HFF diaphragm seal · Flush process-facing diaphragm · Rotating flange
Flush Flanged Diaphragm Seal
Reduced-cavity isolation for flanged off-line pressure measurement.
The HFF positions the diaphragm at the process-facing flange surface to reduce the recessed pocket where difficult media can collect. Haygor publishes ANSI Raised Face, Ring Type Joint, and DIN EN 1092-1 choices, with standard ANSI sizes from 2 to 4 inches and classes from 150 through 2500.
- Flush process-facing diaphragm
- Rotating flange for alignment
- ANSI Class 150 through 2500
Quick answer
What is a flush flanged diaphragm seal?
A flush flanged diaphragm seal is a pressure-isolation assembly that bolts directly to a flanged process connection and places the sensing diaphragm at the process-facing flange surface. The diaphragm separates the process media from the pressure instrument, while a sealed hydraulic fill fluid transfers pressure to a gauge, transmitter, or switch.
The Haygor HFF combines that flush geometry with a rotating flange and configurable ANSI or DIN interfaces. It is intended for off-line pressure points where a recessed chamber is undesirable and where flange size, class, face style, diaphragm material, and optional flushing access must be matched to the process.
Hydraulic pressure transfer
How the HFF seal works
The HFF forms a process-compatible barrier at the flange face while transferring pressure to the connected instrument.
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1
The rotating flange bolts to the process
The selected flange standard, size, rating, and face geometry mate with the process nozzle or branch connection.
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2
Process pressure acts on the flush diaphragm
The process-facing diaphragm responds without the deeper chamber used by a recessed off-line seal.
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3
Fill fluid transfers pressure
Diaphragm movement displaces the sealed hydraulic fill through the upper insert 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 flush flanged seal is a strong choice
The HFF is designed for off-line flanged pressure points where reducing the process recess can improve cleanability, media exposure, or maintenance access.
Installation advantages
- Process-facing diaphragm reduces the recessed pocket
- Rotating flange helps align bolt holes during installation
- Raised Face, Ring Type Joint, and DIN flange selections
- Direct-mounted or remote pressure instruments
- Optional calibration or flushing ring
Selection conditions that favor the HFF
- A recessed chamber could retain, coat, or plug with the media
- The flange standard, size, rating, and face are known
- The diaphragm can be exposed directly at the process-facing surface
- The selected wetted material is compatible with the media
- The complete assembly pressure and temperature limits are verified
Common industrial settings
Built for difficult flanged pressure-measurement points
- Chemical processing
- Refining
- Petrochemical
- Oil & gas
- Power & utilities
- Water & wastewater
Catalog specifications
HFF flange, rating, connection, and dimension choices
The values below summarize the HFF selections published in Haygor's diaphragm seal ordering guide.
Three published face families
ANSI Raised Face, ANSI Ring Type Joint, and DIN Raised Face.
Published ANSI sizes
2-, 3-, and 4-inch flange selections.
Published ANSI classes
Class 150, 300, 600, 900, 1500, and 2500.
Published DIN sizes
PN combinations through PN250, size dependent.
| Selection | Published choices | Catalog note |
|---|---|---|
| Flange type | ANSI Raised Face; ANSI Ring Type Joint; DIN Raised Face EN 1092-1 | Match the mating flange face, gasket or ring, bolting, and applicable piping standard. |
| ANSI process size | 2, 3, and 4 in. | Additional sizes may be available by request. |
| DIN process size | DN50, DN80, DN100, and DN125 | Availability depends on the selected PN rating. |
| ANSI pressure class | 150, 300, 600, 900, 1500, and 2500 | The complete assembly must be checked for pressure and temperature capability. |
| DIN PN rating | PN10/40 for DN50; PN10/16 and PN25/40 for DN80-DN125; PN63, PN100, PN160, and PN250 for DN50-DN125 | Confirm current combinations and dimensions with Haygor. |
| Instrument connection | Weld, 1/4 NPT, or 1/2 NPT | The weld connection is not listed with Titanium or Zirconium upper inserts. |
| Upper insert | 316/316L stainless steel, Titanium, or Zirconium 702 | Titanium or Zirconium upper inserts are required with matching diaphragm materials. |
Published ANSI Raised Face dimensions
Dimensions are in inches. A through E correspond to the dimensional drawing in Haygor's ordering guide. RTJ dimensions and groove numbers are published separately in the guide.
