operation (fast reset in the line)
Design
(U.S. Patent #6,367,498 applies; Worldwide Patents Pending)
The design of the BPRV™ is based upon the offset shaft
butterfly valve concept. The offset of the shaft results in a turning moment
being generated about the valve shaft when a pressure differential is applied
across the device. A Buckling Pin mounted externally to the process normally
resists this turning moment. By calibrating the Buckling Pin to collapse at a
load coincident with that resulting from the shaft torque at a predetermined
differential pressure, the BPRV provides accurate pressure relief.
Buckling Pin technology provides an accurate and reliable
means of calibrating a pressure relief device. When an axial load is applied to
a straight cylindrical pin, it will buckle at a specific load according to
Euler's Law. Buckling Pins that are manufactured from the same material and
have the same configuration will buckle at predictable and repeatable loads.
Three Primary BPRV Components
1-Rotating Disc. A rotating disc normally
closes the flow path and turns through 90 degrees in response to an
overpressure/underpressure condition. The rotating disc is constructed from
metal and has a hollow design. This maximizes the flow path through the BPRV
and ensures the stability of the disc during normal service and at the time of
opening. (See catalog cover photo).
2-Flanged Body. A flanged body contains the
rotating disc, holding it in place using shaft connections that are sealed
within the body and pass through bearings to permit free rotation of the disc
within the body. The body is a 1-piece design with no constructional welds or
other potential external leak paths.
3-External Enclosure and Mechanism. The
external enclosure and mechanism provides the set pressure control for the
BPRV. The mechanism is designed to resist the turning moment of the disc shaft
during normal service pressure conditions. When the desired set pressure is
reached, the mechanism releases the disc due to the function of a Buckling Pin
which has been built with sufficient strength to resist disc rotation until
that point. The mechanism is contained within a stainless steel enclosure. The
enclosure door includes a seal to permit service under severe environmental
conditions.
Three Set Pressure Calibration Controls
1-The Offset of the BPRV Disc Shaft from the Center
Line.
A large offset will generate a higher shaft load; a small
offset will generate a lower shaft load. For BPRV devices supplied for
applications within the ANSI 150/DIN PN10 flange pressure range, a standard
offset is used that does not exceed 1"/25mm, even for the largest
installation.
2-The Buckling Strength of the Buckling Pin.
This is a function of the 4th power of the pin diameter, the
Modulus of Elasticity of the Pin material, and the inverse of the Pin length.
Buckling Pin diameter is used for significant set pressure tuning, length adjustment
is used for fine tuning.
3-The Enclosure Mechanism Uses a Lever Principal.
This enables a wide range of BPRV set pressures to be
obtained with modest Buckling Pin lengths and diameters while using a standard
disc shaft offset. This enables the mechanism to be compact and results in a
simple Pin installation procedure that can be completed by a single operator
without special tools. Note: The BPRV is calibrated before shipment
to meet the users required set pressure and tolerance.
Size and Set Pressure Capability
The BPRV is available with a standard range of sizes and set
pressures designed to suit applications that are compatible with ANSI 150, DIN
PN 10 or similar flange specifications as shown in Table 1.
In addition to these standard specifications, the BPRV is
capable of meeting a wide range of dedicated customer requirements that have
already included:
High Set Pressures: Over 2000 psi/138 Bar in a
6"/150mm nominal size installed between ANSI 900 flanges.
Low Set Pressure: 20" Water Column/50 mBar in a
24"/600mm nominal size
Please consult BS&B Safety Systems with your special
applications.
Table 1-Set Pressure Capability: Standard
Size
Set Pressure
Minimum Maximum
in
mm
psig barg psig barg
1" 25
40 2.76
275 18.96
1 1/2"
40
10 0.69
275 18.96
2" 50
5 0.34
720 49.64
3"-6" 80-150
5 0.34
275 18.96
8" -
16" 200-400
3 0.21
275 18.96
18" -
24" 450-600
1 0.07
150 10.34
26" -
36" 650-900
1 0.07
125 8.62
38" -
60" 950-1500
1 0.07
100 6.89
Set Pressure Certification and Tolerance
In line with International Standards, the BPRV is certified
at the customer requested set pressure. This certification is a result of
Buckling Pin tests conducted in the BPRV to confirm compliance with set
pressure and tolerance expectations. The BPRV is certified with a single set
pressure tolerance, as indicated in Table #2. For set pressures between 20
psi/1.38 Bar and 40 psi/2.76 Bar, the BPRV provides a superior set pressure
tolerance option of +/-5% compared to other non-reclosing pressure relief
devices.
When certified according to ASME/North American standards,
the BPRV is marked with the customer requested set pressure (Table #1). When
certified according to European (PED) standards, the BPRV is marked with the
customer requested set pressure and the tolerance based upon Table 2.
