A safety valve is the last automatic barrier between a pressurized refrigeration or process system and an overpressure accident. When control valves, regulators, and instrumentation fail—or when thermal expansion, blocked outlets, or compressor surges push pressure beyond design limits—the safety relief valve must open on its own, discharge enough capacity, and reseal without external power. Dofun’s SRV Type Series​ is presented on the company product pages alongside double stop valves, pressure gauge valves, and cartridge filters as part of a complete refrigeration safety portfolio. Built on Dofun’s Liaocheng production base—more than 30 acres, over 10,000 m² of workshop, and 30+ invention patents—and supported by the DOFUN-CTP modular platform, the SRV range applies spring-loaded actuation and sealed seating technology to ammonia, fluorinated refrigerant, and CO₂ duties. This article explains the spring-adjuster logic, seat-sealing principles, and practical setting rules that make an SRV reliable as an overpressure protector.

Why Overpressure Protection Starts with a Self-Actuated Device

An overpressure event can originate from several independent causes:

• Compressor control failure or incorrect capacity modulation
• Blocked discharge, isolated vessel, or closed downstream valve
• Thermal expansion of trapped liquid in a closed branch
• Fire exposure raising vapor pressure
• Control regulator failure in ammonia or CO₂ circuits
• Air ingress or non-condensable accumulation in condenser/receiver sections

Active control systems may solve the first symptom, but they can lose power, signal, or calibration. A spring-loaded safety relief valve uses only system pressure and spring force, so it remains functional during power loss. In refrigeration, the safety valve protects receivers, separators, intercoolers, surge drums, pump headers, and any closed vessel whose pressure can exceed the maximum allowable working pressure.

Dofun positions safety products within its “Thermal Control & Specialized Environments” application sector, where precise temperature control and energy efficiency depend on stable, leak-free pressure boundaries. For energy and chemical duty, Dofun also notes extreme low-temperature, high-pressure, and strong-corrosion conditions, which make passive overpressure protection even more important.

Spring-Loaded SRV Principle: Force Balance, Not External Signals

A conventional spring safety relief valve balances three things:

1. Inlet pressure force​ acting on the disc/seat projected area
2. Spring preload​ holding the disc closed
3. Spring reaction​ as the disc lifts and the spring compresses further

At set pressure, inlet force overcomes spring preload. The disc lifts, process fluid discharges through the nozzle, and pressure drops. When inlet force falls below the reseating force, the spring pushes the disc back to the seat.

For Dofun SRV products, the documented function is straightforward: when system pressure exceeds the set value, the valve opens and discharges part of the gas/fluid to atmosphere or outside the pipeline; when pressure returns within the allowable value, the system avoids overpressure accidents. This passive operation is the reason SRVs are specified as independent protection layers rather than as control elements.

Adjustment Mechanism

Spring setting is normally changed through an adjuster at the spring housing:

• Rotating the adjustment screw/bolt increases spring compression → higher set pressure
• Releasing compression reduces set pressure
• A locking nut, cap, or seal prevents unauthorized field changes after commissioning
• Spring selection must match the target set band; one spring range cannot correctly cover every pressure class

Dofun SRV product data illustrates how narrow spring ranges are used instead of one universal spring. For example, public SRV product pages list:

Model context	Pressure data found	Refrigerant/media	Temperature
SRV1-type refrigeration safety valve	Max PN 6.3 MPa; pressure scope 10–27 bar; working pressure recommended below 15% of set pressure for better sealing	Ammonia, CO₂, Freon/fl uorinated refrigerants; not suitable for corrosive media such as chlorine	Not stated on sampled page
SRV3-type ammonia/Freon safety valve	Max working pressure 2.8 MPa; adjustment 150–400 psi	R12, R22, R502, R134a, R404A, R507, R717 and other refrigerants	−35°C to +100°C

These figures are model-specific examples, not the full Dofun SRV catalog. Final spring range, orifice size, and set pressure must be selected per vessel MAWP, refrigerant, and local code.

