HMT diaphragm seal · Compact all-welded NPT design
All-Welded Threaded Mini Diaphragm Seal
Compact, gasket-free pressure-instrument isolation for threaded off-line process connections.
The HMT combines an all-welded metal seal assembly with male or female NPT process connections. Three diaphragm sizes provide published maximum working pressures from 1,000 to 5,000 psi, depending on configuration.
- All-welded construction with no gasket or bolting
- Male or female NPT process connections
- Published ratings up to 5,000 psi, size dependent
Quick answer
What is an all-welded threaded mini diaphragm seal?
An all-welded threaded mini diaphragm seal is a compact pressure-isolation device installed on an off-line process tap. The HMT separates a gauge, transmitter, or pressure switch from the process media while a sealed fill fluid transfers pressure from the metal diaphragm to the instrument.
Unlike a conventional bolted threaded seal, the HMT uses welded construction with no gasket and no body bolting. Male and female NPT process connections make it adaptable to common threaded piping and instrument takeoffs.
All-welded pressure transfer
How the HMT seal works
The HMT isolates the pressure instrument from the process while transmitting pressure hydraulically through a compact welded assembly.
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1
Process pressure enters
Media reaches the lower chamber through the selected male or female NPT process connection.
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2
The diaphragm deflects
Pressure acts on the metal diaphragm, which is welded into the seal assembly and isolates the process media.
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3
Fill fluid transfers pressure
The sealed hydraulic fill transmits diaphragm movement to the connected gauge, transmitter, or switch.
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4
The instrument measures
The pressure instrument responds to the transmitted pressure without its sensing element contacting the process media.
Application fit
When an all-welded threaded mini seal is a strong choice
The HMT is intended for compact off-line pressure connections where threaded flexibility, welded construction, and configurable wetted materials are important.
Installation advantages
- Compact piping taps and packaged equipment
- Male or female NPT process connections
- Direct-mounted gauges, transmitters, or switches
- Optional single or dual flushing connections
- Applications where a flange is unnecessary
Selection conditions that favor the HMT
- All-welded construction is preferred over a gasketed body
- The pressure range fits the selected diaphragm-size rating
- A compatible alloy is required between process and instrument
- Available space favors a compact threaded seal
- The media will not plug a recessed process chamber
Common markets
Built for industrial pressure-measurement systems
- Chemical processing
- Oil & gas
- Refining
- Petrochemical
- Water & wastewater
- OEM and process skids
Catalog specifications
HMT sizes, pressure ratings, connections, and dimensions
The values below reproduce the HMT data published in Haygor's diaphragm seal ordering guide. Dimensions are in inches.
1.5 in. diaphragm
2,000 psi published maximum working pressure.
2.0 in. diaphragm
1,000 psi published maximum working pressure.
1.0 in. diaphragm
5,000 psi high-pressure configuration.
Male or female
1/4 in. through 1 in. process connections, depending on size.
| Size code | Diaphragm | Published MWP | Process connections | Instrument connection | Flush connection |
|---|---|---|---|---|---|
| 1 | 1.5 in. | 2,000 psi | 1/4 or 1/2 in. NPT, male or female | Weld, 1/4 NPT, or 1/2 NPT | None, single, or dual 1/4 NPTF |
| 2 | 2.0 in. | 1,000 psi | 1/4, 1/2, 3/4, or 1 in. NPT, male or female | Weld, 1/4 NPT, or 1/2 NPT | None, single, or dual 1/4 NPTF |
| 3 | 1.0 in. | 5,000 psi | 1/4 or 1/2 in. NPT, male or female | Weld, 1/4 NPT, or 1/2 NPT | None, single, or dual 1/4 NPTF |
Published dimensional summary
Reference letters follow Haygor's HMT dimensional drawing. Overall height B changes with process-connection style and flush-port selection.
| Configuration | A | C | D | B - female, no flush | B - female, flush | B - male, no flush | B - male, flush |
|---|---|---|---|---|---|---|---|
| Size 1 · 1.5 in. diaphragm | 1.40 | 1.50 | 1.75 | 2.20 | 2.70 | 2.80-2.93 | 3.30-3.43 |
| Size 2 · 2.0 in. diaphragm | 1.90 | 2.00 | 2.25 | 2.20 | 2.70 | 2.80-3.08 | 3.30-3.58 |
The published guide does not show Size 3 dimensional data. Confirm current dimensions, material availability, pressure limits, temperature limits, and the rating of the complete seal-and-instrument assembly with Haygor before order entry.