Alternatively, European certification allows for marking the BPRV with a
minimum/maximum set pressure (which will also be calculated from Table 2).
Table 2-Set Pressure Tolerances
Pressure
Tolerance
Over 40psi/2.76
Bar
+/-5% Standard
From 1-40 psi/0.07-2.76
Bar
+/-0.14 Bar/2 psi Standard
Over 20 psi/1.38
Bar
+/-5% Upon Request
Operating Pressure Ratio
Buckling Pin technology provides outstanding resistance to
operating pressure conditions. The BPRV can be operated up to 95% of minimum
set pressure. This is called the 'Operating Pressure Ratio'. Subject to special
testing, there is the ability to increase this ratio further.
Note: Remember to subtract the negative set pressure
tolerance in the case of a BPRV marked with 'set pressure' rather than a
defined min/max.
Pressure Cycling Service
Buckling Pin devices are well suited to cyclic service
pressure conditions. Operating under compression, the Buckling Pin is not
subject to tensile fatigue failure. The BPRV can be cycled to its maximum
operating pressure ratio thousands of times.
Materials of Construction
The user may specify the material of construction for each
of the three major BPRV components: Standard materials are as follows:
Valve Body. The standard materials are carbon
steel and
stainless steel. Alternate materials include Hastelloy®*
C-276, Monel®*, Alloy 20, and metals that can be obtained in the form of cut
plate or a forging (depending upon the size of the device to be fabricated).
Valve Disc. The minimum material is stainless
steel. The disc provides the valve sealing surface, therefore a resistant
surface must be ensured. Alternate materials are the same as for the valve
body.
Enclosure. The standard material is stainless steel with
Viton door seals. Alternates may be requested.
Seals
The primary seal in the BPRV is mounted in the 1-piece body,
held in place by a sealing ring. This seal engages a curved surface on the
leading edge of the disc and has a profile that provides a tight shut-off from
both the inlet and outlet sides of the device. The standard seal material is
fluoropolymer (alternates are available upon request).
On the outlet side of the disc, there are two shaft
connections that hold the disc freely within the body. These are also fitted
with standard fluoropolymer seals. Free rotation of the disc about the shaft is
assured by the use of either bushings or bearings (depending upon size and set
pressure) installed with a fluoropolymer seal on either side. The shaft seals
are not in process contact from the inlet side when the BPRV is in the closed
position. (Alternate shaft seals are available upon request).
Installation
The BPRV is designed for “in-line” installation between pipe
flanges. Each device is a 'full face' design with the pipe flange bolting
typically passing through the perimeter of the body. Some flange specifications
have a compact bolting pattern that would interfere with the bushings or
bearings if through bolt holes were used; in these cases, a threaded blind bolt
hole is provided on both sides of the BPRV so a full set of flange bolts is
installed.
The piping may run horizontally, vertically, or at an oblique
angle. The BPRV can be supplied set-pressure certified for any of these
orientations. The user must identify the installation configuration at time of
order to ensure appropriate calibration testing of the BPRV.
The BPRV body can be fitted with lifting lugs to ease
maneuver of the device into place between pipe flanges.
Field Reset
When a Buckling Pin has functioned and the BPRV is to be
reset, this can typically be accomplished while the device remains installed in
the piping system. The enclosure is opened, the used Buckling Pin removed, the
disc rotated back into the closed position, a replacement Buckling Pin
installed and the mechanism reset. This takes only a few minutes and can be
completed by a single operator, even with the largest size BPRV.
Temperature
The materials of construction for the BPRV permit a wide
range of service temperatures. Each device has two different temperature
considerations:
1. Compatibility of service temperature with seal materials.
2. Buckling Pin coincident temperature at time of function.
The standard fluoropolymer seals can be operated between
-40ºF/-40ºC and +400ºF/260ºC. While flowing, temperatures down to cryogenic
conditions can be handled. Seal performance is regained once the fluoropolymer
seal has returned to the recommended operating range.
With the Buckling Pin installed in the enclosure, the
process temperature does not reach the pin. In general, the Buckling Pin will
be at ambient temperature making certification of the Pin lot at 72ºF/22ºC
appropriate.
Variation of ambient temperature causes minimal change in
Buckling Pin performance - as little as 1% over the range -40ºF/-40ºC to
200ºF/93ºC. Ambient temperature conditions for each application should be
reviewed with BS&B Safety Systems, L.L.C.
