Kunkle safety and relief valves are among the most trusted pressure protection products in industrial and commercial applications. Now part of the Emerson portfolio, Kunkle's product line covers steam, air, gas, and liquid service — spanning sizes from ¼" NPT to 6" flange, with pressure ratings from vacuum to 7,500 psig and temperature capability up to 800°F.
Kunkle's origins date to 1875, when Erastus B. Kunkle patented a safety valve to prevent locomotive overpressure. That engineering legacy now spans over 150 years and encompasses the full range of modern pressure relief applications. Today, Kunkle operates under the Emerson Automation Solutions umbrella, with manufacturing and quality standards that remain among the most rigorous in the industry.
F.W. Webb carries an extensive selection of Kunkle relief valves, backed by our nationwide distribution network and knowledgeable product specialists. Whether you're sourcing for a boiler room, compressor system, or process application, you'll find the right model here — with the support to match.
Kunkle relief valves are used to protect pressurized equipment and systems from dangerous overpressure conditions. When system pressure exceeds a pre-set limit, the valve automatically opens to release excess pressure and reseats once normal operating conditions are restored.Common applications include:
Steam boilers and heating systems — protecting against overpressure in both low-pressure heating boilers and high-pressure power boilers
Compressed air systems — providing overpressure relief on air compressors, receivers, and distribution lines
Liquid service — offering bypass relief and pump protection across a wide range of fluid types, including water, hydraulic fluid, and process liquids
Gas service — relieving pressure in systems handling non-hazardous gases in industrial and commercial settings
Process and petrochemical applications — safeguarding pipelines, pressure vessels, and heat exchangers in demanding industrial environments
Kunkle's broad product line means there is typically a model suited for nearly any pressure relief requirement, from a residential hot water heating boiler to a high-pressure industrial process system.
Kunkle valves are certified to multiple ASME Boiler and Pressure Vessel Code sections, covering a wide range of equipment types and service conditions:
In addition to ASME certification, many Kunkle models carry National Board certification, PED (European Pressure Equipment Directive) approval, CRN (Canadian Registration Numbers) for use across Canadian provinces, and TU and Chinese certifications for international applications. Certain models are also available in non-code configurations for applications where code certification is not required.
When selecting a Kunkle valve, confirming the required code section and certifications for your specific application and jurisdiction is an important first step.
Kunkle relief valves cover an exceptionally wide pressure range, making them suitable for everything from low-pressure heating systems to high-pressure industrial processes. Across the full product line, Kunkle valves handle pressures from vacuum conditions up to 7,500 psig.
In practice, the applicable pressure range depends on the specific model and service:
Low-pressure steam heating — Models like the 930 are designed for systems operating under 15 psig
Standard commercial and industrial steam — Many models cover the 15–300 psig range common in process and utility steam applications
High-pressure air and gas — Steel-body models such as the 300 and 600 series handle elevated pressures in compressed air and gas systems
High-pressure liquid and process — Certain models are rated for pressures well into the thousands of psig range for demanding industrial service
Temperature capability is equally broad, ranging from cryogenic service up to 800°F, ensuring Kunkle valves can perform reliably across extreme operating environments. Always consult the specific model's datasheet to confirm pressure and temperature ratings for your application.
Yes, the majority of Kunkle safety and relief valves carry National Board of Boiler and Pressure Vessel Inspectors (NB) certification. National Board certification means a valve's relieving capacity has been independently tested and verified, and that the valve bears either the NB stamp or is listed in the National Board's published capacity database.
This certification is a code requirement in most U.S. jurisdictions for valves protecting ASME-stamped equipment, including boilers and pressure vessels. For end users and contractors, specifying a National Board-certified valve helps ensure compliance with local inspection requirements and insurance standards.
It's worth noting that Kunkle also manufactures non-code models for applications where ASME and National Board certification are not required — such as non-code liquid service on unregistered vessels or certain OEM applications. If your project has specific code compliance requirements, confirm the certification status of the individual model before ordering.
Sizing a Kunkle pressure relief valve correctly is critical — an undersized valve won't relieve pressure fast enough, while an oversized valve can chatter and wear prematurely. The right sizing method depends on the service type and the specific Kunkle model.
General sizing steps:
Kunkle's published Technical Reference guide (available through Emerson) contains the full sizing formulas, orifice tables, and correction factor charts for each model family. For complex applications or if you need assistance confirming a valve selection, FW Webb's product specialists can help identify the right model for your requirements.
Yes, select Kunkle models are designed and rated for cryogenic service. Kunkle's product line spans from cryogenic temperatures up to 800°F, providing coverage across one of the widest temperature ranges in the pressure relief valve industry.
For cryogenic applications, material selection is the key consideration. Standard carbon steel and iron body valves are not suitable for extremely low temperatures, as these materials can become brittle and fail at cryogenic conditions. Kunkle's stainless steel-body models — including valves from the 910–919 series — are the appropriate choice for cryogenic service, as stainless steel maintains its ductility and mechanical integrity at low temperatures.
Other important considerations for cryogenic relief valve selection include:
If your application involves liquefied gases, cryogenic storage, or low-temperature process fluids, confirm the specific temperature rating and material compatibility of the model you select before installation.
