Water Seal
Reliable Flashback Prevention and Pressure Isolation with Engineered Water Seals
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Liquid barrier protection against flashback and backpressure
CRA Water Seals are engineered flare safety devices designed to prevent flame flashback and provide pressure isolation between the process header and flare stack. By maintaining a liquid barrier within the seal vessel, the system blocks flame propagation while allowing controlled gas flow to the flare. Designed for continuous industrial service, CRA water seals are built for safe flare operation during normal, upset, and emergency conditions.
Function
Flashback & pressure isolation
Moving Parts
None (passive)
Barrier
Liquid seal
Application
Flare header isolation
What is a Water Seal?
A water seal is a passive flare safety device that maintains a liquid barrier inside a seal vessel, blocking flame propagation from the flare stack back into process piping while allowing controlled gas flow through to the flare under normal and emergency conditions.
How it works
Relief gas enters through a dip pipe submerged below the liquid surface and bubbles up through the liquid layer, which physically blocks any flame from travelling back from the flare stack.
Relief gas enters the seal vessel through a dip pipe submerged below the liquid surface.
Gas bubbles up through the liquid layer before continuing on to the flare.
The liquid column physically blocks any flame from the flare stack travelling back through the gas, while also isolating the upstream header from flare backpressure fluctuations.
Dip-tube submergence depth and seal liquid level are sized to the design flow rate and required backpressure margin.
Key Benefits
Liquid seal barrier prevents flame propagation from the flare stack into process piping.
Isolates upstream equipment from flare backpressure and pressure fluctuations.
Operates without moving parts, for reliable performance with low maintenance.
Maintains safe system separation during normal and emergency flare conditions.
Designed for high-temperature, corrosive, and variable flare gas environments.
Projects That Push Boundaries
Complete gas conditioning train transforming raw digester gas into clean, usable fuel for a city utility.
The CRA Edge
CRA has deep expertise in flare system safety and protection devices.
Water seals are hydraulically sized to the flare system duty.
Designed in line with accepted flare safety practices.
Water seals are compatible with CRA and third-party flare systems.
Applications
Frequently Asked Questions
What does a water seal do in a flare system?
A water seal is a flare safety device that holds a liquid barrier inside a seal vessel. The barrier blocks flame propagation from the flare stack back into the process piping while allowing controlled gas flow through to the flare. It also provides pressure isolation between the process header and the flare stack, so upstream equipment is protected from flare back-pressure and pressure fluctuation. CRA designs water seals for its own flares and for third-party flare systems.
How does a water seal prevent flashback without moving parts?
The liquid level inside the seal vessel physically blocks the flame path. Gas enters below the liquid surface through a dip pipe, bubbles up through the liquid and leaves on the flare side, and a flame cannot pass back through the liquid barrier into the header. Because the barrier is passive, a correctly maintained water seal keeps working through normal, upset and emergency conditions without an active control system. CRA's water seals have no moving parts.
How is a water seal sized for a specific flare header?
CRA sizes each water seal hydraulically for the specific flare duty, including the seal depth, the back-pressure the header can tolerate and the expected relief flow. The vessel size is specific to each application. The sizing follows accepted flare safety practice for the relief flow and pressure conditions, and the vessel is designed for the high-temperature, corrosive and variable gas the flare header carries.
Where does a water seal fit relative to a knock-out drum?
A water seal is commonly installed downstream of the flare knock-out drum. The knock-out drum removes entrained liquid from the relief gas first, and the water seal then provides flashback protection and pressure isolation, so together they form a layered flare safety system in which each device covers one function. CRA designs both vessels to work together and to be compatible with CRA and third-party flare systems.
What service conditions can a CRA water seal handle?
CRA water seals are engineered for high-temperature, corrosive and variable flare gas, and for continuous industrial service under normal, upset and emergency conditions. They are used for redundant flare safety protection, emergency and relief gas discharge, high-pressure relief events and pressure isolation between process units and the flare. Typical installations are refinery, chemical and petrochemical flare headers, and landfill and wastewater biogas flares. Freeze protection is included where the climate requires it.