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norm broshous 02-09-2013 07:42 AM

hood latch
I am building a fiber glass tilt front that operates on hydraulics,and need a locking device that once the hood has been sucked up home to the fire wall,it will not allow the hood to migrate slowing open (only a 1/2" )but requires that I constantly bump the hyd. to bring it back home...I want to develop a lock that will sense the position ,then screw motor type locking and hold until electrically released.....thanks for any ideas---norm

timothale 02-09-2013 09:45 AM

old Caddy
Caddy's from the 70's or 80's had a easy close trunk latch. push it down, the latch would grab the lid, and slowly pull it all the way down and lock. use one on each side.

evolvo 02-09-2013 11:11 AM

You can do this with your hydraulics by adding one of these to the system...

Google Image Result for

norm broshous 02-09-2013 02:52 PM

hood lock
great idea on the check valve for hyd.system==thanx

evolvo 02-09-2013 04:06 PM

Your welcome:D I said you could do this with one pilot operated check valve, and that's true, if you just want to keep the hood from opening when pulled down tight. But if the hood bleeds down when it's in the fully opened position you might want to use two valves, as shown in the lower right of the drawing!!

norm broshous 02-09-2013 04:39 PM

thats all I want to do ---hold it closed,when it opens it has a chain stop to hold it at the end of the cyliner stroke,(also over top dead center)I am not sure I understand the piping required to do this with 1-valve---can you make me a sketch and e-mail me---thanx

evolvo 02-09-2013 11:33 PM

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:cool:

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:nono:
Now that's clear as mud, isn't it! You should click on the "view page" button for a more concise explanation!

evolvo 03-05-2013 08:28 PM

Norm, any progress on getting your hood sorted out?

norm broshous 03-07-2013 10:55 AM

hood latch
I have deceided to purssue something in the solenoid type release,the hyd. lock will put pressure on the cyl or system all the time and that concerns me ( mid 80s gm conv,pump and cyl...thanks norm

evolvo 03-08-2013 08:09 PM

It's your choice, of course, but I still think the PO valve would be the best answer for your situation. Pressure is what makes hydraulics work, it's what they are designed to work around. Your system now generates pressure to move the cylinders, opened or closed. It's the lack of captured pressure in the cylinders when the pump is stopped that allows your hood to creep open. Putting a PO check valve in the hydraulic line between the cylinder and the spool valve/pump will lock the cylinders in the closed position with a negligible amount of pressure. Since the spool valve/pump will be idle when the hood is locked closed there will be no extra load placed on them.
Remember, hydraulic oil is sometimes called "liquid steel" with a system like I've described the PO valve is nothing more than a latch.
Just sayin' :thumbup:

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