Question 1

What causes water hammer in check valves and how to prevent it?

Accepted Answer

Water hammer in check valves occurs when forward flow suddenly stops (pump shutdown, valve closure), causing the fluid momentum to compress and create a pressure surge that travels back through the system. This can exceed 10x normal working pressure, damaging pipes, supports, and the check valve itself. Prevention methods include: (1) using slow-close check valves (spring-loaded or weighted), (2) installing surge relief devices or accumulators, (3) providing proper pump discharge check valve sizing, (4) using controls to gradually reduce pump speed. For Jeddah and Riyadh water transmission pipelines, our anti-surge check valves with hydraulic damping are specified.

Question 2

What's the difference between swing check and tilting disc check valves?

Accepted Answer

Swing check valves have a disc that swings outward on a hinge pin to allow flow and swings back to seat when flow reverses. They offer low pressure drop and work best in horizontal installation with flow upward. Tilting disc check valves have a disc that tilts to open (approximately 80 degrees) and is balanced by a weighted or spring-loaded lever to close quickly. Tilting disc design provides faster closure (reducing water hammer), can be installed horizontally or vertically, and handles higher flow velocities. For Saudi Arabian water pipelines, tilting disc is often preferred for its superior anti-surge characteristics.

Question 3

When to use a silent check valve vs swing check?

Accepted Answer

Silent check valves (also called spring-loaded or nozzle-check) use a spring-loaded disc that closes quickly as flow reverses, minimizing water hammer and eliminating the slapping noise of swing checks. Use silent checks when: (1) water hammer prevention is critical, (2) installation is in buildings or noise-sensitive areas, (3) vertical installation with flow upward is required, (4) space is limited. Swing checks are better for: (1) large pipe sizes (above 24 inches) where silent check cost is prohibitive, (2) raw water intake where debris may interfere with spring mechanism, (3) applications where some pressure drop is acceptable. For Dubai and Abu Dhabi high-rise buildings, silent checks are specified to prevent noise complaints.

Question 4

What is non-slam check valve design for pump protection?

Accepted Answer

Non-slam check valves are designed to close rapidly just before flow reversal, preventing the disc from slamming against the seat and causing water hammer. They achieve this through: (1) hydraulic damping that senses flow reversal and accelerates closure, (2) spring assistance for fast closure, (3) aerodynamic disc profile that provides natural lift at low velocities. The check valves are sized so the disc begins closing at approximately 10% reverse flow, achieving full closure before significant reversal occurs. For Saudi Arabian seawater cooling pumps and UAE desalination plant booster pumps, non-slam check valves are specified to protect impellers and seals.

Parameter	Value
Size Range	1/2" to 24"
Pressure Rating	150# to 2500#

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