Bought a big scissor a while back. Guy thought it was something to do with the hydraulics but I could tell the engine was not pulling the load right. When under harder loads, the engine stumbled and bogs down but otherwise idles perfect and if I tickle the high idle right, it will run at top RPM fine. I think when it wants more fuel from a hard load, it is going lean. I have never been in a Propane system and to make this worse, someone has bastardized the system to run on the small 20lb bottles and all the plumbing is not OEM. I need to see how we figure out if there is something going on with the regulator and valving or if the carb just needs cleaned and tuned? Anyone sharp on propane stuff?
Not sharp, but I do remember working on them. Is this an air cooled engine? Does it have a heated converter (liquid to vapor) or just a regulator for vapor only? 20lb bottle will freeze down and fail to provide vapor if you're pulling much out of them. Sometimes it's nothing more than wear in the linkage. The old forklifts and such I worked on the carbs were bone simple butterfly for the air, metering valve for the fuel, and there was an adjustable link between the levers for them. Loosen locknuts rotate center barrel to shorten as I recall makes it richer (just move the fuel lever in the same direction the throttle linkage moves to open the carb up.) couple turns at a time until it pulls good, one or two more to keep it running cool. You can smell it in the exhaust if you get carried away. But then maybe you have a newer style carb. Spark plug gap can be an issue too, these engines run so clean the plug don't need changed for fouling, but eventually the spark erodes the electrodes until the gap is so wide they'll misfire under hard load.
I ran some numbers and want to see if I am on track. I estimated that at full load on this 24HP engine, I could need as much as 250K btu/hr from the cylinder. It does not seem like a 20# cylinder can produce enough vapor to supply the engine at full load. Can anyone verify this? The OEM tank was a 60# or 15gal. The scissor will not need full engine power too long but when lifting, it struggles and the outriggers pull it down to a stall. However, when you consider some forklifts, the math does not compute. I know I had a big fork running a big V6 rated at probably 150HP or more, running off a 15gal cylinder.
That's what I was saying, most forklifts pull liquid from the tank and a heated converter makes the vapor to deliver to the carb. Only small engines, usually air cooled, use vapor direct from the tank, and I have seen air cooled engines with heated converters as well but it's not as common. If you have a liquid system and the tanks are giving you vapor that won't work well either. The tanks will be freezing if you're pulling more gas than they can vaporize with ambient air temp.
Well, this all seems to be lining up as I can pretty much verify this is a vapor only system. Vapor coming off the top of the BBQ style tank. Not even sure if you can even get an emulsion tube in one..... So, it is dual fuel but of course the gasoline fuel system is missing so I will have to setup a gravity system for now to get going. However, I do like the idea of propane as they work well in a building. Assuming that I want to convert this BACK to the liquid system that was likely on it to start with, What all do I need to do that? How do these work at start up if there is no exhaust heat? I did talk with one company that indicated I would need to place the converter next to the exhaust, which is no biggy, but I am stuck trying to figure out how those systems work now. Why doesn't the convert just freeze up? The heat from the exhaust is enough to keep things going? Do you then go through a low pressure fuel reg like the Garretson I have or does the converter feed vapor to the engine directly?
Most converters have the regulator function built in, the liquid cooled engines run coolant through to warm the liquid propane. When starting there is no fuel flow so no heat is absorbed until the engine begins pulling fuel, and by that time coolant is circulating. 24hp air cooled, you should be able to run on a vapor system, but you may need a bigger tank, not sure. Have any pictures of the current setup? There should be a filter in the line somewhere, or maybe that's only on liquid systems....
I think to do this right, it should be on liquid. However, I just don't have the time so I have devised a plan. I am going to run 2 20# tanks in parallel which should double my BTU capacity and run them mostly full all the time. The vapor capacity is a function of how many gallons I have on board so it if ran half ass on an 1/4full tank, it might be enough to get us by on 2 full tanks. This assumes the engine would not really be at full capacity. They actually built this scissor with a 20HP engine so I am hoping the numbers will wiggle out and I might be down on HP just a bit.
