DA22F-40P（DAH-15A，DAH-20A，DAH-25A）Cryogenic Safety Valves

| Product Overview

The DA22F-40P is a spring-loaded cryogenic safety valve engineered for overpressure protection in deep-cryogenic systems operating down to −196°C. It is a vertical, L-type pressure-relief device whose function is to open automatically when the system pressure exceeds a preset threshold, vent the excess gas, and reseat once normal pressure is restored—protecting cryogenic storage tanks, dewars, piping, and process vessels from the pressure build-up caused by boil-off, thermal expansion, or upstream over-supply.

The valve combines a stainless steel body with brass fittings, a material pairing chosen for the full industrial gas spectrum—LOX (liquid oxygen), LIN (liquid nitrogen), LAr (liquid argon), and LNG (liquefied natural gas). The stainless steel body provides deep-cryogenic toughness and corrosion resistance, while the brass fittings offer reliable, machinable connection hardware for standard pipe threading. The sealing element is a PTFE seat, which provides a tight, leak-free closure at cryogenic temperatures where metal-to-metal seats are prone to leakage due to differential thermal contraction.

Two design features distinguish this valve in field service. First, its high-streamline internal flow path minimizes turbulence and pressure drop through the valve, allowing precise, repeatable opening behavior. Second, its bidirectional sealing with high-precision pop-action means the valve closes tightly from both directions and lifts off the seat with a crisp, decisive action at the set point—eliminating the ambiguous "simmer" (slow leakage) that can occur in less precisely engineered relief valves. The valve is rated for a maximum pressure of 580 psig, with the set pressure adjustable across a 75–500 psig range, and is offered in standard NPT sizes (1/2-14, 3/4-14, and 1-11.5 NPT), allowing direct installation into existing pipework with common tools.

The valve is manufactured in compliance with ISO 4126 (safety devices for protection against excessive pressure) and the Chinese regulatory standard TSG ZF001, giving users a documented basis for acceptance in both domestic and export installations. Its spring-loaded, self-reseating design means it can be reused across repeated overpressure events without replacement—unlike frangible devices such as rupture discs—and its compact vertical form factor makes it well suited to cryogenic skids, manifolds, and space-constrained installations.

| Working Principle

The Closed State — Spring Preload and Bidirectional Sealing:

Inside the valve, a compression spring is preloaded against the valve disc through the adjustable mechanism on top. The spring force presses the disc onto the PTFE seat, forming a gas-tight seal between the process side and the discharge side. The bidirectional sealing design means the sealing line is effective regardless of the direction from which pressure is applied—whether from the upstream process pressure pushing the disc against the seat or from differential forces across the disc. This dual-direction sealing integrity is essential in cryogenic systems where pressure transients and temperature-induced contraction can shift load paths. The preload is set so that the downward spring force balances the upward force exerted by the process pressure acting on the disc area. At normal operating pressure—below the set point—the spring force exceeds the pressure force, and the valve remains closed with zero leakage.

The Opening Event — High-Precision Pop-Action at the Set Point:

As the system pressure rises—from boil-off accumulation, thermal expansion of trapped liquid, or upstream over-supply—the upward pressure force on the disc increases. The high-streamline internal flow path keeps the pressure field around the disc clean and predictable, eliminating turbulence-induced chatter or premature opening. When the process pressure reaches the set point, the upward force overcomes the spring preload, and the disc lifts off the seat with a crisp, decisive pop action. This rapid, full opening—rather than a gradual, leaking simmer—ensures that the valve vents the excess pressure cleanly and reseats without seat erosion. The excess gas is discharged through the outlet connection, which is oriented to vent safely away from personnel.

The Reseating Event — Pressure Restored:

Once the overpressure condition is relieved and the system pressure falls back below the set point, the spring force again exceeds the pressure force, and the disc is pushed back onto the PTFE seat. The valve closes automatically and re-establishes the gas-tight seal from both directions. This self-reseating behavior is the defining advantage of a spring-loaded safety valve: it can protect against repeated overpressure events over its service life without replacement, and it vents only the minimum amount of gas required to restore safe pressure.