Set Pressure, Reseat, and Blowdown

• Set pressure​ – inlet pressure at which the valve begins to open; defined by spring preload and disc area
• Opening pressure tolerance​ – depends on standard, model, and set band; confirmed by bench test, not estimated in the field
• Reseat pressure​ – pressure at which the disc重新seats; usually below set pressure
• Blowdown​ – difference between set and reseat expressed as a percentage; influenced by spring, disc geometry, and any adjusting ring where fitted

For spring SRVs without variable ring control, stable reseat depends heavily on seat flatness, spring linearity, and absence of debris. Dofun’s general guidance for SRV1-class refrigeration valves recommends keeping normal working pressure sufficiently below set pressure—sampled data suggest below 15% of set pressure—to maintain sealing and avoid premature weepage.

Seat Technology: The Sealing “Heart” of the SRV

The seat and disc interface decides two contradictory requirements: tight sealing at normal pressure and clean lift at overpressure. Dofun SRV documentation describes the safety valve’s role as opening when pressure exceeds the set value and discharging fluid to keep system pressure within allowable limits; the seat design must therefore support both leak-tightness and full lift.

Metal-to-Metal Seat

Used where temperature, refrigerant compatibility, or cleanliness requirements make soft seals unsuitable. Advantages:

• Stable at wider temperature range and after thermal cycling
• Resistant to swelling, extrusion, or chemical attack from refrigerant oil mixtures
• Suitable for high set pressures and abrasive trace contaminants

Requirements for reliability:

• Finished seat and disc faces with controlled surface roughness
• Correct alignment through guided stem/nozzle
• Spring force sufficient for positive contact but not so high that the disc sticks after lift
• Periodic inspection because metal seats can show wire-drawing after repeated near-set events

Soft-Sealed or Composite Seat

Soft inserts—depending on refrigerant and temperature—improve bubble-tight sealing at low differential and reduce simmer leakage. They are common in refrigeration where the working pressure sits well below set pressure for long periods.

Selection rules:

• Confirm elastomer or polymer compatibility with ammonia, CO₂, or specific fluorinated refrigerant and with lubricant/oil
• Check maximum temperature against seat material limit; do not apply a low-temperature-soft compound above its rated thermal ceiling
• For ammonia service, verify chemical resistance explicitly—some elastomers degrade in ammonia unless specified for R717
• For CO₂ transcritical high-side protection, confirm pressure/temperature envelope before selecting any soft seat

Dofun’s broader valve technology uses imported sealing materials in multi-level structures for other series; for SRV applications, seat material should be specified by Dofun application engineering based on refrigerant, temperature, and set pressure rather than assumed from a general catalog.

Seat Geometry and Lift Type

Spring SRVs are commonly divided by lift behavior:

• Full-lift / pop-action​ – rapid opening, suitable for vapor/gas where high relieving capacity is needed
• Moderate-lift​ – balanced capacity and reseat control
• Micro-lift​ – primarily for liquid thermal-relief where full vapor capacity is not required

Refrigeration safety selection must match lift type to phase being relieved. A receiver protecting against vapor overpressure needs different orifice/lift behavior than a liquid line protecting against thermal expansion. Dofun SRV model pages should be consulted for approved refrigerant, orifice, and capacity certification before final specification.

Dofun SRV in Ammonia, Fluorinated, and CO₂ Refrigeration

Dofun safety valve product samples list ammonia and fluorinated refrigerants for SRV1, and R12/R22/R502/R134a/R404A/R507/R717 for SRV3; other sourcing data for Dofun safety ranges also mention CO₂ and nominal-pressure options such as 4.0 MPa and 6.3 MPa for selected safety products. Because ammonia, fluorinated blends, and CO₂ have different densities, temperatures, and relief thermodynamics, SRV specification cannot use one generic table.

Ammonia (R717)

• Toxic and flammable-only-under-limited-conditions; ventilation and discharge routing are safety-critical
• Seat materials must resist ammonia and ammonia/lubricant mixture
• Set pressure must protect the lowest-MAWP component in the protected section
• Dofun energy/chemical messaging highlights low-temperature, high-pressure, strong-corrosion duty, which aligns with industrial ammonia installations but still requires model-specific corrosion and temperature confirmation

Fluorinated refrigerants (R134a, R404A, R507, etc.)