| Diaphragm | Flange | Bolt pattern | A | B | C | D | E |
|---|---|---|---|---|---|---|---|
| 2.4 in. | 2 in. Class 150 | (4), 0.75 in. holes, 4.75 in. B.C. | 0.68 | 6.00 | 3.62 | 0.33 | 2.23 |
| 3.5 in. | 3 in. Class 150 | (4), 0.75 in. holes, 6.00 in. B.C. | 0.87 | 7.50 | 5.00 | 0.33 | 2.23 |
| 3.5 in. | 4 in. Class 150 | (8), 0.75 in. holes, 7.50 in. B.C. | 0.87 | 9.00 | 6.19 | 0.33 | 2.23 |
| 2.4 in. | 2 in. Class 300 | (8), 0.75 in. holes, 5.00 in. B.C. | 0.81 | 6.50 | 3.62 | 0.33 | 2.23 |
| 3.5 in. | 3 in. Class 300 | (8), 0.88 in. holes, 6.62 in. B.C. | 1.06 | 8.25 | 5.00 | 0.33 | 2.23 |
| 3.5 in. | 4 in. Class 300 | (8), 0.88 in. holes, 7.88 in. B.C. | 1.18 | 10.00 | 6.00 | 0.33 | 2.23 |
| 2.4 in. | 2 in. Class 600 | (8), 0.75 in. holes, 5.00 in. B.C. | 1.00 | 6.50 | 3.62 | 0.33 | 2.23 |
| 3.5 in. | 3 in. Class 600 | (8), 0.88 in. holes, 6.62 in. B.C. | 1.25 | 8.25 | 5.00 | 0.33 | 2.23 |
| 3.5 in. | 4 in. Class 600 | (8), 1.00 in. holes, 8.50 in. B.C. | 1.50 | 10.75 | 6.00 | 0.33 | 2.23 |
| 2.4 in. | 2 in. Class 900/1500 | (8), 1.00 in. holes, 6.50 in. B.C. | 1.50 | 8.50 | 3.62 | 0.33 | 2.23 |
| 3.5 in. | 3 in. Class 900 | (8), 1.00 in. holes, 7.50 in. B.C. | 1.50 | 9.50 | 5.00 | 0.33 | 2.23 |
| 3.5 in. | 4 in. Class 900 | (8), 1.25 in. holes, 9.25 in. B.C. | 1.75 | 11.50 | 6.00 | 0.33 | 2.66 |
| 3.5 in. | 3 in. Class 1500 | (8), 1.25 in. holes, 8.00 in. B.C. | 1.88 | 10.50 | 5.00 | 0.33 | 2.66 |
| 3.5 in. | 4 in. Class 1500 | (8), 1.38 in. holes, 9.50 in. B.C. | 2.12 | 12.25 | 6.00 | 0.33 | 3.31 |
| 2.4 in. | 2 in. Class 2500 | (8), 1.12 in. holes, 6.75 in. B.C. | 2.00 | 9.25 | 3.62 | 0.33 | 2.66 |
| 3.5 in. | 3 in. Class 2500 | (8), 1.38 in. holes, 9.00 in. B.C. | 2.62 | 12.00 | 5.00 | 0.33 | 3.31 |
Confirm current dimensions, flange-standard availability, pressure and temperature limits, diaphragm displacement, material compatibility, gasket or ring selection, bolting, fill fluid, and the rating of the complete seal-and-instrument assembly with Haygor before order entry.
Configure the complete assembly
HFF materials, flushing rings, ports, and options
Start with the process conditions, then define the flange interface, diaphragm material, upper insert, optional calibration or flushing ring, instrument connection, fill system, and documentation.
Flange and face
Specify ANSI or DIN, nominal size, pressure class or PN rating, Raised Face or RTJ geometry, and mating-connection details.
