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Chewing the fat here, more than anything else:
I was running my goofy Drexel forklift on Sunday, unloading some large oak logs. The heaviest, according to my forestry book, should weight around 3500lbs. The forklift lifted it up like it was no problem, even beyond the free-lift range. I've also used this forklift to pick up (barely) one of my Pacemaker lathes after removing the carriage and tailstock (with the carriage and tailstock, it weighs about 6000 lbs). This Drexel forklift supposedly has a lifting capacity of 3000 lbs. but the truck itself weighs some 12,500 lbs. (more typical of a 5-6k capacity truck). It does have a swing mast, so I always assumed the 3k rating and the ridiculously heavy truck weight was because you could carry the load 90* to the direction of travel, making tipping over more of a hazard.
But here's the interesting part: it seems like it can lift quite a bit more than 3k lbs. I expected the pressure relief valve to open when the load was at 3k-ish lbs. (let's say 3500 lbs.). The service manual says that 2500 psi is the setting of the pressure relief valve and I verified that it does build to 2500 psi before opening by running the mast all the way up with a gauge on the valve block. The free-lift cylinder is 2.5" diameter rod, so I figure that's an area of 4.9 square inches. That, times 2500 psi yields 12,270 lbs. force. So I would expect the free-lift capacity to be about 6000 lbs. since the lift chains act as a 2:1 "overdrive". Anecdotally, I don't think it will lift 6000 lbs., but it sure seems to lift more than 3000 lbs.
What am I missing? Do they really just slap a tag on it that says the capacity is only 3000 lbs. even though, mechanically / hydraulically, it will lift much more? I would have thought that they would design everything with a factor of safety but then limit the actual amount it can pick up by dialing down the hydraulic pressure...?
I was running my goofy Drexel forklift on Sunday, unloading some large oak logs. The heaviest, according to my forestry book, should weight around 3500lbs. The forklift lifted it up like it was no problem, even beyond the free-lift range. I've also used this forklift to pick up (barely) one of my Pacemaker lathes after removing the carriage and tailstock (with the carriage and tailstock, it weighs about 6000 lbs). This Drexel forklift supposedly has a lifting capacity of 3000 lbs. but the truck itself weighs some 12,500 lbs. (more typical of a 5-6k capacity truck). It does have a swing mast, so I always assumed the 3k rating and the ridiculously heavy truck weight was because you could carry the load 90* to the direction of travel, making tipping over more of a hazard.
But here's the interesting part: it seems like it can lift quite a bit more than 3k lbs. I expected the pressure relief valve to open when the load was at 3k-ish lbs. (let's say 3500 lbs.). The service manual says that 2500 psi is the setting of the pressure relief valve and I verified that it does build to 2500 psi before opening by running the mast all the way up with a gauge on the valve block. The free-lift cylinder is 2.5" diameter rod, so I figure that's an area of 4.9 square inches. That, times 2500 psi yields 12,270 lbs. force. So I would expect the free-lift capacity to be about 6000 lbs. since the lift chains act as a 2:1 "overdrive". Anecdotally, I don't think it will lift 6000 lbs., but it sure seems to lift more than 3000 lbs.
What am I missing? Do they really just slap a tag on it that says the capacity is only 3000 lbs. even though, mechanically / hydraulically, it will lift much more? I would have thought that they would design everything with a factor of safety but then limit the actual amount it can pick up by dialing down the hydraulic pressure...?
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