Actually vapor delivery is a function of ambient temperature and surface area of the tanks. The pressure in the tanks keeps the propane in liquid form, when demand pulls vapor off the top the pressure drops and heat is absorbed through the tank walls to replace what's lost in the conversion from liquid to vapor. Adding a tank should essentially double vapor delivery capability. You'll find out soon enough if that solves the problem.
newer style bbq tanks also have a flow limiter built in so adding 2 tanks for a 24hp engine should help in that department also , found this out triing to run a portable genset on one tank along time ago
Well, we are MUCH closer! Machine will now at least operate without stalling and will take high idle without stuttering. It won't take a high idle boost while operating a function but we can live with it for now. I ended up running two BBQ grill reg/hose units to the lockoff valve, then to the fuel valve. Works great! However, I now have a couple other issues showing up. 1. Wheel brakes are NOT working and that became a quick point of safety just testing it on a little grade! It is designed to be towed so I am hoping there is something simple here like a brake bypass lever? Sort of need brakes! I can hit reverse and stop it but it gets interesting. 2. Wheel power seems to be nearly nothing. It has good flat ground travel speed but give it any incline at all and even at high idle, it won't do it and it almost sounds like I am hitting a bypass or pressure relief valve. I know it should be able to handle some grade. I am going to see if my high idle is up to spec but I suspect something more is going on because I should be able to crawl into position, not power my way into it. I hope the drive motors are running ok.
Scissor lifts typically are not designed for much if any grade, basket lifts on the other hand usually will climb some. Make and model?
I had forgotten that, I'm old school, no fancy gadgets and if you want liquid turn the tank upside down, set it on the collar.
Lift is a Marklift RT40G. Being a Rough terrain lift, I would sure think it could handle some grade. Were doing some testing and when the wheels are under load in a climb it goes right to a pressure bypass and the engine really does not bog much. I think it has more in it and suspect the valve has an issue. I cannot find ANY service manuals for this thing so I am purely guessing with it. I have a parts manual and it mentions a brake bypass valve and even an old sticker on the machine at the back but there are no hydro lines to any brakes and certainly no valves. Just two lines to the drive motors, that is it. I am a little confused right now.
Ah, my bad you are correct, brain cramp. http://manuals.gogenielift.com/operators/English/TerexAerials/Marklift/17205.pdf Early versions apparently just used the motors for braking, there is what looks like a needle valve mentioned as a "Freewheeling Valve" which you open for short distance towing at low speeds, this may well be your issue with lack of drive power and braking ability. If there's a valve with two lines on it, make sure the knob is tightened to the right to close off the bypass. There are also some cushion cylinders that have quad ring seals on the pistons, if those are toast they may also cause similar symptoms, or of course a bad motor. Later units apparently were fitted first with disk brakes and even later spring brakes.
Well here is what I know. The drive motors are run with only two lines, no case drains and I believe them to be the gerotor type. I know what the manuals state but i can tell you about half of this machine has been completely screwed up. The cushion cylinders are GONE, there is no brake valve, there are no lines to any brakes, etc. I know the machine was built beyond 1986 because the drawings I have show the valves that are what I have. There is basically only one spool valve that operates the drive motors. Push/pull and when one side goes high, the other side opens up to the return to the tank. However, i got to thinking about this and VERY confused as to why when I stop all motion, why does it freewheel like a bicycle? There is pretty much no resistance! Now, one might reason that freewheeling with no prob coupled with no drive power is likely two toasted drive motors and massive internal leakage BUT I am confused now as to why once the motors get in a bind trying to work, the system hits a relieve valve and you can hear it bypassing like crazy. I would not think a motor that was that worn out as to freewheel would plug things enough to hit a relief valve. I am still wondering if that relief has problems though since it seems to come in rather early before the engine really bogs much. I guess a simple test might be to jack it up, spin the wheels, then blockoff the hydro lines and see what it does. I would be just fine with the motors doing the braking but I also got to thinking about how they would handle the shock of a stop? When you slam the spool closed, it really should block off all flow and they should lock up. However, I determined the brakes are in there, a wet multi disc type, and they have GOT to be complete toast because there is no line at all to them and with bellevilles in there, they should be locked down. So the brakes are not taking any pressure off a stopping condition, no cushions for the motors, it seems like things are setup to break the way it is. When I was testing, when I got off the travel button, it ran right down a hill, but I could use reverse to slow it down. I did not know if it would hurt something but I sort of needed to stop. It certainly did not immediately change direction, but it worked. From the looks of things, I think as things broke, some super intelligent person took those broke parts and file 41'd them as "not needed". Always pisses me off to see how people maintain stuff.
