is provided in fig3 referring to fig3 an electronically controlled valve 30 receives signals from the controller 28 fig2 opening and closing air ports a and b in the valve 30 more particularly an electronic signal from the controller 28 will energize a solanoid not shown in valve 30 allowing air to be supplied by a suitable pressurized air source not shown through port b and conduit 32 the air flow from open port b causes air cylinder piston 34 which is operably connected to dampener control arm 36 to move the dampener control arm 36 downwardly thereby closing the dampener 26 as the control arm 36 and piston 34 move downwardly air is exhausted from the cylinder 38 through conduit 40 which is attached to port a conversely the dampener 26 is moved to the open position allowing air to flow through the drum and to be exhausted by removing the electronic signal from the solanoid valve 30 thereby causing air to be supplied through port a air supplied through port a and conduit 40 into cylinder 38 moves the piston 34 and arm 36 upwardly moving the dampener 26 to an open position preferably an adjustable stop collar 42.