Hi All,
Just found this forum & hope to learn a lot about hydraulics in the future.
I have a simple question: I mounted a used forklift attachment to the rear of my old farm tractor.
The long hyd.cylinder is a One-Way type....fluid is fed into the base of cylinder to lift forks up,& they lower under their own weight.(or weight of the load).
There is a small 90Deg elbow fitting at the top of this cylinder,that appears to be an air outlet.The hole would only be about 1/3 inch diameter.
I am using a valve bank from a small dozer to control this forklift,& need suggestions about "plumbing" it all together ,to get it working.
The valve bank was originally used in conjunction with normal Two-Way cylinders.
On a final note,the forklift is to be used on my property for lifting fence posts,drums,etc...no heavy ,commercial work near other people.
Any advice is appreciated.I can give more info upon request.

Thanks
Jim

You need to provide your tractor hydraulic circuit and this attachment can only be teed if your tractor hydraulic system is open loop. There are two cylinders for a forklift, one is lifting and the other is tilting. I guess the forlift tilting has a counterbalance valve(or maybe a pilot operated check valve and the lifter might be equipped with a pilot operated check(to hold the load). The loader bank valve have this components but it might be a power beyond. If your tractor is open loop and have a power beyond valve, you can just connect the return line of the tractor power beyond valve to the P of the loader valve and connect the loader return to the reservoir. Again if your tractor is open loop.

One question to those who use power beyond valves, is the return line seals strong enough that when is is subjected to a higher pressure it won't leak?

I remember that to connect another high pressure line to a power beyond, the end plate has to be modified. I guess, there should be a drain line or low pressure line that must be retained so that the handle seals are not subjected to high pressure. I am sure lots of people here can help you, just be patient. There are a lot if good active mobile hydraulic people here.

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One question to those who use power beyond valves, is the return line seals strong enough that when is is subjected to a higher pressure it won't leak?

That's why you need to feed your downstream valve from a power beyoned port, it won't back pressure the tank port of the valve.

quote:

I remember that to connect another high pressure line to a power beyond, the end plate has to be modified.

On a lot of valves, you can replace the plug in the unused PB port with a power beyoned sleeve, or in the case of a close center valve, remove the blocking plug and install the PB sleeve. On older valves that you can't get parts for, you can sometimes modify the endcover.

quote:

I guess, there should be a drain line or low pressure line that must be retained so that the handle seals are not subjected to high pressure

The tank line is still used, so you now have a pump line, a PB line and a tank line.

quote:

There are two cylinders for a forklift

Usually three, one lift and two tilts. CB valves are common on tilts, but not always. I've never come across a lift cylinder with a counter balance or lock valve, they usually do have a throttle valve, or a checked orifice in the base cap of the cylinder, so the load won't drop too fast. On two speed mast arrangements there is often a check valve built in to the piston, but as there is a vent line on this cylinder, I doubt it was a two speed.
It's hard to say what you can do safely without knowing specific information about your tractor valve and the valve you intend to use for the lift cylinder. If you tractor is a John Deere with a pressure compensated radial piston pump, then you would need a closed center valve and it would be teed parallel to your existing closed center valve. If your tractor has a fixed displacement pump, then you need the above power beyoned arrangement, or a selector valve, and the lift valve must be open or tandem center or the pump will dead head.
In using a control valve designed to control a double acting cylinder, you will have a problem lowering the lift cylinder, as the pump will be dead headed into the port that is not used, so the trick here is to have that port teed into the tank line, so the pump is unloaded when lowering. Or you could have the spool modified to bypass internally in the lower position, but you'll have to take it to a hydraulic shop that knows what they're doing, and in most cases you'll be told it can't be done.