Question 1

What is a check valve or non-return valve?

Accepted Answer

It is a valve that allows fluid flow in only one direction, closing automatically when flow reverses. It requires no manual operation or actuator: the system differential pressure itself opens and closes it. It is a fundamental safety component in pumping, compression, and distribution systems.

Question 2

What types of check valves exist?

Accepted Answer

The main types are: swing check, with a pivoting disc offering low pressure drop; and dual plate (double disc or wafer), compact and lightweight for installation between flanges. The choice depends on available space, permissible pressure drop, and service conditions.

Question 3

When is a check valve needed?

Accepted Answer

It is needed in any installation where reverse flow could cause damage: downstream of pumps (to prevent backflow at shutdown), in compression systems, in parallel with relief valves, in distribution headers, and at any point where flow reversal could compromise process safety or damage rotating equipment.

Question 4

What standards apply to check valves?

Accepted Answer

The main standards are API 594 for wafer and dual plate check valves, API 6D for pipeline valves including swing check type, ASME B16.34 for pressure-temperature ratings, and API 600 for cast body valve design. NACE MR0175 applies for sour service.

Question 5

How to select the right check valve?

Accepted Answer

Selection depends on available space (dual plate is more compact), permissible pressure drop (swing offers less restriction), and service conditions (pressure, temperature, fluid). For systems with water hammer risk, spring-loaded or dampened check valves are recommended.

Welded Body Trunnion

Check Valves: The Defense Line Against Backflow.

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