The NACOL accumulator uses a much stronger poppet spring to hold the poppet open. So even though there is a pressure drop across the poppet, the spring holds the poppet open until all of the oil has been discharged from the accumulator. The net result is that you get full oil discharge from the NACOL accumulator. How "Preclosure" happens. As oil starts to discharge from the accumulator, there is a pressure drop across the poppet at the bottom of the accumulator. The flow results in a greater pressure on the top of the poppet. The higher pressure on top the poppet combined with the oil flow around the poppet tends to slam the poppet shut before all the oil has discharged from the accumulator. This is called "Preclosure". The result is that much of the oil is trapped inside the accumulator. As oil flows out of the NACOL accumulator, a strong spring prevents the poppet from closing. Oil discharging from the accumulator causes a pressure drop at the poppet. "Preclosure" happens when an accumulator shuts itself off, trapping oil inside the accumulator, resulting in decreased oil volume out of the accumulator.     As oil flows out of the NACOL accumulator, a strong spring prevents the poppet from closing. Oil discharging from the accumulator causes a pressure drop at the poppet.         When all of the oil has been discharged, the bladder forces the poppet closed The poppet closes, trapping oil in the accumulator.