HFL diaphragm seal · Recessed diaphragm · RF or RTJ flange
Flanged Off-Line Diaphragm Seal
Configurable pressure-instrument isolation for flanged branch connections.
The HFL combines a recessed diaphragm with a flanged process connection for off-line pressure measurement. Haygor publishes 2.4-, 2.9-, and 4.1-inch diaphragm sizes, ANSI Raised Face or Ring Type Joint configurations, and flange classes through 1500.
- Three published diaphragm sizes
- ANSI Raised Face or Ring Type Joint
- Optional single or dual flushing connections
Quick answer
What is a flanged off-line diaphragm seal?
A flanged off-line diaphragm seal is a pressure-isolation device mounted on a flanged branch or vessel connection. Process pressure acts on a diaphragm inside the seal, and a sealed fill fluid transfers that pressure to a gauge, transmitter, or pressure switch without exposing the instrument's sensing element to the process media.
The Haygor HFL uses a recessed diaphragm within a bolted upper-and-lower assembly. It can be configured with ANSI Raised Face or Ring Type Joint geometry, multiple diaphragm diameters, specialty wetted materials, optional linings, and flushing connections.
Hydraulic pressure transfer
How the HFL seal works
The HFL creates a compatible flanged barrier between the process and the pressure instrument while preserving hydraulic pressure transmission.
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1
The seal bolts to the process
The selected flange size, pressure class, and face style mate with the off-line process connection.
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2
Pressure reaches the diaphragm
Process media enters the recessed lower chamber and applies pressure to the selected metal or PTFE diaphragm.
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3
Fill fluid transfers pressure
Diaphragm movement displaces the sealed hydraulic fill through the upper assembly or a remote capillary.
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4
The instrument measures
The connected gauge, transmitter, or switch responds to pressure while remaining isolated from the process media.
Application fit
When a flanged off-line seal is a strong choice
The HFL is intended for off-line pressure points where flange compatibility, configurable wetted materials, and access to the recessed chamber are important.
Installation advantages
- Flanged branch, nozzle, and vessel connections
- ANSI Raised Face or Ring Type Joint interfaces
- Direct-mounted or remote pressure instruments
- Optional single or dual flushing connections
- Three diaphragm diameters for application matching
Selection conditions that favor the HFL
- The process connection requires a flanged seal
- The flange standard, size, class, and face are known
- A recessed process chamber is acceptable for the media
- The selected material stack is chemically compatible
- The complete assembly pressure and temperature limits are verified
Common industrial settings
Designed for flanged pressure-measurement systems
- Chemical processing
- Refining
- Petrochemical
- Oil & gas
- Power & utilities
- Water & wastewater
Catalog specifications
HFL diaphragm, flange, connection, and flushing choices
The values below summarize the HFL selections published in Haygor's diaphragm seal ordering guide.
Two flange-face families
ANSI Raised Face and Ring Type Joint configurations.
Published diaphragm diameters
2.4, 2.9, and 4.1 inches.
Published class range
Standard Class 150-600 with extended configurations through Class 1500.
Mounting configurations
Through-bolt and stud-bolt arrangements, size dependent.
| Size code | Diaphragm diameter | Face style | Catalog description |
|---|---|---|---|
| 2 | 2.4 in. | ANSI Raised Face | Small RF diaphragm configuration |
| 3 | 2.9 in. | ANSI Raised Face | Medium RF diaphragm configuration |
| 4 | 4.1 in. | ANSI Raised Face | Large RF diaphragm configuration |
| 5 | 2.4 in. | Ring Type Joint | Small RTJ diaphragm configuration |
| 6 | 2.9 in. | Ring Type Joint | Medium RTJ diaphragm configuration |
| 7 | 4.1 in. | Ring Type Joint | Large RTJ diaphragm configuration |
Published connection and assembly envelope
Availability depends on diaphragm size, flange class, material, lining, and mounting configuration.
| Selection | Published choices | Important catalog note |
|---|---|---|
| Process flange size | 1/2, 3/4, 1, 1-1/2, 2, 3, and 4 in. | Feature summary identifies 1/2-3 in. as standard; 4 in. appears in ordering and dimensional tables. |
| Pressure class | 150, 300, 600, 900, and 1500 | Standard range is stated as Class 150-600; higher classes are extended configurations. |
| Instrument connection | Weld, 1/4 NPT, or 1/2 NPT | Weld connection is not listed with Titanium or Zirconium upper material. |
| Flushing connection | None; single or dual 1/4 NPTF; single or dual 1/2 NPTF; single or dual pipe socket weld | 1/2-inch ports are limited to the 2.9- and 4.1-inch diaphragm sizes. Lined lowers do not accept flush connections. |
| Mounting configuration | A through-bolt; B stud-bolt; C through-bolt | The dimensional matrix assigns the configuration by flange size, class, and diaphragm size. |
Confirm current dimensions, flange-standard availability, pressure and temperature limits, material compatibility, bolting, gasket selection, fill fluid, and the rating of the complete seal-and-instrument assembly with Haygor before order entry.
