Applications
Pump Stations & Rising Mains
Surge protection, pump control and check valves for pressurised rising mains.
Rising mains present some of the most demanding hydraulic conditions in water infrastructure. Pump trips, rapid valve closure and column separation can generate pressure transients that are many times the steady-state working pressure. Getting the protection strategy right at the design stage is far less costly than dealing with the consequences of a surge failure.
Overview
A rising main is defined by the fact that it must work against gravity. When a pump trips, the water column decelerates and then reverses. The rate at which the column reverses, and the check valve response to that reversal, determines whether the system experiences a manageable pressure transient or a damaging slam. On long mains and high-head installations, the difference between a well-protected and a poorly-protected system can mean the difference between decades of reliable operation and repeated pipe failures.
The Surge Problem
Surge pressure on a rising main can exceed the rated working pressure of the pipeline by a factor of two or more in severe cases. The primary causes are pump trip without adequate discharge-side protection, rapid closure of isolation valves and column separation at high points where vacuum forms during pump deceleration. A hydraulic transient analysis will identify the peak pressures at each point along the main profile and determine which combination of protective measures is required to bring them within acceptable limits.
Non-Slam Check Valves
A spring-loaded non-slam check valve closes before significant reverse flow has developed, eliminating the slam that occurs when a conventional swing check disc is picked up by reverse flow and then dropped onto the seat. For mains up to DN350, compact axial spring-loaded designs fit within a standard flanged spool and require no external pipework or controls. For larger mains from DN400 to DN1200, axial-flow nozzle check valves provide the same slam-free performance with the lowest pressure loss of any check valve geometry, which is an important consideration on long mains where pumping costs are significant.
Pump Control Valves
A hydraulic pump control valve on the pump discharge provides two-stage closure: fast through the first 80 to 90 percent of travel to stop reverse flow quickly, then slow through the final portion to bring the column to a controlled stop and limit the pressure rise to manageable levels. The slow-close rate is set by adjusting a needle valve in the pilot circuit and can be re-tuned during commissioning or as operating conditions change. On booster stations where the pump starts against a pressurised downstream main, the same valve provides a controlled opening sequence to prevent startup surge.
Air Release on Rising Mains
Air pockets at high points on rising mains are a direct cause of column separation during pump deceleration. Air that enters the pipeline during commissioning or through leaking joints accumulates at high points and reduces the effective cross-sectional area available to flow. Anti-shock combination air release valves should be installed at every high point on the profile. Their adjustable needle mechanism controls the rate of re-entry when water arrives at the valve, preventing the pressure spike that would otherwise occur when the float closes against a full-flow water front.
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