Table of contents
- What is an Apollo Relief Valve?
- What is a Kunkle Relief Valve?
- Apollo Relief Valves vs. Kunkle Relief Valves: Which One Fits Your Application Best?
- Apollo Relief Valves vs. Kunkle Relief Valves: A Tabular Comparison
- Apollo Relief Valves: Best Applications and Industries
- Kunkle Relief Valves: Best Applications and Industries
- Apollo Relief Valves vs. Kunkle Relief Valves: How to Choose the Right Safety Relief Valve for Your Operations
- Choose the Right One from Apollo Relief Valves and Kunkle Relief Valves with Control Specialties
- Frequently Asked Questions (FAQs)
In pressure-critical systems, safety relief valves are not just another component. They are the last line of defense between stable operation and catastrophic overpressure. That's exactly why the debate between Apollo relief valves and Kunkle relief valves continues across manufacturing plants, steam systems, chemical facilities, and industrial processing environments.
At first glance, both brands appear to check the same boxes: ASME-certified, industry-approved, and widely specified by engineers. But once you evaluate real-world operating conditions, pressure range, media compatibility, temperature demands, installation environment, and maintenance expectations, the differences become far more significant.
The right choice is not about which valve is "better." It's about which valve is engineered for your specific application. In this comparison, we'll examine where Apollo excels, where Kunkle dominates, and how to determine the best fit for your operational, safety, and compliance requirements.
What is an Apollo Relief Valve?
Apollo relief valves are designed for systems where dependable overpressure protection is essential, but oversized industrial-grade valve assemblies are unnecessary.
Manufactured by Conbraco Industries, Apollo has built a strong reputation across commercial plumbing, hydronic heating, boiler protection, and mechanical system applications by delivering reliable, code-compliant valves that are practical, durable, and easy to maintain.
Unlike many heavy industrial relief valves engineered for extreme process environments, Apollo valves are commonly selected for commercial facilities, institutional buildings, and light industrial systems where space efficiency, corrosion resistance, and installation simplicity are major priorities.
What is a Kunkle Relief Valve?
Kunkle relief valves are engineered for industrial environments where pressure protection is not just a requirement; it's a critical part of operational safety, regulatory compliance, and equipment reliability.
As part of the Emerson portfolio, Kunkle has built a long-standing reputation in high-pressure and high-temperature applications where systems demand durable, ASME-certified safety relief solutions.
For decades, Kunkle valves have been widely specified across steam systems, compressed air networks, pressure vessels, oil and gas applications, and industrial processing facilities because of their ability to perform consistently under demanding operating conditions.
Apollo Relief Valves vs. Kunkle Relief Valves: Which One Fits Your Application Best?
At first glance, Apollo and Kunkle may seem to offer similar overpressure protection solutions. But once you evaluate pressure capability, certifications, material flexibility, and application demands, the differences become much more noticeable.
Apollo is heavily focused on commercial mechanical systems, while Kunkle is engineered for high-pressure industrial environments where operating conditions are far more demanding.
To make the selection process easier, here's a detailed comparison of where each brand performs best.
1. Pressure and Temperature Capability
Apollo
Built primarily for commercial heating and low-pressure steam systems, Apollo valves are designed to operate within standard ASME Section IV environments. They are commonly used in hot water boilers, hydronic systems, and HVAC mechanical rooms where moderate pressure and temperature conditions are expected.
Apollo performs best in:
- Commercial heating systems
- Hot water boiler applications
- Low-pressure steam service
- Institutional HVAC systems
Kunkle
Kunkle valves operate in an entirely different pressure class. Many models are engineered for industrial steam generation, compressed gas systems, and process piping applications that involve significantly higher pressures and temperatures. Certain configurations exceed 3,000psi ratings.
Kunkle is commonly used in:
- Industrial steam systems
- High-pressure process piping
- Compressed air and gas systems
- Power generation facilities
The Verdict:
- Apollo is ideal for standard commercial operating ranges.
- Kunkle is the stronger choice for high-pressure industrial service.
2. Material Selection and Fluid Compatibility
Apollo
The Apollo 19 Series valves feature bronze-body construction, a trusted material choice for water and low-pressure steam systems. Bronze offers dependable corrosion resistance while keeping installation and maintenance straightforward.
Key advantages of the Apollo bronze construction:
- Excellent for water service
- Reliable in low-pressure steam applications
- Strong corrosion resistance
- Well-suited for HVAC and plumbing systems
Kunkle
Kunkle offers far greater material flexibility across its valve portfolio. Depending on the series, users can select from different material configurations for compatibility with more aggressive industrial environments.
