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Old 02-09-2013, 11:33 PM
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evolvo evolvo is offline
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Norm, I'll just do this here if that's OK. Others may benefit, besides, I can't draw on the computer, I'll have to use my words

So open that link again and look at the lower right illustration (D) you'll see it has two PO check valves. Just above (D) is illustration (C) showing the symbol for a pilot operated check valve used on hydraulic drawings. Let's start there. The dotted line is the pilot line. The horizontal solid line represents the hydraulic line.The sideways V and the ball are the check valve. When hydraulic fluid is pumped from left to right it lifts the ball off the seat and flows on down stream. When it tries to flow from right to left the ball is forced against the seat and flow is blocked. If the pilot line is pressurized it lifts the ball off the seat and flow is enabled from right to left.
Now illustration D. You will want to eliminate the PO check valve in hydraulic line B and the T fitting in line A that connects the pilot line to the B line valve. You'll need to add a T fitting to line B that connects to the pilot line of the Valve in line A. In illustration (D) when line A is pressurized it retracts the cylinder, which I think is the same as your system. While you are closing your hood hydraulic pressure in line A is free flowing past the check valve into the rod side of the hydraulic cylinder causing it to retract. Oil on the other side of the piston is flowing out of the cylinder through line B and returning to tank.When you stop the hydraulic pump the check valve closes and the cylinder is locked in the closed position. The check valve prevents hydraulic bleed off of oil past the spool valve so your hood doesn't creep open. Now when you want to open the hood line B is pressurized which in turn pressurizes the pilot line to the check valve in line A which opens and allows the oil on the rod side of the cylinder piston to flow through line A and back to tank.
You'll have to find out what pressure your system operates at so you can source a compatible PO check valve. You'll want one that is configured like illustration (A) 4C check valve. The other one (B) 2C check valve uses an external drain, you don't want that
Now that's clear as mud, isn't it! You should click on the "view page" button for a more concise explanation!
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