Enclosure and Mechanism Construction
Three standard mechanisms are employed to met the torque
requirements of the BPRV nominal sizes 1”- 60” (25 mm-150 mm). In all cases,
the mechanism is fitted to a solid stainless steel baseplate to ensure
rigidity. The mechanism is either installed inside a stainless steel enclosure
or has an enclosure bolted to the baseplate (see M4200 photo). The M16000
mechanism handles low torque applications typical of BPRV sizes 1”-6” (25
mm-150 mm). The more substantial M4200 mechanism handles the torque range
typical for higher pressure 4” (100 mm) BPRV devices through low pressure 24”
(600 mm) size. The M1600 mechanism is designed to handle the very high torque
requirements of BPRV devices sized 24”-60,” nominal size. (The light duty M600
mechanism for small size BPRV devices is offered with an economic, light-weight
glass fiber enclosure as an option).
The mechanism front cover is provided with a latch tongue
that aligns with another on the side to allow the user to add a preferred
locking mechanism. Turn latches mounted on the front of the enclosure energize
the door elastomer seal.
All mechanisms comprise of stainless steel and protective
coated high tensile steel components. This combination avoids seizing of moving
parts through the use of similar metals, and provides excellent corrosion
resistance. The mechanism is fully sealed within the enclosure when the door is
latched shut.
Mechanism Function
The BPRV mechanisms use a lever principal to balance input
load from the rotating disc against output load applied to the Buckling Pin.
When the (input load) x (distance from lever load input to the fulcrum) >
the (Buckling Pin collapse load) x (distance from fulcrum to the lever load
output), the BPRV will open.
The input load is provided by the pressure generated torque
on the disc shaft This loads the input side of the lever arm. When the Buckling
Pin operates, the lever is free to move, allowing the shaft to rotate through
90 degrees into the full open position. At most set pressures, the BPRV will
latch in the full open position to ensure the greatest flow rate through the
device. The location of the fulcrum is tailored by BS&B Safety
Systems, L.L.C. during the calibration of each BPRV. This set pressure control
feature of the BPRV design is used for fine tuning. The fulcrum location is
factory set and wire sealed for tamper evidence.
Customized BPRV Units/Command Activation
The BPRV can be user command activated in two different
configurations:
BPRV-CAE
If it is known that the BPRV will always sense a positive
differential pressure, an actuator (e.g. solenoid or pneumatic piston)
installed adjacent to the buckling pin can be used to buckle the pin on demand.
This will release the BPRV mechanism and allow the disc to rotate freely under
pressure.
This is known as a “command activated enclosure,” or CAE,
and allows the valve to be used as both a pressure relief device and a command
actuated quick opening valve.
BPRV-CAS
If command actuation is desired in an application where
positive differential pressure cannot be guaranteed, a powered actuator can be
installed on the free shaft of the BPRV. When the operating conditions require
the valve open, the actuator is powered to overcome both the buckling pin and
any back pressure induced torque on the BPRV shaft to open the device.
This is known as a “command activated shaft,” or CAS, and
allows the BPRV to be used as both a pressure relief device and a command
actuated quick opening valve.
The BPRV-CAE and BPRV-CAS are examples of customized design
options that can be satisfied with this versatile pressure relief technology.
BS&B Safety Systems welcomes the opportunity to develop solutions to unique
applications.
Information Required to Order the BPRV
General
- Tag
Number
- Line
Size
- Flange
Specification
Operating Conditions
- Set
Pressure and Tolerance Requested
- Set
Temperature (Pin Conditions)
Service Conditions
- Fluid
- Vapor/Gas:
Molecular Weight
- Liquid:
Specific Gravity
- Required
Flow Capacity (if known)
- Normal
Service Pressure
- Vacuum
Conditions
- Back
Pressure Conditions
- Normal
Service Temperature (Process)
- Flowing
Temperature (Process)
- Static
or Pulsing Service Pressure
Materials
- Valve
Disc
- Valve
Body
- Disc
Seal
- Enclosure
Installation/Flow Path
- Vertical,
Horizontal, Oblique (specify angle to Horizontal)
Accessories
- Sensor
— Visual/Electrical
- Sensor
Electrical Requirements
- Buckling
Pin or Buckling Pin Cartridge
- Quantity
of Pins/Cartridges
Note: When the BPRV opens, the disc may project beyond the
body cavity within which it is retained when closed. When installing or
removing the BPRV from service it is essential the disc is in the closed
position to avoid damage to the disc and mechanism. Please seek advice from
BS&B Safety Systems when the BPRV is to be installed close to a “T-piece”
or other piping path that may present an unusual flow pattern to the device.
Quality Assurance
Every BPRV is thoroughly tested before shipment.
Pre-delivery
inspection can be divided into:
- Dimensional
Inspection
- Leak
Tightness Verification
- Buckling
Pin Calibration and Set Pressure Testing
Before the BPRV is assembled from component parts, each
component is dimensionally verified for its critical features. After assembly,
the performance of the seals is checked. ANSI standard B16.104 is typically
followed with a minimum test standard of Class IV established. Many BPRV
devices are supplied to the stricter Class V and Class VI limits which require
a 'bubble tight' construction.