Available Kunkle material options include:
- Bronze
- Cast iron
- Carbon steel
- Stainless steel
Best suited for:
- Corrosive process fluids
- Chemical applications
- High-temperature service
- High-purity systems
The Verdict:
- Apollo covers standard commercial fluid requirements effectively.
- Kunkle provides broader material versatility for industrial applications.
3. ASME Certifications and Code Coverage
Apollo
For heating boiler protection, Apollo provides the certifications most commercial facilities require without adding unnecessary complexity.
Apollo certifications include:
- ASME Section IV
- National Board (NB) listing
These certifications satisfy the compliance requirements of most commercial and institutional boiler systems.
Kunkle
Kunkle supports multiple ASME code sections, making it a stronger fit for industrial facilities operating diverse pressure equipment.
Kunkle certification coverage includes:
- ASME Section I
- ASME Section IV
- ASME Section VIII
- UV stamp options
- VR stamp options
This expanded certification range is especially important in regulated industrial environments.
The Verdict:
- Apollo fully supports commercial boiler compliance.
- Kunkle offers broader multi-code industrial coverage.
4. Application and Industry Alignment
Apollo
Apollo has become a trusted specification throughout commercial mechanical infrastructure because the valves are purpose-built for building service systems.
Apollo is widely used in:
- Commercial buildings
- Schools and universities
- Hospitals and healthcare facilities
- Multi-family housing
- HVAC mechanical rooms
- Domestic hot water systems
Kunkle
Kunkle dominates industries where pressure protection directly impacts operational safety, compliance, and production continuity.
Kunkle is commonly specified in:
- Oil and gas facilities
- Chemical processing plants
- Refineries
- Industrial manufacturing
- Power generation systems
- Process steam operations
The Verdict:
- Apollo leads in commercial building applications.
- Kunkle is the preferred valve for industrial processing environments.
5. Valve Sizes and Connection Configurations
Apollo
The Apollo 19 series valves focus on the connection styles most commonly used in commercial systems.
Typical Apollo configuration advantages:
- Threaded NPT connections
- Compact valve footprint
- Easier installation in tight spaces
- Simplified replacement in existing piping systems
Kunkle
Industrial systems often require larger valve sizes and more robust piping connections, areas where Kunkle offers significantly more flexibility.
Kunkle configuration options include:
- Threaded connections
- Flanged connections
- Larger line sizes
- Industrial piping compatibility
Flanged configurations are particularly valuable in high-pressure systems where threaded fittings may not meet code requirements.
The Verdict:
- Apollo simplifies commercial installations.
- Kunkle supports broader industrial piping requirements.
6. Availability and Procurement
Apollo
One reason Apollo remains popular in commercial markets is how easy the valves are to source.
Apollo procurement advantages:
- Widely stocked by HVAC distributors
- Readily available through plumbing suppliers
- Faster turnaround for replacements
- Strong North American distribution support
Kunkle
Kunkle valves are also broadly available, although specialized industrial models may involve additional lead time because of material or certification requirements.
Kunkle procurement considerations:
- Standard models are commonly stocked
- Specialty configurations may require longer lead times
- Industrial trim options increase customization flexibility
The Verdict:
- Apollo offers faster access for standard commercial replacements.
- Kunkle may require additional planning for specialty industrial configurations.
7. Cost and Long-Term Value
Apollo
For commercial facilities, Apollo delivers strong value without overengineering the application.
Why Apollo is cost-effective:
- Lower upfront cost
- Commercial-focused design
- Reliable ASME compliance
- Reduced installation complexity
Kunkle
Kunkle valves typically cost more because they are built for harsher operating environments and broader compliance requirements.
What drives Kunkle's higher cost:
- Expanded pressure capability
- Industrial-grade materials
- Broader certification support
- Higher durability expectations
However, in industrial systems, the higher investment is often justified by improved reliability and regulatory protection.
The Verdict:
- Apollo offers better value in commercial systems.
- Kunkle's premium pricing aligns with industrial performance demands.
8. Brand Reputation and Technical Support
Apollo
Within the commercial plumbing and HVAC industry, Apollo has built a reputation around dependable performance and easy accessibility.
Apollo support strengths include:
- Strong distributor network
- Consistent manufacturing standards
- Reliable replacement part availability
- Familiarity among contractors and facility teams
Kunkle
Kunkle's industrial reputation is reinforced by its connection to Emerson, one of the largest global names in industrial automation and process control.
Kunkle support advantages include:
- Extensive engineering resources
- Long-term industrial product support
- Global industrial recognition
- Strong technical documentation and compliance backing
The Verdict:
- Apollo is highly trusted in commercial markets.
- Kunkle offers a deeper industrial support infrastructure.
