decreases. Once the pressure is below the accumulator pre-charge pressure, the entire system pressure will degrade quickly. In a closed system such a pallet-decoupled application, the system is subject to pressure changes relative to the ambient temperature fluctuations of the fluid captured in the system. As the ambient temperature increases or decreases, so will the relative pressure in the system. The function of the accumulator in this instance is to act as a cushion to help accommodate, or minimize the effects of these temperature / pressure changes. The following formula can be used to estimate the anticipated pressure change resulting from temperature change in a closed system.
Interface with automated load/unload stations is more difficult Pressure loss from a leak in the system may exceed of the accumulator’s capacity More susceptible to contamination into the hydraulic system due to the repeated connection of the hydraulic supply hose(s).
ACCUMULATOR An accumulator is a device that temporarily stores a volume of fluid under pressure.
Vektek uses a sealed piston to separate a gaseous space in the accumulator from the hydraulic space. The gas side is charged to a pre-determined pressure with nitrogen. Nitrogen is an inert, non-combustible gas. Never use any gas other than nitrogen for accumulator pre-charge. Until the hydraulic system pressure exceeds the gas pre-charge pressure, no additional hydraulic fluid is induced into the accumulator. As the system pressure increases above the precharge pressure, the nitrogen further compresses, and oil is forced into the accumulator. This stored fluid is used to help stabilize the pressure and / or flow in a decoupled system. In the event of a minor leak in a closed system, the hydraulic fluid stored in the accumulator under pressure will be drawn into the system to try to offset the effects of that fluid loss. However, as the fluid is drawn into the system, the pressure will degrade until the supply of fluid under pressure is exhausted. This application is to help minimize the effects of the pressure decay so that the system problem can be detected and repaired. When unclamping a system, the accumulator will discharge it’s oil as the system pressure
( ) ( ×
+
459.67 )
459.67 T P p T Where: = 2 P Resultant pressure 1 2 1 2 + =
= 1 P Initial pressure (PSI.) = 1 T Initial temperature ( F ° ) = 2 T Final temperature ( F ° )
In certain applications, a very brief, but high pressure rise, or spike may occur in the system. This may be from the actuation of a control valve operating a system that has a great deal of pressure, the intermittent pumping of an air/oil pump, the reciprocating action of a piston pump, or a shock load such as dropping a dead weight onto the actuator. In many of these situations, an accumulator might be utilized to absorb some of the shock, or pressure spikes induced into the hydraulic system. The pre-charge of an accumulator should be checked periodically to ensure proper system integrity. A simple way to do this is to start with a system that is fully clamped and then simulate a very slow system leak (i.e. connect the hose from the power supply to the pallet
Hydraulic Clamping Fundamentals Aug 09 Rev - D
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