• Broad family with different pressures and oil compatibility
• Soft seats may improve sealing, but temperature and oil swell must be verified
• SRV3 sample data covers several fluorinated options with −35°C to +100°C temperature range

CO₂ (R744)

• Transcritical high side can reach higher pressures than traditional subcritical ammonia/fluorine loops
• Selected Dofun safety/sourcing data list CO₂ compatibility and higher nominal-pressure classes, but the SRV model, orifice, and certification must be matched to subcritical or transcritical service separately
• Avoid assuming an ammonia spring range is valid for CO₂ high-side protection

DOFUN-CTP and SRV Serviceability

The DOFUN-CTP modular shared platform reduces variety through standardized parts, enables function switching without pipeline disassembly, simplifies selection, and increases flexibility in design, installation, and maintenance. For safety valves, modular thinking applies mainly to:

• Standard spring kits and identification by set range
• Interchangeable seat inserts where the model and code allow field service
• Unified documentation for spare discs, guides, seals, and caps
• Faster recommissioning after bench testing because component naming follows one platform logic

Safety valves still require controlled setting procedures. Even with CTP standardization, spring change, set-pressure adjustment, and reseal verification should follow Dofun’s approved workflow and any jurisdictional inspection rules.

Sizing and Setting Workflow for Dofun SRV

A conservative specification workflow prevents most overpressure-protection failures:

1. Define Protected Equipment MAWP

Identify the vessel or circuit segment MAWP. The SRV set pressure should not exceed the MAWP of any component in the protected envelope.

2. Determine Relieving Scenario

Select the controlling case:

• Blocked outlet
• Fire exposure
• Thermal expansion of trapped liquid
• Compressor surge or control failure
• Loss of condenser cooling
• CO₂ transcritical high-side anomaly

Each scenario produces a different required relieving rate and phase.

3. Select Refrigerant and Temperature Envelope

Use Dofun model data: for example, SRV1 sampled range 10–27 bar and Max PN 6.3 MPa; SRV3 sampled 150–400 psi, max working 2.8 MPa, −35°C to +100°C. Do not extrapolate one model’s range to another without confirmation.

4. Choose Orifice and Lift Type

Orifice area determines relieving capacity. Lift type determines whether the valve is optimized for vapor pop-action, general refrigeration relief, or liquid thermal relief. Dofun application engineering should validate orifice designation against expected refrigerant state and required capacity.

5. Specify Seat Material

For ammonia: confirm ammonia-compatible metal or approved soft insert.

For CO₂: confirm high-pressure/temperature capability.

For fluorinated blends: confirm oil/elastomer compatibility.

For mixed refrigerant plants: specify per circuit, not per corporate standard.

6. Set Spring Within Model Range

Adjust only within the spring range stamped or documented for the valve. For SRV1-class guidance, keep working pressure below approximately 15% of set pressure to support sealing; for other models, follow Dofun’s model-specific instruction and code requirements.

7. Test and Document

• Bench test set pressure with the actual refrigerant-equivalent medium or approved substitute
• Record set pressure, reseat pressure, model, orifice, spring code, seat material, and tag number
• Apply seal/wire where required
• Keep records for audit, especially in pharmaceutical cold chain, chemical, and public-safety installations

Installation Practices That Preserve Spring and Seat Performance

Even a well-designed SRV fails if installed incorrectly.

• Mount vertically with the spindle upright​ unless the model instruction permits another orientation; vertical installation keeps spring load aligned with disc travel.
• Keep inlet piping short and unobstructed; excess inlet pressure loss changes effective set behavior and can cause chatter.
• Avoid isolation between vessel and SRV; if a isolating valve is necessary for maintenance, it must remain open and secured/sealed.
• Route discharge safely; for ammonia, discharge should go to a safe location, relief header, or treatment system per local code, never into confined working space.
• Prevent liquid lock; in refrigeration services where liquid can reach the SRV inlet, use appropriate layout, heat tracing, or auxiliary devices per Dofun recommendation.
• Protect the spring housing​ from contamination, ice, oil accumulation, and mechanical impact.
• Do not field-modify spring preload beyond the approved range; unauthorized adjustment can shift set pressure and invalidate test records.