If it's the later style with the internal spring brakes, there would have been a brake valve which diverted pressure to release the brakes when you start to move the machine, you say it's not there? Typically given the spring brake, the control valve would have a "motor" spool which means both lines are open to tank in neutral, and that makes sense given the instructions for using the later model freewheeling valve, you close the valve and then bump the drive, this releases the spring brakes and locks the fluid until you reopen the freewheeling valve. The motors have to be open to tank to freewheel. Cushion cylinders were only used on the earlier machines with no brakes I think, so those machines would have had a normal cylinder type spool which blocks both work ports in neutral, this give the braking effect and why they needed the cushion cylinders? Best thing of course would be to repair the brakes and install a brake valve, the only other alternative would be a counterbalance valve to lock the motors hydraulically, but it's a compromise at best, hard on the motors as you say and not a secure parking brake.
I honestly still cannot even see a port where the hydros would hook up the brake but I see something in the diagrams. I am so used to CAT books. This stuff is a joke. Get all wound up to learn what that fitting is, the books just says "fitting". So helpful. I am still amazed the brakes are not hooked up. Nothing.... There is a port on the valve block that says "brake" but plug looks factory. No way this machine is safe without brakes but will use is on soil, not concrete for now.
Yeah, confusing much. Okay, I think in the PDF I posted the link for the right hydraulic drawing is: SCHE Page 8 Section 2 figures 3 and 5 show tube and hose connections for the brake valve And the brake valve itself is Section 3 Figure 42. After some more perusing, it looks like the control valve is indeed a motor spool, all ports open to tank in neutral. The brake valve contains a shuttle to provide spring brake release when the control valve sends pressure to the motors. It also contains a counterbalance valve to provide cushion and hydraulic braking before the spring brakes lock up and some orifices to control motor speed. There are two needle valves for freewheeling on this variant, one with a check valve to hold pressure in the spring brake lines when closed so they stay released, a second basic needle valve that is opened to allow the oil to flow in a loop between motor ports. Sounds like you're missing all the valving.
Thank you for the help! So if I simply connect a brake to the brake port, the port should be hot all the time UNLESS I am traveling, in which it will remove pressure? I don't need any return loop? What I am considering is trying to just connect one of the brakes to that port after port testing and see if I can just get one brake to work. I would be fine with that for now and certain it will be enough for now. Also, could you help me verify which relief valve is for the travel motors? I am looking for a way to splice in to test the pressure as I am pretty sure that machine should have more power than it does. When I am lifting the platform, the engine bogs, when I drop the outriggers, it bogs, but when I try to travel up any incline at all, it just hits the relief but does not seem to pull hard on the engine. I really think being an RT lift, it should be able to handle a "little" grade. I am fighting to get it up even the smallest incline. I posted a couple pics of the hub/drive motor area. You can see there is next to no room there. In the second pic you can see a small threaded area that I can only suspect is the right port. There is only a small window to access the area and there is no port visible on the other side so someone could have had that hub off and did not rotate it right. EDIT...... Scratch that. Head in the clouds. with no pressure on the brake and still holding nothing, it is obvious the brakes are toast. That won't work.
