Lincoln, NE--Disconnecting a hose from a tractor's hydraulic power source sounds like a simple operation, but it isn't always so. A tractor's hydraulic system typically operates at about 2,900 psi, and operators who disconnect at pressure typically get sprayed by a stream of hydraulic oil. Worse, many can't muster up sufficient strength to disconnect under pressure. To get around that, most operators de-pressurize the hydraulic system before disconnecting, then re-pressurize afterwards.
Using a specially designed quick-disconnect coupling, however, tractor operators can now eliminate all those steps. Designed by engineers at Parker Hannifin's Quick Coupling Division, the agricultural coupling allows tractor operators to connect and disconnect hydraulic apparatus, such as plows, planters, and disc implements, while the system is pressurized.
Key to the new coupling is the incorporation of a miniature spool valve within its body. Each quick disconnect coupling consists of an outer housing that contains a cartridge assembly. The cartridge includes a stationary retainer sleeve, a valve body, and an attached spool.
During connection or disconnection, the cartridge assembly slides axially within the housing. When an operator connects the coupling, for example, the cartridge shifts backward. This movement opens up the spool valve on the end of the cartridge, allowing trapped pressurized oil to vent out a port at the rear of the spool to the tractor's reservoir. As a result, the pressure level in the coupling drops to zero, even though the hydraulic implement remains under pressure. "It only dumps a very small amount of oil," explains Ken Koch, engineering manager for Parker Fluid Connectors. "The oil may be at high pressure, but the volume released is very small."
During disconnection, the cartridge assembly moves the other way and the spool valve opens in the opposite direction, venting pressurized oil through the front of the spool. As a result, pressure in the coupling drops to zero, and operators don't get sprayed with oil during disconnection.
Koch says that the key to the valve's operation is the incorporation of the miniature spool valve. That wouldn't have been possible, however, without the development of a special spool seal to withstand pressure during connection and disconnection. The solution: An elastomeric urethane seal that seals the area between the spool and the stationary retainer surrounding it. To enable the seal to work reliably, they also developed a special manufacturing process to burnish and polish the sealing surfaces that contact the urethane material. "If we didn't develop this seal, the unit wouldn't have held pressure and the coupling wouldn't have worked," Koch notes. Conventional spool valves, he says, typically don't use elastomeric seals.
The new Phase III coupling requires much lower pull force and dramatically reduces oil spillage. "The concept of putting a spool valve on the end of a coupling is unique," Koch says. "Andit has allowed us to simplify the process of connecting and disconnecting hydraulic lines."
Additional detailsÖContact Ken Koch, Parker Hannifin Quick Coupling Div., 13400 "O" St., Box 81247, Lincoln, NE 68501, (402) 486-9182
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