Forklift hydraulics: do they use double pilot check valves?

[jas67]

I just purchased a Crown 20MT walkie-stacker/straddle lift type fork lift. I finally used it this weekend to put all my off-season implements up on pallet racks -- really freed up some floor space!

Anyway, I noticed that one of the hoses is quite chafed from getting pinched in an area that it shouldn't be getting into. I'm going to replace this hose, and make whatever changes are necessary to protect this hose.

This fork lift has a two-stage mast that has two cylinders, once of which moves with the first stage. I assume that forklifts use single acting cylinders, and lower with gravity. There appears to be two hoses this moving cylinder, one to each end? Is this a double acting cylinder? This upper hose is the one that is chaffed.

I am thinking of making a man-lift cage for this lift, as it would be quite handy to have to install lighting and other things on 10 1/2 ft. high ceiling in my shop, but seeing this damaged hose has had me rethink the safety issues with doing this. Do forklifts have any kinda of safety valving to protect against a sudden drop of the load in the event of a hose rupture? I'm thinking a device like a double-pilot check valve (or whatever the equivalent would be for single-acting cylinder).

Sorry for the non-tractor post, but this info could also apply to any of the number of people here that have retrofitted forklift masts onto their tractors.

Thanks,
Jay

 

[oldnslo]

We have a Big Joe walk behind lift and a Yale riding lift. On both of them the top hose is just a drain hose. I.e. They carry any leakage of the piston seals back to tank.

Can you put down pressure on your forks? My guess is no so this would indicate single acting cylinder and the top hose is a drain line.

Dual P.O. checks on the mast is a no.

Roy

 

[J_J]

I just purchased a Crown 20MT walkie-stacker/straddle lift type fork lift. I finally used it this weekend to put all my off-season implements up on pallet racks -- really freed up some floor space!

On some forklift's, I believe it is possible to lower the cyl, and if the forklift slide gets jammed up, the cylinder can fully retract and the lift will be left suspended in the air, and could rapidly descend with disastrous results. .

Some forklift's do have them, and some don't. If you look at the hyd schematic, you might be able to see if it has any safety valves.

Anyway, I noticed that one of the hoses is quite chafed from getting pinched in an area that it shouldn't be getting into. I'm going to replace this hose, and make whatever changes are necessary to protect this hose.

This fork lift has a two-stage mast that has two cylinders, once of which moves with the first stage. I assume that forklifts use single acting cylinders, and lower with gravity. There appears to be two hoses this moving cylinder, one to each end? Is this a double acting cylinder? This upper hose is the one that is chaffed.

I am thinking of making a man-lift cage for this lift, as it would be quite handy to have to install lighting and other things on 10 1/2 ft. high ceiling in my shop, but seeing this damaged hose has had me rethink the safety issues with doing this. Do forklifts have any kinda of safety valving to protect against a sudden drop of the load in the event of a hose rupture? I'm thinking a device like a double-pilot check valve (or whatever the equivalent would be for single-acting cylinder).

Sorry for the non-tractor post, but this info could also apply to any of the number of people here that have retrofitted forklift masts onto their tractors.

Thanks,
Jay

I am not sure that forklift's are required to have safety valves/ velocity fuses. If I remember correctly a driver is required to be in the seat when lifting. That is not to say that you can not shift the valves with remote cables. I think the gist of all this is that the forklift is not the desired lifting device of choice. You will probably use it for whatever, it is your machine, and if anybody else uses it for anything, you are responsible for their safety.

However aerial lift booms/trucks are required to have safety valves in case of a hose bursting.

Some good reading. for you and others.

FLUID POWER SAFETY INSTITUTE™ - Safety Alert #39

 

[oldnslo]

Here is a quick way to check to see if you have a P.O. check.

Raise the mast part way. Disconnect the power supply. Try to lower the mast, if it lowers with out the pump running you do not have P.O. checks.

Roy

 

[jas67]

Here is a quick way to check to see if you have a P.O. check.

Raise the mast part way. Disconnect the power supply. Try to lower the mast, if it lowers with out the pump running you do not have P.O. checks.

Roy

It goes down w/o power -- at a very reasonable and controlled speed.
J.

 

[js5020]

The 20MT does not incorporate a pilot operated check valve in the lift/lower circut, Crown did use these valves in the tilt circut on other models. Most of the lift/lower circuts did use a velocity fuse however, due to serial number/date of manufacture and changing build/osha standards I would confirm that a velocity fuse was incorporated into the lift cylinder for safetys sake,, better safe than sorry,,, the MT series was available at one time with remote controls enabiling lift/lower control from a lifted platform, when or if they were discontinued I do not recall, I have only seen this option on the real old models of this machine though. Here are a few links for you for supporting dealers in the area and if all else fails call the factory.

Lift Incorporated - About Us > Locations

Action Lift, Inc: Materials Handling Specialists

Crown Equipment - Contact Us

 

[jas67]

The 20MT does not incorporate a pilot operated check valve in the lift/lower circut, Crown did use these valves in the tilt circut on other models. Most of the lift/lower circuts did use a velocity fuse however, due to serial number/date of manufacture and changing build/osha standards I would confirm that a velocity fuse was incorporated into the lift cylinder for safetys sake,, better safe than sorry,,, the MT series was available at one time with remote controls enabiling lift/lower control from a lifted platform, when or if they were discontinued I do not recall, I have only seen this option on the real old models of this machine though. Here are a few links for you for supporting dealers in the area and if all else fails call the factory.

Lift Incorporated - About Us > Locations

Action Lift, Inc: Materials Handling Specialists

Crown Equipment - Contact Us

js5020 -- thanks for the info!

 

[Wayne County Hose]

Joe beat me to it. The hose in the top of the cylinder is a drain back to the tank for when the lift seal leaks. These machines are very popular in smaller, food processing and medical facilities so when the lift seal does leak, they didn't want oil all over the floor so they made a drain back to the tank. Maintenance platforms are popular on these trucks. They do not have check valves but do have flow controls. They also made the lines and fittings to the lift cylinders so small that you could cut the hose clean off and it still wouldn't lower very fast. They are a decent, dependable little truck. Easy to troubleshoot and fix. The 2 batteries in the door are for travel and the 2 under the pump for lift. Keep an eye on battery water. If it dies, check the switch inside the door hinge just to the left of the power unit batteries. Make sure the wires didn't slip off. This switch cuts out travel so it won't run with the door open. Other than batteries and a directional switch, not much else goes wrong on them.

Oh, you place a service call to a dealer, be ready to shell out at least $300 bare minimum.

 

[jas67]

Thanks for the info?

I wonder why the batteries aren't just shared for all functions? The batteries that the PO put in don't last very long. I think they are start batteries, instead of deep cycle batteries. I assume that golf-cart batteries would work well. Where is a good place to buy them?

Any idea where I can get (free) schematics or service manuals for this?



Thanks,
jay

 

[js5020]

The parts/service manuals are available through a Crown dealer, it includes the schematics and parts breakdowns,, cost according to the Crown website is $15.00 if it is a part number PF2629-00M check with the parts dept of your local dealer as the info only lists the lift build date back to 8/1992 to double check that number. Sometimes if you get the right person at the dealership they might do you a favor and fax/email you a schematic for your particular serial number.

Golf cart batteries will work and many folks get those at Sams club from my understanding,,, as Andy stated keep a check on the water level many folks get into the habit of not checking the pair under the pump motor as they are not as easy to access and guess which ones will use the most water.

Here is the link I used to access the manual data

Crown Equipment - Parts & Service Support

Select walkie stacker from the drop down menu, and on the next screen select M for your model and your zip for your local dealer and your golden.