In a cylinder circuit, when using logic elements to emulate a four-way directional valve function, minimising decompression shock when changing from extend to retract can be a challenge. The larger the volume of oil being compressed (ie, the larger the cylinder bore and/or stroke), the larger the 'shock' potential due to the stored hydraulic energy.
Since this stored energy in the cap end of a cylinder is a 'fact of life' (and do not forget that the machine frame and product being compressed can also add to the total stored energy), the goal is to release this energy in a controlled and consistent manner, in the shortest time that will achieve an 'acceptable' decompression rate (which is usually determined subjectively). The use of dedicated decompression circuit components (ie, staged pilot ratio check valves, orifices, solenoid valves controlled using electrical time delay logic) can be expensive, have questionable reliability, are not always consistent, and consume excess cycle time.
A simplified solution is by using Sun DK*R Balanced Logic Elements with a 2-way DAAL-*CN pilot valve and a Sun PRDB pressure reducer/reliever, the result is a zero leak, reliable, consistent, uncomplicated, and cost effective cap-end-to-tank, normally closed logic element. (A DO*R cartridge can be used in place of the DK*R if a normally open function is desired. Either cartridge can also include Sun's T-8A cavity, ie, DK*R-8 and DO*R-8, to accommodate the pilot control function as an integral unit.) Since this product is 'balanced', operating pressures on the work ports have no effect on the opening speed of the valve. (A typical 'poppet style' logic element exposes more and more area as the poppet moves to the open position, with the attendant increase in opening force.) So, by adjusting the pilot pressure via the reducer, an acceptable and repeatable opening time can be easily set. This approach has proved to be an acceptable solution in minimising decompression shock in the shortest time with consistent results. (Using the newer DAAL-SCN 'soft shift' 2-way as the pilot valve, can further enhance tuning for shock reduction.)
NOTE: Using Series 4 size cartridges, flows up to 80 gpm (320 L/min) with a nominal 100 psi (689 kPa) pressure drop can be achieved. However, when even larger flows are required, two, three and four DKJR logic elements have been successfully applied in parallel and have accommodated flows up to 320 gpm (1280 l/min). (With multiple elements, an external pilot valve sized for the number of cartridges involved, would be required in lieu of integral solenoid pilots in each element.) Also, keep in mind that a balanced logic element can be used as a standalone valve in a machine with a common spool valve circuit if that machine is experiencing excessive decompression shock.
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