Valve Selection for the Safe Operation & Protection of the Pump Station

GIL Automation
Valve Selection for the Safe Operation & Protection of the Pump Station
Proper valve selection that helps ensure safe operation and protection of the pump station can present a challenge to the engineer and owner. Common considerations include preventing the damaging consequences of surge pressure transients (water hammer), related safety issues, pipeline breaks, fitting failures, cross connection, flooding and water loss. Additional concerns may include minimizing check valve slam, elimination of air pockets and vacuum conditions, surge relief valve necessity and size, pump control valve considerations and options, valve operating speeds, reducing pumping energy costs and dependable isolation valve service.   
The technical parameters of the pumping application should be acquired early in the pump station design phase to establish a knowledge of the system. The nature of the fluid, pressure and flow ranges, valve sizes, industry norms, and the preferences of the owner and consulting engineer are all taken into account. Using governing fluid mechanics equations, the possibility for surge pressure transients (water hammer) may then be investigated. During a surge occurrence, the maximum surge pressure potential, the surge time, line velocity, surge wave speed, pipeline constant, and total system head potential should all be examined and addressed. These findings will be used to guide the use of check valves, pump control valves, surge relief valves, and air valves to reduce surge pressure.

Check valves are used to prevent the backflow of fluid through the pump by closing before flow reversal can occur. Check valves are installed on clean and dirty applications. Various closure devices are available that include air cushion, oil control, bottom buffers, lever and weight, external lever and spring or internal spring.

Surge relief valves are typically installed downstream of the check or pump control valves on the pump discharge header with the valve inlet connected to the side outlet of a tee and the valve outlet piped back to the sump. The normally closed surge relief valve opens quickly when the system pressure rises above its adjustable relief-pressure setting, allowing fluid to be discharged from the system through the open surge relief valve to a controlled, contained location—typically some form of sump. While the surge relief valve is open, the system is no longer contained, fluid compression is limited and surge pressure is controlled. The valve will remain open as long as the system pressure exceeds the valve’s relief-pressure setting. The valve will slowly begin to close at an adjustable rate as the surge pressure subsides and the system pressure falls below the valve’s relief-pressure setting.

Air release valves remove small air pockets that form at the high points of a pipeline and restrict flow. Air and vacuum valves expel large amounts of air when filling the pipeline and admit air to relieve a vacuum when draining the pipeline.

Isolation valves are typically one of three types—butterfly, plug or knife gate. Selection of an isolation valve depends on various factors including full flow requirements, media type and solids content, temperature, etc. An isolation valve will usually be located after the pump control valve or check valve to isolate both the valve and the pump for maintenance capability. An isolation valve is also required for the pressure relief valve.

 

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