HFT diaphragm seal · Flush male NPT connection
Threaded Flush Diaphragm Seal
Compact, high-pressure instrument isolation with the diaphragm positioned at the process end of the threads.
The flush diaphragm reduces the recessed volume where viscous, coating, crystallizing or solids-bearing media can collect, while the sealed fill system transfers pressure to a gauge, transmitter or switch.
- 3/4 in. through 2 in. standard NPT sizes
- Up to 9,000 psi MWP, depending on size
- Multiple corrosion-resistant material options
Quick answer
What is a threaded flush diaphragm seal?
A threaded flush diaphragm seal is a pressure-isolation device with a male threaded process body and a diaphragm located at the end of the threads. Process pressure acts on the diaphragm, and a sealed fill fluid transfers that pressure to the attached measuring instrument without exposing the instrument's sensing element to the process media.
Compared with a recessed threaded seal, the HFT profile places the sensing surface closer to the process opening. That geometry helps reduce pockets where viscous fluids, solids or crystallizing media can accumulate.
Flush-face pressure transfer
How the HFT seal works
The HFT isolates the process from the instrument while keeping the pressure-sensing diaphragm at the process end of the connection.
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1
Media reaches the flush face
The male NPT connection places the diaphragm at the end of the threads, close to the process stream.
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2
The diaphragm deflects
Process pressure acts on the flexible metallic diaphragm while the process remains isolated from the instrument.
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3
Fill fluid transfers pressure
A sealed hydraulic fill system carries the pressure signal from the diaphragm to the measuring instrument.
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4
The instrument measures
The gauge, transmitter or switch responds to pressure without direct contact with the process media.
Application fit
When a threaded flush seal is a strong choice
The HFT is designed for installations that need a compact male threaded connection, a process-facing diaphragm and size-dependent high-pressure capability.
Installation advantages
- Compact instrument takeoffs and skids
- Existing male NPT process connections
- High-pressure service within the selected size rating
- Direct-mounted gauges, transmitters or switches
- Applications where a flange is impractical
Media conditions that benefit from a flush face
- Viscous or coating process fluids
- Slurries and solids-bearing media
- Crystallizing or polymerizing processes
- Corrosive media requiring compatible alloys
- Service where reduced recess volume is valuable
Common markets
Applicable across demanding process industries
- Oil & gas
- Refining
- Chemical processing
- Petrochemical
- Pulp & paper
- General industrial
Catalog specifications
HFT sizes, pressure ratings and dimensions
The values below reproduce the standard HFT data published in Haygor's diaphragm seal ordering guide. Dimensions are in inches.
3/4 in. NPTM
9,000 psi MWP with a 0.88 in. diaphragm diameter.
1 in. NPTM
9,000 psi MWP with a 1.16 in. diaphragm diameter.
1-1/2 in. NPTM
6,000 psi MWP with a 1.75 in. diaphragm diameter.
2 in. NPTM
4,000 psi MWP with a 2.08 in. diaphragm diameter.
| Process size | MWP | A - diaphragm | B | C | D | E - hex |
|---|---|---|---|---|---|---|
| 3/4 in. NPTM | 9,000 psi | 0.88 | 2.50 | 1.30 | 1.25 | 1.75 |
| 1 in. NPTM | 9,000 psi | 1.16 | 2.50 | 1.30 | 1.25 | 1.75 |
| 1-1/2 in. NPTM | 6,000 psi | 1.75 | 2.70 | 1.30 | 1.25 | 2.50 |
| 2 in. NPTM | 4,000 psi | 2.08 | 2.70 | 1.30 | 1.25 | 2.50 |
The ordering guide also lists factory-reviewed 1/2 in. NPT, 1-1/4 in. NPT and special 1 in. G1B configurations. Confirm current availability, final rating and complete assembly limits with Haygor.
Configure the complete assembly
HFT materials, options and selection inputs
Choose the process connection first, then define the instrument interface, wetted materials, coating options and filled-system requirements around the actual process.
Connection and pressure
Specify the male NPT size, operating pressure, maximum pressure, instrument range and any pressure spikes or vacuum exposure.
Body and diaphragm material
Catalog choices include stainless steels and specialty alloys. Select materials for the actual chemical concentration, temperature and solids content.
Instrument interface
Choose 1/4 in. NPT, 1/2 in. NPT or an eligible weld connection, then define direct mount, cooling element or capillary requirements.
Optional diaphragm treatments
Gold plating, PTFE non-stick coating and material certification options can be considered when appropriate for the service.
Catalog material codes
Body and diaphragm combinations
- 316 / 316L stainless steel
- 304 / 304L stainless steel
- Alloy 20
- Alloy C-276
- Alloy B-3
- Monel 400
- Alloy 600
- Alloy 2205
- Nickel 200
- Titanium
- Zirconium 702
- 316 SS body / C-276 diaphragm
Compare connection styles
Related Haygor diaphragm seals
Compare a recessed threaded seal, an all-welded mini format or flush flanged options when the process connection or maintenance strategy calls for a different geometry.
Frequently asked questions
Threaded flush diaphragm seal FAQ
These answers summarize the published HFT product data. Final configuration should be based on the complete process and instrument requirements.
Ask Haygor a technical questionWhat is the difference between a threaded flush seal and a standard threaded seal?
The HFT places its diaphragm at the end of the male process threads. A standard threaded off-line seal typically has a recessed internal diaphragm chamber. The flush profile reduces the process cavity where viscous material, crystals or solids can collect.
What HFT process sizes are standard?
Haygor's ordering guide lists standard 3/4 in., 1 in., 1-1/2 in. and 2 in. male NPT flush connections. Additional non-catalog or special connections require factory confirmation.
What is the maximum working pressure?
The published maximum working pressure depends on size: 9,000 psi for the 3/4 in. and 1 in. configurations, 6,000 psi for 1-1/2 in., and 4,000 psi for 2 in. The completed assembly and application must be reviewed before use.
Which materials are available?
The catalog lists stainless steels, Alloy 20, Alloy C-276, Alloy B-3, Monel 400, Alloy 600, Alloy 2205, Nickel 200, Titanium, Zirconium 702 and a 316 stainless body with C-276 diaphragm. Material selection must match the actual process media and temperature.
Can the diaphragm be coated?
The ordering guide lists gold plating and a PTFE non-stick coating option. Haygor specifically identifies the PTFE coating as non-stick only, not as corrosion protection.
What information should I provide for a quote?
Provide the process media and concentration, solids or viscosity, pressure range and maximum pressure, process and ambient temperature, NPT size, instrument model and connection, mounting orientation, material preference, coating needs and documentation requirements.
Move from process data to an HFT configuration
Configure a threaded flush diaphragm seal or send the application to Haygor.
Use the product configurator for a guided starting point, or request a quote for application-specific review.