In the hydraulic schematic, in the "Drive control" section there's a dump valve with a 900 psi relief to tank. It needs to be activated to close off the line to the relief valve, and then the pressure can rise to the 1,800 psi main relief setting. Don't know why I missed it, but finally found the right electrical schematic, it's page 56 in the pdf, SCHE Page 10. There's a "Hi Torq" solenoid valve controlled by a 12 foot cut-off limit switch. Apparently once you've lifted to 12 feet, the limit switch cuts out high speed drive and also lowers the drive torque dramatically. So, either you have a bad switch, broken wire, or bad solenoid coil?
Here are some pics with notes. However, I think you are onto something! I know for sure there is a fast/slow switch on the pendant and it does work. However, that is obviously a flow control not a pressure control and my problems are pressure related. You can just hear that valve block screaming when it is dumping all that pressure off. I will look at the electrics again and try to find it! That just has to be it!!! I was ready to chase down a relief valve because I just know it is not getting enough pressure. Could we possibly say that the solenoid is defaulted in the low pressure position and needs power to get full 1800psi as a default safety? I would highly doubt any safeties are left on it! Hell, it doesn't even have brakes! I have to setup RR ties on the driveway as a safety when testing because if the engine cuts out, I have no way to stop! If I can get full drive power, I can for now operate with a spotter and wheel chalk to just get things done. Thank you again!
Yes, according to the hydraulic schematic, if it's drawn properly, the default is to allow oil to pass to the low pressure relief, so you need power to the coil to activate the valve which will close off that line and increase the pressure. Best guess and it should be safe and easy to try, on the close end of the manifold there, there's a large square section bolted on with two solenoid coils close together right on top. The book says this is the drive section. The Yellow lead is obviously the common ground for all the coils. The coil on the right has a wire connected to it, I'm guessing this is high/low speed, you could verify that if you wanted to by simply unplugging either wire from the coil. The coil on the left has no wire connected to the top terminal. Best guess this is the Hi Torq valve. Connect power to the coil and try driving. If the right hand coil is actually the high and low, just pull that wire off and move it to the other coil for testing purposes, see what happens. I bet this will be a nice unit, you get her knocked back into shape a bit!
LOL. I found and did exactly what you described as you typed it. All I did was verify that RH solenoid was in fact the hi/low in which all of this is proximal to the motor drive part of the block. Other solenoid had no wire. I swapped it around confirming that no power to hi/low defaults to low. What I did find is without brakes, this makes for a BIG issue in high torque! That thing will straight rip ass and after it was rolling down the rock driveway a bit, I reversed to slow it, and it spun the tires and returned in the opposite direction real damn quick! Too quick. I am sure that ain't good on anything and I about stalled the engine. I am thinking a momentary switch for the hi-torque for now. I really need that machine like yesterday but I sort of need brakes. So again, if I repaired a brake (assuming I can find parts, Ross motor/brake unit), and ran a line to it from that brake port on the block, will it drop pressure off correctly when drives are enabled? As a quick fix for now, I figured I could just install a needle or ball valve on that line and all I need to do is trap pressure in the brake so I could run it up on the riggers, fire the drives, and close the valve. As for the rest of the unit, the hydro oil is crystal clear, engine runs like a top now other than some minor tuning I need to do, lift works nice, riggers work nice, and a huge 6x12 platform. Not a bad rig. Rather have a boom lift but the price was right.
Well, that's progress at least. Actually Ross motor, MICO brake, which is a good thing I think, parts wise. View attachment MICO Brake.pdf A SUN counterbalance unit with brake shuttle will run you about $400 or so, I would seriously recommend looking into that, if you have a local hydraulics outfit they can help you dial in the specs. Something like this should be close: http://www.sunhydraulics.com/model/YCCW Will give you hydraulic braking before the spring brakes come on, supply brake release pressure and will take some of the snap out of the on/off. If you go the needle valve route get one with a free flow check, so oil pressure flows freely to the brakes to release them, then set the needle so it takes a couple seconds to completely lock back up. If you need it to be towable should the engine fail or whatever, you will need a valve like this anyway, and one plain needle plumbed so it tees into both motor lines, you close the brake needle, activate the drive to release the brakes, then open up the bypass needle to let oil flow as the motors turn.
