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Safety Relief Valve

J.E. Lonergan Company

The J.E. Lonergan Company is a premier manufacturer of Lonergan pressure relief valves (PRV), safety relief valves (SRV), and pressure safety valves. They also manufacture aftermarket parts for Reyco, ARI-Reyco, ARI-Armaturen, Anderson Greenwood, Pentair, and Kunkle. These parts are certified genuine factory new parts with Mill Test Reports (MTR). The products are primarily made in the USA.  The product line on parts includes discs, nozzles, all trim, gaskets, body, bonnet caps, and the entire valve. Standard internal parts are manufactured with high-quality 316 stainless steel material. When ordering it is important to understand the distinction between a PRV and a PSV, or SRV. The terminology throughout the industry pertaining to operating characteristics, applicable governing code, blowdown requirements prescribed, and definitions outlined by pressure vessel inspectors are highlighted below. These definitions are often misused or misunderstood. We will clarify pressure relief valve, pressure relief valves in series, relief valves in series, relief valve versus safety valve. 

Types of Pressure Relief Valve

Pressure relief devices can be closing and non-reclosing. The closing types are spring-loaded and pilot-operated. Spring-loaded can either be conventional or bellows type. Pilot-operated can either be pop-action or modulating-action. Each is defined as either flowing or non-flowing. 

Relief Valves 

A Relief Valve is a safety device designed to protect a pressurized vessel against an overpressure event. Overpressure might cause pressure in a vessel or system to exceed a specified design pressure or maximum allowable working pressure (MAWP). The purpose of a Relief Valve is to vent steam, air, gas, or ing fluid from an overpressurized vessel. 

Safety Valves 

Pop Safety Valves control the pressure of steam within a boiler when it approaches the set pressure of the valve. The steam pressure on the underside of the actuating disc approaches the pressure of a spring applied to the outer side of the disc. As the pressure increases, when equilibrium is passed, the disc starts to lift off its seat. The Steam is released to huddling chamber. The increased pressure inside the chamber area under steam pressure makes the pressure unbalanced in the valve discharge opening and pops the valve into the open position. The valve seat pops, preventing wiredrawing caused by slow opening.

Pressure Relief Valves

Pressure relief valves (PRV) provide this protection against overpressure. Special relief valves known as vacuum relief valves, safeguard against excessive vacuum. Such devices actuate when pressure (or vacuum) for vapor service exceeds a specified design value. A PRV is a spring-loaded valve that opens at a designated pressure. The construction of a spring-loaded PRV includes an inlet nozzle, a movable disk that regulates flow through the nozzle, and a spring that controls the position of the disk. The rapid opening type is a Pop Safety Valve. There are also designs with balanced bellows, or gradual lift designs. 

Relieving Pressure

Pressure at the outlet of a PRV is called backpressure. Backpressure causes variations in opening pressure, flow capacity, and relieving pressure. A bellows, a sealed piston, or other means of balancing the valve disk will stabilize the backpressure and permit more consistent operation. A balanced PRV can serve to isolate the guide, spring, bonnet, and other top works parts within the valve. The minimum rule onset pressure, or relieving pressure is that the set pressure be 110% of the maximum allowable working pressure (MAWP) if protected by a single pressure relief device sized for operating (non-fire) contingencies.

Set Pressure

Relief valve set pressure and relief valve relieving pressure are often cited as interchangeable terms. The set pressure is the inlet gauge pressure at which the pressure relief valve is set to open under service conditions. However, Relieving pressure is the valve set pressure plus overpressure.

Relieving Capacity 

Relieving Capacity refers to the proportion of the measured relieving capacity permitted by the applicable code or regulation to be used as a basis for the application of a pressure relief device.

Relief Valve Orifice Sizes

API, The American Petroleum Institute (API) has developed a series of inlet size, orifice, and outlet size combinations for relief valves. There are a series of fourteen standard orifice sizes, by a letter, ranging from D through to T. The controlling relieving rate is a function of the required relief valve orifice size determined using the appropriate equation given in the API code. For the required relief valve orifice size, an actual orifice size equal to or greater than the calculated orifice size is chosen from the standard range. The maximum flow through this actual orifice will be the valve’s capacity.

Stamped Capacity

The rated relieving capacity appears on the device nameplate. It is based on the set pressure or burst pressure plus the allowable overpressure for compressible fluids and the differential pressure for incompressible fluids.

Overpressure Allowance 

Overpressure is the pressure increase over the set pressure of the relieving device, expressed in pressure units or as a percentage. It is the same as accumulation when the relieving device is set at the maximum allowable working pressure of the vessel. The Overpressure allowance is the maximum allowable working pressure plus the accumulation.

Closing Pressure 

Closing Pressure is the value of decreasing inlet static pressure at which the valve disk re-establishes contact with the seat or at which lift becomes zero.

Pressure Relief Devices

Pressure Relief Devices are a generalized term that encompasses Pressure Relief Valves (PRV), Pressure Safety Valves (PSV), Rupture Discs, and Vacuum Relief Valves. More specifically it plays host to a glossary of engineering language to help define the proper valve. System pressure, opening pressure, liquid service, steam or vapor service, maximum allowable working pressure, fluid flow, excess pressure, inlet static pressure, liquid or compressible fluid, initial opening pressure, pressure vessel code, national board, discharge piping, inlet piping, atmospheric pressure, static pressure, predetermined set pressure, predetermined temperature and compressible fluid are considerations when sizing and choosing a pressure relief device. 

