Max Obtainable Hydraulic Pressure on 925A2 Hydraulic System?

[74M35A2]

I believe the factory relief valve of an M925A2 hydraulic system is set at 1800psi or 1850psi or so. I'm looking to add dump cylinders to my cargo bed this spring, and if I can up this pressure, I can reduce the cylinder diameter/weight/size/cost. Has anybody messed with their relief valve, or otherwise know how much pressure the pump can develop if this is increased? Some general cylinders are rated up to 3000psi. I understand that the 1800psi is likely a factory of winch max loading (no shear pin), so I would just install a pressure gauge and not exceed 1800psi when using the winch. This gauge could be somewhat handy and be a possible indicator of winch load, assuming 1850psi is 20,000lb load (depending upon layers of cable). I would also have to increase the pressure delivery hose rating, but I would be switching to electric solenoids by then anyway. I'm targeting to be able to lift the full 10 ton rated bed capacity for on-road. So using simplistic math, wanting each cylinder to push half of that, which can be easily found by using force = area x pressure. Cylinder area being radius x radius x 3.14, then x pressure = force. Some weight will be on the hinges, but I would size it this way to "just be sure". Would hate to have a loader fill up the truck, and the bed can't tilt, and then I' up there for seven hours unloading with a hand shovel until it can tilt. There is also the geometry factor of the cylinder angle not conveying all of the force to lifting straight up.

 

[Ddmk18]

Yes the pressure can be raised but the factory winch valve won't handle the pressure either will the winch. I am running 2750 on my dump hoist on the up side and 1500 on the retraction side. I have a short bed but I have dumped 8 ton no problem.

 

[JohnnyBM931A2]

Yes the pressure can be raised but the factory winch valve won't handle the pressure either will the winch. I am running 2750 on my dump hoist on the up side and 1500 on the retraction side. I have a short bed but I have dumped 8 ton no problem.

Do you have any info regarding your setup? I can't remember if you did a thread on it or not..

 

[Ddmk18]

No I did not do a thread on it I posted in some threads on what I did but no dedicated thread. I can get you some info tonight after I get home from work. Basically I added electronic valves and made the system more usable by adding other lines and auxiliary hook ups.

 

[Floridianson]

I thought that you need to match close to PSI and GPM and meet spec's the ram calls for to work correct.

 

[tobyS]

Size it so you don't have to turn the pressure up. In the size you are talking, going up 25% is not going to save you much on the cylinder cost.

Get a pump number and we can find your rating, but I would not be surprised that it's a 2500 psi pump. Don't forget your reservoir has to be larger and valve changed to two spool, open center. Or we can talk more complex valving, remote 24vdc.

Your mechanical advantage or disadvantage is going to play a big factor. Are you talking scissor, direct mount to the bed center or a telescoping front mount? Whats the bed length?

I was going to do the same and then bought an 817 (now sold), so did a lot of research on lifting a cargo bed (I design sawmill hydraulics).

 

[74M35A2]

925A2 so 14' cargo bed. Dual cylinders direct mount from frame rail outside to bed center boxed cross member, kind of like a Volvo dump truck. Probably 60" stroke, cylinder bore TBD. I don't want to lift my bed for scissor mech clearance, and if flipped I think the axle diff would crash into the lowered hoist mech at full articulation. Plus the look of outboard mounted cylinders would look kind of fun. There was an M35 posted in the Deuce threads that did the twin direct bolt cylinders inboard of the frame rails, 4" bore x 45" stroke, tilts to 45 degrees. Looks really clean, I want to copy this but go outboard of the frame rails, and inboard of my single rear wheels. Understood on the hydro circuitry layout, I'd convert to a parallel D05 manifold with 24v solenoids, 5 channels total. Winch, dump bed, rear winch, aux with quick connectors, and unused spare.

How do you know the stock vale can't handle additional pressure?

 

[JohnnyBM931A2]

No I did not do a thread on it I posted in some threads on what I did but no dedicated thread. I can get you some info tonight after I get home from work. Basically I added electronic valves and made the system more usable by adding other lines and auxiliary hook ups.

Cool If I get another 5 ton, I think I will have an M931A2 set up like your M932.. Shortened bed with a hydraulic dump setup. Talk about perfect for yard work and other stuff around the house

I really think you should do a dedicated mod thread with pictures. I think that would help out others in the future.

 

[74M35A2]

Yes the pressure can be raised but the factory winch valve won't handle the pressure either will the winch. I am running 2750 on my dump hoist on the up side and 1500 on the retraction side. I have a short bed but I have dumped 8 ton no problem.

Is that with the stock MV pump? If so, that is what I was looking for. What configuration of dump hoist are you using? If scissor, did you have to raise bed, or does it hit axle doffs at full axle travel, and what is you full dump angle? Sorry for all the questions, thanks.

 

[Ddmk18]

Yes that's the stock pump. That's the pressure my relief valve is set at. The only time I have ever hit that pressure is when the ram hits the end of its stroke. I have never had a problem dumping 8 ton and I can tell you it's not close to that pressure while raising the load because when you hit the relief valve you can tell the engine grunts. But I only raise at idle speed because it calls for 6gpm optimum flow rate for my hoist.

 

[tobyS]

925A2 so 14' cargo bed. Dual cylinders direct mount from frame rail outside to bed center boxed cross member, kind of like a Volvo dump truck. Probably 60" stroke, cylinder bore TBD. I don't want to lift my bed for scissor mech clearance, and if flipped I think the axle diff would crash into the lowered hoist mech at full articulation. Plus the look of outboard mounted cylinders would look kind of fun. There was an M35 posted in the Deuce threads that did the twin direct bolt cylinders inboard of the frame rails, 4" bore x 45" stroke, tilts to 45 degrees. Looks really clean, I want to copy this but go outboard of the frame rails, and inboard of my single rear wheels. Understood on the hydro circuitry layout, I'd convert to a parallel D05 manifold with 24v solenoids, 5 channels total. Winch, dump bed, rear winch, aux with quick connectors, and unused spare.