You know your stuff Lantraxco. i think I might need some schooling on the counterbalance valving to better understand things. This valve will be able to cushion things and function as the brake release? Links and docs are great to soak up some principals of operation. I can tell you, maybe because the brakes no worky, that thing is very jerky. I am used to machines with variable controls. Let me just ask for the sake of asking, do you need special valving to modulate the flow rates on these valves? I know we need to vary the throw of the spool but was not sure if i varied the voltage to the solenoid, if that will function as intended or if you need a special valve setup? It may be easier to consider improvements hydraulicly. just trying to learn. it is pretty obvious the fast open and close of the drive motor valve needs a little buffering.
Now and then I get a little wood on the ball. I can't really find a good explanation of the counterbalance setup, or what some folks call a "dual overcenter valve" The SUN link I posted shows a functional diagram, that manifold has a shuttle valve for the two pressure lines from the valves (v1 and V2) whichever is hte higher pressure is directed to the brake port. The next two valves marked CBCA are the counterbalance valves, one for each line. They have free flow checks to allow oil to pass to the motor as pressure builds on one line, let's say V2. The opposite side carries oil coming out of the motor, but it's stopped by the counterbalance valve.. as pressure builds on the inlet of V2, it's carried by the dotted line over to the opposite valve, where it opens the counterbalance valve which throttles the outlet oil passing out of V1, maintaining a backpressure on the motor outlet. If you start to run downhill say where the motor tries to run faster than the oil coming to it, pressure on the inlet drops and the valve on the outlet side will throttle down to maintain the pressure. The two other valves marked RDDA are fast direct acting relief valves set up crossport so in any case where pressure exceeds a safe setting they pass oil across from one line to the other. These are for sudden spikes like when you start or stop moving and if for some reason the machine gets pushed or on too steep a slope a valve will open to release pressure rather than damage the motors. By the way, just noticed that SUN manifold is designed for use mounted directly to a charlynn motor so don't order that one, sorry. As to modulating the valves in the machine, I'm betting they're not really made for that, pretty much on or off, and the coils probably wouldn't like it either. Yeah, the valve you have is what's known as a slam-bang valve, on or off only. For feathering you would need a proportional valve. Since there's a single pressure line going to the forward/reverse drive valve it would be possible to put a single proportional valve in that line from the manifold if you wanted speed control. Just select forward or reverse and then dial in the speed you want maybe.
Great! a few things to confirm. One function of the counterbalance is modulating the output side of the motor to get consistent speed/load on different grades without the engine constantly hunting to match to load? It would also add a short circuit relief valve but not sure when that might be needed if the motors go to drain when the the main valve is close and when open the main system relief should take care of that? I am trying to figure out how this will work with the brakes and if the brake port that is on the current manifold may provide the correct function directly? Seems like the block has some of this built in. However, I know that buffering the way this rig functions needs to happen. The way it would start and stop. I think if the brake works right to slowly engage/disengage, it could work well to buffer things since a delay on release can kind of stop the drives from jolting and a delay on stop could sort of coast things a few inches to a stop rather than a dead stop. Another question on the brakes, before I jump into them, is there anything that is going to be insane sucky about working on them? bolts with insane tension, shrink fits, etc?