Dofun’s QA framing—”Quality as Foundation”—supports treating SRV commissioning as a documented qualification step rather than a quick field tweak.

Maintenance and Predictive Checks

An SRV is passive, but it is not maintenance-free.

Routine Inspection

• Check for external leakage at seat/bonnet
• Verify set-pressure tag and seal integrity
• Inspect spring housing for corrosion, ice, or mechanical damage
• Confirm discharge path is unobstructed
• Review operating logs: repeated pressure approaches near set indicate underlying control problems, not SRV defects

Scheduled Recertification

Interval depends on refrigerant, operating temperature, regulatory regime, and service severity. In ammonia plants, annual or per-jurisdiction testing is common industry practice; Dofun SRV models should follow the instruction manual plus the site’s pressure-equipment compliance schedule.

Common Failure Modes

• Simmer/seepage at seat​ – wrong spring set, seat damage, soft-seal aging, or working pressure too close to set
• Failure to open​ – spring selection error, disc sticking, debris, guide misalignment
• Chatter​ – excessive inlet pressure loss, undersized inlet pipe, or wrong orifice/spring combination
• Failure to reseat​ – seat scoring, foreign particles, thermal distortion, or damaged soft insert
• Set drift after adjustment​ – improper locking, worn spring, or unauthorized field change

Because Dofun uses standardized parts through DOFUN-CTP, many internal kits—springs, guides, discs, seats, seals—can be managed as planned spares, reducing emergency sourcing.

Application Examples by Dofun Sector

Thermal control and refrigeration​ – SRV on receivers, low-side drums, CO₂ racks, and ammonia liquid lines. Spring setting follows receiver MAWP; seat material follows refrigerant and temperature sample ranges such as SRV1/SRV3 data.

Energy and chemicals​ – low-temperature, high-pressure, corrosive units benefit from passive spring relief where power-dependent controls cannot be the sole protection. Material and seat selection must be confirmed for the exact chemical environment.

Public welfare and health​ – pharmaceutical and food cold chains require documented set pressure, traceable service records, and hygienic/accessible installation. Dofun’s sanitary and polishing experience in other valve lines supports audit-friendly documentation even though SRV function remains pure overpressure protection.

Heavy industry and resources​ – remote refrigeration or compressed-air/process systems can use standardized SRV kits to simplify inventory in abrasive or maintenance-difficult sites.

Defense and security​ – specialized low-temperature or high-reliability packages can be configured with Dofun application engineering; SRV spring independence is valuable where electrical control may be unavailable.

Conclusion

Dofun SRV Type safety valves prevent overpressure through a simple, passive principle: system pressure acts on a disc, spring preload defines the set point, and the seat interface decides whether the valve remains tight or opens cleanly when needed. Spring adjustment converts a target set pressure into reproducible mechanical preload; seat technology converts that force balance into leak-tight service at normal conditions and reliable discharge during emergencies. Supported by Dofun’s Liaocheng manufacturing base, 30+ invention patents, and the DOFUN-CTP modular spare strategy, the SRV Series can be specified for ammonia, fluorinated, and selected CO₂ refrigeration duties when model data—such as SRV1 10–27 bar / Max PN 6.3 MPa or SRV3 150–400 psi / −35°C to +100°C—are matched to the actual vessel MAWP, relieving scenario, and refrigerant compatibility.

For any new project, send Dofun application engineering the protected equipment MAWP, refrigerant, worst-case relieving scenario, temperature range, required capacity, and discharge routing. The team can then select the correct SRV model, spring range, orifice, and seat material—and document set pressure, reseat, and maintenance intervals so the valve performs as the “heart” of the plant’s overpressure protection system rather than as an untested accessory.