Configure the complete assembly
HMT materials, flush ports, and selection inputs
Start with the process conditions, then select the diaphragm size, NPT connection, wetted material, instrument interface, flushing arrangement, and documentation.
Pressure and diaphragm size
Match operating pressure, maximum pressure, vacuum exposure, and pressure spikes to the published 1,000, 2,000, or 5,000 psi size rating.
Thread and instrument interface
Define process NPT size and gender, then choose a weld, 1/4 NPT, or 1/2 NPT instrument connection and the required mounting arrangement.
Wetted material
Select the lower body and matching diaphragm material for the actual media, concentration, temperature, and corrosion mechanism.
Flush ports and documentation
Choose no flush port, one port, or two ports; add matching-material plugs and material certification with MTRs when required.
Catalog material codes
Lower body and matching diaphragm materials
- 316 / 316L stainless steel
- Alloy 20
- Alloy C-276
- Alloy B-3
- Monel 400
- Alloy 600
- Alloy 2205
- Nickel 200
- Titanium
- Zirconium 702 · contact factory
Compare connection styles
Related Haygor diaphragm seals
Compare a larger bolted threaded seal, a flush threaded face, or an in-line connection when the process media, pressure range, or piping geometry calls for a different design.
Frequently asked questions
All-welded threaded mini seal FAQ
These answers summarize Haygor's published HMT product data. Final configuration should be based on the complete process and instrument requirements.
Ask Haygor a technical questionWhat does all-welded construction mean on the HMT?
The HMT seal body and diaphragm assembly use welded construction rather than a gasketed, bolted body joint. Haygor describes the product as having no gasket and no bolting.
What HMT diaphragm sizes and pressure ratings are published?
Haygor lists a 1.5-inch diaphragm rated to 2,000 psi, a 2.0-inch diaphragm rated to 1,000 psi, and a 1.0-inch high-pressure diaphragm rated to 5,000 psi. Ratings are configuration-dependent maximum working pressures.
Which process connections are available?
The HMT can be ordered with male or female NPT process connections. The ordering guide lists 1/4-inch and 1/2-inch NPT for the range, with 3/4-inch and 1-inch NPT limited to the 2.0-inch diaphragm size.
Can the HMT include flushing connections?
Yes. Published flushing choices are none, one 1/4-inch NPT female flush connection, or two 1/4-inch NPT female flush connections. Matching-material plugs are available for single or dual flush ports.
Which wetted materials are listed for the HMT?
The ordering guide lists 316/316L stainless steel, Alloy 20, Alloy C-276, Alloy B-3, Monel 400, Alloy 600, Alloy 2205, Nickel 200, Titanium, and Zirconium 702. The diaphragm material matches the selected lower material, and some alloys require a matching upper material.
When should I compare the HMT with the HFT threaded flush seal?
Choose the HMT when compact all-welded construction and male or female NPT flexibility are priorities. Compare the HFT when a flush process-facing diaphragm is needed to reduce cavities where viscous, coating, crystallizing, or solids-bearing media can collect.
What information should I provide for a quote?
Provide the process media and concentration, operating and maximum pressure, process and ambient temperature, process connection size and gender, instrument model and connection, mounting arrangement, material requirements, flush-port preference, and documentation needs.
Move from process data to an HMT configuration
Configure an all-welded threaded mini seal or send the application to Haygor.
Use the configurator for a guided starting point, or request a quote for material, pressure, connection, flushing, and instrument review.