Diaphragm and wetted parts
Select a diaphragm alloy compatible with the actual media, concentration, pressure, temperature, and cleaning method.
Ring and flushing access
Choose no ring or a calibration/flushing ring, then define single or dual threaded or socket-weld ports when needed.
System and service details
Define direct or remote mounting, instrument connection, fill fluid, capillary, ambient conditions, cleaning needs, and documentation.
Published diaphragm materials
Match the process-facing diaphragm to the media
- 316 / 316L stainless steel
- 304 / 304L stainless steel
- Tantalum
- Alloy 20
- Alloy C-276
- Alloy B-3
- Monel 400
- Alloy 600
- Alloy 2205
- Nickel 200 / 201
- Titanium
- Zirconium 702
Material availability can depend on flange type, upper insert, ring selection, and fabrication method. Confirm every wetted component in the final configuration.
Published option codes
Surface treatments, plugs, and documentation
- /AU
- Gold-plated diaphragm
- /NS
- PTFE-coated diaphragm for non-stick service only
- /P1
- Single pipe plug for flush port
- /P2
- Dual pipe plugs for flush ports
- /MC
- Material certification with MTRs
Selection note
Use system-level limits, not a single component value
The usable HFF range depends on the flange standard and rating, diaphragm and flange materials, process pressure and temperature, fill fluid, instrument, capillary length and routing, ambient conditions, mounting orientation, and required measurement performance.
Compare flange and diaphragm geometry
Related Haygor diaphragm seals
Compare recessed, wafer, and threaded designs when the process media, piping geometry, flange arrangement, or maintenance strategy calls for a different interface.
Frequently asked questions
Flush flanged diaphragm seal FAQ
These answers summarize Haygor's published HFF product data. Final selection should be based on the complete process, flange, instrument, and installation requirements.
Ask Haygor a technical questionWhat is a flush flanged diaphragm seal?
A flush flanged diaphragm seal mounts directly to a flanged process connection and positions the sensing diaphragm at the process-facing flange surface. A sealed fill fluid transfers pressure to a gauge, transmitter, or switch while isolating the instrument from the process media.
Why use a flush diaphragm instead of a recessed diaphragm?
The flush position reduces the process cavity ahead of the diaphragm. This can be advantageous for viscous, coating, crystallizing, solids-bearing, or otherwise difficult media that could collect in a recessed chamber. Final suitability still depends on the complete process and installation.
Which flange standards and face styles are listed for the HFF?
Haygor lists ANSI Raised Face, ANSI Ring Type Joint, and DIN Raised Face to EN 1092-1. The flange standard, nominal size, pressure class or PN rating, face geometry, bolting, and gasket arrangement must all match the process connection.
What sizes and pressure ratings are published?
The published HFF range includes ANSI 2-, 3-, and 4-inch flange sizes with Classes 150, 300, 600, 900, 1500, and 2500. DIN selections include DN50, DN80, DN100, and DN125 with listed PN combinations through PN250, depending on nominal size.
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 inserts.
Which diaphragm materials are offered?
Published diaphragm choices include 316/316L stainless steel, 304/304L stainless steel, Tantalum, Alloy 20, Alloy C-276, Alloy B-3, Monel 400, Alloy 600, Alloy 2205, Nickel 200/201, Titanium, and Zirconium 702.
Can the HFF include a calibration or flushing ring?
Yes. The HFF can be specified without a ring or with a ring in several metals or PTFE. Published flushing choices include no ports, single or dual 1/4-inch or 1/2-inch NPT female ports, and single or dual 1/4-inch or 1/2-inch pipe socket-weld connections.
What information should I provide for an HFF quote?
Provide the process media and concentration, operating and maximum pressure, process and ambient temperature, flange standard, nominal size, class or PN rating, face style, instrument model and connection, wetted-material requirements, calibration or flushing ring details, mounting method, fill-fluid requirements, and documentation needs.
Move from flange data to an HFF configuration
Configure a flush flanged seal or send the complete application to Haygor.
Use the configurator for a guided starting point, or request a quote for flange, diaphragm, material, flushing-ring, fill-fluid, and instrument review.