HSU diaphragm seal · Immersed pressure sensing · Open or perforated cover
Submersible Diaphragm Seal
Immersed pressure isolation for tanks, pits, sumps, basins, and engineered hydrostatic level systems.
The Haygor HSU is configurable with 2.4-, 2.9-, or 4.1-inch diaphragms; 3.48-, 4.00-, or 5.40-inch standard outside diameters; open or perforated cover plates; and welded 8 mm, 1/4-inch NPT, G 1/4, or 1/2-inch NPT instrument connections.
- Three diaphragm and outside-diameter envelopes
- Open or perforated cover plate
- 316 stainless steel configuration
Quick answer
What is a submersible diaphragm seal?
A submersible diaphragm seal is an immersed pressure-sensing assembly. The seal is positioned below the liquid surface at the desired measurement elevation, where pressure acts on the process-facing diaphragm. A sealed fill fluid transfers that pressure to a gauge, transmitter, switch, or controller while isolating the instrument from the process liquid.
The HSU can be used as the process interface in an engineered hydrostatic level system or wherever a remote instrument needs to sense pressure at an immersed location. The cover style, diaphragm size, outside diameter, fill system, capillary, support method, and instrument range must be selected as one measurement assembly.
Immersed hydraulic pressure transfer
How the HSU seal works
The HSU places the diaphragm at the pressure-sensing elevation and transfers the signal through a sealed liquid-filled path.
- 1
The seal is located at the measurement elevation
The assembly is supported or suspended so its diaphragm senses pressure at a defined depth in the liquid.
- 2
The cover admits process pressure
An open or perforated cover allows liquid pressure to reach the diaphragm while matching the installation's exposure and protection needs.
- 3
The diaphragm responds to local pressure
The process-facing diaphragm deflects without allowing the process liquid into the instrument or fill passage.
- 4
Fill fluid carries the signal to the instrument
The attached instrument or remote capillary system converts the transferred pressure into pressure or level indication.
Application fit
Immersed pressure sensing where a conventional vessel nozzle is not the measurement point
The HSU is designed for installations that place the sensing diaphragm in the liquid itself. Application engineering should confirm that the media, solids, pressure, temperature, mounting, retrieval, and filled-system behavior are suitable.
Common application settings
- Open tanks, basins, reservoirs, and process vessels
- Sumps, pits, wet wells, and collection chambers
- Hydrostatic head or inventory measurements in compatible services
- Remote-mounted gauges or transmitters above the liquid
- Water, wastewater, chemical, and industrial utility systems
Selection conditions to verify
- Liquid chemistry, solids, fibers, deposits, and cleaning method
- Density or specific gravity and expected composition changes
- Operating, maximum, vacuum, and transient pressure
- Process and ambient temperature plus fill-fluid limits
- Support, retrieval, clearance, cable or capillary protection, and cover style
Typical industries and systems
- Water & wastewater
- Chemical processing
- Industrial utilities
- Bulk storage
- Environmental systems
- Process tanks
- Pits & sumps
Current configurable envelope
HSU size, cover, connection, and construction selections
These selections summarize Haygor's current online HSU configurator. Confirm current availability and the completed filled-system pressure and temperature limits before release.
2.4 in. diaphragm
3.48 in. standard outside diameter. Use /CD when a custom outside diameter is required.
2.9 in. diaphragm
4.00 in. standard outside diameter. Balance sensitivity, clearance, and process conditions.
4.1 in. diaphragm
5.40 in. standard outside diameter for the largest published HSU diaphragm envelope.
W / 2 / 3 / 4
Welded 8 mm, 1/4-inch NPT, G 1/4, or 1/2-inch NPT instrument-side connection.
Open or perforated
The configurator lists open cover plate code C and perforated cover plate code P.