Back Pressure

Back Pressure is the term used to describe the pressure that exists at the outlet of a pressure relief device as a result of the pressure in the discharge system. For example the blowdown system. It is the total of the superimposed and built-up backpressure. 

Discharge Side

The discharge side of the valve, the outlet is the location of the actual flow rate of discharge, expressed in mass flow units. Also called the relief valve capacity.

Pressure Relief Valve PRV

The PRV is a valve used to secure the pressure on an incompressible fluid in a vessel. The valve does not open suddenly but in proportion to the pressure condition. A PRV is a type of safety valve. The valve opens gradually during normal operation to maintain an optimal pressure level inside the vessel.

Pressure Safety Valve PSV and Safety Relief Valve SRV

The PSV and SRV are used to secure the pressure on a compressible fluid or gas in a pipeline or vessel. They fully open when the pressure achieves a set point. If the PRV fails to maintain optimal pressure, the PSV takes over. The valve opens quickly to avoid over-pressurization when a set pressure is reached, preventing a potential safety incident.

Relief Safety Valve Type and Pressure Classes

J.E. Lonergan D series valves, now the Reyco-Lonergan R series, is available with enclosed spring ASME of section 8, DS with exposed spring ASME of section 8, DB with bellows ASME section of 8, and DO the O-ring seat types of valves. The Lonergan safety relief valves are made of carbon steel body, bonnet, and alloy steel spring in various designs:

Conventional Valve Enclosed Spring. Conventional Valve Enclosed Spring O-ring Seat. Balanced Bellows, Enclosed Spring Balanced Bellows. Enclosed Spring O-ring Seat. Open Yoke Exposed Spring. Conventional Valve Enclosed Spring, Steam Jacketed Body. Balanced Bellows Enclosed Spring, Steam Jacketed Body.

Inlet/Outlet Connections (RF connections are standard)Orifice sizes range across orifices D, E, F, G, H, J, K, L, M, N, P, Q, R, and T. 

Inlet and Outlet Flange classes are ANSI Class 150 × 150, Class 600 × 150, Class 300LW, Class 900 × 150, Class 900 x 300, Class 1500 × 300, Class 1500 x 150, Class 300 × 150 and Class 2500 × 300. These safety valves come with an option of set pressures ranging from 0 to 6000 PSIG. They also have several options for Alpha spring material like Inconel, high-temperature alloy steel, stainless steel, nickel, aluminized, Monel, and steel cadmium plating.

The Alpha valve series has distinctive features including ASME section 8 (liquid), ASME section 8 (air/gas), ASME section 8 (steam), liquid, non-code (air/gas), and non-code.

Relief Safety Valve Materials 

Lonergan pressure relief valves (PRV), safety relief valves (SRV), and pressure safety valves are built with a full complement of materials depending upon the service media (steam, air, gas, liquid, etc.) Body and trim combinations can be interchanged according to specification, in Bronze, Cast Iron, Carbon Steel, Stainless Steel, Hastelloy C, Monel and NACE MR-01-75 and MR-01-03 in Carbon Steel, plus NACE MR-01-75 and MR-01-03 in Stainless Steel. There are also aftermarket parts manufactured for Reyco, ARI-Reyco, ARI-Armaturen, Anderson Greenwood, Pentair, and Kunkle. 

Valve ASME Code Certification

Safety relief valves, SRV, and pressure relief valves PRV are manufactured in conformance to Section VIII of the ASME Boiler and Pressure Vessel Code for air, steam, and liquid service. Capacities certified by the National Board of Boiler and Pressure Vessel Inspectors. NACE Code valve certification included.

How to Order a Pressure Safety Valve PSV and Safety Relief Valve SRV

Submit your RFQ on Authorized Parts website easy to use form at:  and we will quote. 

Please include Size and Model Number, or: Size, Valve Type, Body and Trim material, Pressure Class, end connections, and any special code requirements. Include set pressure, service media, and temperature, and required capacity, if any


Yes. Other manufacturer’s valves cross-reference easily and vice versa. Lonergan, Spence, Consolidated, Crosby, Lunkenheimer, Reyco, and Kunkle are examples of manufacturers with equivalent products. However, not all design features are the same, so care should be taken when evaluating.

Yes. All valve testing requirements can be made available, including MTR’s, NDE, Pressure Testing, Radiography Testing, Magnetic Particle, Dye Penetrant, PMI, Positive Material Identification, Hardness Testing, and Failure Analysis.

Yes. Only the first letter in the model number has changed. Form, fit, and function remain the same.

ARI-Reyco Division of ARI-Armaturen now owns Lonergan-Reyco

PRV’s can be closing and non-reclosing. The closing types are spring-loaded and pilot-operated. Spring-loaded can either be conventional or bellows type. Pilot-operated can either be pop-action or modulating-action. Each is defined as either flowing or non-flowing.

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