All Buckling Pins that are supplied as a lot are
manufactured from a single batch of raw material at the same time. The
BPRV set pressure is established through Buckling Pin destructive testing. Once
the appropriate Pin configuration has been achieved for the required set
pressure, the lot of Pins is completed within very tight dimensional
tolerances. BS&B Quality Assurance personnel witness set pressure tests for
certification purposes. All Buckling Pins are supplied tagged with a traceable
lot number, set pressure and the serial number of the BPRV unit for which they
have been calibrated. SAF-T-PIN™ Buckling Pin Cartridges are recommended
for optimum control and traceability.
When fully calibrated and certified, wire seals are
installed at the
following key locations:
- Junction
of the Body and the Enclosure
- Fulcrum
Connection to the Enclosure Baseplate
- Junction
of the Sensor to the Shaft (where fitted)
Codes and Standards
Several International standards recognize Buckling Pin
devices and provide guidelines for their certification. These include ASME, in
the form of code case 2091, and TUV AD Merkblatt A1 and the European Pressure
Equipment Directive (PED). The BPRV can be supplied to all established
standards.
Maintenance
If desired, the Buckling Pin can be removed and the BPRV
tested by rotating the disc into the open position triggering the
mechanism. There must be no pressure on the device. The Buckling
Pin can then be reinstalled.
Occasionally it will be necessary to replace the disc seal.
This can be accomplished quickly and easily. The disc seal is held in place by
a seal ring that inserts into the inlet of the one-piece body. This seal ring
is simply removed using simple tools and the used seal pulled out from the BPRV
body. After inspecting the seating area and clearing away any debris, the
BS&B replacement seal is installed and the seal ring put back in place. Seal
replacement does not require disassembly of the BPRV body or mechanism. It is
recommended a spare disc seal is purchased for each BPRV.
Testing In Place
Since the BPRV might be interpreted as a relief valve, many
users wish to perform scheduled maintenance to ensure the set pressure has not
been compromised while the valve is in service. The normal procedure for
testing of many types of relief valves is to remove the valve from service and
send to a valve repair shop for a pop test and re-certification. The advantage
of the BPRV is that the valve can be re-tested in-situ. The offset shaft is
designed with a hexagon drive in the enclosure. The user can leave the valve in
service between the flanges and attach a torque wrench to the hex. All the user
needs to do is load the shaft with a torque wrench until the valve opens.
BS&B Safety Systems, L.L.C. can supply a torque value range which, when
applied to the hex drive of the offset shaft, will buckle the pin and activate
(open) the valve. Once the value recorded on the torque wrench lies within this
torque range supplied by BS&B, the user knows that the valve set pressure
has not been compromised and the product is now re-tested. This allows users to
re-check the valve within 10-15 minutes, without having to remove it from
service.
Testing in place greatly reduces the maintenance expenses
compared with relief valves by dramatically reducing the time and labor
involved with the re-validation process.
Optional SAF-T-PIN™ Buckling Pin Cartridge
The BPRV can be provided with Buckling Pin Cartridges that
are installed like an electrical fuse. The SAF-T-PIN™ Buckling Pin Cartridge
allows a "Quick-Change" option of Buckling Pins with a simple
push-in/pull-out design for installation within the enclosure. Each SAF-T-PIN™
Cartridge contains a calibrated Buckling Pin that is perfectly mounted for
optimum performance.
The SAF-T-PIN cartridge locates into the BPRV mechanism in
one direction only ensuring fail-safe installation.
The transparent cartridge permits visual inspection of the
Buckling Pin, and the stainless steel ends of the cartridge are marked with
full set pressure and traceability information including the serial number of
the BPRV device. The SAF-T-PIN cartridge avoids the need for special
installation procedures and any concern of handling bare Buckling Pins.
Worldwide patents pending.
Sensor/Indicator Option
Both a visual and electrical signal to confirm BPRV status
is available. Mounted on the free shaft not used by the mechanism, the BPRV
sensor comprises a sealed enclosure (typically to Nema IV standard) that houses
a colored dome indicating 'Open' (colored Red) or 'Closed' (colored Green). The
dome is rotated by a shaft extension that moves in unison with the disc of the
BPRV. Electrical switching compatible with the users requirements can be added
to the enclosure to provide a remote signal or alarm when the BPRV operates.
This can be provided to meet intrinsically safe requirements.
SmartDisk™ Compatible
The BPRV can be supplied with SmartDisk™ wireless sensor
technology that allows an electrical signal to be generated at a monitoring
station located up to several thousand feet away from the BPRV without the cost
of hard wiring. Please refer to catalog 77-1016 for more information.