316 stainless steel
S6 is listed for upper, lower, diaphragm, and bolting; the bolting selection carries a 50% rating-reduction note.
| Size code | Diaphragm diameter | Standard outside diameter | Custom diameter path |
|---|---|---|---|
| 2 | 2.4 in. | 3.48 in. | Add /CD and specify inches |
| 3 | 2.9 in. | 4.00 in. | Add /CD and specify inches |
| 4 | 4.1 in. | 5.40 in. | Add /CD and specify inches |
Pressure-rating safeguard: the current HSU configurator does not state one universal maximum working pressure and notes that listed 316 stainless steel bolting reduces the applicable pressure rating by 50%. Use the lowest limit of the seal, bolting, instrument connection, instrument, capillary, fill fluid, temperature condition, and installation—and obtain Haygor's approved assembly rating.
Configuration guidance
Select the HSU as an immersed measurement system—not as an isolated component
Start with the diaphragm and outside-diameter envelope, then confirm cover style, instrument attachment, filled-system design, material compatibility, support, and retrieval.
Perforated cover plate
A perforated plate provides a guarded process-facing surface while openings admit liquid pressure to the diaphragm.
Open cover plate
An open cover presents the diaphragm with minimal obstruction for compatible, controlled immersed installations.
Custom outside diameter
The standard outside diameter follows the selected diaphragm size. Add /CD and specify inches when the installation requires a different envelope.
Instrument attachment
- W: welded 8 mm connection
- 2: 1/4-inch NPT
- 3: G 1/4
- 4: 1/2-inch NPT
- Confirm direct versus remote mounting
- Define capillary length, routing, armor, and support
The instrument, attachment, capillary, and fill fluid are part of the pressure-transfer system and must be reviewed together.
Current material selections
- Upper: 316SS, code S6
- Lower: 316SS, code S6
- Diaphragm: 316SS, code S6
- Bolting: 316SS, code S6
- Verify corrosion, erosion, solids, and cleaning compatibility
The online configuration envelope may change. Confirm current alloy availability for the exact process and requested options.
Available options
- /CD: custom outside diameter in inches
- /AU: gold-plated diaphragm
- /NS: PTFE-coated diaphragm, non-stick
- Match option purpose to the actual failure mechanism
- Confirm option compatibility with size and cover style
Treat /NS as a non-stick surface option, not as a substitute for corrosion-compatible base construction.
| Component | Code | Current selection | Engineering check |
|---|---|---|---|
| Size | 2 | 2.4 in. diaphragm / 3.48 in. O.D. | Range, sensitivity, clearance, solids |
| 3 | 2.9 in. diaphragm / 4.00 in. O.D. | Range, sensitivity, clearance, solids | |
| 4 | 4.1 in. diaphragm / 5.40 in. O.D. | Range, sensitivity, clearance, solids | |
| Instrument connection | W | Welded 8 mm | Attachment and fill method |
| 2 | 1/4 in. NPT | Instrument or capillary interface | |
| 3 | G 1/4 | Parallel-thread instrument or capillary interface | |
| 4 | 1/2 in. NPT | Instrument or capillary interface | |
| Cover style | C | Open cover plate | Impact, solids, cleaning, access |
| P | Perforated cover plate | Fouling, response, debris protection | |
| Construction | S6 | 316SS upper | Media, temperature, erosion, rating, service life |
| S6 | 316SS lower | ||
| S6 | 316SS diaphragm | ||
| S6 | 316SS bolting; current configurator notes 50% rating reduction | ||
| Options | /CD | Custom diameter, inches | Physical fit and support |
| /AU | Gold-plated diaphragm | Application-specific barrier purpose | |
| /NS | PTFE-coated diaphragm, non-stick | Deposit release; not corrosion protection |
Configuration sequence
Build the HSU deliberately
- 1. Measurement basis
- Pressure or hydrostatic level
- 2. Size
- 2.4, 2.9, or 4.1 in. diaphragm
- 3. Outside diameter
- Standard O.D. or /CD custom value
- 4. Cover
- Open C or perforated P
- 5. Connection
- W, 2, 3, or 4
- 6. Construction/options
- S6 materials plus /AU or /NS as needed
Information to confirm before release
- Liquid, concentration, solids, density, and expected composition changes
- Operating, maximum, transient, and vacuum pressure
- Process and ambient temperature plus cleaning method
- Measurement span, seal elevation, vessel reference pressure, and required accuracy
- Open or perforated cover and required outside diameter
- Instrument model, range, connection, mounting, capillary, and fill fluid
- Support, suspension, retrieval, clearance, and mechanical protection
- Required approved MWP, calibration, testing, and documentation
Compare process interfaces
Related Haygor diaphragm seals
Use the HSU when the diaphragm must sense pressure at an immersed location. Compare these designs when the process connection is threaded, mounted through a pipe wall, or uses a specialized flush interface.
