An Unconventional Check Valve
AK Steel Corp., a steel mill in Ashland, Ky., was having a recurring problem at its quenching station. Staff was frequently replacing the conventional swing check valves installed in a vertical flow-up application.
In the quenching station, coke comes out of the oven at 1,200°F and is cooled with spray water. The water then drains into a pit where a pump recirculates the coke and water (approximately 2% concentration) 10 ft vertically through a swing check valve and into a cooling station where it is reused. Once the pump is turned off and dewatering conditions occur, the coke fines settle on top of the valve disc. When the pump is turned back on, the valve disc will not fully open due to the additional weight of the coke fines.
The result is reduced flow efficiency and increased headloss. In addition, the abrasive nature of the coke fines abraded the valve seat and body of the valve, causing leakage and requiring frequent maintenance for the valve to seal properly.
The first swing check valve AK Steel installed clogged within days of use or backflushing, with the seat leaking a few months after installation. AK Steel replaced the first valve with two different manufacturers’ springloaded swing check valves. These replacement valves gave the same results.
Comparson with Conventional Valves
Trivaco, a Val-Matic representative in Ohio, suggested replacing the existing swing check valve with a Val-Matic Swing-Flex check valve with a backflow actuator (Figure 1). Val-Matic’s simple design is the key to the performance and long life of the Swing-Flex check valve. A conventional swing check valve uses outside levers with weights or springs in an attempt to reduce slam, which pulls the disc down into the flow. Pulling the disc down into the flow creates high headloss and causes the disc to flutter under flow conditions. As a result, the shaft, bearings and shaft seal are subjected to severe wear and reduced service life. This wear, caused by abrasion from the corrosive coke fines, explains why AK Steel had to replace the valves so often.
The Swing-Flex’s clog-resistant performance is achieved by maintaining an unobstructed 100% flow area, domed cover and smooth streamlined body contour. Unlike a conventional horizontal swing check valve, the Swing-Flex has no packing or O-rings, mechanical hinges, shafts, pivots pins or bearings to wear out. Reliability is achieved by utilizing just one moving part, the Memory-Flex disc.
Extended life is designed into the disc by the inclusion of steel and nylon that are precision-molded into the disc. By using this check valve with a rubber disc, the seat no longer leaked as a result of the abrasive application. The Swing-Flex resilient seat is able to withstand the corrosive nature of the coke fines (or other abrasive materials) much better than metal-to-metal seats.
AK Steel had the innovative idea to use the standard port on the dome cover as a flush port (Figure 2) to remove the occasional coke fines that settle behind the disc. By using the cover as the flush port, it has eliminated the offline time and maintenance costs caused by taking the valve out of line and doing a complete backwash. The mill also uses the backflow actuator to sporadically backflush the pump.
AK Steel was replacing the swing check valve once every three months. After installing the Swing-Flex, the steel mill has saved significantly on replacements and installation costs. The new check valve has been installed for more than a year, and the company has been so impressed by its performance that it has purchased additional valves for its sister mill in Ohio.