How do you know the stock vale can't handle additional pressure?

I don't think you are going to have enough stroke to get a 14' bed high enough to dump out. Make a scale drawing. If you are not more than 45* then try again. My dump bed trailer sucks because it only goes to 45*. The 817 goes to about 80*, which dumps completely. A single, end mount telescoping was what I wanted but the stroke does get long (holds a lot of fluid)(and they are more expensive). You can do two sides, center mount with telescope...which gets pricey too. If it was easy...

 

[74M35A2]

tobys, this is good info, thanks. I was looking for somebody to say 45 degrees is not working for them, to know if I should target more. I'll do some geometry before I order cylinders, to get the longest I can. Telescopic ones are nearly 5x the cost, each. Ugh....

 

[goldneagle]

What about getting the dump body or hydraulics off a junked dump truck. I'm sure you can find some wrecked ones out there.

 

[74M35A2]

I looked into it, I want to keep the cargo bed. Also, the factory dump is a twin cylinder big bore short stroke mechanism that uses a roller and ramp configuration for the initial push-up. Pretty smart and unique. This stuff is kind of hard to come by, and the curved ramp is a part of the dump bed underbody.

I also looked into making some type of bed floor vibrator, as they seem to sell them for such. The vibrator in a pager or phone is just a motor with an off-set weight, so why could it not be duplicated on a larger scale?

 

[lindsey97]

I looked into it, I want to keep the cargo bed. Also, the factory dump is a twin cylinder big bore short stroke mechanism that uses a roller and ramp configuration for the initial push-up. Pretty smart and unique. This stuff is kind of hard to come by, and the curved ramp is a part of the dump bed underbody.

I also looked into making some type of bed floor vibrator, as they seem to sell them for such. The vibrator in a pager or phone is just a motor with an off-set weight, so why could it not be duplicated on a larger scale?

For a bed vibrator, use a direct drive starter motor with an out of balance weight on the end. That is all the commercial ones are, a starter motor with some mounts and a weld on plate with threaded bolt holes.

No I don't own one, yes I have seen them work and they work well.

 

[74M35A2]

Genius! And now we're all a bit smarter...

 

[tobyS]

I have some (commercial vibrators) that are 120 volt. I used them for breaking the bridging of sawdust in an overhead sawdust hopper with limited success. Don't count on one (or more) making up for not having enough angle. I wish there was a simple and cheap way.

 

[74M35A2]

You drove me to study further stroke cylinder(s), and I found they are available, new, for less than I anticipated. I could do one of these at the front and center: http://www.baileyhydraulics.com/Chi...Ton-Series_4?gclid=CLXAt7TB6MoCFZE0aQodl0QLIw Or, one of these on each (out)side of the frame rail: http://www.baileyhydraulics.com/Chi...Ton-Series_3?gclid=CISS193B6MoCFYI8aQodB_sMiA Either way, I'd still be into it less than $1000 for cylinders, which is less than an under-bed scissor type, stronger, and no axle travel clearance issues when off-road. Would need to fab cylinder mounts to do the twins, but no problem. For the big single up front, the trunion pins are where it would need to be already. May need to move spare tire around, TBD. I think I am liking the big single so far. If you mount this upside down, the body of the cylinder can pivot away from the bed so it does not need a doghouse in the bed for angling. Plus, it would only need to be lifting half of the total load, so 10,000lbs max, since it is fully at one end of the bed. I'll have to run some math on it, as the pic below looks less than 45 degree dump angle. But, the cargo bed is hinged in from the end point, so that will help some. Acts like a 12' bed or so instead of a 14' when pivoting. If I even found my low cost knuckle-boom (does it exist?), I'd have to change to the side type cylinders anyway, so maybe I should just do those to begin with. Here is an example of that I got I all excited about:

 

[tobyS]

Yes, you can get reasonably priced ones.

Re. length. An equilateral triangle is easy, all sides are equal and the angle is 60*. Less and you may not dump completely (and easy on the math). The stroke of a 14' bed length (168") would be the same, 168" (or around there). I would not want one that is very much less than that angle because you will do too much shoveling.

The end push does seem to have enough area 4.42/ 2 = 2.21" radius and 2.21 x 2.21 x pi = 15.34 square inches. At 1800# that would lift 27,600#...so would be plenty, unless the math is off.

Think about using a large angle iron that would run the length of the beds frame and go down each side. When down it would saddle the frame for strength and provide lateral reinforcement. On the one I started and stopped, I used the back clevis as hinge pivot to get going (and add in more outer hinge with a longer pin)

 

[74M35A2]

Math looks ok. Bed length would effectively be 13' in length in this specific case for calculations only, because the hinges would be at the end of the frame rails, which are set in exactly 1 foot from the end of the bed. From this perspective, one can ignore the extra foot that hangs past the hinges, as it will actually tilt down and below the hinges when dumping. The cylinder gets weaker as the telescoping sections extend, but is OK as the load lessens as it angles up. Plus, lifting from one end, the load should be half of the bed contents anyway. I stopped home at lunch and peeked, I would for sure lose my spare tire by doing this. No way to move things around and make it work with the bed where it is, and I don't want it hanging further off the back. Now just torn between the single cylinder or telescoping side ones (to keep the spare on the truck). I guess it only makes sense to keep the spare tire if I carry around enough hardware to be able to change the tire. If I don't have the jack, blocks, and tools to remove lugs on board, then it doesn't make sense to be carrying around the tire.