OK, after some thought, my ideas will not work. That brake port on the main block would have no way of knowing when the motors are fired because main system pressure is just remoted over to the main motor spool valve. I feel certain the OEM system used a counter balance valve to keep things moving nice and smooth. Why someone ripped all that out is way beyond me! I was then thinking about a relief valve on the drain line of the motor spool but two problems arise, A, there are two pressures to deal with 900/1800 so that might be interesting. B, I would have no freewheel function left to tow the machine if needed and I already have the towing frame which will be handy. I would really like to get the motors under better control for downhills but for now, it might be best to simply try to get one or both brakes working. This brings me to my questions of how we set that up to get pressure to the brakes? I realize as it works now, the dump side of the motor spool simply dumps directly to the tank but I think that pressure has to stay under 100psi to keep brakes released. I will probably need to plumb something in that connects to both motor sides and regardless of which side is hot, sends pressure to the brakes, hoping of course that 1800psi is OK for the brakes but I read that though it might only take 200-300psi to release them, they are made to do this. Lantrax, I believe you mentioned the CB valve doing just this while also adding the other functions. I guess I could see if I could get the factory valve but that will be a long shot. I think they had two valves for freewheeling. One locks pressure at the brakes to release them, the other might have bypassed the motor dump side relief so the motors would freewheel. EDIT: Damnit, that might not work either! Thinking more, on a decline, gravity may take over and though the motors seem to have control of the load right now, I am betting the inlet or P side of the motors in that situation is near nothing. If we would be looking for pressure in those lines to operate the brakes, that could be quite a problem in that the brakes would come in due to the loss of pressure and could be a damaging event. I can't really see a way around this other than do it right and use a counter balance valve with relief valve on the outlet side which would maintain pressure on the P side of the motor thus holding the brakes off while also better controlling motion. Never an easy way.....
I think you can use the brake port on the manifold if you want, when they added the CB valve it was a lot closer to the motors so they used the shuttle and brake port in that to provide brake release. The existing brake port will have pressure any time you turn the motors on, as long as there's sufficient load to provide backpressure. As you surmised on a downhill or even just running ahead of the pump after the initial surge, incoming pressure will drop and the brakes will come on. Your idea of adding a relief in the return from the directional valve is not bad, I happen to know that style valve will deal with some back pressure. Maybe something on the order of 300 psi would at least give you some drag, without losing too much drive torque. But it will only work when the motors are on, the second the valve returns to neutral all ports open to tank and you lose the braking effect. You mentioned the crossport reliefs in the CB valve, due to the nature of the CB valve it locks the oil on the motor side, so even though the directional valve is open to tank, you need reliefs to allow oil to cross from one side to the other in case the motors are submitted to excess torque, or you get a spike starting or stopping. I can't find a spec in the book but typically these will be set somewhat lower than system pressure to provide some cushioning effect. I'll ask my local vendor if they can suggest a CB valve manifold unit.
I think what I my concerns are with the brake port on the main manifold is there is really no way for that port to know when the motors are running or not. There is nothing in that block that is fired when the motors run. There is no additional spool or such. I am wondering if it was an option on the block but was never used. I know the plug in that port appears to be factory installed. Every coil on that block as been accounted for so not sure we could use that option without additional configuring. Probably smarter to just install a CB with shuttle that is a one shot deal. I just cringe that the tuning though because if the dual pressure situation. Have to tune it for the lower pressure of 900psi. The the short circuit relief, I am wondering if that would be needed since all motor ports go to drain when motor spool is in neutral. I can sort of see why you would not want to freewheel this machine for 20 miles though. It seems the motors would be spinning without oil.
That had me going for a bit too, but here's how that system works: Since the pump is turning all the time, oil flows continuously through that manifold, the flow gets divided at the high/low speed valve in low, part of the oil goes off to tank there in low speed. The rest of the oil flows on to the external directional valve and since all ports are open in neutral, it just goes back to tank. When the directional valve shifts into either forward or reverse it closes off the passage to tank and the pressure line connects to one of the motor lines. The back pressure from the motor raises the pressure all the way back to the pump and that pressure is seen at the brake port as well. Not sure what you mean by tuning to the lower pressure? Do you mean tuning the CB valve or? The crossport reliefs: tried to explain that in post #29. The CB valve closes off the motor lines and locks the oil flow on both lines in and out of the motor, so the motor spool is irrelevant to the motor, it's only open on the backside of the CB valve, not to the motor ports. This page applies to freewheeling: View attachment Towing.pdf So unless you can get the drive wheels up off the ground, I would say you would be limited to about the length of a football field before the motors started heating badly, just a guess.