Apollo Relief Valves vs. Kunkle Relief Valves: A Tabular Comparison
| Factor | Apollo Relief Valves | Kunkle Relief Valves |
|---|---|---|
| Pressure and Temperature Range | Built for moderate-pressure commercial heating and steam systems | Designed for high-pressure and high-temperature industrial service |
| Body Material Options | Primarily available in bronze construction | Offered in bronze, cast iron, carbon steel, and stainless steel |
| ASME Certifications and Code Coverage | Supports ASME Section IV and NB-certified applications | Covers ASME Sections I, IV, VIII, including UV and VR options |
| Industry and Application Fit | Common in HVAC, plumbing, and commercial boiler systems | Widely used in oil and gas, chemical, and power industries |
| Size and Connection Options | Available mainly in compact threaded NPT configurations | Offers threaded and flanged options in broader size ranges |
| Availability and Procurement | Widely stocked for fast commercial replacements | Specialty industrial models may require longer lead times |
| Cost and Value | Cost-effective for standard commercial applications | Premium pricing for industrial-grade performance and compliance |
| Brand Reputation and Support | Trusted in commercial, mechanical, and plumbing markets | Backed by Emerson's global industrial engineering support |
Apollo Relief Valves: Best Applications and Industries
Apollo pressure relief valves are best suited for commercial and institutional systems operating within moderate pressure and temperature ranges. Their bronze-body construction and ASME Section IV compliance make them a practical choice for heating boilers, hot water systems, and light steam applications where reliability, simplicity, and cost-efficiency are key priorities.
Rather than being designed for extreme industrial process conditions, Apollo valves excel in everyday mechanical system protection where compact installation, easy maintenance, and dependable code compliance matter most.
Common Apollo Application Environments
Apollo relief valves are frequently used in:
- Hydronic heating systems
- Commercial hot water boilers
- Domestic water heaters and storage tanks
- Low-pressure steam heating systems
- HVAC mechanical rooms with limited installation space
- Retrofit and replacement projects using bronze-body valves
- Schools, hospitals, office buildings, and institutional facilities
One of Apollo's biggest advantages is installation simplicity. The valves are easy to source, straightforward to replace, and commonly stocked across HVAC and plumbing distribution networks.
For contractors and facility engineers working within standard commercial building regulations, Apollo delivers dependable overpressure protection without unnecessary industrial-grade complexity.
Kunkle Relief Valves: Best Applications and Industries
Kunkle relief valves are engineered for industrial environments where pressure protection requirements are more demanding and regulatory compliance plays a much larger role. These valves are commonly selected for systems involving elevated pressures, high-temperature steam, aggressive media, and pressure vessel protection across multiple ASME code sections.
Their broader certification coverage, material flexibility, and industrial pressure capability make Kunkle a preferred choice for critical process applications where reliability and compliance cannot be compromised.
Common Kunkle Application Environments
Kunkle relief valves are widely used in:
- High-pressure steam boilers
- Industrial pressure vessels
- Chemical and petrochemical plants
- Oil and gas processing facilities
- Power generation systems
- Compressed air and industrial gas systems
- Refineries and manufacturing plants
- Corrosive or high-purity process applications requiring stainless steel components
Facilities operating under OSHA Process Safety Management (PSM), insurance inspections, or strict jurisdictional compliance standards often specify Kunkle because of its long-standing industrial reputation and broad ASME certification support, including UV and VR stamp availability.
In highly regulated industrial environments, Kunkle's established compliance history and Emerson-backed engineering support provide an additional level of confidence for plant operators, engineers, and safety teams.
Apollo Relief Valves vs. Kunkle Relief Valves: How to Choose the Right Safety Relief Valve for Your Operations
Selecting the right safety relief valves is not simply about choosing a trusted brand; it's about matching the valve to your system's pressure conditions, compliance requirements, fluid characteristics, and operational environment.
A valve that performs perfectly in a commercial boiler room may be completely unsuitable for a high-pressure industrial process line.
To simplify the selection process, focus on these five key decision points.
Step 1: Start with the Applicable ASME Code Section
Before evaluating valve size, pressure range, or material, determine which ASME code governs your equipment.
Common ASME Classifications Include:
- Section IV: Heating boilers and commercial hot water systems.
- Section I: Power boilers and high-pressure steam systems.
- Section VIII: Pressure vessels and industrial process equipment.
In General:
- Apollo valves are primarily designed for ASME Section IV applications.
- Kunkle supports Sections I, IV, and VIII across various model lines.
Why This Matters:
The governing ASME code immediately narrows down which valve family is appropriate for your application.
Step 2: Evaluate Pressure and Temperature Requirements
Next, identify your system's:
- Maximum Allowable Working Pressure (MAWP)
- Maximum operating temperature
- Steam or fluid conditions
Choose Apollo If:
- Your system operates at standard commercial pressures
- You are protecting hydronic or hot water systems
- Low-pressure steam service is involved
Choose Kunkle If:
- Your application involves elevated steam temperatures
- The system operates under high pressure
- Industrial process conditions exceed commercial valve ranges
Simple Rule:
As pressure and temperature demands increase, Kunkle becomes the stronger fit.
