Old Hyster Forklift with double acting lift cylinder?

fastline · Jan 21, 2017

Needing, but not expecting to find a possible double acting cylinder on an old 10K forklift? Is this possible? This one has a larger port that is fully connected to the system with a hose and everything. There is also a small, low pressure hose connected to the head, which I can only assume for any bleed by so the cylinder hopefully would never spill fluid on the ground?

Now, I am NOT trying to say the fork is actually setup to apply downforce, but I can only hope that the cylinder is actually double acting? No idea why there is a hose on it but I really need to convert the cylinder and would help if it can be used as double acting.

buickanddeere · Jan 22, 2017

The seals may not be suitable for "down pressure" . Sometimes some applications are fitted with double acting cylinders just to reduce the size of the hydraulic reservoir.

NCWayne · Jan 22, 2017

Many forklifts, especially the older ones, don't have an actual seal in them. Even those that do usually have some sort of bleed valve that allows oil on top of the pistol. I've worked on, and seen, both over the years, on everything from Hyster's to CAT's to Komatsu's and even a Toyota or two.

In the case of those without a true seal, they rely soley on the difference in surface area of the bottom side of the piston and the top side, and the differential pressure created by that size difference, to provide the lift.

Those with a seal on the piston simply use the surface area on the bottom to achieve lift, and then will dump some of that pressure to the top of the cylinder, when the cylinder tips out to prevent damage.

Too this arrangement insures no more oil than is necessary has to be put into, or taken out of, the cylinder to achieve the best possible lift, and lower speeds.

Regardless of any of that, the ONLY thing the top hose does is to provide a low pressure bleed port(to the tank) for any oil that happens to be on top of the piston.

Bob Bancroft · Jan 22, 2017

The "seal" in my little old forklift is a cup, much like the old hand water pumps. Before I replaced it, enough oil would leak by it that the relief line on top couldn't keep up, and the seal would push out of the top of the cylinder!

Must be your cylinder is not repairable? Certainly a modern cylinder would work. If you go that route, it wouldn't be a bad idea to squirt a little oil in the top part, to keep things coated in oil, as a new cylinder could be tight enough that the top end would stay dry.

MJ in the UK · Jan 22, 2017

I have been involved with Manitou rough terrain fork lifts fo 40 years and have never heard of double acting lift ram.
As Wayne pointed out they have displacement lift rams and the only seal in the ram is in the top cap and it is very
seldom they leak. I have just checked my records and I have only sold 48 seal kits since I started my little buisness
35 years ago. MJ

fastline · Jan 22, 2017

Ah, so the head seal might be there but the piston was probably designed with minimal or no seals thus making any chance of operating as double acting a no-go?

Steve@Advance · Jan 22, 2017

If you'll notice, the OD of the ram extending out is only a few thousandths smaller than the cylinder bore. So even of you could modify the upper seal to hold pressure, there would be no return force.

mj · Jan 22, 2017

Seems like you got a lot of good info in the replies. Here is more info >>>>>> http://rocketseals.com/ 8)

442 · Jan 22, 2017

Some hyster forklifts have a double acting lift cyl.,both ends connected to lift pressure,for fast speed at low pressure.When pressure got to a certain preset,it would move a valve dumping rod end flow to sump,which was for high pressure,low speed.

Old Hyster Forklift with double acting lift cylinder?

fastline

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buickanddeere

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NCWayne

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Bob Bancroft

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MJ in the UK

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fastline

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Steve@Advance

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mj

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442

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