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Author: Subject: any hydraulic engineers in?
Talon Motorsport

posted on 8/10/14 at 04:05 PM Reply With Quote
any hydraulic engineers in?

My transit 190 recovery started life as a £250 near death tipper, the ali buck was removed and replaced with a 3m 80x40mm box section fixed bed to which a 1.5m removable beaver tail was added when needed, how ever I'm now looking at building a cheap tilt and slide of sorts.
I had the foresight to keep the 10t ram and pump from the buck so the 'tilt' is sorted but it's the 'slide' I need advise about.
What I have in mind is to make the bed with a 4-6 degree down beaver tail and still use ramps, tilts say 10-12' and slides maybe 1000-1500mm so it's not quite so much of a complete body off job.
What I need to know is what size ram(s) will I need to pull 1500kg up a 10-12 degree slope? Is it the same as with winches ie a 200kg line pull will move 1500kg along the flat on wheels but you need a 500-1000kg winch to pull 1500kg up a 30 degree slope or have I missed the point?
Fabrication and welding no problem, maths and physics err....no not really. Please be gentle?

[Edited on 8/10/14 by Talon Motorsport]

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daniel mason

posted on 8/10/14 at 05:15 PM Reply With Quote
Think laptobrob is hydraulic engineer. Give him a buzz.






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43655

posted on 8/10/14 at 10:00 PM Reply With Quote
I would say yes you'd have the same kind of ratio as with a winch, it's still power to move an object. assuming they're both on wheels a sliding object is much harder naturally
however a ram's power is determined by the pump pressure and surface area
Force = Pressure x area
(area being pi x diameter of the piston squared)
or:
area = force / pressure

for example
500kg pull (~5,000N force - weight x gravity (9.81m/s^2))
100 bar (1 bar = 100,000n/m^2) available from pump
5000/100000 = 0.05m^2
(square root 0.05 ) / Pi = 0.071m = 71mm diameter

Someone correct me if i'm wrong or misleading
I'm tired and don't work with hydraulics!

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Dingz

posted on 9/10/14 at 08:47 AM Reply With Quote
Yes thats about it but you will have some losses as the cylinder will not be 100% efficient. Assuming you want it double acting bear in mind that the rod side of the cylinder has a lower effective area of piston ie. subtract the rod area so you will get less force on that side.





Phoned the local ramblers club today, but the bloke who answered just
went on and on.

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dhutch

posted on 9/10/14 at 11:52 AM Reply With Quote
Assuming you have space for a non-telescopic ram in the slide system, and plan to have a fairly free sliding bed, that would most likely by what I woudl do. Retract would most likely lower, extend sliding it back up against gravity. At which point you may well find the limiting factor is ensuring the ram does not buckle when extending, although even this can be countered to extend by constraining the ram at cylinder at the gland end.

The only other consideration would be the event of a hyd failure, I dont know whats common in the tilt-and-slide truck industry but in ours we end up with load hold check valves, or counter balance valves, on the majority of rams to guard against hose failures, etc, and have to have mechanical interlocks on things light hyd lowering tow hitches so that they do not fall even the event of ram failure.


Daniel

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Talon Motorsport

posted on 9/10/14 at 05:14 PM Reply With Quote
So if I understand this correctly rams are stronger in the force they exert when they are extending but more prone to buckling and weaker in force when retracting but get stronger as they get shorter? That will help with my choice of ram(s) and which way round to mount it/them. Thanks a lot for your help.
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43655

posted on 9/10/14 at 08:35 PM Reply With Quote
hydraulic rams are stronger when extending becuase when they are compressing, the rod of the ram takes up space in the cylinder.
as mentioned they rely on surface area for power
but the side of the piston with the rod attached will have say 1/4 of the area taken up by the rod, and therefor be only 3/4 is the power (not convinced this is correct?) of the extending stroke.

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Dingz

posted on 10/10/14 at 10:09 AM Reply With Quote
Side loading is a problem if the cylinder is rigidly mounted. If say you have a 1m long cylinder with a 10kg side load, when the cylinder is retracted the piston is at the bottom of the cylinder there is a short bit of rod out the end exerting a side force on the gland bearing. When fully extended the side load is now like a torque wrench 10kg x 1m acting on the gland, plus the piston is now at the gland end offering very little support to the load. Needs a picture really but I hope you can understand my ramblings.





Phoned the local ramblers club today, but the bloke who answered just
went on and on.

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dhutch

posted on 10/10/14 at 08:09 PM Reply With Quote
quote:
Originally posted by 43655..and therefor be only 3/4 is the power (not convinced this is correct?) of the extending stroke.

Depends on the diameter of the rod and the diameter of the cylinder.

But you are right, the force in extend is the pressure multiplied by the area of the piston.
And the force in the retracting direction is the pressure multiplied by the area of the piston minus the area of the rod.

So you are right, that for for a typical ram where the rod is around half the diameter of the cylinder, the ratio of forces would be about as you say.

quote:
Originally posted by Dingz
Side loading is a problem if the cylinder is rigidly mounted.

Its unlikely you would have a rigid mounted cylinder, trunnion mounted could work well, but you might be on what you get hold of rather than anything else by the sounds!


Daniel

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