Set-Point Adjustment:

The opening pressure is determined by the spring preload, adjustable within the rated range of 75–500 psig. Turning the adjustment mechanism compresses or relaxes the spring, raising or lowering the set point within this range, up to the valve's maximum rated pressure of 580 psig. This allows a single valve model to be field-tuned to different protection requirements, though in practice the set point is typically locked and tagged after factory calibration to prevent unauthorized tampering.

NPT Connection and Installation:

Both the inlet and outlet use standard NPT (National Pipe Thread) connections, enabling direct, tool-standard installation into existing cryogenic pipework. The vertical L-type configuration routes the inlet and outlet at right angles, so the vented gas can be directed perpendicular to the incoming line—useful where discharge orientation flexibility is needed in compact skids and manifolds.

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 Factory Shoot

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 Application Video

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 Product parameters

| Data Sheet

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Comment & FAQ

1:  What is a cryogenic safety valve and where is it used? 

A: A cryogenic safety valve is an overpressure protection device designed specifically for deep-cryogenic systems—those handling liquefied gases such as liquid nitrogen (−196°C), liquid oxygen (−183°C), liquid argon (−186°C), or LNG (−162°C). Its job is to open automatically when system pressure exceeds a safe threshold, vent the excess gas, and prevent tanks, dewars, piping, or process vessels from being damaged or ruptured by pressure build-up. Typical applications include vapor-space protection of cryogenic storage tanks, liquid nitrogen dewar relief, oxygen pipeline overpressure protection, LNG storage and transport facilities, and any low-temperature process that requires "vent automatically when pressure gets too high."

2.  What does the model DA22F-40P mean? How is it different from a DA21F? 

A: The model number is a manufacturer's code for the valve's structure, sealing form, and pressure rating. "DA" denotes the cryogenic safety valve series, "22" denotes a vertical, L-type spring-loaded structure, "F" denotes soft sealing (PTFE seat), "40" denotes the nominal pressure rating (PN40 system, about 40 bar), and "P" denotes a stainless steel body. The key difference from a DA21F-type valve is structural: the "22" type adopts a vertical, right-angle (L-type) configuration with brass fittings, whereas the "21" type typically uses a more compact inline arrangement with a plain stainless body. Both are spring-loaded cryogenic relief valves, but their connection geometry and fitting materials differ, so choose based on your piping layout and installation constraints.

3.  What is the difference between the 580 psig rating and the 75–500 psig set range? 

A: The 580 psig figure is the valve's maximum rated pressure—the highest pressure the valve body is designed to withstand, defining the structural limit of the device. The 75–500 psig figure is the adjustable set-pressure range—the window within which you can tune the actual opening (relief) pressure via the spring preload. Think of it this way: the set point is where the valve opens (chosen within 75–500 psig to suit your system), while the 580 psig rating guarantees the valve can safely contain the pressure it protects against. You should always select a set point that both meets your process requirement and leaves adequate margin below the valve's structural rating.

4.  What is an NPT connection and why does it matter? 

A: NPT stands for National Pipe Thread, a U.S. standard tapered pipe thread widely used for pressure connections. Its tapered thread form creates a seal by metal-to-metal wedging as the fittings are tightened, making it a reliable, tool-standard connection for gas and liquid service. This matters because the DA22F-40P's inlet and outlet use standard NPT sizes (1/2-14, 3/4-14, and 1-11.5 NPT), meaning it can be installed directly into existing cryogenic pipework with common pipe wrenches—no special flanges or welding required—and it is compatible with a broad ecosystem of NPT fittings, reducers, and accessories worldwide.

5.   Why stainless steel body with brass fittings? Isn't brass a problem at cryogenic temperatures?

A: The material pairing is deliberate. The stainless steel body provides deep-cryogenic toughness (excellent impact resistance at −196°C) and corrosion resistance against the full industrial gas spectrum—critical for the pressure-containing structure that sees the coldest temperatures and highest stresses. The brass fittings serve a different role: they are machinable, work-hardening connection hardware that provides reliable, dimensionally stable threads for the NPT connections, and brass retains adequate ductility and strength in the moderate-temperature connection zone while offering good corrosion resistance to the environment. The design places each material where it performs best—stainless where the cryogenic extremes and structural integrity matter, brass where reliable, standard threading and assembly convenience matter.