Question for the Hydraulics Folks

[bigdaddylee82]

Alright Hydraulic Gurus:

I've seen hydraulic rams used to control the rate that something falls/opens. Think like a large door/ramp hinged at the bottom slowly folding open. I believe these would be one way acting/single action rams, because the same ram is used to close the door. I have been told that what allows the ram to slow whatever is falling/opening is some kind of special valve. Originally I was told this is valve is called a "blocker valve" but I haven't been able to find anything about blocker valves. Do any of you have a clue what I'm talking about, and the possible other names for said valves, correct name for the valve, or even an OE application of such an apparatus?

I appreciate any input.

- Lee

[beyondhelp]

Look at lowrider hydraulic diagrams for an idea of how it works. I think what you're looking for is a slow down. Basically a device that regulates the flow of the hydraulic fluid back to the reservoir.

http://www.coolcars.org/cce/slowdownvalves.htm
Slow-down valves are bi-directional valves that adjusts the speed of oil flow through the valve.
In lowriders this valve adjusts how fast the car drops down after you hit the dump switch.

[roverjohn]

I think what you would need is a hydraulic fitting with restriction built into it. It will have the same part# as regular fitting but followed by "R" and then some number which denotes the orifice size. Gravity drives the fluid through the small orifice which acts as a brake. To close the door a pump reverses the flow. No need for fancy valves as long as you are in no rush to close the door which likely you are not.

[osirus]

It's called a needle valve.

You can also orfice the fitting in the cylinder.

[bigdaddylee82]

So you've got a restrictor in line and maybe a ball valve? Close the ball valve apply pressure via pump and the door closes; open the ball valve with the pump off, and the restrictor allows the door to open slowly?

Something like that?

The guy I was talking to said that there was a check valve safety in the system that would keep the door from falling were you to ever burst a line/ spring a leak. So how would that work into the system?

Thanks for the info so far fellas :beer:.

- Lee

[roverjohn]

Your ball valve would act only as a lock. There is no reason to over think this. A restriction in a fitting coming out of the cylinder provides all the "safety" you could ever have. So, you have a very simple loop with one valve to open the loop( allows door to drop) and then a small pump parallel to the valve to reverse the flow(raises door) when the valve is closed. That's it. Add a ball valve or solenoid controlled equivalent in series to act as a lock if your DOT mandated pin or padlock securing the safety chain is removed.

[roverjohn]

I should add that the valve you use to lower the door should be a spring loaded needle type that is normally closed, not a ball valve. That way the operator has some control over the lowering process and if he stokes out in the middle of doing so the door will stop and not crush the first responders.

[bigdaddylee82]

Your ball valve would act only as a lock. There is no reason to over think this. A restriction in a fitting coming out of the cylinder provides all the "safety" you could ever have. So, you have a very simple loop with one valve to open the loop( allows door to drop) and then a small pump parallel to the valve to reverse the flow(raises door) when the valve is closed. That's it. Add a ball valve or solenoid controlled equivalent in series to act as a lock if your DOT mandated pin or padlock securing the safety chain is removed.

I guess it really doesn't have to be all that complicated does it? The guy I was originally talking to about it sure made it seem awfully complicated though, but he's Canadian :D.

Here's (http://www.stageline.com/en/main_nav/produits/tous-les-modeles/sl100/montage/vr-modelise/) where I'm getting the idea from (you've got to have Quicktime, and give it a minute to load). They lower the sides of the trailer this way to create a stage floor. I couldn't figure out how they were doing it, no cylinders visible in the animation anyway, so I called and asked.

- Lee