APCO Double-Acting Throttling Device (DAT)
Air/Vacuum Valves efficiently discharge air from deep well pump columns when combined with an APCO Double-Acting Throttling Device (DAT). The DAT has an exclusive Throttling Air-Out/Full Flow Air-In design. Regardless of the amount of air throttling out, there is assured full line capacity air inflow on pump stop to prevent vacuum and water column separation. Because the pipeline media does not contact the Double Acting Throttling Device, it can be used on pipelines containing dirty fluids.
Throttling devices have been used on vertical turbine pumps for decades. Old style, one-way throttling devices are only able to regulate flow to restrict air out. Restricting air out helps minimize shock with each pump start, preventing damage to the pump, valves and piping. This establishes back pressure on the rising column of water, thereby reducing shock, pressure surge and water hammer when the water column hits the closed pump discharge check valve. However, on pump stop, the pump discharge check valve closes and the vertical turbine air valve opens to allow air to re-enter the pump column to prevent vacuum and/or water column separation. Because an old-style, one-way throttling device restricted air re-entry at the same rate as air out, vacuum and water column separation can occur, damaging pump seals, packing, and gasketed joints. Additionally, the pump may be called to start while the column is still full, putting a severe strain on the pump shaft, motors and electrical controls.
The APCO Double Acting Throttling Device features a PTFE tapered plug that is pushed into the throttle position by a very light-weight, stainless steel spring. The plug stays in this position due to the force of air being discharged from the pump suction on pump start. On pump stop, the tapered plug moves from its throttle air-out position to the full-air-in position due to negative pressure inside and atmospheric forces of air rushing into the valve. The desired tapered plug position for throttling air out is regulated by an adjusting screw that can be locked in place when satisfactory throttling of air is achieved.
