ASHCROFT 330 All-Welded Flush Seal-Isolators Instruction Manual
- June 3, 2024
- ASHCROFT
Table of Contents
ASHCROFT 330 All-Welded Flush Seal-Isolators
Introduction
A diaphragm seal is a device that attaches to the process side of a pressure- measuring instrument to separate the instrument from the process fluid while transmitting pressure across a flexible membrane. The volume enclosed by the diaphragm, the top housing, and the measuring element is completely filled with a pressure transfer fluid. A change in pressure at the process connection causes a displacement of the filling fluid due to deflection of the diaphragm, transferring the change in pressure to the sensing element of the pressure instrument.
Safety Information
WARNING: Serious injury or equipment damage can result from failure to properly install, maintain, or operate these components. To assure safe operation and maintenance procedures, read carefully and follow the instructions in this manual.
- Follow all instructions in this document to avoid exposure to pressurized fluid
- Use proper tools and safety equipment in installing or maintaining components
- Assure that process pressure and temperatures are properly monitored and maintained, and the process fluid is appropriate and compatible with the wetted materials of the diaphragm seal
- Follow all of your company’s safety procedures in the event of a leak or diaphragm seal failure
Diaphragm Seal Components
Though the exact components will vary between specific models, most diaphragm seals will share the same essential parts.
Top Housing
The top housing of the diaphragm seal is used to connect to the pressure
measurement instrument. The fill port allows for assemblies to be vacuum
filled, then sealed with a ball bearing in a conical seat and secured with a
set screw.
Diaphragm
The diaphragm serves to separate the process fluid from the filling fluid, and
as such is a component wetted to the process. Diaphragms can be welded or
threaded into the top housing, which in turn can be welded or clamped to a
lower housing. Changes in pressure cause the diaphragm to deflect, displacing
fill fluid and transmitting pressure to the pressure-measuring instrument. It
is important to ensure that a diaphragm has sufficient displacement to operate
a pressuremeasuring instrument across its entire span. For detailed diaphragm
seal and instrument compatibility, see Ashcroft Product Information Page DS-
PI-82, “Minimum and Maximum Pressures for Diaphragm Seals,” found at
Ashcroft.com
Fill Fluid
A filling fluid (sometimes referred to as “system fill,” “pressure sensing
fluid,” or, “hydraulic fluid”) is required to transmit pressure from the
diaphragm membrane to the pressure sensing device. Diaphragm seal assemblies
are filled via a vacuum filling process that ensures the system contains no
air gaps. Fill fluids are normally selected based on operating conditions;
primarily temperature. Though normally not in contact with the process media,
a diaphragm failure may bring process media in contact with the fill fluid, so
compatibility with the process media should be a consideration.
Specifications
330 Flush Seals
- Connections: 330 flush threaded process
- Process Connection Sizes: 1 NPT male
- Instrument Connection Sizes: ¼ NPT female
- Pressure Ratings: 330: 3000 psi
- Added Instrument Tolerance: 330: ± 1% typical
- Wetted Components: 330: diaphragm and threads
- Non-Wetted Components: Top housing
Thermal Dissipation
Seals will dissipate thermal energy, though ambient and process conditions
will greatly affect the amount of heat that can be lost through the seal.
Accessories designed for dissipating heat, such as siphons or capillaries,
should be used whenever dealing with elevated process temperatures.
Fill Fluid Specifications
Installation
General Information
Instruments attached and filled to diaphragm seals should never be tightened
or loosened at the top housing. Doing so will alter the dynamics of the fill
fluid and diaphragm movement, causing errors in the reading. Assemblies should
ONLY be installed and/ or tightened at the diaphragm seal lower housing. 330
seals can be purchased with instrument welded to the top housing of the seal
to prevent tampering (XDU). Diaphragm seals should be installed in accordance
with any safety precautions or installation specifications applicable to the
end user. That said, the general principles in the following sections still
apply.
Threaded Seals
Note: Torque should never be applied to the pressure instrument when
installing the diaphragm seal. Most seals are supplied with either wrench
flats or spanner holes to be used when installing the seal into process
piping. 330 seals are only supplied with NPT threads per ASME B1.20.1. NPT
threads require the use of a suitable thread sealant, such as pipe dope or
PTFE tape, and must be tightened securely to prevent galled threads and to
ensure a leak-tight seal. Torque values will vary by connection size, though
2-3 full turns past fingertight is often used as a guideline. Refer to ASME
B1.20.1 for detailed information regarding NPT threads.
Maintenence
Storage
Diaphragm seal assemblies should be stored in accordance with the storage
requirements for all instruments attached, as well as any temperature limits
listed above. Common instrumentation is shown in the table below. Refer to the
respective data sheets or maintenance guides for detailed storage requirements
for Ashcroft pressure instruments. Note that certain fill fluids (e.g.,
distilled water) may have storage and process temperature limitations narrower
than the below data.
Frequency of Inspection
Inspection frequency is application-specific and depends on the severity of
the service and how critical the accuracy of the pressure instrument is. For
example, a monthly inspection may be necessary for severe service
applications, such as corrosive process media or heavy pulsation and
vibration. Annual inspections, or even less frequent schedules, are often
employed in non-critical applications.
Removal from Service
Diaphragm seals should be properly isolated and vented from the process prior
to disassembly. 330 diaphragm seals can be inspected by removing the diaphragm
seal from the process and observing the condition of the diaphragm
Diaphragm Seal Failures and Troubleshooting
All Ashcroft diaphragm seals, with the exception of 310 Mini Seals, are
continuous duty as defined by ASME B40.2. Should the pressure instrument fail
or be removed accidentally, the diaphragm will seat against a matching surface
in the top housing preventing damage to the diaphragm or leakage of the
process fluid. In the event that a diaphragm failure is suspected, the
assembly should be immediately isolated from the process and the cause for
failure determined. Most diaphragm failures are caused by corrosion, high
temperatures, or fill leakage. Process media build-up in the lower housing can
also require cleaning or replacement. In the event of a diaphragm failure due
to corrosion, it is critical that the wetted materials of the assembly be
evaluated for compatibility before it is replaced
Troubleshooting Guide
© 2022 Ashcroft Inc. 250 East Main Street 06614, Tel: 203-378-8281
Fax: 203-378-0499, All
specifications are subject to change without notice.
All sales subject to standard terms and conditions.
www.ashcroft.com All rights reserved.
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