Step 3: Match the Valve Material to the Fluid Service
Material compatibility plays a major role in valve longevity, safety, and compliance.
Apollo Bronze Valves Work Well For:
- Water systems
- Low-pressure steam
- Non-corrosive commercial fluids
Kunkle Material Options are Better For:
- Corrosive chemicals
- Aggressive industrial media
- High-purity process fluids
- Elevated-temperature applications
Key Difference:
Apollo focuses mainly on bronze construction, while Kunkle offers broader industrial material flexibility.
Step 4: Use a Quick Decision Matrix
| Criteria | Choose Apollo Relief Valves | Choose Kunkle Relief Valves |
|---|---|---|
| Application Type | HVAC, hot water, and commercial boiler systems | Industrial process and high-pressure steam systems |
| Pressure Requirement | Moderate commercial operating pressures | High-pressure industrial environments |
| Material Requirement | Standard bronze construction is sufficient | Multiple material options are required |
| Budget Priority | Cost-effective commercial solution | Premium industrial-grade protection |
| Compliance Requirement | ASME Section IV applications | ASME Sections I, IV, or VIII applications |
Step 5: Confirm Specifications with Manufacturer Data Sheets
Even after narrowing down the valve family, the final selection should always be verified against the manufacturer's latest product documentation.
Always Confirm:
- Pressure ratings
- Temperature limits
- Capacity requirements
- Material compatibility
- Connection configuration
- Certification details
Keep in mind that ratings and certifications can vary by model series, trim option, and valve configuration.
For facilities needing application guidance, sizing assistance, or replacement support, working with an experienced distributor like Control Specialties can help ensure the selected valve matches both operational and code requirements.
Choose the Right One from Apollo Relief Valves and Kunkle Relief Valves with Control Specialties
Both Apollo relief valves and Kunkle relief valves provide trusted ASME-certified overpressure protection, but the right choice depends entirely on your operating environment. Apollo valves are ideal for commercial HVAC, hot water, and low-pressure boiler systems, while Kunkle valves are engineered for demanding industrial applications involving higher pressures, temperatures, and compliance requirements.
With decades of experience supporting commercial and industrial control valves, Control Specialties helps engineers, contractors, and facility teams select the right relief valve based on pressure ratings, materials, certifications, and application needs.
Choosing the right valve depends on your system pressure, fluid type, certification needs, and operating conditions. Get in touch with our valve specialists to identify the correct safety relief valve for commercial and industrial applications with expert product guidance and sourcing support.
Frequently Asked Questions (FAQs)
What is the difference between Apollo valves and Kunkle valve relief valves?
Apollo relief valves are designed mainly for commercial HVAC and hot water systems, while Kunkle valves support higher-pressure industrial applications with broader ASME certifications, material options, and temperature capabilities.
What industries commonly use the Apollo 19 series relief valve?
The Apollo 19 series is widely used in HVAC systems, commercial boiler rooms, hydronic heating systems, schools, hospitals, and domestic hot water applications requiring ASME Section IV-compliant overpressure protection.
Are Kunkle relief valves ASME certified?
Yes. Kunkle relief valves are ASME certified and National Board listed, with select models offering UV and VR stamps for industrial boilers, pressure vessels, and regulated process applications.
How do I choose the right safety relief valve size?
Relief valve sizing depends on system pressure, temperature, fluid type, and required relieving capacity. The selected valve must meet ASME code requirements and safely handle the system's maximum operating conditions.
Can Apollo and Kunkle relief valves be used interchangeably?
Not always. Any replacement valve must match the original set pressure, capacity, connection type, and ASME certification requirements before substitution is considered safe or compliant.
Who manufactures Apollo valves?
Apollo valves are manufactured by Conbraco Industries, a North Carolina-based U.S. valve manufacturer known for commercial plumbing, HVAC, and flow control products across North America.
What pressure ranges do Kunkle relief valves support?
Kunkle relief valves cover a wide operating range, including select industrial models rated for pressures exceeding 3,000psi, depending on the valve series and configuration.
Where can I buy Apollo or Kunkle relief valves?
Both Apollo and Kunkle relief valves are available through Control Specialties, which provides product sourcing, technical support, and application guidance for commercial and industrial systems.
How do I know which relief valve I need?
Choosing the right relief valve depends on your system pressure, temperature, media type, flow capacity, and code requirements. You should also consider valve material compatibility, set pressure accuracy, connection size, and whether the application requires ASME-certified safety relief valves.