Configure the complete assembly
HFL materials, gaskets, bolting, and options
Start with the process conditions, then define the flange interface, diaphragm size, wetted material stack, instrument connection, flush access, gasket, bolting, and documentation.
Flange and face
Specify flange standard, nominal size, pressure class, Raised Face or RTJ geometry, and the mating-pipe requirements.
Diaphragm and wetted parts
Select the diaphragm diameter and compatible lower-body, diaphragm, and optional lining materials for the actual media.
Gasket and bolting
Match gasket chemistry and temperature limits, then verify bolting material and any resulting pressure derating.
System and service details
Define direct or remote mounting, instrument connection, fill fluid, flush ports, cleaning needs, and required documentation.
Catalog wetted materials
Lower-body and diaphragm choices
- 316 / 316L stainless steel
- 304 / 304L stainless steel
- Alloy 20
- Alloy C-276
- Alloy B-3
- Monel 400
- Alloy 600
- Duplex Alloy 2205
- Nickel 200 / 201
- Titanium
- Zirconium 702
- PTFE diaphragm option
- Carbon-steel lower body
- 316SS lower with PTFE lining
- 316SS lower with tantalum lining
The exact lower-body and diaphragm menus are not identical. Confirm that every wetted component is available in the selected configuration.
Published gasket limits
Temperature references in the ordering guide
- Klinger C4401
- 450 °F maximum · standard
- Grafoil
- 700 °F maximum
- Gylon 3510
- 300 °F maximum
- PTFE O-ring
- 350 °F maximum
- Viton O-ring
- 400 °F maximum
- Buna-N O-ring
- 250 °F maximum
- Kalrez O-ring
- 500 °F maximum
Temperature note
Use the lowest-rated component in the assembled system
The gasket values are catalog maxima for the listed gasket choices, not universal HFL operating-temperature ratings. The usable system range also depends on process pressure, flange rating, diaphragm and body materials, fill fluid, instrument, capillary, ambient conditions, and installation geometry.
Compare diaphragm position and connection style
Related Haygor diaphragm seals
Compare flush-face, wafer, and threaded designs when the process media, piping geometry, flange arrangement, or maintenance strategy calls for a different interface.
Frequently asked questions
Flanged off-line diaphragm seal FAQ
These answers summarize Haygor's published HFL product data. Final selection should be based on the complete process, flange, instrument, and installation requirements.
Ask Haygor a technical questionWhat is a flanged off-line diaphragm seal?
A flanged off-line diaphragm seal mounts to a flanged branch connection and hydraulically transfers process pressure to a gauge, transmitter, or switch while isolating the instrument from the process media. The HFL uses a recessed diaphragm inside the process-side chamber.
Which diaphragm sizes and flange-face styles are available for the HFL?
Haygor publishes 2.4-inch, 2.9-inch, and 4.1-inch diaphragm sizes. Each size is listed in ANSI Raised Face and Ring Type Joint configurations.
What flange sizes and pressure classes are published?
The HFL feature summary lists standard ANSI flange sizes from 1/2 inch through 3 inches, standard Class 150 through 600, and extended ratings through Class 1500. The ordering and dimensional tables also show 4-inch variants, so current availability should be confirmed with Haygor.
Can the HFL include flushing connections?
Yes. Published selections include no flush connection, single or dual 1/4-inch NPT female ports, single or dual 1/2-inch NPT female ports on the 2.9-inch and 4.1-inch diaphragm sizes, and comparable pipe socket-weld choices.
Which wetted materials and linings are listed?
Published lower-body choices include stainless steels, Alloy 20, Alloy C-276, Alloy B-3, Monel 400, Alloy 600, duplex Alloy 2205, Nickel 200, Titanium, Zirconium 702, and carbon steel. PTFE-lined and tantalum-lined 316 stainless lower assemblies are also listed, with flush connections unavailable on the lined versions.
When should I compare the HFL with a flush flanged seal?
The HFL is a recessed-diaphragm design. Compare the HFF flush flanged seal when the process media is likely to coat, crystallize, settle, or plug a recessed cavity, or when a process-facing diaphragm is otherwise required.
What instrument connections are available?
The ordering guide lists a weld connection, 1/4-inch NPT, and 1/2-inch NPT. The weld connection is not listed with Titanium or Zirconium upper assemblies.
What information should I provide for an HFL quote?
Provide the process media and concentration, operating and maximum pressure, process and ambient temperature, flange size, class, face style and standard, instrument model and connection, preferred diaphragm size, wetted materials, flush-port arrangement, mounting method, fill-fluid requirements, and documentation needs.
Move from flange data to an HFL configuration
Configure a flanged off-line seal or send the complete application to Haygor.
Use the configurator for a guided starting point, or request a quote for flange, diaphragm, material, gasket, flushing, fill-fluid, and instrument review.