Valves in cooling-water systems
Cooling-water systems have their own family of problems. The medium — river or seawater — is corrosive and erosive. Add to that large pipe diameters, air admission and release, and pressure surges after a pump or turbine trip. The valves must withstand all that for years: corrosion- and erosion-resistant and easy to maintain.
Corrosion and erosion
River and seawater is a harsh environment: it is corrosive and erosive. A hard-rubber lining protects the underlying metal against corrosion and erosive loading, matched to the medium and operating conditions; for the most demanding conditions the valves are available in exotic materials, up to fully super duplex and Inconel.
Isolation and control: butterfly valves in cooling water
As working and control valves in the cooling-water circuit, butterfly valves are used, optionally hard-rubber lined. That keeps isolation and control reliable in a medium that would otherwise quickly attack components.
Preventing backflow: slanted-seat check valves
After a pump or turbine trip the cooling water must not flow back. For that, slanted-seat check valves are used, optionally hard-rubber lined. The angled seat lets the disc close quickly and calmly against the seat before any appreciable return flow develops, which limits pressure surges. The dynamics of that closing before flow reversal are in principle the same as in pressure pipelines; they are set out in the water-hammer note. The same working principle, but a different design principle: in brackish and seawater the main shaft in the flow is no objection, whereas with influent water (sewage) it is a problem due to clogging — such as stubborn fibres from wet wipes — so there the main shaft is positioned out of the flow.
Air admission and release of the cooling-water lines
Air in the cooling-water line costs capacity and increases the surge risk; sub-atmospheric pressure after a pump stop threatens the line. For this EURAD prefers two separate valves: air release valves that vent air under operating pressure, and vacuum breakers that admit air when sub-atmospheric pressure threatens — each a dedicated, optimised design rather than a single valve doing both. So the bore stays clear and the line is protected against too deep a vacuum. The mechanism is the same as in pressure pipelines; in cooling water, resistance to corrosion and erosion is added as a requirement.
Large diameters and maintenance
Cooling-water valves are often large in diameter and hard to reach — in culverts, below ground or partly submerged. That makes installation and removal expensive, and taking a cooling-water line out of service is undesirable while the installation is running. A reliable, corrosion- and erosion-resistant design that lasts and can be isolated in service pays off doubly there.
Selection per situation
Water type (fresh or salt), pipe diameter, operating regime and maintenance access together determine the choice — from lining and seating concept to air admission and release. EURAD advises and supplies on the basis of the application.