Frequently asked questions
Submersible seal FAQ
These answers summarize the current HSU configurator and general filled-system engineering. Final selection requires review of the actual process, mounting, hydrostatic basis, and complete instrument assembly.
Ask Haygor a technical questionWhat is a submersible diaphragm seal?
A submersible diaphragm seal is positioned below the liquid surface so process pressure acts directly on its diaphragm. A sealed fill fluid transfers that pressure to a connected gauge, transmitter, switch, or remote instrument while isolating the instrument from the process liquid.
Can the HSU be used for hydrostatic level measurement?
It can be applied as the immersed pressure-sensing element in a properly engineered hydrostatic level system. Level accuracy depends on liquid density or specific gravity, vessel reference pressure, seal elevation, fill fluid, capillary routing, instrument range, and temperature effects.
Which HSU sizes are available?
Haygor's current configurator lists three size codes: Size 2 with a 2.4-inch diaphragm and 3.48-inch outside diameter, Size 3 with a 2.9-inch diaphragm and 4.00-inch outside diameter, and Size 4 with a 4.1-inch diaphragm and 5.40-inch outside diameter.
What is the difference between the open and perforated cover plates?
The open cover exposes the diaphragm face with minimal obstruction. The perforated cover places a protective plate over the diaphragm while openings admit process pressure. Select the cover based on solids, mechanical exposure, cleaning, response needs, and the installation environment.
Which instrument connections are listed for the HSU?
The current configurator lists a welded 8 mm connection under code W, 1/4-inch NPT under code 2, G 1/4 under code 3, and 1/2-inch NPT under code 4. Confirm the attachment, fill system, capillary, and instrument interface as a complete assembly.
Which materials are listed in the current HSU configurator?
The current configurator lists 316 stainless steel, code S6, for the upper, lower, diaphragm, and bolting selections. Final material suitability must be reviewed against the actual process chemistry, temperature, solids, cleaning method, and expected service life.
What is the pressure rating of the HSU?
A universal HSU pressure rating is not stated on the current configurator. The completed assembly must be reviewed for its lowest applicable limit, and the configurator specifically notes that its listed 316 stainless steel bolting reduces the applicable pressure rating by 50 percent. Obtain an approved maximum working pressure for the exact configuration.
What does the /CD option do?
The /CD option specifies a custom outside diameter in inches. Use it when installation clearance, protective hardware, support geometry, or an existing opening requires an outside diameter different from the standard 3.48-, 4.00-, or 5.40-inch envelope.
Is the /NS PTFE-coated diaphragm option corrosion protection?
No. Haygor identifies /NS as a non-stick PTFE-coated diaphragm option. Choose the base wetted material for chemical compatibility; do not treat the coating as a substitute for corrosion-resistant construction.
What should I provide for an HSU quote?
Provide the liquid and concentration, solids or debris, operating and maximum pressure, process and ambient temperature, liquid density or specific gravity, measurement span, seal elevation, cover style, required outside diameter, instrument model and range, connection, capillary length and routing, fill-fluid constraints, mounting or retrieval method, and documentation requirements.
Move from immersed measurement point to an HSU configuration
Configure a Submersible Seal or send the complete pressure or hydrostatic-level application to Haygor.
Use the configurator for a guided starting point, or request a quote with the liquid, solids, density, pressure, temperature, seal elevation, size, cover, outside diameter, instrument, capillary, fill fluid, mounting, retrieval, and documentation requirements.